Science.gov

Sample records for absorption photoluminescence pl

  1. Metallic-like photoluminescence and absorption in fused silica surface flaws

    SciTech Connect

    Laurence, T A; Bude, J D; Shen, N; Feldman, T; Miller, P; Steele, W A; Suratwala, T

    2008-09-11

    Using high-sensitivity confocal time-resolved photoluminescence (PL) techniques, we report an ultra-fast PL (40ps-5ns) from impurity-free surface flaws on fused silica, including polished, indented or fractured surfaces of fused silica, and from laser-heated evaporation pits. This PL is excited by the single photon absorption of sub-band gap light, and is especially bright in fractures. Regions which exhibit this PL are strongly absorptive well below the band gap, as evidenced by a propensity to damage with 3.5eV ns-scale laser pulses.

  2. Raman, photoluminescence and absorption studies on high quality AlN single crystals

    NASA Astrophysics Data System (ADS)

    Senawiratne, J.; Strassburg, M.; Dietz, N.; Haboeck, U.; Hoffmann, A.; Noveski, V.; Dalmau, R.; Schlesser, R.; Sitar, Z.

    2005-05-01

    High quality AlN single crystals grown by physical vapour transport and by sublimation of AlN powder were investigated by Raman, photoluminescence (PL) and absorption spectroscopy. Absorption edges of the AlN single crystals varying from 4.1 eV to 5.9 eV as determined by transmission measurements. Near band edge absorption, PL and glow discharge mass spectroscopy identified impurities such as oxygen, silicon, carbon, and boron that contribute to the absorption and emission bands below the bandgap. The absorption coefficients were derived from UV (6 eV) to FIR (60 meV) spectral range. The exact crystal orientation of the samples, and their low carrier density were confirmed by Raman spectroscopy.

  3. Absorption and photoluminescence properties of Er-doped and Er/Yb codoped soda-silicate laser glasses

    SciTech Connect

    Li, S.F.; Zhang, Q.Y.; Lee, Y.P.

    2004-11-01

    Er-doped and Er/Yb codoped soda-silicate laser glasses with various concentrations of Er and Yb were fabricated. The absorption and the photoluminescence (PL) spectra were measured and analyzed. For the Er- doped soda-slilicate glasses, the optimum Er concentration for the PL intensity at 1536 nm turns out to be 0.5 at. %, and the full width at half maximum (FWHM) of PL spectrum increases from 18 to 26 nm, with the increase of the concentration from 0.1 to 0.8 at. %. The PL intensity of Er/Yb codoped soda-silicate glasses with an Er concentration of 0.5 at. % is enhanced approximately by four times, and the optimum Yb concentration for the PL intensity at 1536 nm is analyzed to be 3.0 at. %. The PL spectrum becomes broader with increasing the Yb concentration, up to a FWHM of 80 nm at 6.0 at. %. Yb. The relation between the absorption and PL spectra, together with the mechanism of PL broadening, has also been addressed.

  4. Quasi-Fermi level splitting and sub-bandgap absorptivity from semiconductor photoluminescence

    NASA Astrophysics Data System (ADS)

    Katahara, John K.; Hillhouse, Hugh W.

    2014-11-01

    A unified model for the direct gap absorption coefficient (band-edge and sub-bandgap) is developed that encompasses the functional forms of the Urbach, Thomas-Fermi, screened Thomas-Fermi, and Franz-Keldysh models of sub-bandgap absorption as specific cases. We combine this model of absorption with an occupation-corrected non-equilibrium Planck law for the spontaneous emission of photons to yield a model of photoluminescence (PL) with broad applicability to band-band photoluminescence from intrinsic, heavily doped, and strongly compensated semiconductors. The utility of the model is that it is amenable to full-spectrum fitting of absolute intensity PL data and yields: (1) the quasi-Fermi level splitting, (2) the local lattice temperature, (3) the direct bandgap, (4) the functional form of the sub-bandgap absorption, and (5) the energy broadening parameter (Urbach energy, magnitude of potential fluctuations, etc.). The accuracy of the model is demonstrated by fitting the room temperature PL spectrum of GaAs. It is then applied to Cu(In,Ga)(S,Se)2 (CIGSSe) and Cu2ZnSn(S,Se)4 (CZTSSe) to reveal the nature of their tail states. For GaAs, the model fit is excellent, and fitted parameters match literature values for the bandgap (1.42 eV), functional form of the sub-bandgap states (purely Urbach in nature), and energy broadening parameter (Urbach energy of 9.4 meV). For CIGSSe and CZTSSe, the model fits yield quasi-Fermi leveling splittings that match well with the open circuit voltages measured on devices made from the same materials and bandgaps that match well with those extracted from EQE measurements on the devices. The power of the exponential decay of the absorption coefficient into the bandgap is found to be in the range of 1.2 to 1.6, suggesting that tunneling in the presence of local electrostatic potential fluctuations is a dominant factor contributing to the sub-bandgap absorption by either purely electrostatic (screened Thomas-Fermi) or a photon

  5. Optical absorption, photoluminescence and structural analysis of CdS quantum dots in weak confinement

    NASA Astrophysics Data System (ADS)

    Mishra, Rakesh K.; Vedeshwar, A. G.; Tandon, R. P.

    2014-02-01

    The diffusion-controlled growth of CdS quantum dots (QDs) dispersed in a silicate glass matrix was investigated. It was found that the size of CdS QDs can be controlled by either heat treatment at various temperatures for a fixed duration or varying times at a constant temperature. Pastel yellow colored glass samples were obtained due to the presence of CdS petite crystals. X-ray diffraction (XRD) was used for determining the average dot size which varied from 3.8 to 30 nm. The typical quantum confinement effect was clearly observed from the blue shift measured in the optical absorption edge with decreasing dot size in the absorption spectroscopy. The band gap of CdS QDs ranges from 2.41 to 2.82 eV. Measured photoluminescence (PL) at an excitation wavelength of 350 nm showed the red shift of emission wavelength with increasing thermal treatment time and temperature in agreement with the increasing dot sizes. The half-width of PL spectra seems to indicate qualitatively the size distribution of dots and is consistent with the treatment parameters.

  6. Quasi-Fermi level splitting and sub-bandgap absorptivity from semiconductor photoluminescence

    SciTech Connect

    Katahara, John K.; Hillhouse, Hugh W.

    2014-11-07

    A unified model for the direct gap absorption coefficient (band-edge and sub-bandgap) is developed that encompasses the functional forms of the Urbach, Thomas-Fermi, screened Thomas-Fermi, and Franz-Keldysh models of sub-bandgap absorption as specific cases. We combine this model of absorption with an occupation-corrected non-equilibrium Planck law for the spontaneous emission of photons to yield a model of photoluminescence (PL) with broad applicability to band-band photoluminescence from intrinsic, heavily doped, and strongly compensated semiconductors. The utility of the model is that it is amenable to full-spectrum fitting of absolute intensity PL data and yields: (1) the quasi-Fermi level splitting, (2) the local lattice temperature, (3) the direct bandgap, (4) the functional form of the sub-bandgap absorption, and (5) the energy broadening parameter (Urbach energy, magnitude of potential fluctuations, etc.). The accuracy of the model is demonstrated by fitting the room temperature PL spectrum of GaAs. It is then applied to Cu(In,Ga)(S,Se){sub 2} (CIGSSe) and Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) to reveal the nature of their tail states. For GaAs, the model fit is excellent, and fitted parameters match literature values for the bandgap (1.42 eV), functional form of the sub-bandgap states (purely Urbach in nature), and energy broadening parameter (Urbach energy of 9.4 meV). For CIGSSe and CZTSSe, the model fits yield quasi-Fermi leveling splittings that match well with the open circuit voltages measured on devices made from the same materials and bandgaps that match well with those extracted from EQE measurements on the devices. The power of the exponential decay of the absorption coefficient into the bandgap is found to be in the range of 1.2 to 1.6, suggesting that tunneling in the presence of local electrostatic potential fluctuations is a dominant factor contributing to the sub-bandgap absorption by either purely electrostatic (screened Thomas-Fermi) or

  7. Temperature-dependent excitonic photoluminescence excited by two-photon absorption in perovskite CsPbBr_3 quantum dots

    NASA Astrophysics Data System (ADS)

    Wei, Ke; Xu, Zhongjie; Chen, Runze; Zheng, Xin; Cheng, Xiangai; Jiang, Tian

    2016-08-01

    Recently lead halide nanocrystals (quantum dots) have been reported with potential for photovoltaic and optoelectronic applications due to their excellent luminescent properties. Herein excitonic photoluminescence (PL) excited by two-photon absorption in perovskite CsPbBr3 quantum dots (QDs) have been studied across a broad temperature range from 80K to 380K. Two-photon absorption has been investigated with absorption coefficient up to 0.085 cm/GW at room temperature. Moreover, the photoluminescence excited by two-photon absorption shows a linear blue-shift (0.25meV/K) below temperature of ~220K and turned steady with fluctuation below 1nm (4.4meV) for higher temperature up to 380K. These phenomena are distinctly different from general red-shift of semiconductor and can be explained by the competition between lattice expansion and electron-phonon couplling.Our results reveal the strong nonlinear absorption and temperature-independent chromaticity in a large temperature range from 220K to 380K in the CsPbX3 QDs, which will offer new opportunities in nonlinear photonics, light-harvesting and light-emitting devices.

  8. Temperature-dependent excitonic photoluminescence excited by two-photon absorption in perovskite CsPbBr3 quantum dots.

    PubMed

    Wei, Ke; Xu, Zhongjie; Chen, Runze; Zheng, Xin; Cheng, Xiangai; Jiang, Tian

    2016-08-15

    Recently, lead halide perovskite quantum dots have been reported with potential for photovoltaic and optoelectronic applications due to their excellent luminescent properties. Herein excitonic photoluminescence (PL) excited by two-photon absorption in perovskite CsPbBr3 quantum dots (QDs) has been studied at a broad temperature range, from 80 to 380 K. Two-photon absorption has been investigated and the absorption coefficient is up to 0.085 cm/GW at room temperature. Moreover, the PL spectrum excited by two-photon absorption shows a linear blue-shift (0.32 meV/K) below the temperature of 220 K. However, for higher temperatures, the PL peak approaches a roughly constant value and shows temperature-independent chromaticity up to 380 K. This behavior is distinct from the general red-shift for semiconductors and can be attributed to the result of thermal expansion, electron-phonon interaction and structural phase transition around 360 K. The strong nonlinear absorption and temperature-independent chromaticity of CsPbBr3 QDs observed in temperature range from 220 to 380 K will offer new opportunities in nonlinear photonics, light-harvesting, and light-emitting devices. PMID:27519098

  9. Nonlinear absorption and photoluminescence emission in nanocomposite films of Fuchsine Basic dye-polymer system

    NASA Astrophysics Data System (ADS)

    Sreekumar, G.; Louie Frobel, P. G.; Sreeja, S.; Suresh, S. R.; Mayadevi, S.; Muneera, C. I.; Suchand Sandeep, C. S.; Philip, Reji; Mukharjee, Chandrachur

    2011-04-01

    Fuchsine Basic dye-polyvinyl alcohol composite films were fabricated and their structure, nonlinear absorption as well as linear absorption and photoluminescence properties were investigated. Switchover from saturable absorption to two-photon assisted excited state absorption with increase in intensity was observed in the open aperture Z-scan study (Nd:YAG, 532 nm, 7 ns). The effective two-photon absorption coefficient β was found to be several orders higher than that reported for rhodamine B. The dye-polymer films were characterized as nanocomposites with dye microdomains encapsulated between molecules of the amorphous polymer and having average surface roughness as low as ≈0.46 nm. The samples also exhibited intense photoluminescence emission when excited with 534 nm radiation.

  10. Thermal annealing and UV irradiation effects on structure, morphology, photoluminescence and optical absorption spectra of EDTA-capped ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Osman, M. A.; Othman, A. A.; El-Said, Waleed A.; Abd-Elrahim, A. G.; Abu-sehly, A. A.

    2016-02-01

    Monodispersed ZnS nanoparticles (NPs) were prepared by the chemical precipitation method. Thermally induced structural, morphological and optical changes have been investigated using x-ray diffraction, high-resolution transmission electron microscopy, optical absorption, photoluminescence (PL), and Fourier transform infrared and Raman spectroscopy. It was found that D increases with increasing annealing temperature (T a). The onset of the ZnS phase transition from cubic to hexagonal structure takes place at 400 °C, while cubic ZnS transforms into hexagonal ZnO via thermal oxidation in air at 600 °C. It is also noted that increasing T a results in the red shift of the optical band gap (E\\text{g}\\text{opt} ) and the thermal bleaching of exciton absorption. The PL spectrum of as-prepared ZnS nanopowder shows UV emission bands at 363 and 395 nm and blue and green emission at 438 and 515 nm, respectively. With increasing T a up to 500 °C, these bands were quenched and red-shifted. In addition, the UV irradiation effects on colloidal ZnS NPs were investigated. UV irradiation at a dose  <13 J cm-2 leads to a decrease in D, the blue shift of E\\text{g}\\text{opt} and the enhancement of PL intensity. This behavior was explained in terms of surface modification by photopolymerization, the formation of a ZnSO4 passivation layer, as well as the reduction of D by photocorrosion. At a UV irradiation dose  <13 J cm-2 both E\\text{g}\\text{opt} and D did not change and PL intensity was quenched, which were caused by the creation of nonradiative surface states by the photodegradation of the capping agent and photopassivated layer. The mechanism of the PL emission process in ZnS NPs was discussed and an energy band diagram was proposed.

  11. Influence of thermally induced structural and morphological changes, and UV irradiation on photoluminescence and optical absorption behavior of CdS nanoparticles

    NASA Astrophysics Data System (ADS)

    Osman, M. A.; El-Said, Waleed A.; Othman, A. A.; Abd-Elrahim, A. G.

    2016-04-01

    Polycrystalline cubic CdS nanoparticles (NPs) with a crystallite size ({{D}\\text{Sch}} ) ~3 nm were synthesized by chemical precipitation method at room temperature. Thermal induced structural and morphological changes have been investigated using x-ray diffraction, high-resolution transmission electron microscope, x-ray fluorescence, Fourier transform infrared and Raman spectroscopy. The influence of these changes on optical absorption and photoluminescence (PL) characteristics have been studied. It was found that increasing annealing temperature (T a), results in structural phase transitions at 300 and 700 °C, increasing {{D}\\text{Sch}} and red shift of the optical band gap (E\\text{g}\\text{opt} ) due to the improvement in crystallinity. The photoluminescence emission spectrum of nonstoichiometric CdS (Cd-rich) nanopowder reveals emission bands at 365, 397, and 434 nm. Furthermore, PL spectrum of colloidal solution exhibits additional green and red emission bands at 535, 570 and 622 nm. To explain the mechanism of PL emission in CdS NPs, trapping and radiative recombination levels have been identified and the corresponding energy band diagrams are suggested. Annealing process results in an overall enhancement in PL intensity due to the improvement in crystallinity associated with the reduction of nonradiative surface state defects. Irradiation of CdS NPs colloidal solution at UV irradiation dose  <13 J cm-2 leads to the enhancement of PL quantum efficiency and blue shift of E\\text{g}\\text{opt} (i.e. photo-brightening) due to the decrease in the particle size deduced from Brus equation ≤ft({{D}\\text{Brus}}\\right) , This behavior is due to UV irradiation effects such as photopolymerization, the formation of CdSO4 passivation layers due to photooxidation and the reduction in {{D}\\text{Brus}} by photocorrosion process. At UV irradiation dose  <13 J cm-2, PL emission intensity continuously enhances without any change in both E

  12. Polarization-selective three-photon absorption and subsequent photoluminescence in CsPbBr3 single crystal at room temperature

    NASA Astrophysics Data System (ADS)

    Clark, D. J.; Stoumpos, C. C.; Saouma, F. O.; Kanatzidis, M. G.; Jang, J. I.

    2016-05-01

    We report on highly polarization-selective three-photon absorption (3PA) in a Bridgman-grown single crystal of CsPbBr3 oriented along the (112) direction, which is an inorganic counterpart to emerging organic-inorganic hybrid halide perovskites for solar-cell and optoelectronic applications. The crystal exhibits strong photoluminescence (PL) at room temperature as a direct consequence of 3PA of fundamental radiation. Interestingly, 3PA disappears when the input polarization is parallel to the (-110 ) direction. This 3PA effect is strongest when orthogonal to (-110 ) and the corresponding 3PA coefficient was measured to be γ =0.14 ±0.03 cm3/GW2 under picosecond-pulse excitation at the fundamental wavelength of λ =1200 nm. The laser-induced damage threshold was also determined to be about 20 GW/cm2 at the same wavelength. Based on relative PL intensities upon λ tuning over the entire 3PA range (1100 -1700 nm), we determined the nonlinear optical dispersion of the 3PA coefficient for CsPbBr3, which is consistent with a theoretical prediction. Experimentally observed significant polarization dependence of γ was explained by relevant selection rules. The perovskite is potentially important for nonlinear optical applications owing to its highly efficient 3PA-induced PL response with a sharp on/off ratio by active polarization control.

  13. Temperature dependence of the band-band absorption coefficient in crystalline silicon from photoluminescence

    NASA Astrophysics Data System (ADS)

    Nguyen, Hieu T.; Rougieux, Fiacre E.; Mitchell, Bernhard; Macdonald, Daniel

    2014-01-01

    The band-band absorption coefficient in crystalline silicon has been determined using spectral photoluminescence measurements across the wavelength range of 990-1300 nm, and a parameterization of the temperature dependence has been established to allow interpolation of accurate values of the absorption coefficient for any temperature between 170 and 363 K. Band-band absorption coefficient measurements across a temperature range of 78-363 K are found to match well with previous results from MacFarlane et al. [Phys. Rev. 111, 1245 (1958)], and are extended to significantly longer wavelengths. In addition, we report the band-band absorption coefficient across the temperature range from 270-350 K with 10 K intervals, a range in which most practical silicon based devices operate, and for which there are only sparse data available at present. Moreover, the absorption coefficient is shown to vary by up to 50% for every 10 K increment around room temperature. Furthermore, the likely origins of the differences among the absorption coefficient of several commonly referenced works by Green [Sol. Energy Mater. Sol. Cells 92, 1305 (2008)], Daub and Würfel [Phys. Rev. Lett. 74, 1020 (1995)], and MacFarlane et al. [Phys. Rev. 111, 1245 (1958)] are discussed.

  14. Cross-polarized optical absorption of single-walled carbon nanotubes probed by photoluminescence excitation spectroscopy, UV-Vis-IR and polarized Raman Scatterings

    NASA Astrophysics Data System (ADS)

    Maruyama, Shigeo

    2008-03-01

    Because of the depolarization effect, or so-called antenna effect, optical absorption of single-walled carbon nanotubes (SWNTs) is weak when excited by light polarized perpendicular to the nanotube axis. However, in photoluminescence (PL) excitation spectra of isolated SWNTs, PL peaks due to cross-polarized excitation can be clearly identified. By decomposing the cross-polarized component, the optical transition energy of E12 or E21 can be? measured, and the smaller exciton binding energy for perpendicular excitations is concluded [1]. Cross-polarized absorption is dominant in the absorption of a vertically aligned film of SWNTs [2] when excited from the top of the film. In our previous study, a pi-plasmon absorption at 5.25 eV was revealed in contrast to 4.5 eV for parallel excitation [3]. Resonant Raman scattering from such a film is also influenced by the cross-polarized excitation [4]. Even though a Kataura plot for the E33 and E44 range has been proposed by using such a vertically aligned film [5], polarized Raman scattering spectra reveal more complicated features in the system because of the small bundle size, typically 5-8 nanotubes [6]. References: [1] Y. Miyauchi, M. Oba, S. Maruyama, Phys. Rev. B 74 (2006) 205440. [2] Y. Murakami, S. Chiashi, Y. Miyauchi, M. Hu, M. Ogura, T. Okubo, S. Maruyama, Chem. Phys. Lett. 385 (2004) 298. [3] Y. Murakami, E. Einarsson, T. Edamura, S. Maruyama, Phys. Rev. Lett. 94 (2005) 087402. [4] Y. Murakami, S. Chiashi, E. Einarsson, S. Maruyama, Phys. Rev. B 71 (2005) 085403. [5] P. T. Araujo, S. K. Doorn, S. Kilina, S. Tretiak, E. Einarsson, S. Maruyama, H. Chacham, M. A. Pimenta, A. Jorio, Phys. Rev. Lett. 88 (2007) 067401. [6] E. Einarsson, H. Shiozawa, C. Kramberger, M. H. Ruemmeli, A. Gruneis, T. Pichler, S. Maruyama, J. Phys. Chem. C (2007) published on Web.

  15. Absorption and photoluminescence study of Al 2O 3 single crystal irradiated with fast neutrons

    NASA Astrophysics Data System (ADS)

    Izerrouken, M.; Benyahia, T.

    2010-10-01

    Colour centers formation in Al 2O 3 by reactor neutrons were investigated by optical measurements (absorption and photoluminescence). The irradiation's were performed at 40 °C, up to fast neutron ( E n > 1.2 MeV) fluence of 1.4 × 10 18 n cm -2. After irradiation the coloration of the sample increases with the neutron fluence and absorption band at about 203, 255, 300, 357 and 450 nm appear in the UV-visible spectrum. The evolution of each absorption bands as a function of fluence and annealing temperature is presented and discussed. The results indicate that at higher fluence and above 350 °C the F + center starts to aggregate to F center clusters (F 2, F 2+ and F22+). These aggregates disappear completely above 650 °C whereas the F and F + centers persist even after annealing at 900 °C. It is clear also from the results that the absorption band at 300 nm is due to the contribution of both F 2 center and interstitial Ali+ ions.

  16. IRRS, UV-Vis-NIR absorption and photoluminescence upconversion in Ho 3+-doped oxyfluorophosphate glasses

    NASA Astrophysics Data System (ADS)

    Karmakar, Basudeb

    2005-09-01

    Infrared reflection spectroscopic (IRRS), ultraviolet-visible-near infrared (UV-Vis-NIR) absorption and photoluminescence upconversion properties with special emphasis on the spectrochemistry of the oxyfluorophosphate (oxide incorporated fluorophosphates) glasses of the Ba(PO 3) 2-AlF 3-CaF 2-SrF 2-MgF 2-Ho 2O 3 system have been studied with different concentrations (0.1, 0.3 and 1.0 mol%) of Ho 2O 3. IRRS spectral band position and intensity of Ho 3+ ion doped oxyfluorophosphate glasses have been discussed in terms of reduced mass and force constant. UV-Vis-NIR absorption band position has been justified with quantitative calculation of nephelauxetic parameter and covalent bonding characteristics of the host. NIR to visible upconversion has been investigated by exciting at 892 nm at room temperature. Three upconverted bands originated from the 5F 3→ 5I 8, ( 5S 2, 5F 4)→ 5I 8 and 5F 5→ 5I 8 transitions have found to be centered at 491 nm (blue, medium), 543 nm (green, very strong) and 658 nm (red, weak), respectively. These bands have been justified from the evaluation of the absorption, normal (down conversion) fluorescence and excitation spectra. The upconversion processes have been explained by the excited state absorption (ESA), energy transfer (ET) and cross relaxation (CR) mechanisms involving population of the metastable (storage) energy levels by multiphonon deexcitation effect. It is evident from the IRRS study that the upconversion phenomena are expedited by the low multiphonon relaxation rate in oxyfluorophosphate glasses owing to their high intense low phonon energy (˜600 cm -1) which is very close to that of fluoride glasses (500-600 cm -1).

  17. Study of self-defocusing, reverse saturable absorption and photoluminescence in anthraquinone PMMA nanocomposite film.

    PubMed

    Zafar, Sana; Khan, Zahid H; Khan, Mohd Shahid

    2014-01-24

    The nanocomposite film of 1,5-diamino-9,10-anthraquinone in poly methyl methacrylate has been fabricated by following guest-host method. Intense reverse saturable absorption and self-defocusing effect have been investigated by employing Z-scan technique with low power CW laser at 532 nm with different intensities for the dye-polymer composite film. The estimated values of nonlinear absorption coefficient β, nonlinear refractive index n2 and third order susceptibility χ((3)) of the composite film are of the order of 10(-3) (m/W), 10(-11) (m(2)/W) and 10(-4) (esu), respectively. The dye molecules have been encapsulated uniformly between molecules of polymer as a nanocomposite with average roughness ∼7.96 nm as characterized by AFM technique. The nanocomposite film also exhibited strong photoluminescence emission when excited with 532 nm. The second order hyperpolarizability of composite film has also been estimated. The evaluated figure of merit W having a value greater than 1, and the results obtained suggest that the composite film of 1,5-diamino-9,10-anthraquinone-PMMA has potential applications in nonlinear optical devices.

  18. Ultra-fast photoluminescence as a diagnostic for laser damage initiation

    SciTech Connect

    Laurence, T A; Bude, J D; Shen, N; Miller, P E; Steele, W A; Guss, G; Adams, J J; Wong, L L; Feit, M D; Suratwala, T I

    2009-10-30

    Using high-sensitivity confocal time-resolved photoluminescence (CTP) techniques, we report an ultra-fast photoluminescence (40ps-5ns) from impurity-free surface flaws on fused silica, including polished, indented or fractured surfaces of fused silica, and from laser-heated evaporation pits. This fast photoluminescence (PL) is not associated with slower point defect PL in silica which has characteristic decay times longer than 5ns. Fast PL is excited by the single photon absorption of sub-band gap light, and is especially bright in fractures. Regions which exhibit fast PL are strongly absorptive well below the band gap, as evidenced by a propensity to damage with 3.5eV ns-scale laser pulses, making CTP a powerful non-destructive diagnostic for laser damage in silica. The use of CTP to provide insights into the nature of damage precursors and to help develop and evaluate new damage mitigation strategies will be presented.

  19. The relationship between photoluminescence (PL) decay and crystal growth kinetics in thioglycolic acid (TGA) capped CdTe quantum dots (QDs).

    PubMed

    Lv, Xiangying; Xue, Xiaogang; Huang, Yang; Zhuang, Zanyong; Lin, Zhang

    2014-06-21

    The PL lifetime optimization of CdTe QDs capped with TGA has yet to be understood from a perspective of growth kinetics. In this work, the growth kinetics and PL properties of CdTe QDs growing in aqueous solutions of two TGA concentrations, 0 mM and 57 mM, were systematically investigated using UV, TEM, and PL methods. CdTe QDs in 0 mM TGA solution were found to follow the mixed OA (Oriented Attachment)-OR (Ostwald Ripening) growth kinetics. The PL peaks experienced a red-shift with almost unchanged intensity and the PL lifetimes increased gradually. In 57 mM TGA solution, the QDs followed the OA dominated growth mechanism. The PL peak broadened greatly with a red-shift and its intensity decreased significantly. The PL lifetime increased much higher than that in 0 mM TGA solution. Based on the different growth kinetic models of the two systems, we suggest that in the low (0 mM) TGA solution, the increased surface defects induced by TGA desorption and the existence of partial internal defects caused by OA growth were the main reasons for the gradual increase of PL lifetime, while in high (57 mM) TGA solution, the increase of PL lifetime was ascribed to the abundant internal defects produced by OA collision. Finally, kinetic data showed the effect of the TGA concentration on crystal growth and PL lifetime of CdTe QDs. The results might provide guidance for understanding the mechanism behind the phenomena of ligand-related PL properties.

  20. Label-free assay for the detection of glucose mediated by the effects of narrowband absorption on quantum dot photoluminescence

    NASA Astrophysics Data System (ADS)

    Khan, Saara A.; Smith, Gennifer T.; Ellerbee, Audrey K.

    2014-03-01

    We present a novel strategy for label-free detection of glucose based on CdSe/ZnS core/shell quantum dots (QDs). We exploit the concentration-dependent, narrowband absorption of the hexokinase-glucose 6-phosphate dehydrogenase enzymatic assay to selectively filter a 365-nm excitation source, leading to a proportional decrease in the photoluminescence intensity of the QDs. The visible wavelength emission of the QDs enables quantitative readout using standard visible detectors (e.g., CCD). Experimental results show highly linear QD photoluminescence over the clinically relevant glucose concentration range of 1-25mM, in excellent agreement with detection methods demonstrated by others. The method has a demonstrated limit of detection of 3.5μM, also on par with the best proposed methods. A significant advantage of our strategy is the complete elimination of QDs as a consumable. In contrast with other methods of QD-based measurement of glucose, our system does not require the glucose solution to be mixed with the QDs, thereby decreasing its overall cost and making it an ideal strategy for point-of-care detection of glucose in low-resource areas. Furthermore, readout can be accomplished with low-cost, portable detectors such as cellular phones, eliminating the need for expensive and bulky spectrophotometers to output quantitative information. The general strategy we present is useful for other biosensing applications involving chemistries with unique absorption peaks falling within the excitation band of available QDs.

  1. Defect-Induced Photoluminescence Blinking of Single Epitaxial InGaAs Quantum Dots

    NASA Astrophysics Data System (ADS)

    Hu, Fengrui; Cao, Zengle; Zhang, Chunfeng; Wang, Xiaoyong; Xiao, Min

    2015-03-01

    Here we report two types of defect-induced photoluminescence (PL) blinking behaviors observed in single epitaxial InGaAs quantum dots (QDs). In the first type of PL blinking, the ``off'' period is caused by the trapping of hot electrons from the higher-lying excited state (absorption state) to the defect site so that its PL rise lifetime is shorter than that of the ``on'' period. For the ``off'' period in the second type of PL blinking, the electrons relax from the first excited state (emission state) into the defect site, leading to a shortened PL decay lifetime compared to that of the ``on'' period. This defect-induced exciton quenching in epitaxial QDs, previously demonstrated also in colloidal nanocrystals, confirms that these two important semiconductor nanostructures could share the same PL blinking mechanism.

  2. Measurement procedure for absolute broadband infrared up-conversion photoluminescent quantum yields: Correcting for absorption/re-emission

    SciTech Connect

    MacDougall, Sean K. W.; Ivaturi, Aruna; Marques-Hueso, Jose; Richards, Bryce S.

    2014-06-15

    The internal photoluminescent quantum yield (iPLQY) – defined as the ratio of emitted photons to those absorbed – is an important parameter in the evaluation and application of luminescent materials. The iPLQY is rarely reported due to the complexities in the calibration of such a measurement. Herein, an experimental method is proposed to correct for re-emission, which leads to an underestimation of the absorption under broadband excitation. Although traditionally the iPLQY is measured using monochromatic sources for linear materials, this advancement is necessary for nonlinear materials with wavelength dependent iPLQY, such as the application of up-conversion to solar energy harvesting. The method requires an additional measurement of the emission line shape that overlaps with the excitation and absorption spectra. Through scaling of the emission spectrum, at the long wavelength edge where an overlap of excitation does not occur, it is possible to better estimate the value of iPLQY. The method has been evaluated for a range of nonlinear material concentrations and under various irradiances to analyze the necessity and boundary conditions that favor the proposed method. Use of this refined method is important for a reliable measurement of iPLQY under a broad illumination source such as the Sun.

  3. Photoluminescence Enhancement of Adsorbed Species on Si Nanoparticles.

    PubMed

    Matsumoto, Taketoshi; Maeda, Masanori; Kobayashi, Hikaru

    2016-12-01

    We have fabricated Si nanoparticles from Si swarf using the beads milling method. The mode diameter of produced Si nanoparticles was between 4.8 and 5.2 nm. Si nanoparticles in hexane show photoluminescence (PL) spectra with peaks at 2.56, 2.73, 2.91, and 3.09 eV. The peaked PL spectra are attributed to the vibronic structure of adsorbed dimethylanthracene (DMA) impurity in hexane. The PL intensity of hexane with DMA increases by ~3000 times by adsorption on Si nanoparticles. The PL enhancement results from an increase in absorption probability of incident light by DMA caused by adsorption on the surface of Si nanoparticles.

  4. Optical absorption and photoluminescence studies of gold nanoparticles deposited on porous silicon.

    PubMed

    Amran, Tengku Sarah Tengku; Hashim, Md Roslan; Al-Obaidi, Nihad K Ali; Yazid, Hanani; Adnan, Rohana

    2013-01-01

    We present an investigation on a coupled system consists of gold nanoparticles and silicon nanocrystals. Gold nanoparticles (AuNPs) embedded into porous silicon (PSi) were prepared using the electrochemical deposition method. Scanning electron microscope images and energy-dispersive X-ray results indicated that the growth of AuNPs on PSi varies with current density. X-ray diffraction analysis showed the presence of cubic gold phases with crystallite sizes around 40 to 58 nm. Size dependence on the plasmon absorption was studied from nanoparticles with various sizes. Comparison with the reference sample, PSi without AuNP deposition, showed a significant blueshift with decreasing AuNP size which was explained in terms of optical coupling between PSi and AuNPs within the pores featuring localized plasmon resonances. PMID:23331761

  5. Optical absorption and photoluminescence studies of gold nanoparticles deposited on porous silicon

    NASA Astrophysics Data System (ADS)

    Amran, Tengku Sarah Tengku; Hashim, Md Roslan; Al-Obaidi, Nihad K. Ali; Yazid, Hanani; Adnan, Rohana

    2013-01-01

    We present an investigation on a coupled system consists of gold nanoparticles and silicon nanocrystals. Gold nanoparticles (AuNPs) embedded into porous silicon (PSi) were prepared using the electrochemical deposition method. Scanning electron microscope images and energy-dispersive X-ray results indicated that the growth of AuNPs on PSi varies with current density. X-ray diffraction analysis showed the presence of cubic gold phases with crystallite sizes around 40 to 58 nm. Size dependence on the plasmon absorption was studied from nanoparticles with various sizes. Comparison with the reference sample, PSi without AuNP deposition, showed a significant blueshift with decreasing AuNP size which was explained in terms of optical coupling between PSi and AuNPs within the pores featuring localized plasmon resonances.

  6. IRRS, UV-Vis-NIR absorption and photoluminescence upconversion in Ho{sup 3+}-doped oxyfluorophosphate glasses

    SciTech Connect

    Karmakar, Basudeb . E-mail: basudebk@cgcri.res.in

    2005-09-15

    Infrared reflection spectroscopic (IRRS), ultraviolet-visible-near infrared (UV-Vis-NIR) absorption and photoluminescence upconversion properties with special emphasis on the spectrochemistry of the oxyfluorophosphate (oxide incorporated fluorophosphates) glasses of the Ba(PO{sub 3}){sub 2}-AlF{sub 3}-CaF{sub 2}-SrF{sub 2}-MgF{sub 2}-Ho{sub 2}O{sub 3} system have been studied with different concentrations (0.1, 0.3 and 1.0 mol%) of Ho{sub 2}O{sub 3}. IRRS spectral band position and intensity of Ho{sup 3+} ion doped oxyfluorophosphate glasses have been discussed in terms of reduced mass and force constant. UV-Vis-NIR absorption band position has been justified with quantitative calculation of nephelauxetic parameter and covalent bonding characteristics of the host. NIR to visible upconversion has been investigated by exciting at 892 nm at room temperature. Three upconverted bands originated from the {sup 5}F{sub 3}{yields}{sup 5}I{sub 8} ({sup 5}S{sub 2}, {sup 5}F{sub 4}){yields}{sup 5}I{sub 8} and {sup 5}F{sub 5}{yields}{sup 5}I{sub 8} transitions have found to be centered at 491 nm (blue, medium), 543 nm (green, very strong) and 658 nm (red, weak), respectively. These bands have been justified from the evaluation of the absorption, normal (down conversion) fluorescence and excitation spectra. The upconversion processes have been explained by the excited state absorption (ESA), energy transfer (ET) and cross relaxation (CR) mechanisms involving population of the metastable (storage) energy levels by multiphonon deexcitation effect. It is evident from the IRRS study that the upconversion phenomena are expedited by the low multiphonon relaxation rate in oxyfluorophosphate glasses owing to their high intense low phonon energy ({approx}600 cm{sup -1}) which is very close to that of fluoride glasses (500-600 cm{sup -1})

  7. Infrared photoluminescence of composite films containing quasi-isolated multiwalled carbon nanotubes and carbon nanoshells.

    PubMed

    Reyes-Reyes, M; Segura-Cardenas, E; Gorbatchev, A Yu; López-Sandoval, R

    2010-07-01

    Films of small irregular-shaped aggregates composed by several layers of turbostratic graphite encapsulating iron nanoparticles, like carbon nanoshells, and quasi-isolated multi-walled carbon nanotubes (MWCNTs), were synthesized by the chemical vapor deposition method on glass substrates. Quasi-isolated MWCNTs were found emerging in different directions on the agglomerates composed of carbon nanoshells. The morphological properties of the films were characterized using scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy, whereas their optical properties were investigated using optical absorption and photoluminescence (PL) spectroscopy. The studies show a high-intensity PL signal in the infrared at room temperature. This PL signal shows several peaks, which cannot be explained by a blackbody emission. However, the overall PL signal could be a combination of the black emission and electronic transitions. Furthermore, the observed infrared PL emission could be ideal for potential applications such as in gas sensors, infrared detectors and so on. PMID:21128424

  8. Near-infrared photoluminescence and ligand K-edge x-ray absorption spectroscopies of AnO2Cl42-(An:u, NP, Pu)

    SciTech Connect

    Wilkerson, Marianne P; Berg, John M; Clark, David L; Conradson, Steven D; Hobart, David E; Kozimor, Stosh A; Scott, Brian L

    2008-01-01

    We have used photoluminescence and X-ray absorption spectroscopies to investigate electronic structures and metal-ligand bonding of a series of An02CI/ ' (An = U, Np, Pu) compounds. Specifically, we will discuss time-resolved near-infrared emission spectra of crystalline Cs2U(An)02C14 (An = Np and Pu) both at 23 K and 75 K, as well as chlorine Kedge X-ray absorption spectra ofCs2An02CI4 (An = U, Np).

  9. Photoluminescence and extended X-ray absorption fine structure studies on cadmium telluride material

    NASA Astrophysics Data System (ADS)

    Liu, Xiangxin

    The direct-band-gap semiconductor CdTe is an important material for fabricating high efficiency, polycrystalline thin-film solar cells in a heterojunction configuration. The outstanding physical properties of this material such as its good band-gap match to the solar spectrum, ease of fabrication of stoichiometric films, and easy grain boundary passivation make it an important candidate for large area, thin-film solar cells. However, there are several poorly understood processing steps that are commonly utilized in cell fabrication. One of these is a CdCl2 treatment near 400°C in the presence of oxygen, which can improve the cell efficiency a factor of two or more. Another factor is the role of copper in cell performance. In high performance CdS/CdTe thin-film solar cells, copper is usually included in the fabrication of low-resistance back contacts to obtain heavy p-type doping of the absorber CdTe at the contact. However, most of the copper is not electrically active. For example, secondary ion mass spectroscopy (SIMS) on typical CdTe cells has shown Cu concentrations of 1019 atoms/cm3 and even higher, although capacitance-voltage (C-V) measurements indicate typical ionized acceptor levels on the order of 1014/cm 3. Thus, there is great interest in the location and role of this inactive copper in CdTe photovoltaic (PV) devices. In this thesis, I will describe results obtained on magnetron-sputtered CdTe films that were diffused with copper following the procedure used for creating a cell back contact. Extended X-ray Absorption Fine Structure (EXAFS) measurements identified the chemical environment of the majority of the copper and show major differences depending on whether the CdTe film has been treated with chloride prior to the Cu diffusion. The EXAFS data indicate that the Cu chemistry is strongly affected by the chloride treatments---predominantly Cu2Te when Cu was diffused into the as-deposited CdTe film, but a Cu2O environment when Cu was diffused after

  10. Temperature dependent photoluminescence from lead sulfide nanosheets and nanocubes.

    PubMed

    Kim, Jungdong; Kim, Seung Gi; Oh, Eunsoon; Kim, Sang Hyuk; Choi, Won Jun

    2016-01-29

    We studied temperature dependent photoluminescence (PL) spectra in the mid-infrared range from lead sulfide (PbS) nanosheets with an average thickness of 25 nm and nanocubes grown by solvothermal and hydrothermal methods. Distinct bandedge PL emission was observed in the whole temperature range between 10 and 300 K, indicating the high optical quality of these nanostructures. The PL peak of the nanosheets was found at 0.326 eV at 10 K, about 40 meV higher than that of bulk PbS due to the quantum confinement effect, whereas no confinement effect was observed for the nanocubes. We also demonstrate that the absorption edges of the nanocubes and nanosheets in the transmission spectra agree very well with their fundamental bandgap.

  11. Thermally Engineered Blue Photoluminescence of Porous Anodic Alumina Membranes for Promising Optical Biosensors

    NASA Astrophysics Data System (ADS)

    Bu, Sang Don; Cho, Sam Yeon; Choi, Yong Chan; Kim, Jin Woo; Han, Jin Kyu; Kwak, Jin Ho; Yang, Sun A.

    Optical biosensors based on porous anodic alumina membranes (PAAMs) have shown to be an effective device because of their unique optical properties and biocompatibility. Among various optical properties, photoluminescence (PL) emission derived from PAAMs is one of the most suitable characteristics. However, the origin of PL from PAA is unclear and still in doubt. Therefore, it is essential for further potential practical applications to understand the origin of PL and PL variations. Here, we investigate the effects of post-annealing temperatures on the blue PL of amorphous PAAMs fabricated in oxalic acid. We find that the blue PL emission is strongly dependent on the thermal properties. A strong blue PL at a peak of ~460 nm is observed from the initial PAAM (not annealed PAAM) and this PL band can be divided into two Gaussian components at 458 ~ +/- ~ 4 nm (P1 band) and 517 ~ +/- 7nm (P2 band). As the temperature increases to 600 ° C , the intensities of two PL bands gradually increase. During temperature increases from 600 to 700 ° C , the P2 band increases but the P1 band decreases. The analyses of electron paramagnetic resonance, Fourier transform infrared spectroscopy, and ultraviolet-visible absorption spectroscopy show that the P1 and P2 bands originate from the unstable carboxylates and the stable carboxylates, respectively.

  12. Surface-plasmon-enhanced photoluminescence of quantum dots based on open-ring nanostructure array

    NASA Astrophysics Data System (ADS)

    Kannegulla, Akash; Liu, Ye; Cheng, Li-Jing

    2016-03-01

    Enhanced photoluminescence (PL) of quantum dots (QD) in visible range using plasmonic nanostructures has potential to advance several photonic applications. The enhancement effect is, however, limited by the light coupling efficiency to the nanostructures. Here we demonstrate experimentally a new open-ring nanostructure (ORN) array 100 nm engraved into a 200 nm thick silver thin film to maximize light absorption and, hence, PL enhancement at a broadband spectral range. The structure is different from the traditional isolated or through-hole split-ring structures. Theoretical calculations based on FDTD method show that the absorption peak wavelength can be adjusted by their period and dimension. A broadband absorption of about 60% was measured at the peak wavelength of 550 nm. The emission spectrum of CdSe/ZnS core-shell quantum dots was chosen to match the absorption band of the ORN array to enhance its PL. The engraved silver ORN array was fabricated on a silver thin film deposited on a silicon substrate using focus ion beam (FIB) patterning. The device was characterized by using a thin layer of QD water dispersion formed between the ORN substrate and a cover glass. The experimental results show the enhanced PL for the QD with emission spectrum overlapping the absorption band of ORN substrate and quantum efficiency increases from 50% to 70%. The ORN silver substrate with high absorption over a broadband spectrum enables the PL enhancement and will benefit applications in biosensing, wavelength tunable filters, and imaging.

  13. Synthesis and characterization of a new photoluminescent material, tris-[1-10 phenanthroline] aluminium

    NASA Astrophysics Data System (ADS)

    Kumar, Rahul; Dvivedi, Avanish; Bhargava, Parag

    2016-05-01

    A new photoluminescent material namely tris-[1-10 Phenanthroline] Aluminium Al(Phen)3 has been synthesized and characterized. This material was characterized by fourier transform infrared spectroscopy (FTIR),nuclear magnetic resonance (NMR),mass spectroscopy, thermal gravimetric analysis (TGA),ultraviolet-visible spectroscopy(UV) and photoluminescence (PL). This material shows thermal stability up to 300°C. This material showed absorption maxima at 352nm which may be attributed to the moderate energy (π-π*) transition. Photoluminescence spectra for this material showed the most intense peak at 423 nm and the time resolved photoluminescence spectra showed two life time components. The decay times of the first and second component were 1.4ns and 4.8 ns respectively.

  14. Photoluminescence and structural properties of CdSe quantum dot-gelatin composite films

    NASA Astrophysics Data System (ADS)

    Borkovska, L.; Korsunska, N.; Stara, T.; Gudymenko, O.; Kladko, V.; Stroyuk, O.; Raevskaya, A.; Kryshtab, T.

    2014-11-01

    Optical and structural properties of composite films of CdSe quantum dots (QDs) embedded in gelatin matrix have been investigated by photoluminescence (PL), optical absorption and X-ray diffraction (XRD) methods. The optical absorption of the composite in the visible spectral range is found to be determined mainly by light absorption in the QDs. The decrease of the film transparency and the shift of the absorption edge to lower energies observed upon thermal annealing of the films at 140-160 °C are ascribed to the formation of chromophore groups in gelatin matrix. XRD patterns of the composite revealed helix to coil transition in gelatin matrix under thermal annealing of the composite at 100-160 °C. It is found that PL spectra of the composite are dominated by exciton and defect-related emission of the QDs and also contain weak emission of gelatin matrix. It is found that thermal annealing of the composite at 100-160 °C changes PL intensity and produces the shift of the PL bands to lower energies. As the annealed composite was kept in air for several months, the shift of exciton-related PL band position restored partially and the PL intensity increased. It is proposed that the increase of the PL intensity upon the thermal annealing of composite at 140 °C can be used for enhancement of the QD-related PL. Changes that occurred in the PL spectra of composite are ascribed to structural and chemical transformations in gelatin matrix and at the QD/gelatin interface.

  15. Enhanced photoluminescence due to two-photon enhanced three-photon absorption in Mn{sup 2+}-doped ZnS quantum dots

    SciTech Connect

    Subha, Radhu; Nalla, Venkatram; Ji, Wei; Feng, Xiaobo; Vijayan, C.

    2014-10-15

    In this work, we have investigated the multi-photon absorption induced photoluminescence in Mn{sup 2+}-doped ZnS quantum dots in the wavelength range 860 – 1050 nm (Near-Infrared Window I). The observed three-photon action cross-section has been compared with the theoretical prediction under four band approximation. An enhancement of four to five orders has been observed in the range from 970 to 1050 nm compared to the theoretical value, which is attributed to two-photon enhanced three-photon absorption. Transient lifetime measurements reveal a lifetime of 0.35 ± 0.3 ms, which is four to five orders higher than other conventional fluorescent probes.

  16. Bifunctional Ce(1-x)Eu(x)O2 (0 ≤x≤ 0.3) nanoparticles for photoluminescence and photocatalyst applications: an X-ray absorption spectroscopy study.

    PubMed

    Sharma, Aditya; Varshney, Mayora; Park, Jaehun; Ha, Tae Kyun; Chae, Keun Hwa; Shin, Hyun Joon

    2015-11-28

    Ce1-xEuxO2 (0 ≤x≤ 0.3) nanoparticles (NPs) were synthesized by the chemical precipitation method. The microstructures and morphology were characterized by synchrotron X-ray diffraction and high resolution transmission electron microscopy. X-ray absorption near edge structure (XANES) spectra at the Eu M5,4-edge and atomic-multiplet calculations revealed that Eu(3+) was predominantly present in the CeO2 lattice and Eu(2+) was negligibly present within the entire doping range. The detailed analysis of the Ce M5,4-edge and the O K-edge has shown strong dependence of the Ce(3+)/Ce(4+) ratio and oxygen vacancy with Eu content. Extended X-ray absorption fine structure (EXAFS) spectra at the Ce K-edge, along with theoretical fitting, have shown systematic variation in the coordination number, bond length and Debye-Waller factor with Eu doping. A blue shift in the absorption edge was observed which implies a net increase in the charge transfer gap between the O 2p and Ce 4f bands due to the increased number of Ce(3+) ions in the Eu doped samples. The excitation and emission spectra of pure CeO2 NPs did not show any photoluminescence (PL) characteristic; however, Ce1-xEuxO2 (x = 0.1-0.3) NPs showed significant improvements in the 4f-4f, (5)D0-(7)F2 and (5)D0-(7)F1 transitions induced luminescence properties. Eu doping has two major effects on the electronic structure and optical properties of CeO2 NPs: the first, at an Eu content of 10 mol%, is the formation of Ce(4+)-O-Eu(3+) networks, i.e., Eu(3+) ions substitute the Ce(4+) ions and introduce oxygen vacancies and Ce(3+) ions in the host lattice, which favors the (5)D0-(7)F2 induced PL properties. The other, at an Eu doping over 10 mol%, is the formation of both Ce(4+)-O-Eu(3+) and Ce(3+)-O-Eu(3+), i.e., Eu(3+) ions not only take substitutional sites of Ce(4+) ions but also replace a fraction of Ce(3+) ions in the CeO2 lattice which favors (5)D0-(7)F1 induced PL properties. As an application of CeO2 NPs towards the

  17. Similarities in photoluminescence in hafnia and zirconia induced by ultraviolet photons

    NASA Astrophysics Data System (ADS)

    Ito, Toshihide; Maeda, Motohiro; Nakamura, Kazuhiko; Kato, Hiromitsu; Ohki, Yoshimichi

    2005-03-01

    Photoluminescence (PL) spectra induced by ultraviolet photons were measured for amorphous hafnia and zirconia deposited by plasma-enhanced chemical-vapor deposition (PECVD), amorphous hafnia deposited by pulse laser deposition, and crystalline yttria-stabilized zirconia. Two kinds of samples were prepared for both hafnia and zirconia deposited by PECVD using different source alkoxides in different deposition chambers. A PL peak was observed around 2.8eV similarly in all hafnia and zirconia samples, irrespective of the difference in crystallinity, oxygen deficiency, source alkoxide, deposition method, or the substrate material. The decay profile of this PL is also similar in all the samples. These facts clearly show that neither impurities, oxygen vacancy, nor defects at the interface between the sample and the substrate are responsible for the PL. It is a luminescence inherent in hafnia and zirconia and is most likely due to radiative recombination between localized states at the band tails. When the samples were annealed in oxygen, a new PL peak appeared around 4.2eV in all the amorphous samples. Its decay profile is also in common with these samples. Vacuum-ultraviolet absorption measurements and PL excitation measurements indicate that the 4.2-eV PL is excited due to the interband absorption.

  18. Effect of graphene on photoluminescence properties of graphene/GeSi quantum dot hybrid structures

    SciTech Connect

    Chen, Y. L.; Ma, Y. J.; Wang, W. Q.; Ding, K.; Wu, Q.; Fan, Y. L.; Yang, X. J.; Zhong, Z. Y.; Jiang, Z. M.; Chen, D. D.; Xu, F.

    2014-07-14

    Graphene has been discovered to have two effects on the photoluminescence (PL) properties of graphene/GeSi quantum dot (QD) hybrid structures, which were formed by covering monolayer graphene sheet on the multilayer ordered GeSi QDs sample surfaces. At the excitation of 488 nm laser line, the hybrid structure had a reduced PL intensity, while at the excitation of 325 nm, it had an enhanced PL intensity. The attenuation in PL intensity can be attributed to the transferring of electrons from the conducting band of GeSi QDs to the graphene sheet. The electron transfer mechanism was confirmed by the time resolved PL measurements. For the PL enhancement, a mechanism called surface-plasmon-polariton (SPP) enhanced absorption mechanism is proposed, in which the excitation of SPP in the graphene is suggested. Due to the resonant excitation of SPP by incident light, the absorption of incident light is much enhanced at the surface region, thus leading to more exciton generation and a PL enhancement in the region. The results may be helpful to provide us a way to improve optical properties of low dimensional surface structures.

  19. Imaging electronic trap states in perovskite thin films with combined fluorescence and femtosecond transient absorption microscopy

    DOE PAGES

    Xiao, Kai; Ma, Ying -Zhong; Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin

    2016-04-22

    Charge carrier trapping degrades the performance of organometallic halide perovskite solar cells. To characterize the locations of electronic trap states in a heterogeneous photoactive layer, a spatially resolved approach is essential. Here, we report a comparative study on methylammonium lead tri-iodide perovskite thin films subject to different thermal annealing times using a combined photoluminescence (PL) and femtosecond transient absorption microscopy (TAM) approach to spatially map trap states. This approach coregisters the initially populated electronic excited states with the regions that recombine radiatively. Although the TAM images are relatively homogeneous for both samples, the corresponding PL images are highly structured. Themore » remarkable variation in the PL intensities as compared to transient absorption signal amplitude suggests spatially dependent PL quantum efficiency, indicative of trapping events. Furthermore, detailed analysis enables identification of two trapping regimes: a densely packed trapping region and a sparse trapping area that appear as unique spatial features in scaled PL maps.« less

  20. Photoluminescence of dense nanocrystalline titanium dioxide thin films: effect of doping and thickness and relation to gas sensing.

    PubMed

    Mercado, Candy; Seeley, Zachary; Bandyopadhyay, Amit; Bose, Susmita; McHale, Jeanne L

    2011-07-01

    The photoluminescence (PL) of dense nanocrystalline (anatase) TiO(2) thin films is reported as a function of calcination temperature, thickness, and tungsten and nickel doping. The dependence of the optical absorption, Raman spectra, and PL spectra on heat treatment and dopants reveals the role of oxygen vacancies, crystallinity, and phase transformation in the performance of TiO(2) films used as gas sensors. The broad visible PL from defect states of compact and undoped TiO(2) films is found to be much brighter and less sensitive to the presence of oxygen than that of mesoporous films. The dense nanocrystalline grains and the nanoparticles comprising the mesoporous film are comparable in size, demonstrating the importance of film morphology and carrier transport in determining the intensity of defect photoluminescence. At higher calcination temperatures, the transformation to rutile results in the appearance of a dominant near-infrared peak. This characteristic change in the shape of the PL spectra demonstrates efficient capture of conduction band electrons by the emerging rutile phase. The W-doped samples show diminished PL with quenching on the red side of the emission spectrum occurring at lower concentration and eventual disappearance of the PL at higher W concentration. The results are discussed within the context of the performance of the TiO(2) thin films as CO gas sensors and the chemical nature of luminescent defects. PMID:21702459

  1. Synthesis, Characterization and its Photoluminescence Properties of Group I-III-VI2 CuInS2 nanocrystals

    NASA Astrophysics Data System (ADS)

    Oda, Masaru; Miyaoka, Tomotari; Yamada, Shuhei; Tani, Toshiro

    We report the synthesis, characterization, and photoluminescence (PL) properties of colloidal I-III-VI2 CuInS2 and CuInS2/ZnS nanocrystals (NCs). Absorption shoulder and PL bands of the NCs are located at higher energy than those of band gap energy of bulk crystals due to a quantum-confinement effect. The PL band has a relatively large Stokes-shift, broad linewidth, and long decay-time, which suggests that the PL originates from a recombination of confined-excitions associated with donor(s) and/or acceptor(s). We found that quantum yield of the PL depends strongly on the photon-energy of excitation light and that it is up to 40-50% in resonant excitation at the energy positions corresponding to the absorption shoulder. Detailed properties and possible dynamics will be described. We also present preliminary results of PL properties focused on single NCs. There exist highluminescent NCs exhibiting so-called PL blinking as similar with II-VI NCs, while the others are dark NCs. 73.21.La, 78.47.jd, 78.67.Bf, 78.67.Hc

  2. Light trapping efficiency comparison of Si solar cell textures using spectral photoluminescence.

    PubMed

    Barugkin, Chog; Allen, Thomas; Chong, Teck K; White, Thomas P; Weber, Klaus J; Catchpole, Kylie R

    2015-04-01

    The band-to-band absorption enhancement due to various types of light trapping structures is studied experimentally with photoluminescence (PL) on monocrystalline silicon wafers. Four basic light trapping structures are examined: reactive ion etched texture (RIE), metal-assisted etched texture (MET), random pyramid texture (RAN) and plasmonic Ag nanoparticles with a diffusive reflector (Ag/DR). We also compare two novel combined structures of front side RIE/rear side RAN and front side RIE/rear side Ag/DR. The use of photoluminescence allows us to measure the absorption due to band-to-band transitions only, and excludes parasitic absorption from free carriers and other sources. The measured absorptance spectra are used to calculate the maximum generation current for each structure, and the light trapping efficiency is compared to a recently-proposed figure of merit. The results show that by combining RIE with RAN and Ag/DR, we can fabricate two structures with excellent light trapping efficiencies of 55% and 52% respectively, which is well above previously reported values for similar wafer thicknesses. A comparison of the measured band-band absorption and the EQE of back-contact silicon solar cells demonstrates that PL extracted absorption provides a very good indication of long wavelength performance for high efficiency silicon solar cells. PMID:25968804

  3. Anti-stokes photoluminescence of II-VI nanoparticles with different emitting states

    NASA Astrophysics Data System (ADS)

    Ozturk, Birol; Wang, Yimg; Chen, Wei; Kotov, Nicholas A.

    2003-03-01

    Anti-stokes photoluminescence of II-VI nanoparticles with different emitting states Birol Ozturk(a), Wei Chen(b), Yimg Wang(a), Nicholas Kotov (a) (a) Department of Chemistry, Oklahoma State University,Stillwater,OK 74078,USA (b) Nomadics Inc., 1024South Innovation Way, Stillwater, OK 74074, USA Abstract Anti-stokes photoluminescence (ASPL) in II-VI colloidal nanoparticles of CdTe and CdSe was studied in dispersions. The measurements showed that photoluminescence PL and ASPL were likely to originate from different although close-lying electronic states. Temperature dependence measurements between 10K and 300K showed that there is no thermal excitation step involved in ASPL emission. Emission intensity dependence on excitation intensity is linear which indicates deviation from the classical two-photon absorption mechanism. The ASPL excitation scheme involving a long-lived intermediate state is discussed.

  4. Spin-Controlled Photoluminescence in Hybrid Nanoparticles Purple Membrane System

    PubMed Central

    2016-01-01

    Spin-dependent photoluminescence (PL) quenching of CdSe nanoparticles (NPs) has been explored in the hybrid system of CdSe NP purple membrane, wild-type bacteriorhodopsin (bR) thin film on a ferromagnetic (Ni-alloy) substrate. A significant change in the PL intensity from the CdSe NPs has been observed when spin-specific charge transfer occurs between the retinal and the magnetic substrate. This feature completely disappears in a bR apo membrane (wild-type bacteriorhodopsin in which the retinal protein covalent bond was cleaved), a bacteriorhodopsin mutant (D96N), and a bacteriorhodopsin bearing a locked retinal chromophore (isomerization of the crucial C13=C14 retinal double bond was prevented by inserting a ring spanning this bond). The extent of spin-dependent PL quenching of the CdSe NPs depends on the absorption of the retinal, embedded in wild-type bacteriorhodopsin. Our result suggests that spin-dependent charge transfer between the retinal and the substrate controls the PL intensity from the NPs. PMID:27018195

  5. Photoluminescence of a Plasmonic Molecule.

    PubMed

    Huang, Da; Byers, Chad P; Wang, Lin-Yung; Hoggard, Anneli; Hoener, Ben; Dominguez-Medina, Sergio; Chen, Sishan; Chang, Wei-Shun; Landes, Christy F; Link, Stephan

    2015-07-28

    Photoluminescent Au nanoparticles are appealing for biosensing and bioimaging applications because of their non-photobleaching and non-photoblinking emission. The mechanism of one-photon photoluminescence from plasmonic nanostructures is still heavily debated though. Here, we report on the one-photon photoluminescence of strongly coupled 50 nm Au nanosphere dimers, the simplest plasmonic molecule. We observe emission from coupled plasmonic modes as revealed by single-particle photoluminescence spectra in comparison to correlated dark-field scattering spectroscopy. The photoluminescence quantum yield of the dimers is found to be surprisingly similar to the constituent monomers, suggesting that the increased local electric field of the dimer plays a minor role, in contradiction to several proposed mechanisms. Aided by electromagnetic simulations of scattering and absorption spectra, we conclude that our data are instead consistent with a multistep mechanism that involves the emission due to radiative decay of surface plasmons generated from excited electron-hole pairs following interband absorption. PMID:26165983

  6. Photoinduced spectral changes of photoluminescent gold nanoclusters

    NASA Astrophysics Data System (ADS)

    Matulionytė, Marija; Marcinonytė, Raminta; Rotomskis, Ričardas

    2015-05-01

    Ultrasmall photoluminescent gold nanoclusters (Au NCs), composed of several atoms with sizes up to a few nanometers, have recently stimulated extensive interest. Unique molecule-like behaviors, low toxicity, and facile synthesis make photoluminescent Au NCs a very promising alternative to organic fluorophores and semiconductor quantum dots (QDs) in broad ranges of biomedical applications. However, using gold nanoparticles (Au NPs) for bioimaging might cause their degradation under continuous excitation with UV light, which might result in toxicity. We report spectral changes of photoluminescent 2-(N-morpholino) ethanesulfonic acid (MES)-coated (Au-MES) NCs under irradiation with UV/blue light. Photoluminescent water soluble Au-MES NCs with a photoluminescence (PL) band maximum at 476 nm (λex=420 nm) were synthesized. Under irradiation with 402 nm wavelength light the size of photoluminescent Au-MES NCs decreased (λem=430 nm). Irradiating the sample solution with 330 nm wavelength light, nonluminescent Au NPs were disrupted, and photoluminescent Au NCs (λem=476 nm) were formed. Irradiation with 330 nm wavelength light did not directly affect photoluminescent Au-MES NCs, however, increase in PL intensity indicated the formation of photoluminescent Au NCs from the disrupted nonluminescent Au NPs. This study gives a good insight into the photostability of MES-coated Au NPs under continuous excitation with UV/blue light.

  7. Surface plasmon enhanced photoluminescence in amorphous silicon carbide films by adjusting Ag island film sizes

    NASA Astrophysics Data System (ADS)

    Yu, Wei; Wang, Xin-Zhan; Dai, Wan-Lei; Lu, Wan-Bing; Liu, Yu-Mei; Fu, Guang-Sheng

    2013-05-01

    Ag island films with different sizes are deposited on hydrogenated amorphous silicon carbide (α-SiC:H) films, and the influences of Ag island films on the optical properties of the α-SiC:H films are investigated. Atomic force microscope images show that Ag nanoislands are formed after Ag coating, and the size of the Ag islands increases with increasing Ag deposition time. The extinction spectra indicate that two resonance absorption peaks which correspond to out-of-plane and in-plane surface plasmon modes of the Ag island films are obtained, and the resonance peak shifts toward longer wavelength with increasing Ag island size. The photoluminescence (PL) enhancement or quenching depends on the size of Ag islands, and PL enhancement by 1.6 times on the main PL band is obtained when the sputtering time is 10 min. Analyses show that the influence of surface plasmons on the PL of α-SiC:H is determined by the competition between the scattering and absorption of Ag islands, and PL enhancement is obtained when scattering is the main interaction between the Ag islands and incident light.

  8. Photoluminescence of monovalent indium centres in phosphate glass

    PubMed Central

    Masai, Hirokazu; Yamada, Yasuhiro; Okumura, Shun; Yanagida, Takayuki; Fujimoto, Yutaka; Kanemitsu, Yoshihiko; Ina, Toshiaki

    2015-01-01

    Valence control of polyvalent cations is important for functionalization of various kinds of materials. Indium oxides have been used in various applications, such as indium tin oxide in transparent electrical conduction films. However, although metastable In+ (5 s2 configuration) species exhibit photoluminescence (PL), they have attracted little attention. Valence control of In+ cations in these materials will be important for further functionalization. Here, we describe In+ species using PL and X-ray absorption fine structure (XAFS) analysis. Three absorption bands in the UV region are attributed to the In+ centre: two weak forbidden bands (1S0 → 3P1, 1S0 → 3P2) and a strong allowed band (1S0 → 1P1). The strongest PL excitation band cannot be attributed to the conventional allowed transition to the singlet excited state. Emission decay of the order of microseconds suggests that radiative relaxation occurs from the triplet excitation state. The XAFS analysis suggests that these In+ species have shorter In–O distances with lower coordination numbers than in In2O3. These results clearly demonstrate that In+ exists in a metastable amorphous network, which is the origin of the observed luminescent properties.

  9. Pressure-induced Co2+ photoluminescence quenching in MgAl2O4

    NASA Astrophysics Data System (ADS)

    Nataf, Lucie; Rodríguez, Fernando; Valiente, Rafael

    2012-09-01

    This work investigates the electronic structure and photoluminescence (PL) of Co2+-doped MgAl2O4 and their pressure dependence by time-resolved spectroscopy. The variations of the visible absorption band and its associated emission at 663 nm (τ = 130 ns at ambient conditions) with pressure/temperature can be explained on the basis of a configurational energy model. It provides an interpretation for both the electronic structure and the excited-state phenomena yielding photoluminescence emission and the subsequent quenching. We show that there is an excited-state crossover (ESCO) [4T1(P)↔2E(G)] at ambient pressure, which is responsible for the evolution of the emission spectrum from a broadband emission between 300 K and 100 K to a narrow-line emission at lower temperatures. Contrary to expectations from the Tanabe-Sugano diagram, instead of enhancing ESCO phenomena, pressure reduces PL and even suppresses it (PL quenching) above 6 GPa. We explain such variations in terms of pressure-induced nonradiative relaxation to lower excited states: 2E(G)→4T1(F). The variation of PL intensity and its associated lifetime with pressure supports the proposed interpretation.

  10. Photoluminescence in Carborane-Stilbene Triads: A Structural, Spectroscopic, and Computational Study.

    PubMed

    Cabrera-González, Justo; Viñas, Clara; Haukka, Matti; Bhattacharyya, Santanu; Gierschner, Johannes; Núñez, Rosario

    2016-09-12

    A set of triads in which o- and m-carborane clusters are bonded to two stilbene units through Ccluster -CH2 bonds was synthesized, and their structures were confirmed by X-ray diffraction. A study on the influence of the o- and m- isomers on the absorption and photoluminescence properties of the stilbene units in solution revealed no charge-transfer contributions in the lowest excited state, as confirmed by (TD)DFT calculations. The presence of one or two B-I groups in m-carborane derivatives does not affect the emission properties of the stilbenes in solution, probably due to the rather large distance between the iodo substituents and the fluorophore. Nevertheless, a significant redshift of the photoluminescence (PL) emission maximum in the solid state (thin films and powder samples) compared to solution was observed; this can be traced back to PL sensitization, most probably due to more densely packed stilbene moieties. Remarkably, the PL absolute quantum yields of powder samples are significantly higher than those in solution, and this was attributed to the restricted environment and the aforementioned sensitization. Thus, the bonding of the carborane clusters to two stilbene units preserves their PL behavior in solution, but produces significant changes in the solid state. Furthermore, iodinated species can be considered to be promising precursors for theranostic agents in which both imaging and therapeutic functions could possibly be combined. PMID:27555050

  11. Photoluminescence properties of Jahn-Teller transition-metal ions

    NASA Astrophysics Data System (ADS)

    Sanz-Ortiz, Marta N.; Rodríguez, Fernando

    2009-09-01

    This work investigates the influence of electron-phonon coupling associated with E ⊗e and T ⊗e Jahn-Teller (JT) effect in different transition-metal (TM) ions on de-excitation phenomena through nonradiative multiphonon relaxation, i.e., photoluminescence (PL) quenching. We developed a configurational curve model which is able to predict from the absorption spectrum whether a given JT-TM ion is PL or quenched. The prediction is made on the basis of an adapted Dexter-Klick-Russell parameter for JT systems, defined in terms of spectroscopic parameters through ΛJT=αΔeabs/Eabs, where Δeabs refers to the splitting of the parent octahedral Eg states by the JT distortion in E ⊗e (α =3/4) or T ⊗e (α =1/4), and Eabs is the energy of the first absorption band involving electronic transition between Eg and T2g. We show that PL in any JT-TM ion occurs whenever ΛJT<0.1 or is quenched if ΛJT>0.2. This result is noteworthy since it allows us to establish structural requirements for the JT-TM ion and the host crystal to be PL. Although PL properties of materials containing TM ions depend on a variety of structural factors such as the electronic configuration, the site symmetry, and the crystal field produced by neighboring atoms, the present model achieves this goal through a simple spectroscopic parameter: ΛJT. In this work we correlated the PL properties of different sixfold-coordinated JT systems such as Ti3+, Cu2+, Mn3+, Cr2+, Fe2+, Co3+, and Ni3+ in halides and oxides with ΛJT obtained from their respective absorption spectra. From this analysis we conclude that depending on the nature of the JT coupling and its strength, PL is either strongly favored or quenched in T ⊗e while it is mostly quenched in E ⊗e systems due to the larger JT distortion.

  12. Dimensional magnetoplasma resonance detected by free-exciton photoluminescence in modulation-doped GaAs/AlxGa1-xAs heterojunctions

    NASA Astrophysics Data System (ADS)

    Ashkinadze, B. M.; Linder, E.; Umansky, V.

    2000-10-01

    We studied the effect of microwave (mw) irradiation on the low-temperature photoluminescence (PL) of high-quality, modulation-doped, wide GaAs/AlxGa1-xAs heterojunctions (HJ's) containing a two-dimensional electron gas (2DEG), in the density range of (0.9-4)×1011 cm-2. The PL arises from excitons that recombine radiatively in the GaAs buffer layer, far from the 2DEG which is confined close to the GaAs/AlxGa1-xAs interface. We observe that the exciton PL is affected by a mw heating of the 2DEG: the mw-induced PL intensity change increases with increasing 2DEG density as well as under a perpendicular magnetic field that corresponds to the 2DEG dimensional magnetoplasma resonance (DMPR) condition. Moreover, the exciton PL intensity shows a bistability at magnetic field strengths that are close to those observed in the DMPR mw absorption. The mw-induced PL modulation effects are interpreted as being due to the interaction of the excitons with low-energy, ballistically propagating acoustic phonons that are emitted by the mw-heated 2DEG. The exciton PL quenching is associated with an exciton drag by the phonon flux towards the opposite HJ interface where the excitons recombine nonradiatively. The rate of phonon emission is determined by the 2DEG state, and thus the exciton PL responds to the changes of the 2DEG parameters.

  13. Anomalous Light Emission and Wide Photoluminescence Spectra in Graphene Quantum Dot: Quantum Confinement from Edge Microstructure.

    PubMed

    Huang, Pu; Shi, Jun-Jie; Zhang, Min; Jiang, Xin-He; Zhong, Hong-Xia; Ding, Yi-Min; Cao, Xiong; Wu, Meng; Lu, Jing

    2016-08-01

    The physical origin of the observed anomalous photoluminescence (PL) behavior, that is, the large-size graphene quantum dots (GQDs) exhibiting higher PL energy than the small ones and the broadening PL spectra from deep ultraviolet to near-infrared, has been debated for many years. Obviously, it is in conflict with the well-accepted quantum confinement. Here we shed new light on these two notable debates by state-of-the-art first-principles calculations based on many-body perturbation theory. We find that quantum confinement is significant in GQDs with remarkable size-dependent exciton absorption/emission. The edge environment from alkaline to acidic conditions causes a blue shift of the PL peak. Furthermore, carbon vacancies are inclined to assemble at the GQD edge and form the tiny edge microstructures. The bound excitons, localized inside these edge microstructures, determine the anomalous PL behavior (blue and UV emission) of large-size GQDs. The bound excitons confined in the whole GQD lead to the low-energy transition. PMID:27409980

  14. Multi-mode interference revealed by two photon absorption in silicon rich SiO{sub 2} waveguides

    SciTech Connect

    Manna, S. E-mail: mattia.mancinelli@unitn.it; Ramiro-Manzano, F.; Mancinelli, M. E-mail: mattia.mancinelli@unitn.it; Turri, F.; Pavesi, L.; Ghulinyan, M.; Pucker, G.

    2015-02-16

    Photoluminescence (PL) from Si nanocrystals (NCs) excited by two-photon absorption (TPA) has been observed in Si nanocrystal-based waveguides fabricated by plasma enhanced chemical vapor deposition. The TPA excited photoluminescence emission resembles the one-photon excited photoluminescence arising from inter-band transitions in the quantum confined Si nanocrystals. By measuring the non-linear transmission of waveguides, a large TPA coefficient of β up to 10{sup −8 }cm/W has been measured at 1550 nm. These values of β depend on the Si NCs size and are two orders of magnitude larger than the bulk silicon value. Here, we propose to use the TPA excited visible PL emission as a tool to map the spatial intensity profile of the 1550 nm propagating optical modes in multimode waveguides. In this way, multimode interference has been revealed experimentally and confirmed through a finite element simulation.

  15. Doped Semiconductor-Nanocrystal Emitters with Optimal Photoluminescence Decay Dynamics in Microsecond to Millisecond Range: Synthesis and Applications

    PubMed Central

    2015-01-01

    Transition metal doped semiconductor nanocrystals (d-dots) possess fundamentally different emission properties upon photo- or electroexcitation, which render them as unique emitters for special applications. However, in comparison with intrinsic semiconductor nanocrystals, the potential of d-dots has been barely realized, because many of their unique emission properties mostly rely on precise control of their photoluminescence (PL) decay dynamics. Results in this work revealed that it would be possible to obtain bright d-dots with nearly single-exponential PL decay dynamics. By tuning the number of Mn2+ ions per dot from ∼500 to 20 in Mn2+ doped ZnSe nanocrystals (Mn:ZnSe d-dots), the single-exponential PL decay lifetime was continuously tuned from ∼50 to 1000 μs. A synthetic scheme was further developed for uniform and epitaxial growth of thick ZnS shell, ∼7 monolayers. The resulting Mn:ZnSe/ZnS core/shell d-dots were found to be essential for necessary environmental durability of the PL properties, both steady-state and transient ones, for the d-dot emitters. These characteristics combined with intense absorption and high PL quantum yields (70 ± 5%) enabled greatly simplified schemes for various applications of PL lifetime multiplexing using Mn:ZnSe/ZnS core/shell d-dots. PMID:27163024

  16. Photoluminescence of MoS2 quantum dots quenched by hydrogen peroxide: A fluorescent sensor for hydrogen peroxide

    NASA Astrophysics Data System (ADS)

    Gan, Zhixing; Gui, Qingfeng; Shan, Yun; Pan, Pengfei; Zhang, Ning; Zhang, Lifa

    2016-09-01

    By cutting MoS2 microcrystals to quantum dots (QDs) of sizes below 10 nm, the photoluminescence (PL) at ca. 450 nm can be detected easily due to the quantum confinement effects across the 2D planes. The PL is stable under continuous irradiation of UV light but gradually quenches when treated with an increasing concentration of hydrogen peroxide. Time-resolved PL and Raman spectra imply that H2O2 causes the partial oxidation of MoS2 QDs. First-principles calculations reveal that the MoS2 QDs with oxygen impurity are of indirect bandgap structures showing no notable PL. And absorption spectra verify that the PL of MoS2 QDs quenched by H2O2 is attributed to the oxidation. The integrated PL intensity and H2O2 concentration show an exponential relationship in the range of 2-20 μM, suggesting that MoS2 QDs are potential fluorescent probes for hydrogen peroxide sensing in a physiological environment.

  17. Doped Semiconductor-Nanocrystal Emitters with Optimal Photoluminescence Decay Dynamics in Microsecond to Millisecond Range: Synthesis and Applications.

    PubMed

    Pu, Chaodan; Ma, Junliang; Qin, Haiyan; Yan, Ming; Fu, Tao; Niu, Yuan; Yang, Xiaoli; Huang, Yifan; Zhao, Fei; Peng, Xiaogang

    2016-01-27

    Transition metal doped semiconductor nanocrystals (d-dots) possess fundamentally different emission properties upon photo- or electroexcitation, which render them as unique emitters for special applications. However, in comparison with intrinsic semiconductor nanocrystals, the potential of d-dots has been barely realized, because many of their unique emission properties mostly rely on precise control of their photoluminescence (PL) decay dynamics. Results in this work revealed that it would be possible to obtain bright d-dots with nearly single-exponential PL decay dynamics. By tuning the number of Mn(2+) ions per dot from ∼500 to 20 in Mn(2+) doped ZnSe nanocrystals (Mn:ZnSe d-dots), the single-exponential PL decay lifetime was continuously tuned from ∼50 to 1000 μs. A synthetic scheme was further developed for uniform and epitaxial growth of thick ZnS shell, ∼7 monolayers. The resulting Mn:ZnSe/ZnS core/shell d-dots were found to be essential for necessary environmental durability of the PL properties, both steady-state and transient ones, for the d-dot emitters. These characteristics combined with intense absorption and high PL quantum yields (70 ± 5%) enabled greatly simplified schemes for various applications of PL lifetime multiplexing using Mn:ZnSe/ZnS core/shell d-dots. PMID:27163024

  18. Photoluminescence of a single complex plasmonic nanoparticle

    PubMed Central

    Zhang, Tianyue; Lu, Guowei; Shen, Hongming; Shi, Kebin; Jiang, Yuanyuan; Xu, Dongsheng; Gong, Qihuang

    2014-01-01

    We report detailed investigations of the photoluminescence (PL) generated from an individual gold nanoflower, a highly branched plasmonic nanoparticle. Compared to nanostructures with simple shapes, such as spheres, nanorods, and bipyramids, nanoflowers exhibit more distinct features, i.e., the PL spectra and far-field emission patterns are strongly dependent on the wavelength and polarization of the excitation light. The experimental results are qualitatively explained using theoretical calculations. In addition, the intrinsic PL signal is highly dominated by localized surface plasmon resonances. The crucial role of plasmonic coupling in complex nanostructures during the plasmon-enhanced PL process is highlighted. The findings contribute to a deeper understanding of the PL properties of metallic nanoparticles. This study will be beneficial for several potential applications, including optical imaging and sensing in the fields of materials science and biology. PMID:24463794

  19. Photoluminescence properties of cerium oxide nanoparticles as a function of lanthanum content

    SciTech Connect

    Deus, R.C.; Cortés, J.A.; Ramirez, M.A.; Ponce, M.A.; Andres, J.; Rocha, L.S.R.; and others

    2015-10-15

    Highlights: • CeO{sub 2} nanoparticles were obtained by microwave-hydrothermal method. • Rietveld refinement reveals a cubic structure. • KOH mineralizer agent exhibit weak agglomeration at low temperature and shorter time. - Abstract: The structural and photoluminescent properties at room temperature of CeO{sub 2} and La-doped CeO{sub 2} particles were undertaken. The obtained particles were synthesized by a microwave-assisted hydrothermal method (MAH) under different lanthanum contents. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman), Ultra-violet spectroscopy (UV–vis) and photoluminescence (PL) measurements were carried out. XRD revealed that the powders are free of secondary phases and crystallize in the cubic structure. Raman data show that increasing La doping content increase oxygen vacancies due to lattice expansion. The UV/vis absorption spectroscopy suggested the presence of intermediate energy levels in the band gap of structurally ordered powders. Lanthanum addition creates oxygen vacancies and shifts the photoluminescence in the low energy range leading to intense PL emission.

  20. Synthesis and photoluminescent and nonlinear optical properties of manganese doped ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Nazerdeylami, Somayeh; Saievar-Iranizad, Esmaiel; Dehghani, Zahra; Molaei, Mehdi

    2011-01-01

    In this work we synthesized ZnS:Mn 2+ nanoparticles by chemical method using PVP (polyvinylpyrrolidone) as a capping agent in aqueous solution. The structure and optical properties of the resultant product were characterized using UV-vis optical spectroscopy, X-ray diffraction (XRD), photoluminescence (PL) and z-scan techniques. UV-vis spectra for all samples showed an excitonic peak at around 292 nm, indicating that concentration of Mn 2+ ions does not alter the band gap of nanoparticles. XRD patterns showed that the ZnS:Mn 2+ nanoparticles have zinc blende structure with the average crystalline sizes of about 2 nm. The room temperature photoluminescence (PL) spectrum of ZnS:Mn 2+ exhibited an orange-red emission at 594 nm due to the 4T 1- 6A 1 transition in Mn 2+. The PL intensity increased with increase in the Mn 2+ ion concentration. The second-order nonlinear optical properties of nanoparticles were studied using a continuous-wave (CW) He-Ne laser by z-scan technique. The nonlinear refractive indices of nanoparticles were in the order of 10 -8 cm 2/W with negative sign and the nonlinear absorption indices of these nanoparticles were obtained to be about 10 -3 cm/W with positive sign.

  1. Anomalous photoluminescence in InP1−xBix

    PubMed Central

    Wu, Xiaoyan; Chen, Xiren; Pan, Wenwu; Wang, Peng; Zhang, Liyao; Li, Yaoyao; Wang, Hailong; Wang, Kai; Shao, Jun; Wang, Shumin

    2016-01-01

    Low temperature photoluminescence (PL) from InP1−xBix thin films with Bi concentrations in the 0–2.49% range reveals anomalous spectral features with strong and very broad (linewidth of 700 nm) PL signals compared to other bismide alloys. Multiple transitions are observed and their energy levels are found much smaller than the band-gap measured from absorption measurements. These transitions are related to deep levels confirmed by deep level transient spectroscopy, which effectively trap free holes and enhance radiative recombination. The broad luminescence feature is beneficial for making super-luminescence diodes, which can theoretically enhance spatial resolution beyond 1 μm in optical coherent tomography (OCT). PMID:27291823

  2. Photoluminescence and energy transfer process in Gd2O3:Eu3+, Tb3+

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, T.; Bose, A. Chandra

    2016-05-01

    Variation in photoluminescence (PL) properties of Eu3+ and Tb3+ as a function of co-dopant (Tb3+) concentration are studied for Gd2-x-yO3: Eu3+x Tb3+y (x = 0.02, y = 0.01, 0.03, 0.05). The crystal structure analysis is carried out by X-ray Diffraction (XRD). Absence of addition peaks corresponding europium or terbium phase confirms the phase purity. Diffuse reflectance spectroscopy (DRS) reveals the absorption peaks corresponding to host matrix, Eu3+ and Tb3+. The bandgap calculated from Kubelka - Munk function is also reported. PL spectra are recorded at the excitation wavelength of 307 nm and the emission peak corresponding to Eu3+ confirms the energy transfer from Tb3+ to Eu3+. The agglomeration of particles acts as quenching centres for energy transfer at higher concentrations.

  3. Anomalous photoluminescence in InP1‑xBix

    NASA Astrophysics Data System (ADS)

    Wu, Xiaoyan; Chen, Xiren; Pan, Wenwu; Wang, Peng; Zhang, Liyao; Li, Yaoyao; Wang, Hailong; Wang, Kai; Shao, Jun; Wang, Shumin

    2016-06-01

    Low temperature photoluminescence (PL) from InP1‑xBix thin films with Bi concentrations in the 0–2.49% range reveals anomalous spectral features with strong and very broad (linewidth of 700 nm) PL signals compared to other bismide alloys. Multiple transitions are observed and their energy levels are found much smaller than the band-gap measured from absorption measurements. These transitions are related to deep levels confirmed by deep level transient spectroscopy, which effectively trap free holes and enhance radiative recombination. The broad luminescence feature is beneficial for making super-luminescence diodes, which can theoretically enhance spatial resolution beyond 1 μm in optical coherent tomography (OCT).

  4. Simple chemical aqueous synthesis of dahlia nanoflower consisting of finger-like ZnO nanorods and observation of stable ultraviolet photoluminescence emission

    NASA Astrophysics Data System (ADS)

    Chakraborty, S.; Tiwary, C. S.; Kumbhakar, P.

    2015-03-01

    In this work, we have reported the synthesis of dahlia flower-like ZnO nanostructures consisting of human finger-like nanorods by the hydrothermal method at 120 °C and without using any capping agent. Optical properties of the samples, including UV-vis absorption and photoluminescence (PL) emission characteristics are determined by dispersing the samples in water as well as in ethanol media. The quenching of PL emission intensity along-with the red shifting of the PL emission peak are observed when the samples are dispersed in water in comparison to those obtained after dispersing the samples in ethanol. It has been found that PL emission characteristic, particularly the spectral nature of PL emission, of the samples remains almost unaltered (except some improvement in UV PL emission) even after thermally annealing it for 2 h at the temperature of 300 °C. Also the synthesized powder samples, kept in a plastic container, showed a very stable PL emission even after 15 months of synthesis. Therefore, the synthesized samples might be useful for their applications in future optoelectronics devices.

  5. Improved photoluminescence and sensing stability of porous silicon nanowires by surface passivation.

    PubMed

    Gan, Lu; He, Haiping; Sun, Luwei; Ye, Zhizhen

    2014-01-21

    Core-shell structured silicon nanowires (Si NWs) were obtained by coating Si NWs with an HfO2 layer. Enhanced photoluminescence (PL) and a slightly decreased PL lifetime are achieved by HfO2 coating. Furthermore, the sensing stability is strongly improved. The improvement of PL properties is interpreted in terms of surface passivation and the Purcell effect.

  6. Effect of Mg diffusion on photoluminescence spectra of MgZnO/ZnO bi-layers annealed at different temperatures

    NASA Astrophysics Data System (ADS)

    Das, Amit K.; Misra, P.; Ajimsha, R. S.; Bose, A.; Joshi, S. C.; Porwal, S.; Sharma, T. K.; Oak, S. M.; Kukreja, L. M.

    2013-11-01

    MgZnO/ZnO bilayers (Mg concentration of ˜30%) have been grown and subsequently annealed at different temperatures in the range of 600-900 °C with the specific interest of studying the effect of inter-diffusion of Mg on the photoluminescence (PL) properties of the bilayers. The influence of Mg diffusion and material homogenization is evaluated through absorption, PL, and secondary ion mass spectrometry (SIMS) measurements. No appreciable change in the spectral positions is seen either in PL or absorption up to an annealing temperature of 700 °C, which is also supported by SIMS. However at higher annealing temperatures, diffusion of Mg into the ZnO layer is clearly evident in SIMS profile, which results in the red-shift (blue-shift) of spectral positions of MgZnO (ZnO) layer, respectively. Finally, for the sample annealed at 900 °C, the two layers are completely merged providing a single peak at ˜3.60 eV in PL/absorption corresponding to a completely homogenized MgZnO layer. Spectroscopic results are corroborated by the numerical simulations based on a simple theoretical model, which correlates the observed PL spectra of the heterostructures with the experimental Mg diffusion profiles across the heterointerface, as measured by SIMS.

  7. Photoluminescence of Diamondoid Crystals

    SciTech Connect

    Clay, William; Sasagawa, Takao; Iwasa, Akio; Liu, Zhi; Dahl, Jeremy E.; Carlson, Robert M.K.; Kelly, Michael; Melos, Nicholas; Shen, Zhi-Xun; /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab. /SIMES, Stanford

    2012-04-03

    The photoluminescence of diamondoids in the solid state is examined. All of the diamondoids are found to photoluminesce readily with initial excitation wavelengths ranging from 233 nm to 240 nm (5.3 eV). These excitation energies are more than 1 eV lower than any previously studied saturated hydrocarbon material. The emission is found to be heavily shifted from the absorption, with emission wavelengths of roughly 295 nm (4.2 eV) in all cases. In the dissolved state, however, no uorescence is observed for excitation wavelengths as short as 200 nm. We also discuss predictions and measurements of the quantum yield. Our predictions indicate that the maximum yield may be as high as 25%. Our measurement of one species, diamantane, gives a yield of 11%, the highest ever reported for a saturated hydrocarbon, even though it was likely not at the optimal excitation wavelength.

  8. Full-color tunable photoluminescent ionic liquid crystals based on tripodal pyridinium, pyrimidinium, and quinolinium salts.

    PubMed

    Tanabe, Kana; Suzui, Yuko; Hasegawa, Miki; Kato, Takashi

    2012-03-28

    Color-tunable luminescent ionic liquid crystals have been designed as a new series of luminescent materials. To achieve tuning of emission colors, intramolecular charge transfer (ICT) character has been incorporated into tripodal molecules. A series of the compounds has three chromophores in each molecule, incorporated with both electron-donating moieties such as alkylaminobenzene and alkoxybenzene, and electron-accepting moieties such as pyridinium, pyrimidinium, and quinolinium parts. These C(3)-symmetrical molecules self-assemble into liquid-crystalline (LC) columnar (Col) structures over wide temperature ranges through nanosegregation between ionic moieties and nonionic aliphatic chains. Photoluminescent (PL) emissions of these tripodal molecules are observed in the visible region both in the self-assembled condensed states and in solutions. For example, a pyrimidinium salt with didodecylaminobenzene moieties exhibits yellowish orange emission (λ(em) = 586 nm in a thin film). Multicolor PL emissions are successfully achieved by simple tuning of changing electron-donating and electron-accepting moieties of the compounds, covering the visible region from blue-green to red. It has been revealed that ICT processes in the excited states and weak intermolecular interactions play important roles in the determination of the PL properties of the materials, by measurements of UV-vis absorption and emission spectra, fluorescence lifetimes, and PL quantum yields.

  9. Magnetic field induced extraordinary photoluminescence enhancement in Er{sup 3+}:YVO{sub 4} single crystal

    SciTech Connect

    Zhang, Junpei; Wang, Xia; Tang, Chaoqun; Zhong, Zhiqiang; Ma, Zongwei; Wang, Shaoliang; Han, Yibo; Han, Jun-Bo Li, Liang

    2015-08-28

    A bright green photoluminescence (PL) from {sup 4}S{sub 3∕2} → {sup 4}I{sub 15∕2} emission band in Er{sup 3+}:YVO{sub 4} single crystal has been observed with the excitation of an argon laser at 488.0 nm. More than two orders of PL enhancement have been obtained under the effect of magnetic fields, and the enhancement factor f reaches 170 when the applied magnetic field is 7.7 T under the sample temperature of 4.2 K. Unusually, the PL enhancements only happen at some certain magnetic fields (B{sub c}s), and a decrease of sample temperature will lead to the increase of f and decrease of B{sub c}. The results confirm that this PL enhancement originates from the resonance excitation of the electron transitions induced by the cross of the laser energy and the absorption energy modulated by both the magnetic field and temperature. This special PL enhancement in Er{sup 3+}:YVO{sub 4} single crystal can be applied in the calibration of pulsed high magnetic field, detection of material fine energy structures, and modulation of magneto-optical devices.

  10. Ga nanoparticle-enhanced photoluminescence of GaAs

    SciTech Connect

    Kang, M.; Al-Heji, A. A.; Jeon, S.; Wu, J. H.; Lee, J.-E.; Saucer, T. W.; Zhao, L.; Sih, V.; Katzenstein, A. L.; Sofferman, D. L.; Goldman, R. S.

    2013-09-02

    We have examined the influence of surface Ga nanoparticles (NPs) on the enhancement of GaAs photoluminescence (PL) efficiency. We have utilized off-normal focused-ion-beam irradiation of GaAs surfaces to fabricate close-packed Ga NP arrays. The enhancement in PL efficiency is inversely proportional to the Ga NP diameter. The maximum PL enhancement occurs for the Ga NP diameter predicted to maximize the incident electromagnetic (EM) field enhancement. The PL enhancement is driven by the surface plasmon resonance (SPR)-induced enhancement of the incident EM field which overwhelms the SPR-induced suppression of the light emission.

  11. Nature of room-temperature photoluminescence in ZnO

    SciTech Connect

    Shan, W.; Walukiewicz, W.; Ager III, J.W.; Yu, K.M.; Yuan, H.B.; Xin, H.P.; Cantwell, G.; Song, J.J.

    2004-11-11

    The temperature dependence of the photoluminescence (PL) transitions associated with various excitons and their phonon replicas in high-purity bulk ZnO has been studied at temperatures from 12 K to above room temperature (320 K). Several strong PL emission lines associated with LO phonon replicas of free and bound excitons are clearly observed. The room temperature PL spectrum is dominated by the phonon replicas of the free exciton transition with the maximum at the first LO phonon replica. The results explain the discrepancy between the transition energy of free exciton determined by reflection measurement and the peak position obtained by the PL measurement.

  12. Structured photoluminescence spectrum in laterally anodized porous silicon

    NASA Astrophysics Data System (ADS)

    Fujiwara, Yasufumi; Nishitani, Hikaru; Nakata, Hiroyasu; Ohyama, Tyuzi

    1992-12-01

    Visible photoluminescence (PL) has been systematically investigated in laterally anodized porous silicon. The PL peak position was dependent on the distance from the meniscus and shifted towards a shorter wavelength with increasing anodization current density. A PL spectrum exhibiting several structures was observed inside the mirrorlike region on the sample surface, which was interpreted by multiple reflection of the luminescence, not by the quantum size effects. Through the analysis of the PL spectrum, the Si density of the porous layer was roughly estimated to be 37 percent by means of the effective-medium model.

  13. Strong photoluminescence emission from resonant Fibonacci quantum wells.

    PubMed

    Chang, C H; Chen, C H; Hsueh, W J

    2013-06-17

    Strong photoluminescence (PL) emission from a resonant Fibonacci quantum well (FQW) is demonstrated. The maximum PL intensity in the FQW is significantly stronger than that in a periodic QW under the Bragg or anti-Bragg conditions. Moreover, the peaks of the squared electric field in the FQW are located very near each of the QWs. The optimal PL spectrum in the FQW has an asymmetrical form rather than the symmetrical one in the periodic case. The maximum PL intensity and the corresponding thickness filling factor in the FQW become greater with increasing generation order. PMID:23787654

  14. Photoluminescence properties of porous silicon

    NASA Astrophysics Data System (ADS)

    Heben, M. J.; Xiao, Y.; McCullough, J. M.; Tsuo, Y. S.; Pankove, J. I.; Deb, S. K.

    1992-12-01

    A porous silicon (PS) layer can be produced on a crystalline silicon substrate by electrochemical or chemical etching in hydrofluoric acid (HF) solutions. There are many properties that make PS thin films interesting for photovoltaic applications, such as a possible direct band gap that can be adjusted between 1.5 and 1.9 eV, textured surfaces for light trapping, the potential for low cost and large-area fabrication, and the possibility of tandem cell structures with Si. We report the fabrication of large area PS (up to 3` diameter) with quite uniform photoluminescence (PL) properties, and studies of the effects of post-hydrogenation treatments on the intensity and stability of the PL from PS. We have observed that a remote-plasma processing treatment can increase the PL emission intensity from PS prepared under certain conditions by 100 times or more. The emission band is narrower and centered more toward the blue for the remote-plasma processed sample, and the PL emission intensity does not degrade in an air ambient over a period of at least several weeks. This result indicates that PS has the potential to become a stable and useful optoelectronic material.

  15. Probing the Quenching of Quantum Dot Photoluminescence by Peptide-Labeled Ruthenium(II) Complexes.

    PubMed

    Scott, Amy M; Algar, W Russ; Stewart, Michael H; Trammell, Scott A; Blanco-Canosa, Juan B; Dawson, Philip E; Deschamps, Jeffrey R; Goswami, Ramasis; Oh, Eunkeu; Huston, Alan L; Medintz, Igor L

    2014-05-01

    Charge transfer processes with semiconductor quantum dots (QDs) have generated much interest for potential utility in energy conversion. Such configurations are generally nonbiological; however, recent studies have shown that a redox-active ruthenium(II)-phenanthroline complex (Ru(2+)-phen) is particularly efficient at quenching the photoluminescence (PL) of QDs, and this mechanism demonstrates good potential for application as a generalized biosensing detection modality since it is aqueous compatible. Multiple possibilities for charge transfer and/or energy transfer mechanisms exist within this type of assembly, and there is currently a limited understanding of the underlying photophysical processes in such biocomposite systems where nanomaterials are directly interfaced with biomolecules such as proteins. Here, we utilize redox reactions, steady-state absorption, PL spectroscopy, time-resolved PL spectroscopy, and femtosecond transient absorption spectroscopy (FSTA) to investigate PL quenching in biological assemblies of CdSe/ZnS QDs formed with peptide-linked Ru(2+)-phen. The results reveal that QD quenching requires the Ru(2+) oxidation state and is not consistent with Förster resonance energy transfer, strongly supporting a charge transfer mechanism. Further, two colors of CdSe/ZnS core/shell QDs with similar macroscopic optical properties were found to have very different rates of charge transfer quenching, by Ru(2+)-phen with the key difference between them appearing to be the thickness of their ZnS outer shell. The effect of shell thickness was found to be larger than the effect of increasing distance between the QD and Ru(2+)-phen when using peptides of increasing persistence length. FSTA and time-resolved upconversion PL results further show that exciton quenching is a rather slow process consistent with other QD conjugate materials that undergo hole transfer. An improved understanding of the QD-Ru(2+)-phen system can allow for the design of more

  16. Probing the Quenching of Quantum Dot Photoluminescence by Peptide-Labeled Ruthenium(II) Complexes

    PubMed Central

    2015-01-01

    Charge transfer processes with semiconductor quantum dots (QDs) have generated much interest for potential utility in energy conversion. Such configurations are generally nonbiological; however, recent studies have shown that a redox-active ruthenium(II)–phenanthroline complex (Ru2+-phen) is particularly efficient at quenching the photoluminescence (PL) of QDs, and this mechanism demonstrates good potential for application as a generalized biosensing detection modality since it is aqueous compatible. Multiple possibilities for charge transfer and/or energy transfer mechanisms exist within this type of assembly, and there is currently a limited understanding of the underlying photophysical processes in such biocomposite systems where nanomaterials are directly interfaced with biomolecules such as proteins. Here, we utilize redox reactions, steady-state absorption, PL spectroscopy, time-resolved PL spectroscopy, and femtosecond transient absorption spectroscopy (FSTA) to investigate PL quenching in biological assemblies of CdSe/ZnS QDs formed with peptide-linked Ru2+-phen. The results reveal that QD quenching requires the Ru2+ oxidation state and is not consistent with Förster resonance energy transfer, strongly supporting a charge transfer mechanism. Further, two colors of CdSe/ZnS core/shell QDs with similar macroscopic optical properties were found to have very different rates of charge transfer quenching, by Ru2+-phen with the key difference between them appearing to be the thickness of their ZnS outer shell. The effect of shell thickness was found to be larger than the effect of increasing distance between the QD and Ru2+-phen when using peptides of increasing persistence length. FSTA and time-resolved upconversion PL results further show that exciton quenching is a rather slow process consistent with other QD conjugate materials that undergo hole transfer. An improved understanding of the QD–Ru2+-phen system can allow for the design of more sophisticated

  17. Effects of organic moieties on the photoluminescence spectra of perovskite-type tin bromide based compounds

    NASA Astrophysics Data System (ADS)

    Papavassiliou, George C.; Vidali, Maria-Sofia; Pagona, Georgia; Mousdis, George A.; Karousis, Nikolaos; Koutselas, Ioannis

    2015-04-01

    The photoluminescence (PL) and optical absorption (OA) spectra of some compounds of the type (SC)SnBr3, (BC)2SnBr4, and (SC)(BC)2Sn2Br7 (where SC is CH3NH3 + or Cs+; BC is C4H9NH3 + ,CH3C6H4CH2NH3 + ,C12H25NH3 + ,C18H37NH3 + and 1-naphthylmethyl ammonium group), in the forms of thin deposits on several substrates, are investigated. Generally, using the 350 nm as excitation line, the obtained PL spectra of compounds of the type (BC)2SnBr4 with short alkyl chain-length in the alkyl ammonium moiety, show broad and strong bands. For example, the PL spectra of compound (C4H9NH3)2SnBr4 exhibit a weak band at ca 475 nm, attributed to free-excitons and a broad and strong band at ca 570 nm, attributed to radiative decay of self-trapped excitons in the inorganic moiety. This is a bright yellow-orange emission, which can be seen by naked eye, even at room temperature. In the case of the compounds with long alkyl chain-length in the alkyl ammonium moiety, the PL spectra are dominated by an excitonic band, which occurs close to the corresponding fundamental OA edge. The PL spectrum of (1-naphthylmethyl ammonium)2SnBr4 shows the strong red band with main maxima at ca 603 and 642 nm, arising from tetramers of naphthyl moieties. Also, the PL spectra of the compounds of the type (SC)SnBr3 and (SC)(BC)2Sn2Br7, after grinding, show strong bands at 600-620 nm.

  18. Oxygen and relative humidity monitoring with films tailored for enhanced photoluminescence

    SciTech Connect

    Cui, Weipan; Liu, Rui; Manna, Eeshita; Park, Joong -Mok; Fungura, Fadzai; Shinar, Joseph; Shinar, Ruth

    2014-10-31

    In this study, approaches to generate porous or doped sensing films, which significantly enhance the photoluminescence (PL) of oxygen optical sensors, and thus improve the signal-to-noise (S/N) ratio, are presented. Tailored films, which enable monitoring the relative humidity (RH) as well, are also presented. Effective porous structures, in which the O2-sensitive dye Pt octaethylporphyrin (PtOEP) or the Pd analog PdOEP was embedded, were realized by first generating blend films of polyethylene glycol (PEG) with polystyrene (PS) or with ethyl cellulose (EC), and then immersing the dried films in water to remove the water-soluble PEG. This approach creates pores (voids) in the sensing films. The dielectric contrast between the films’ constituents and the voids increases photon scattering, which in turn increases the optical path of the excitation light within the film, and hence light absorption by the dye, and its PL. Optimized sensing films with a PEG:PS ratio of 1:4 (PEG’s molecular weight Mw ~8000) led to ~4.4× enhancement in the PL (in comparison to PS films). Lower Mw ~200 PEG with a PEG:EC ratio of 1:1 led to a PL enhancement of ~4.7×. Film-dependent PL enhancements were observed at all oxygen concentrations. The strong PL enhancement enables (i) using lower dye (luminophore) concentrations, (ii) reducing power consumption and enhancing the sensor’s operational lifetime when using organic light emitting diodes (OLEDs) as excitation sources, (iii) improving performance when using compact photodetectors with no internal gain, and (iv) reliably extending the dynamic range.

  19. Oxygen and relative humidity monitoring with films tailored for enhanced photoluminescence

    DOE PAGES

    Cui, Weipan; Liu, Rui; Manna, Eeshita; Park, Joong -Mok; Fungura, Fadzai; Shinar, Joseph; Shinar, Ruth

    2014-10-31

    In this study, approaches to generate porous or doped sensing films, which significantly enhance the photoluminescence (PL) of oxygen optical sensors, and thus improve the signal-to-noise (S/N) ratio, are presented. Tailored films, which enable monitoring the relative humidity (RH) as well, are also presented. Effective porous structures, in which the O2-sensitive dye Pt octaethylporphyrin (PtOEP) or the Pd analog PdOEP was embedded, were realized by first generating blend films of polyethylene glycol (PEG) with polystyrene (PS) or with ethyl cellulose (EC), and then immersing the dried films in water to remove the water-soluble PEG. This approach creates pores (voids) inmore » the sensing films. The dielectric contrast between the films’ constituents and the voids increases photon scattering, which in turn increases the optical path of the excitation light within the film, and hence light absorption by the dye, and its PL. Optimized sensing films with a PEG:PS ratio of 1:4 (PEG’s molecular weight Mw ~8000) led to ~4.4× enhancement in the PL (in comparison to PS films). Lower Mw ~200 PEG with a PEG:EC ratio of 1:1 led to a PL enhancement of ~4.7×. Film-dependent PL enhancements were observed at all oxygen concentrations. The strong PL enhancement enables (i) using lower dye (luminophore) concentrations, (ii) reducing power consumption and enhancing the sensor’s operational lifetime when using organic light emitting diodes (OLEDs) as excitation sources, (iii) improving performance when using compact photodetectors with no internal gain, and (iv) reliably extending the dynamic range.« less

  20. Time-resolved photoluminescence from self-assembled Ge(Si) islands in multilayer SiGe/Si and SiGe/SOI structures

    SciTech Connect

    Yablonskiy, A. N. Baidakova, N. A.; Novikov, A. V.; Lobanov, D. N.

    2013-11-15

    The results of a study of the spectral and temporal characteristics of the photoluminescence (PL) from multilayer structures with self-assembled Ge(Si) islands grown on silicon and 'silicon-on-insulator' substrates in relation to temperature and the excitation-light wavelength are presented. A substantial increase in island-related PL intensity is observed for structures with Ge(Si) islands grown on silicon substrates upon an increase in temperature from 4 to 70 K. This increase is due to the diffusion of nonequilibrium carriers from the silicon substrate into the active layer with the islands. In this case, a slow component with a characteristic time of {approx}100 ns appears in the PL rise kinetics. At the same time, no slow component in the PL rise kinetics and no rise in the PL intensity with increasing temperature are observed for structures grown on 'silicon-on-insulator' substrates, in which the active layer with the islands is insulated from the silicon substrate. It is found that absorption of the excitation light in the islands and SiGe wetting layers mainly contributes to the excitation of the PL signal from the islands under sub-bandgap optical pump conditions.

  1. Detailed photoluminescence studies of thin film Cu{sub 2}S for determination of quasi-Fermi level splitting and defect levels

    SciTech Connect

    Sträter, H. Brüggemann, R.; Bauer, G. H.; Siol, S.; Klein, A.; Jaegermann, W.

    2013-12-21

    We have studied chalcocite (Cu{sub 2}S) layers prepared by physical vapor deposition with varying deposition parameters by calibrated spectral photoluminescence (PL) and by confocal PL with lateral resolution of Δ x≈0.9 μm. Calibrated PL experiments as a function of temperature T and excitation fluxes were performed to obtain the absolute PL-yield and to calculate the splitting of the quasi-Fermi levels (QFLs) μ=E{sub f,n}−E{sub f,p} at an excitation flux equivalent to the AM 1.5 spectrum and the absorption coefficient α(ℏω), both in the temperature range of 20 K≤T≤400 K. The PL-spectra reveal two peaks at E{sub #1}=1.17 eV and E{sub #2}=1.3 eV. The samples show a QFL-splitting of μ>700 meV associated with a pseudo band gap of E{sub g}=1.25 eV. The high-energy peak shows an unexpected temperature behavior, namely, an increase of PL-yield with rising temperature at variance with the behavior of QFL-splitting that decreases with rising T. Our observations indicate that, contrary to common believe, it is not the PL-yield, but rather the QFL-splitting that is the comprehensive indicator of the quality of the excited state in an illuminated semiconductor. A further examination of the lateral variation of opto-electronic properties by confocal PL and the surface contour shows no detectable correlation between Cu{sub 2}S grains/grain boundaries and the PL-yield or QFL-splitting.

  2. [The photoluminescence characteristics of organic multilayer quantum wells].

    PubMed

    Zhao, De-Wei; Song, Shu-Fang; Zhao, Su-Ling; Xu, Zheng; Wang, Yong-Sheng; Xu, Xu-Rong

    2007-04-01

    By the use of multi-source high-vaccum organic beam deposition system, the authors prepared organic multilayer quantum well structures, which consist of alternate organic small molecule materials PBD and Alq3. Based on 4-period organic quantum wells, different samples with different thickness barriers and wells were prepared. The authors measured the lowest unoccupied molecular orbit (LUMO) and the highest occupied molecular orbit (HOMO) by electrochemistry cyclic voltammetry and optical absorption. From the energy diagrams, it seems like type-I quantum well structures of the inorganic semiconductor, in which PBD is used as a barrier layer and Alq3 as a well layer and emitter. From small angle X-ray diffraction measurements, the results indicate that these structures have high interface quality and uniformity. The photoluminescence characteristics of organic multilayer quantum wells were investigated. The PL peak has a blue-shift with the decrease of the well layer thickness. Meanwhile as the barrier thickness decreases the PL peaks of PBD disappear gradually. And the energy may be effectively transferred from PBD to Alq3, inducing an enhancement of the luminescence of Alq3.

  3. Photoluminescence by Interstellar Dust

    NASA Astrophysics Data System (ADS)

    Vijh, U. P.

    2005-08-01

    In this dissertation, we report on our study of interstellar dust through the process of photoluminescence (PL). We present the discovery of a new band of dust PL, blue luminescence (BL) with λpeak˜370 nm in the proto-planetary nebula known as the Red Rectangle (RR). We attribute this to fluorescence by small, 3-4-ringed polycyclic aromatic hydrocarbon (PAH) molecules. Further analysis reveals additional independent evidence for the presence of small PAHs in this nebula. Detection of BL using long-slit spectroscopic observations in other ordinary reflection nebulae suggests that the BL carrier is an ubiquitous component of the ISM and is not restricted to the particular environment of the RR. We present the spatial distribution of the BL in these nebulae and find that the BL is spatially correlated with IR emission structures attributed to aromatic emission features (AEFs), attributed to PAHs. The carrier of the dust-associated photoluminescence process causing the extended red emission (ERE), known now for over twenty five years, remains unidentified. We constrain the character of the ERE carrier by determining the wavelengths of the radiation that initiates the ERE -- λ < 118 nm. We note that under interstellar conditions most PAH molecules are ionized to the di-cation stage by photons with E > 10.5 eV and that the electronic energy level structure of PAH di-cations is consistent with fluorescence in the wavelength band of the ERE. In the last few chapters of the dissertation we present first results from ongoing work: i) Using narrow-band imaging, we present the optical detection of the circum-binary disk of the RR in the light of the BL, and show that the morphology of the BL and ERE emissions in the RR nebula are almost mutually exclusive. It is very suggestive to attribute them to different ionization stages of the same family of carriers such as PAH molecules. ii) We also present a pure spectrum of the BL free of scattered light, resolved into seven

  4. On the relationship between radiation-stimulated photoluminescence and nitrogen atoms in p-4 H-SiC

    NASA Astrophysics Data System (ADS)

    Lebedev, A. A.; Ber, B. Ya.; Bogdanova, E. V.; Seredova, N. V.; Kazantsev, D. Yu.; Kozlovski, V. V.

    2015-12-01

    Photoluminescence (PL) appearing in p-4 H-SiC upon its electron irradiation has been studied. A model that accounts for the dependence of the PL intensity on the irradiation dose is suggested. The conclusion is drawn that nitrogen-radiation defect donor-acceptor pairs are PL activators.

  5. Photoluminescence emission at room temperature in zinc oxide nano-columns

    SciTech Connect

    Rocha, L.S.R.; Deus, R.C.; Foschini, C.R.; Simões, A.Z.

    2014-02-01

    Highlights: • ZnO nanoparticles were obtained by microwave-hydrothermal method. • X-ray diffraction reveals a hexagonal structure. • Photoluminescence emission evidenced two absorption peaks, at around 480 nm and 590 nm wavelengths. - Abstract: Hydrothermal microwave method (HTMW) was used to synthesize crystalline zinc oxide (ZnO) nano-columns at the temperature of 120 °C with a soaking time of 8 min. ZnO nano-columns were characterized by using X-ray analyses (XRD), infrared spectroscopy (FT-IR), thermogravimetric analyses (TG-DTA), field emission gun and transmission electron microscopy (FEG-SEM and TEM) and photoluminescence properties (PL). XRD results indicated that the ZnO nano-columns are free of any impurity phase and crystallize in the hexagonal structure. Typical FT-IR spectra for ZnO nano-columns presented well defined bands, indicating a substantial short-range order in the system. PL spectra consist of a broad band at 590 nm and narrow band at 480 nm corresponding to a near-band edge emission related to the recombination of excitons and level emission related to structural defects. These results show that the HTMW synthesis route is rapid, cost effective, and could be used as an alternative to obtain ZnO nano-columns in the temperature of 120 °C for 8 min.

  6. Hydrothermal synthesis and characteristic photoluminescence of Er-doped SnO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Tuan, Pham Van; Hieu, Le Trung; Nga, La Quynh; Dung, Nguyen Duc; Ha, Ngo Ngoc; Khiem, Tran Ngoc

    2016-11-01

    We report the characteristic photoluminescence (PL) spectra of erbium ion (Er3+)-doped tin dioxide (SnO2)nanoparticles. The materials were prepared via hydrothermal method at 180 °C with in 20 h by using various Er3+ ion concentrations ranging from 0.0 to 1.0 at%. After the synthesis, the materials were characterized through X-ray diffraction and high-resolution transmission electron microscopy. Crystallite SnO2 and its average particle diameter of approximately 5 nm did not change with Er3+ ion dopant concentration. Photoluminescence spectra showed the characteristic light emission from the Er3+ ions. The PL excitation spectra referred to an efficient energy transfer to Er3+ ions in the presence of SnO2nanoparticles. The most intense Er-related emission of SnO2:Er3+ nanoparticles in near infrared region was found in samples containing an Er3+ ion concentration of 0.25 at%. Although the absorption bandgaps of the materials were identified at approximately 3.8 eV, we found that efficient excitation comes with low excitation energy band edge. Excitation is possibly involved in shallow defects in SnO2 nanoparticles.

  7. Synthesis, Photoluminescence and Bio-Targeting Applications of Blue Graphene Quantum Dots.

    PubMed

    Wang, Jigang; Zhou, Ji; Zhou, Wenhua; Shi, Jilong; Ma, Lun; Chen, Wei; Wang, Yongsheng; He, Dawei; Fu, Ming; Zhang, Yongna

    2016-04-01

    Chemical derived graphene oxide, an atomically thin sheet of graphite with two-dimensional construction, offers interesting physical, electronic, thermal, chemical, and mechanical properties that are currently being explored for advanced physics electronics, membranes, and composites. Herein, we study graphene quantum dots (GQD) with the blue photoluminescence under various parameters. The GQD samples were prepared at different temperatures, and the blue photoluminescence intensity of the solution improved radically as the heating temperatures increased. Concerning PL peak and intensity of the quantum dots, the results demonstrated dependence on time under heating, temperature of heating, and pH adjusted by the addition of sodium hydroxide. After hydrothermal synthesis routes, the functional groups of graphene oxide were altered the morphology showed the stacking configuration, and self-assembled structure of the graphene sheets with obvious wrinkles appeared at the edge structures. In addition, absorption, PL, and PLE spectra of the graphene quantum dots increase with different quantities of sodium hydroxide added. Finally, using GQD to target PNTIA cells was carried out successfully. High uptake efficiency and no cytotoxic effects indicate graphene quantum dots can be suitable for bio-targeting.

  8. Synthesis, Photoluminescence and Bio-Targeting Applications of Blue Graphene Quantum Dots.

    PubMed

    Wang, Jigang; Zhou, Ji; Zhou, Wenhua; Shi, Jilong; Ma, Lun; Chen, Wei; Wang, Yongsheng; He, Dawei; Fu, Ming; Zhang, Yongna

    2016-04-01

    Chemical derived graphene oxide, an atomically thin sheet of graphite with two-dimensional construction, offers interesting physical, electronic, thermal, chemical, and mechanical properties that are currently being explored for advanced physics electronics, membranes, and composites. Herein, we study graphene quantum dots (GQD) with the blue photoluminescence under various parameters. The GQD samples were prepared at different temperatures, and the blue photoluminescence intensity of the solution improved radically as the heating temperatures increased. Concerning PL peak and intensity of the quantum dots, the results demonstrated dependence on time under heating, temperature of heating, and pH adjusted by the addition of sodium hydroxide. After hydrothermal synthesis routes, the functional groups of graphene oxide were altered the morphology showed the stacking configuration, and self-assembled structure of the graphene sheets with obvious wrinkles appeared at the edge structures. In addition, absorption, PL, and PLE spectra of the graphene quantum dots increase with different quantities of sodium hydroxide added. Finally, using GQD to target PNTIA cells was carried out successfully. High uptake efficiency and no cytotoxic effects indicate graphene quantum dots can be suitable for bio-targeting. PMID:27451650

  9. Formation of isolated Zn vacancies in ZnO single crystals by absorption of ultraviolet radiation: a combined study using positron annihilation, photoluminescence, and mass spectroscopy.

    PubMed

    Khan, Enamul H; Weber, Marc H; McCluskey, Matthew D

    2013-07-01

    Positron annihilation spectra reveal isolated zinc vacancy (V(Zn)) creation in single-crystal ZnO exposed to 193-nm radiation at 100 mJ/cm(2) fluence. The appearance of a photoluminescence excitation peak at 3.18 eV in irradiated ZnO is attributed to an electronic transition from the V(Zn) acceptor level at ~100 meV to the conduction band. The observed V(Zn) density profile and hyperthermal Zn(+) ion emission support zinc vacancy-interstitial Frenkel pair creation by exciting a wide 6.34 eV Zn-O antibonding state at 193-nm photon-a novel photoelectronic process for controlled V(Zn) creation in ZnO.

  10. Effect of Ag/Au bilayer assisted etching on the strongly enhanced photoluminescence and visible light photocatalysis by Si nanowire arrays.

    PubMed

    Ghosh, Ramesh; Imakita, Kenji; Fujii, Minoru; Giri, P K

    2016-03-21

    We report on the strongly enhanced photoluminescence (PL) and visible light photocatalysis by arrays of vertically aligned single crystalline Si nanowires (NWs) grown by Ag/Au bilayer assisted etching. High resolution FESEM and TEM imaging reveals that the Si NWs are decorated with ultra-small size arbitrary shaped Si nanocrystals (NCs) due to the lateral etching of the NWs. A strong broad band and tunable visible to near-infrared (NIR) photoluminescence (PL) in the range 1.3-2.4 eV are observed for these Si NWs/NCs at room temperature, depending on the etching conditions. Our studies reveal that the visible-NIR PL intensity is about two orders of magnitude higher and it exhibits faster decay dynamics in the bilayer assisted etching case as compared to the Ag or Au single layer etching case. The enhanced PL in the bimetal case is attributed to the longer length and higher density of the Si NWs/NCs, surface plasmon resonance enhanced absorption by residual bimetal NPs and the enhanced radiative recombination rate. Studies on the time evolution of PL spectral features with laser exposure under ambient conditions and laser power dependence reveal that both the quantum confinement of carriers in Si NCs and the nonbridging oxygen hole defects in the SiOx layer contribute to the tunable PL. Interestingly, Si NWs grown by Ag/Au bilayer assisted etching exhibit enhanced photocatalytic degradation of methylene blue in comparison to Si NWs grown by single layer Ag or Au assisted etching. The Schottky barrier present between bimetallic NPs and nanoporous Si NWs with Si-H bonds facilitates the photocatalytic activity by efficient separation of photogenerated e-h pairs. Our results demonstrate the superiority of the Si NW array grown by bilayer assisted etching for their cutting edge applications in optoelectronics and environmental cleaning.

  11. Characterization of silicon-germanium epitaxial layer by photoluminescence intensity and reflectance measurement techniques.

    PubMed

    Back, Dohyun; Lee, Jaehyeong

    2014-12-01

    Si(1-x)Ge(x) epitaxial layers with various Ge fractions sample were characterized by photoluminescence intensity method at room temperature. Photoluminescence intensity was affected by minority carrier lifetime, defect density, and surface condition. PL intensity profile showed misfit dislocation on epitaxial layer for 15%, 21%, 24%, and 26%, since dislocations were one of minority carrier lifetime degradation parameters. It clearly showed misfit dislocation profiles, cross-hatch, and PL intensity was low at dislocation region.

  12. Hydrogenation of the Cu{sub PL} center in silicon

    SciTech Connect

    Yarykin, Nikolai; Weber, Jörg

    2014-07-07

    The Cu{sub PL} center, a complex of four copper atoms in silicon with the zero-phonon photoluminescence line at 1014 meV and the donor level at 0.1 eV above the top of the valence band, is studied in the process of hydrogenation at 380 K. Complexes of a substitutional copper atom (Cu{sub s}) with one and two hydrogen atoms are observed to form in the hydrogenated region at the expense of Cu{sub PL}, while no isolated Cu{sub s} atoms are detected. Our results indicate that the addition of a single hydrogen atom induces the dissociation of all interstitial Cu atoms which decorate the Cu{sub s} core of the Cu{sub PL} center.

  13. Photoluminescence studies in epitaxial CZTSe thin films

    NASA Astrophysics Data System (ADS)

    Sendler, Jan; Thevenin, Maxime; Werner, Florian; Redinger, Alex; Li, Shuyi; Hägglund, Carl; Platzer-Björkman, Charlotte; Siebentritt, Susanne

    2016-09-01

    Epitaxial Cu 2 ZnSnSe 4 (CZTSe) thin films were grown by molecular beam epitaxy on GaAs(001) using two different growth processes, one containing an in-situ annealing stage as used for solar cell absorbers and one for which this step was omitted. Photoluminescences (PL) measurements carried out on these samples show no dependence of the emission shape on the excitation intensity at different temperatures ranging from 4 K to 300 K . To describe the PL measurements, we employ a model with fluctuating band edges in which the density of states of the resulting tail states does not seem to depend on the excited charge carrier density. In this interpretation, the PL measurements show that the annealing stage removes a defect level, which is present in the samples without this annealing.

  14. Origin of blue photoluminescence from colloidal silicon nanocrystals fabricated by femtosecond laser ablation in solution.

    PubMed

    Hao, H L; Wu, W S; Zhang, Y; Wu, L K; Shen, W Z

    2016-08-12

    We present a detailed investigation into the origin of blue emission from colloidal silicon (Si) nanocrystals (NCs) fabricated by femtosecond laser ablation of Si powder in 1-hexene. High resolution transmission electron microscopy and Raman spectroscopy observations confirm that Si NCs with average size 2.7 nm are produced and well dispersed in 1-hexene. Fourier transform infrared spectrum and x-ray photoelectron spectra have been employed to reveal the passivation of Si NCs surfaces with organic molecules. On the basis of the structural characterization, UV-visible absorption, temperature-dependent photoluminescence (PL), time-resolved PL, and PL excitation spectra investigations, we deduce that room-temperature blue luminescence from colloidal Si NCs originates from the following two processes: (i) under illumination, excitons first form within colloidal Si NCs by direct transition at the X or Γ (Γ25 → Γ'2) point; (ii) and then some trapped excitons migrate to the surfaces of colloidal Si NCs and further recombine via the surface states associated with the Si-C or Si-C-H2 bonds. PMID:27348227

  15. Origin of blue photoluminescence from colloidal silicon nanocrystals fabricated by femtosecond laser ablation in solution

    NASA Astrophysics Data System (ADS)

    Hao, H. L.; Wu, W. S.; Zhang, Y.; Wu, L. K.; Shen, W. Z.

    2016-08-01

    We present a detailed investigation into the origin of blue emission from colloidal silicon (Si) nanocrystals (NCs) fabricated by femtosecond laser ablation of Si powder in 1-hexene. High resolution transmission electron microscopy and Raman spectroscopy observations confirm that Si NCs with average size 2.7 nm are produced and well dispersed in 1-hexene. Fourier transform infrared spectrum and x-ray photoelectron spectra have been employed to reveal the passivation of Si NCs surfaces with organic molecules. On the basis of the structural characterization, UV-visible absorption, temperature-dependent photoluminescence (PL), time-resolved PL, and PL excitation spectra investigations, we deduce that room-temperature blue luminescence from colloidal Si NCs originates from the following two processes: (i) under illumination, excitons first form within colloidal Si NCs by direct transition at the X or Γ (Γ25 → Γ‧2) point; (ii) and then some trapped excitons migrate to the surfaces of colloidal Si NCs and further recombine via the surface states associated with the Si-C or Si-C-H2 bonds.

  16. Origin of blue photoluminescence from colloidal silicon nanocrystals fabricated by femtosecond laser ablation in solution

    NASA Astrophysics Data System (ADS)

    Hao, H. L.; Wu, W. S.; Zhang, Y.; Wu, L. K.; Shen, W. Z.

    2016-08-01

    We present a detailed investigation into the origin of blue emission from colloidal silicon (Si) nanocrystals (NCs) fabricated by femtosecond laser ablation of Si powder in 1-hexene. High resolution transmission electron microscopy and Raman spectroscopy observations confirm that Si NCs with average size 2.7 nm are produced and well dispersed in 1-hexene. Fourier transform infrared spectrum and x-ray photoelectron spectra have been employed to reveal the passivation of Si NCs surfaces with organic molecules. On the basis of the structural characterization, UV–visible absorption, temperature-dependent photoluminescence (PL), time-resolved PL, and PL excitation spectra investigations, we deduce that room-temperature blue luminescence from colloidal Si NCs originates from the following two processes: (i) under illumination, excitons first form within colloidal Si NCs by direct transition at the X or Γ (Γ25 → Γ‧2) point; (ii) and then some trapped excitons migrate to the surfaces of colloidal Si NCs and further recombine via the surface states associated with the Si–C or Si–C–H2 bonds.

  17. Surface plasmon resonance induced Er{sup 3+} photoluminescence enhancement in tellurite glass

    SciTech Connect

    Fares, Hssen Férid, Mokhtar; Elhouichet, Habib; Gelloz, Bernard

    2015-05-21

    The melt quenching method is used to prepare tellurite glasses co-activated with erbium ions and silver nanoparticles (Ag NPs). The glass samples are characterized by x-ray diffraction, UV-vis-NIR absorption, transmission electron microscopy (TEM) imaging, and photoluminescence spectroscopy. The XRD pattern shows no sharp peak indicating an amorphous nature of the glasses. The presence of Ag NPs is confirmed from TEM micrograph. The absorption spectra reveal not only the peaks due to Er{sup 3+} ions, but also the surface plasmon resonance band of silver NPs in the 510–535 nm range. The J-O model has been applied to the room temperature absorption intensities of Er{sup 3+} (4f{sup 11}) transitions to establish the so-called J-O intensity parameters: Ω{sub 2}, Ω{sub 4}, and Ω{sub 6}. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) and branching ratios of the Er{sup 3+} transitions from the excited state J manifolds to the lower-lying J' manifolds. Intensified of 1.53 μm band is obtained for the sample containing 0.5 mol. % of AgNO{sub 3} (Ag0.5 glass) using for excitation a laser operating at 980 nm. The simultaneous influence of the Ag NPs → Er{sup 3+} energy transfer and the contribution of the intensified local field effect due to the silver NPs give origin to the enhancement of both the Photoluminescence (PL) intensity and the PL lifetime relative to the {sup 4}I{sub 13/2} → {sup 4}I{sub 15/2} transition, whereas the quenching is ascribed to the energy transfer from Er{sup 3+} ions to silver NPs. Based on the analysis of the temperature dependence of the PL intensity and decay time, we identified a weak back transfer process from Er to the glass host that makes the quenching of the PL intensity weak. Large magnitudes of calculated emission cross-section (σ{sub e}), effective bandwidth (Δλ{sub eff}), and bandwidth quality factor (FWHM × σ{sub e}) relatives to {sup 4}I{sub 13

  18. Influence of cysteine doping on photoluminescence intensity from semiconducting single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kurnosov, N. V.; Leontiev, V. S.; Linnik, A. S.; Karachevtsev, V. A.

    2015-03-01

    Photoluminescence (PL) from semiconducting single-walled carbon nanotubes can be applied for detection of cysteine. It is shown that cysteine doping (from 10-8 to 10-3 M) into aqueous suspension of nanotubes with adsorbed DNA leads to increase of PL intensity. The PL intensity was enhanced by 27% at 10-3 M cysteine concentration in suspension. Most likely, the PL intensity increases due to the passivation of p-defects on the nanotube by the cysteine containing reactive thiol group. The effect of doping with other amino acids without this group (methionine, serine, aspartic acid, lysine, proline) on the PL intensity is essentially weaker.

  19. Photochemical doping of graphene oxide with nitrogen for photoluminescence enhancement

    SciTech Connect

    Liu, Fuchi; Tang, Nujiang; Tang, Tao; Liu, Yuan; Feng, Qian; Zhong, Wei; Du, Youwei

    2013-09-16

    Nitrogen-doped graphene oxide (NGO) was synthesized by irradiation of graphene oxide (GO) in NH{sub 3} atmosphere. NGO obtained by irradiation of GO for 10 min has high N content of 13.62 at. %. The photoluminescence (PL) properties of NGO were investigated. The results showed that compared with GO, NGO exhibits significant PL enhancement with a high enhancement ratio of approximately 1501.57%. It may attribute to the high content of amino-like N, which can effectively enhance PL of GO because of the amino conjugation effect.

  20. Preparation of carbon quantum dots with tunable photoluminescence by rapid laser passivation in ordinary organic solvents.

    PubMed

    Li, Xiangyou; Wang, Hongqiang; Shimizu, Yoshiki; Pyatenko, Alexander; Kawaguchi, Kenji; Koshizaki, Naoto

    2011-01-21

    A simple approach to prepare carbon quantum dots is presented in this communication by laser rapid passivation of nano carbon particles in ordinary organic solvent. The as-prepared carbon dots exhibited visible, tunable and stable photoluminescence (PL). XPS analysis showed that the increased oxygen concentration might be concerned with the origin of PL.

  1. Visible photoluminescence of color centers in LiF crystals for absorbed dose evaluation in clinical dosimetry

    NASA Astrophysics Data System (ADS)

    Villarreal-Barajas, J. E.; Piccinini, M.; Vincenti, M. A.; Bonfigli, F.; Khan, R. F.; Montereali, R. M.

    2015-04-01

    Among insulating materials, lithium fluoride (LiF) has been successfully used as ionizing radiation dosemeter for more than 60 years. Thermoluminescence (TL) has been the most commonly used reading technique to evaluate the absorbed dose. Lately, optically stimulated luminescence (OSL) of visible emitting color centers (CCs) has also been explored in pure and doped LiF. This work focuses on the experimental behaviour of nominally pure LiF crystals dosemeters for 6 MV x rays at low doses based on photoluminescence (PL) of radiation induced CCs. Polished LiF crystals were irradiated using 6 MV x rays produced by a clinical linear accelerator. The doses (absorbed dose to water) covered the 1-100 Gy range. Optical absorption spectra show stable formation of primary F defects up to a maximum concentration of 2×1016 cm-3, while no significant M absorption band at around 450 nm was detected. On the other hand, under Argon laser excitation at 458 nm, PL spectra of the irradiated LiF crystals clearly exhibited the characteristic F2 and F+3 visible broad emission bands. Their sum intensity is linearly proportional to the absorbed dose in the investigated range. PL integrated intensity was also measured using a conventional fluorescence optical microscope under blue lamp illumination. The relationship between the absorbed dose and the integrated F2 and F+3 PL intensities, represented by the net average pixel number in the optical fluorescence images, is also fairly linear. Even at the low point defect densities obtained at the investigated doses, these preliminary experimental results are encouraging for further investigation of CCs PL in LiF crystals for clinical dosimetry.

  2. Bandedge optical properties of MBE grown GaAsBi films measured by photoluminescence and photothermal deflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Beaudoin, M.; Lewis, R. B.; Andrews, J. J.; Bahrami-Yekta, V.; Masnadi-Shirazi, M.; O'Leary, S. K.; Tiedje, T.

    2015-09-01

    The bandedge optical properties of GaAsBi films, as thick as 470 nm, with Bi content varying from 0.7% Bi to 2.8% Bi grown by molecular beam epitaxy on GaAs substrates are measured by photoluminescence (PL) and photothermal deflection spectroscopy (PDS). The PDS spectra were fit with a modified Fernelius model which takes into account multiple reflections within the GaAsBi layer and GaAs substrate. Three undoped samples and two samples that are degenerately doped with silicon are studied. The undoped samples show a clear Urbach absorption edge with a composition dependent bandgap that decreases by 56 meV/% Bi and a composition independent Urbach slope parameter of 25 meV due to absorption by Bi cluster states near the valence band. The doped samples show a long absorption tail possibly due to absorption by gap states and free carriers in addition to a Burstein-Moss bandgap shift. PL of the undoped samples shows a lower energy emission peak due to defects not observed in the usually available thin samples (50 nm or less) grown under similar conditions.

  3. Tuning photoluminescence of reduced graphene oxide quantum dots from blue to purple

    SciTech Connect

    Liu, Fuchi; Tang, Tao; Feng, Qian; Li, Ming; Liu, Yuan; Tang, Nujiang Zhong, Wei; Du, Youwei

    2014-04-28

    Reduced graphene oxide quantum dots (rGOQDs) were synthesized by annealing GOQDs in H{sub 2} atmosphere. The photoluminescence (PL) properties of GOQDs and the rGOQDs samples were investigated. The results showed that compared to GOQDs, a blue to purple tunable PL of rGOQDs can be obtained by regulating the annealing temperature. The increase fraction of the newly formed isolated sp{sup 2} clusters may be responsible for the observed tunable PL.

  4. Fabrication of photoluminescent Si-based layers by air optical breakdown near the silicon surface

    NASA Astrophysics Data System (ADS)

    Kabashin, A. V.; Meunier, M.

    2002-01-01

    A novel "dry" method for the fabrication of Si/SiO x nanostructures exhibiting strong visible photoluminescence (PL) is introduced. The method consists in the treatment of a silicon target surface by air breakdown plasma produced by a CO 2 laser radiation in atmospheric air. The treatment leads to the formation of a thin porous layer on the silicon wafer, which exhibits a 1.9-2.0 eV PL. Possible mechanisms of nanostructure formation and PL origin are discussed.

  5. The emission wavelength dependent photoluminescence lifetime of the N-doped graphene quantum dots

    SciTech Connect

    Deng, Xingxia; Sun, Jing; Yang, Siwei; Ding, Guqiao; Shen, Hao; Zhou, Wei; Lu, Jian; Wang, Zhongyang

    2015-12-14

    Aromatic nitrogen doped graphene quantum dots were investigated by steady-state and time-resolved photoluminescence (PL) techniques. The PL lifetime was found to be dependent on the emission wavelength and coincident with the PL spectrum, which is different from most semiconductor quantum dots and fluorescent dyes. This result shows the synergy and competition between the quantum confinement effect and edge functional groups, which may have the potential to guide the synthesis and expand the applications of graphene quantum dots.

  6. Effect of doping of calcium fluoride nanoparticles on the photoluminescence properties of europium complexes with benzoic acid derivatives as secondary ligands and 2-aminopyridine as primary ligand

    NASA Astrophysics Data System (ADS)

    Sharma, Garima; Narula, Anudeep Kumar

    2015-08-01

    The present article reports the synthesis of three Eu(III) complexes [Eu(BA)3(2-ap)] (1), [Eu(HBA)3(2-ap)] (2) and [Eu(ABA)3(2-ap)] (3) (BA = benzoic acid, HBA = 2-hydroxy benzoic acid, ABA = 2-amino benzoic acid and 2-ap = 2-aminopyridine) carried out in ethanol solution. The complexes were further doped with CaF2 nanoparticles and a change in the photoluminescence properties was observed. The compositions and structural investigation of the complexes were determined by elemental analysis and Fourier transform infrared spectroscopy (FTIR) which suggest the coordination of ligands with the central Eu(III) ion. The optical properties of the complexes were studied by Ultraviolet Visible absorption spectroscopy (UV-Vis) and photoluminescence studies (PL). The relative PL intensity was enhanced in the Eu(III) complexes doped with CaF2 nanoparticles as compared to the pure Eu(III) complexes, however the increase in intensity varied in the order of ligands ABA > HBA > BA. The photoluminescence lifetime decay curves also revealed the longer lifetime (τ) and higher quantum efficiency (η) for europium complexes with ABA ligands suggesting the efficient energy transfer and better sensitizing ability of the ligand to europium ion. The morphology of the synthesized compounds were studied by Scanning Electron Microscopy (SEM) revealing spherical morphology with agglomeration of the nanoparticles.

  7. Modelling of thermally detected optical absorption and luminescence of (In,Ga)N/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Siozade, L.; Leymarie, J.; Disseix, P.; Vasson, A.; Mihailovic, M.; Grandjean, N.; Leroux, M.; Massies, J.

    2000-08-01

    Thermally detected optical absorption (TDOA) and photoluminescence (PL) experiments are performed at 0.35 and 4 K, respectively, on In xGa 1- xN ( x≤0.12) layers grown on GaN by molecular beam epitaxy. The modelling of absorption allows us to extract the absorption coefficients and bandgap energies of (In,Ga)N alloy. A bowing parameter equal to 2.4 eV is deduced. The knowledge of the GaN complex refractive index, previously measured, enables us to account for the Fabry-Perot interferences which structure the TDOA and PL spectra. A procedure is proposed to remove the latter in the PL spectrum of nitride based heterostructures. The model is based on the description of the light propagation in an active layer sandwiched between two heterostructures. The parameters deduced from the absorption line shape adjustment are used to take the absorption and optical path into account in the different layers of the samples.

  8. Photoluminescence of zirconium hydroxide: Origin of a chemisorption-induced ‘red-stretch'

    NASA Astrophysics Data System (ADS)

    Watters, Evan J.; Sengupta, Sandip K.; Peterson, Gregory W.; Whitten, James E.

    2014-01-01

    Zirconium hydroxide particles are reactive and photoluminescent, emitting blue light under ultraviolet (UV) irradiation. Adsorption-induced changes in the photoluminescence (PL) offer opportunities for gas sensor/filtration applications. The PL of Zr(OH)4 is quenched in the presence of molecular oxygen, likely through trapping of surface electrons via the formation of O2-. Heating the powder high enough to desorb hydroxyl groups broadens the PL spectrum toward longer wavelengths. This ‘red-stretch' also occurs upon reaction with sulfur dioxide, which replaces terminal hydroxyl groups with sulfite ones. Excessive UV irradiation correspondingly induces this effect. A mechanism is proposed to account for the red-stretch.

  9. Synthesis, characterization and photoluminescence property of La-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Lang, Jihui; Fang, Yue; Zhang, Qi; Wang, Jiaying; Li, Tianshun; Li, Xiuyan; Han, Qiang; Wang, Dandan; Wei, Maobin; Yang, Jinghai

    2016-10-01

    La-doped ZnO nanoparticles were synthesized via a facile and surfactant-free chemical precipitation route, and the effects of lanthanum doping concentration on the structures, morphologies and photoluminescence properties were investigated by XRD, TEM, EDX, PL and UV-Vis absorption spectra. The results showed that the La3+ ions were successfully incorporated into the ZnO host, and the products were well-crystalline. The average size and band gap of La-doped ZnO nanoparticles were varied with the lanthanum doping concentration. The average size of doped nanoparticles was much smaller as compared to that of undoped ZnO. The increasing of lanthanum doping concentration increased the defects in ZnO and resulted in a red shift of UV emission, indicating the narrow band gap in doped nanoparticles. This was probably attributed to the impurity energy levels in band gap introduced by substitutional La3+ ions.

  10. Photoluminescence Properties Research on Graphene Quantum Dots/Silver Composites.

    PubMed

    Wang, Jun; Li, Yan; Zhang, Bo-Ping; Xie, Dan-Dan; Ge, Juan; Liu, Hui

    2016-04-01

    Graphene quantum dots (GQDs) possess unique properties of graphene and exhibit a series of new phenomena of 0 dimension (D) carbon materials. Thus, GQDs have attracted much attention from researchers and have shown great promise for many applications. Recently, many works focus on GQDs-metal ions and metal nanoparticles (NPs). Although, many researches point out that metal ions and metal NPs have significant effect on photoluminescence (PL) feature of GQDs, mainly focus on PL intensity. Here, for the first time, we reported that metal NPs also affected PL peak position which was dependent on the mix mechanism of metal and GQDs. When GQDs-silver (Ag) composite mixed by physical method and excited at a wavelength of 320 nm, PL peak position of composites first showed blue-shifted then red-shifted with increasing of Ag content. However, if GQDs-Ag composite prepared by chemical method, PL peak position of the composites blue-shifted. Furthermore, the shift of PL peak position of GQDs-Ag prepared both for physical and chemical method displayed excitation-dependent feature. When the excitation wavelength approached to Ag SPR peaks, no obvious PL shift was observed. The mechanism for different PL shifts and the phenomenon of excitation-dependent PL shift as well as the formation mechanism of GQDs-Ag composite by chemical method are discussed in detail in this paper. PMID:27451653

  11. Photoluminescence of Eu³⁺-doped glasses with Cu²⁺ impurities.

    PubMed

    Jiménez, José A

    2015-06-15

    Glasses activated with Eu(3+) ions are attractive as luminescent materials for various photonic applications. Co-doping with copper has been proposed for enhancing material optical properties, but the quenching effect of Cu(2+) impurities on Eu(3+) emission in glass remains largely unexplored. In this work, Eu2O3/CuO-containing barium-phosphate glasses have been prepared by the melt-quench method, and the Eu(3+) photoluminescence (PL) quenching resulting from Eu(3+)→Cu(2+) energy transfer was evaluated. Optical absorption spectroscopy showed that with the increase in CuO concentration the Cu(2+) absorption band resonant with Eu(3+) emission (e.g. (5)D0→(7)F2 transition around 615 nm) developed steadily. As a result, Eu(3+) PL was progressively quenched. Evaluation of the quenching constants as a function of temperature in the 298-673K range showed differences basically within experimental error, consistent with a resonant transfer and lack of phonon-assisted processes. Moreover, analysis of the Eu(3+) emission decay dynamics revealed a strong correlation between the decay rates and Cu(2+) impurity levels. Results imply that for practical applications the levels of Cu(2+) in Eu(3+)/Cu(+)-activated glasses should be reduced if not removed as these will significantly limit device efficiency. PMID:25797222

  12. Effect of capping agent concentration on thermoluminescence and photoluminescence of copper-doped zinc sulfide nanoparticles.

    PubMed

    Wanjari, Lata; Bisen, D P; Brahme, Namita; Sahu, Ishwar Prasad; Sharma, Ravi

    2015-08-01

    Copper-doped zinc sulfide (ZnS:Cu) nanoparticles with varying concentrations of capping agent were prepared using a chemical route technique. These particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy and X-ray diffraction (XRD). Optical absorption studies showed that the absorption edge shifted towards the blue region as the concentration of the capping agent increased. Using effective mass approximation, calculation of the nanoparticle size indicated that effective band gap energy increases with decreasing particle size. The thermoluminescence (TL) properties of sodium hexameta phosphate (SHMP)-passivated ZnS:Cu nanoparticles were investigated after UV irradiation at room temperature. The TL glow curve of capped ZnS:Cu showed variations in TL peak position and intensity with the change in capping agent concentration. The photoluminescence (PL) spectra of ZnS:Cu nanoparticles excited at 254 nm exhibited a broad green emission band peaking around 510 nm, which confirmed the characteristic feature of Zn(2+) as well as Cu(2+) ions as the luminescent centres in the lattice. The PL spectra of ZnS:Cu nanoparticles with increasing capping agent concentrations revealed that the emission becomes more intense and shifted towards shorter wavelengths as the sizes of the samples were reduced.

  13. Enhanced UV absorbance and photoluminescence properties of ultrasound assisted synthesized gold doped ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Sahu, Dojalisa; Panda, N. R.; Acharya, B. S.; Panda, A. K.

    2014-06-01

    Au doped ZnO (ZnO:Au) nanostructures were synthesized by ultrasound assisted wet chemical method. The concentration of dopant was varied and both structural and optical properties of ZnO:Au were investigated. The crystal structure and morphology of the samples were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). These results showed the formation of nanorods of ZnO:Au having wurtzite structure and c-axis orientation. Gradual increase in crystallite size and bond length was also observed with the increase in gold concentration in ZnO intending the expansion of lattice after gold doping. The optical absorption measurements showed high ultraviolet (UV) absorbance property of ZnO:Au with sharp and intense absorption band in this region as compared to pristine ZnO. Photoluminescence (PL) measurements showed excitonic emission band of ZnO around 390 nm for both undoped and Au doped ZnO nanoparticles. Further, a strong emission around 467 nm was observed in the PL spectra of ZnO/ZnO:Au which was attributed to the transitions related to excess of oxygen vacancies. Interestingly, a new band was observed at 582 nm for doped ZnO samples which grew in intensity with doping concentration. This band was ascribed to the gold nanoparticle adsorbed on the surface of ZnO.

  14. Plasmonic enhancement of photoluminescence from aluminium nitride

    NASA Astrophysics Data System (ADS)

    Flynn, Chris; Stewart, Matthew

    2016-03-01

    Aluminium nitride (AlN) films were grown on c-plane sapphire wafers by molecular beam epitaxy (MBE) under aluminium-rich conditions. The excess aluminium (Al) accumulated on the surface of the films as micro-scale droplets 1-10 μm in size, and as Al nanoparticles with diameters in the range 10-110 nm. Photoluminescence (PL) measurements were performed on the AlN samples using a 193 nm Excimer laser as the excitation source. Prior to PL measurements the wafers were cleaved in half. One half of each wafer was submitted to a 10 min treatment in H3PO4 heated to 70 °C to remove the excess Al from the film surface. The remaining half was left in the as-deposited condition. The mean intensities of the near-band-edge PL peaks of the as-deposited samples were 2.0-3.4 times higher compared to the samples subjected to the H3PO4 Al-removal treatment. This observation motivated calculations to determine the optimal Al surface nanosphere size for plasmonic enhancement of PL from AlN. The PL enhancement was found to peak for an Al nanosphere radius of 15 nm, which is within the range of the experimentally-observed Al nanoparticle sizes.

  15. Investigation of temperature-dependent photoluminescence in multi-quantum wells

    PubMed Central

    Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

    2015-01-01

    Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells. PMID:26228734

  16. Absence of quantum confinement effects in the photoluminescence of Si{sub 3}N{sub 4}–embedded Si nanocrystals

    SciTech Connect

    Hiller, D. Zelenina, A.; Gutsch, S.; Zacharias, M.; Dyakov, S. A.; López-Conesa, L.; López-Vidrier, J.; Peiró, F.; Garrido, B.; Estradé, S.; Schnabel, M.; Weiss, C.; Janz, S.

    2014-05-28

    Superlattices of Si-rich silicon nitride and Si{sub 3}N{sub 4} are prepared by plasma-enhanced chemical vapor deposition and, subsequently, annealed at 1150 °C to form size-controlled Si nanocrystals (Si NCs) embedded in amorphous Si{sub 3}N{sub 4}. Despite well defined structural properties, photoluminescence spectroscopy (PL) reveals inconsistencies with the typically applied model of quantum confined excitons in nitride-embedded Si NCs. Time-resolved PL measurements demonstrate 10{sup 5} times faster time-constants than typical for the indirect band structure of Si NCs. Furthermore, a pure Si{sub 3}N{sub 4} reference sample exhibits a similar PL peak as the Si NC samples. The origin of this luminescence is discussed in detail on the basis of radiative defects and Si{sub 3}N{sub 4} band tail states in combination with optical absorption measurements. The apparent absence of PL from the Si NCs is explained conclusively using electron spin resonance data from the Si/Si{sub 3}N{sub 4} interface defect literature. In addition, the role of Si{sub 3}N{sub 4} valence band tail states as potential hole traps is discussed. Most strikingly, the PL peak blueshift with decreasing NC size, which is often observed in literature and typically attributed to quantum confinement (QC), is identified as optical artifact by transfer matrix method simulations of the PL spectra. Finally, criteria for a critical examination of a potential QC-related origin of the PL from Si{sub 3}N{sub 4}-embedded Si NCs are suggested.

  17. Controlled agglomeration of Tb-doped Y{sub 2}O{sub 3} nanocrystals studied by x-ray absorption fine structure, x-ray excited luminescence, and photoluminescence

    SciTech Connect

    Soo, Y.L.; Huang, S.W.; Kao, Y.H.; Chhabra, V.; Kulkarni, B.; Veliadis, J.V.; Bhargava, R.N.

    1999-10-01

    Local environment surrounding Y atoms in Y{sub 2}O{sub 3}:Tb nanocrystals under various heat treatment conditions has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. X-ray excited luminescence (XEL) with the incident x-ray energy near Y {ital K} edge and Tb {ital L} edges has also been measured to investigate the mechanisms of x-ray-to-visible down conversion in these doped nanoparticles. The observed changes in EXAFS, XEL, and photoluminescent data can be explained on the basis of increased average size of the nanoparticles as confirmed by transmission electron microscopy studies. Our results thus demonstrate that the doped nanoparticles can agglomerate to a controllable degree by varying the heat treatment temperature. At higher temperatures, the local environment surrounding Y atoms in the nanoparticles is found to become similar to that in bulk Y{sub 2}O{sub 3} while the XEL output still shows the characteristics of nanocrystals. These results indicate that appropriate heat treatment can afford an effective means to control the intensity and signal-to-background ratio of green luminescence output of these doped nanocrystal phosphors, potentially useful for some device applications. {copyright} {ital 1999 American Institute of Physics.}

  18. Absorption and emission of silicon nanocrystals embedded in SiC: Eliminating Fabry-Pérot interference

    SciTech Connect

    Schnabel, M.; Summonte, C.; Canino, M.; Dyakov, S. A.; López-Conesa, L.; Löper, P.; Janz, S.; Wilshaw, P. R.

    2015-01-28

    Silicon nanocrystals embedded in SiC are studied by spectrophotometry and photoluminescence (PL) spectroscopy. Absorptivities are found to be affected by residual Fabry-Pérot interference arising from measurements of reflection and transmission at locations of different film thickness. Multiple computational and experimental methods to avoid these errors in thin film measurements, in general, are discussed. Corrected absorptivity depends on the quantity of Si embedded in the SiC but is independent of the Si crystallinity, indicating a relaxation of the k-conservation criterion for optical transitions in the nanocrystals. Tauc gaps of 1.8–2.0 and 2.12 eV are determined for Si nanoclusters and SiC, respectively. PL spectra exhibit a red-shift of ∼100 nm per nm nominal Si nanocluster diameter, which is in agreement with quantum confinement but revealed to be an artifact entirely due to Fabry-Pérot interference. Several simple experimental methods to diagnose or avoid interference in PL measurements are developed that are applicable to all thin films. Corrected PL is rather weak and invariant with passivation, indicating that non-paramagnetic defects are responsible for rapid non-radiative recombination. They are also responsible for the broad, sub-gap PL of the SiC, and can wholly account for the form of the PL of samples with Si nanoclusters. The PL intensity of samples with Si nanoclusters, however, can only be explained with an increased density of luminescent defects in the SiC due to Si nanoclusters, efficient tunneling of photogenerated carriers from Si nanoclusters to SiC defects, or with emission from a-Si nanoclusters. Films prepared on Si exhibit much weaker PL than the same films prepared on quartz substrates.

  19. Effect of thickness on nonlinear absorption properties of graphite oxide thin films

    NASA Astrophysics Data System (ADS)

    Sreeja, V. G.; Cheruvalathu, Ajina; Reshmi, R.; Anila, E. I.; Thomas, Sheenu; Jayaraj, M. K.

    2016-10-01

    We report the thickness dependent structural, linear and nonlinear optical properties of graphite oxide (GO) thin films synthesized by spin coating method. We observed that the structural, linear and nonlinear optical properties can be tuned by the film thickness in GO. The nonlinear absorption studies by open aperture z scan technique exhibited a saturable absorption. The nonlinear absorption coefficient and saturation intensity varies with film thickness which is attributed to increased localized defect states in the energy band gap. Our results emphasize relatively large thickness dependent optical nonlinearity of GO thin films and its potential for optical pulse generation, exploring the way to GO based nonlinear applications in Q switched mode locking laser systems. All the coated GO films were characterized by X-Ray diffraction method (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV-Vis absorption spectroscopy (UV-Vis), Photoluminescence (PL) and Scanning electron microscope (SEM) measurements.

  20. Diffusion length and resistivity distribution characteristics of silicon wafer by photoluminescence

    SciTech Connect

    Baek, Dohyun; Lee, Jaehyeong; Choi, Byoungdeog

    2014-10-15

    Highlights: • Analytical photoluminescence efficiency calculation and PL intensity ratio method are developed. • Wafer resistivity and diffusion length characteristics are investigated by PL intensity ratio. • PL intensity is well correlated with resistivity, diffusion length or defect density on wafer measurement. - Abstract: Photoluminescence is a convenient, contactless method to characterize semiconductors. Its use for room-temperature silicon characterization has only recently been implemented. We have developed the PL efficiency theory as a function of substrate doping densities, bulk trap density, photon flux density, and reflectance and compared it with experimental data initially for bulk Si wafers. New developed PL intensity ratio method is able to predict the silicon wafer properties, such as doping densities, minority carrier diffusion length and bulk trap density.

  1. Enhanced 1520 nm photoluminescence from Er3+ ions in di-erbium-carbide metallofullerenes (Er2C2)@C82 (isomers I, II, and III).

    PubMed

    Ito, Yasuhiro; Okazaki, Toshiya; Okubo, Shingo; Akachi, Masahiro; Ohno, Yutaka; Mizutani, Takashi; Nakamura, Tetsuya; Kitaura, Ryo; Sugai, Toshiki; Shinohara, Hisanori

    2007-12-01

    Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C(82) cage such as Er(2)@C(82) (isomers I, II, and III) and (Er(2)C(2))@C(82) (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y(2)C(2))@C(82) (I, II, III), where molecular symmetries of the structures are determined to be C(s), C(2v) and C(3v), respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er(3+) ions in Er(2)@C(82) (I, III) and (Er(2)C(2))@C(82) (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C(82) cage. In particular, the PL intensity of (Er(2)C(2))@C(82) (III) has been the strongest among the isomers of Er(2)@C(82) and (Er(2)C(2))@C(82). Optical measurements indicate that the PL properties of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C(82) cage.

  2. Scanning photoluminescent spectroscopy of bioconjugated quantum dots

    NASA Astrophysics Data System (ADS)

    Chornokur, G.; Ostapenko, S.; Oleynik, E.; Phelan, C.; Korsunska, N.; Kryshtab, T.; Zhang, J.; Wolcott, A.; Sellers, T.

    2009-04-01

    We report on the application of the bio-conjugated quantum dots (QDs) for a "sandwich" enzyme-linked immunosorbent assay (ELISA) cancer testing technique. Quantum dot ELISA detection of the cancer PSA antigen at concentrations as low as 0.01 ng/ml which is ˜50 times lower than the classic "sandwich" ELISA was demonstrated. Scanning photoluminescence (PL) spectroscopy was performed on dried ELISA wells and the results compared with the same QD samples dried on a solid substrate. We confirmed a "blue" up to 37 nm PL spectral shift in a case of QDs conjugated to PSA antibodies. Increasing of the "blue" spectral shift was observed at lower PSA antigen concentrations. The results can be used to improve sensitivity of "sandwich" ELISA cancer antigen detection.

  3. Photoluminescence of SrS:Cu,Ag and SrS 1- xSe x:Cu,Ag thin films

    NASA Astrophysics Data System (ADS)

    Poelman, D.; Wauters, D.; Van Meirhaeghe, R. L.; Cardon, F.

    2000-01-01

    The photoluminescence (PL) of SrS:Cu,Ag and SrS 1- xSe x:Cu,Ag thin films has been investigated. The influence of rapid thermal annealing conditions and Cu dopant concentration on the PL intensity has been studied. The PL emission spectrum was measured as a function of both Cu concentration and temperature. An unexpected PL intensity peak was observed around a temperature of 54 K.

  4. Time Resolved Photoluminescence Studies of ZnO and Zn2SnO4 Nanowires for Solar Cells Applications

    NASA Astrophysics Data System (ADS)

    Yakami, Baichhabi Raj; Mahat, Meg; Chen, Jiajun; Lu, Liyou; Wang, Wenyong; Pikal, Jon M.

    2013-03-01

    Sensitized nanowires (NWs) are a promising option for solar cells. They serve as the support structure for the absorbing centers, provide interfacial charge separation, and transport to the anode. Most work has focused on binary oxides, but ternary oxides have advantages due to flexibility in the properties of the oxide. Here we report on the photoluminescence (PL) and Time Resolved PL (TRPL) of Zinc oxide (ZnO) and Zinc Tin Oxide (ZTO) NWs grown by Chemical Vapor Deposition. The ZnO NWs show strong band gap emission and weak but resolvable defect emission peaks. The PL from the ZTO NWs does not show any band gap emission and absorption measurements confirm that these NWs have a direct forbidden transition. The ZTO NWs do have a board visible emission peak, which is usually attributed defects and oxygen vacancies. TRPL of the band gap emission in ZnO NWs yield a carrier lifetime of 1.4ns. The TRPL of the defect peaks in ZTO NWs are more complicated, showing a multi-exponential decay but with an overall decay rate similar to the ZnO NWs. This indicates that the expected increase in carrier lifetime in the ZTO NWs is not currently realized likely due to defect recombination, and additional optimization of the NW growth process may yield improved performance. DOE

  5. Intensity and temperature-dependent photoluminescence of tris (8-hydroxyquinoline) aluminum films

    SciTech Connect

    Ajward, A. M.; Wang, X.; Wagner, H. P.

    2013-12-04

    We investigate the recombination of excitons in tris (8-hydroxyquinoline) aluminum films by intensity and temperature dependent time-resolved photoluminescence (PL). At low temperature (15 K) and elevated excitation intensity the radiative emission is quenched by singlet-singlet annihilation processes. With rising temperature the PL quenching is strongly reduced resulting in a PL efficiency maximum at ∼170 K. The reduced exciton annihilation is attributed to thermally activated occupation of non-quenchable trapped exciton states. Above 170 K the PL efficiency decreases due to thermal de-trapping of radiative states and subsequent migration to non-radiative centers.

  6. Effect of reactive ion beam etching on the photoluminescence of CdTe epitaxial layers

    SciTech Connect

    Martinez-Pastor, J.; Fuster, D.; Abellan, M.; Anguita, J.; Sochinskii, N. V.

    2008-03-01

    We demonstrated the effect of reactive ion beam etching (RIBE) process on the PL properties of CdTe/sapphire metal organic vapor phase epitaxy layers. At optimum conditions, the RIBE attack does not make significant morphological changes but it results in an increase of the concentration of acceptor impurities. This was revealed by an increase of the overall photoluminescence (PL) intensity and, simultaneously, a decrease of the PL decay time, more important on the low energy side of PL spectrum due to the recombination of carriers in acceptor pairs.

  7. Exciton photoluminescence in resonant quasi-periodic Thue-Morse quantum wells.

    PubMed

    Hsueh, W J; Chang, C H; Lin, C T

    2014-02-01

    This Letter investigates exciton photoluminescence (PL) in resonant quasi-periodic Thue-Morse quantum wells (QWs). The results show that the PL properties of quasi-periodic Thue-Morse QWs are quite different from those of resonant Fibonacci QWs. The maximum and minimum PL intensities occur under the anti-Bragg and Bragg conditions, respectively. The maxima of the PL intensity gradually decline when the filling factor increases from 0.25 to 0.5. Accordingly, the squared electric field at the QWs decreases as the Thue-Morse QW deviates from the anti-Bragg condition. PMID:24487847

  8. Twin extra-high photoluminescence in resonant double-period quantum wells.

    PubMed

    Chang, C H; Cheng, Y H; Hsueh, W J

    2014-12-01

    Twin extra high photoluminescence (PL) in resonant quasi-periodic double-period quantum wells (DPQWs) for higher-generation orders is demonstrated. In the DPQW, the number of maxima in the maximum values of the PL intensity is two, which is different from other quasi-periodic quantum wells (QWs) and traditional periodic QWs. The maximum PL intensity in a DPQW is also stronger than that in a periodic QW under the anti-Bragg condition and that in a Fibonacci QW. Although the peaks of the squared electric field for the twin PL are both located near the QWs, their field profiles are distinct. PMID:25490626

  9. Emission-angle-dependent photoluminescence of rubrene thin films on silver.

    PubMed

    Wakamatsu, Takashi

    2014-07-20

    Rubrene layers with thickness comparable to a visible light wavelength on silver thin film exhibit anomalous photoluminescence (PL) spectra that depend strongly on emission angle. The PL properties demonstrated for rubrene (500 nm)/Ag (50 nm) were modulated from yellow green to red luminescence with an increasing emission angle. The factors influencing the emission-angle-dependent PL spectra are discussed from two viewpoints: spectral modulation of rubrene PL by loss of fluorescence photon energy and additional luminescence resulting from optical interference in the rubrene layer or optical modes excited by rubrene molecules. PMID:25090212

  10. Extraordinary room-temperature photoluminescence in triangular WS2 monolayers.

    PubMed

    Gutiérrez, Humberto R; Perea-López, Nestor; Elías, Ana Laura; Berkdemir, Ayse; Wang, Bei; Lv, Ruitao; López-Urías, Florentino; Crespi, Vincent H; Terrones, Humberto; Terrones, Mauricio

    2013-08-14

    Individual monolayers of metal dichalcogenides are atomically thin two-dimensional crystals with attractive physical properties different from those of their bulk counterparts. Here we describe the direct synthesis of WS2 monolayers with triangular morphologies and strong room-temperature photoluminescence (PL). The Raman response as well as the luminescence as a function of the number of S-W-S layers is also reported. The PL weakens with increasing number of layers due to a transition from direct band gap in a monolayer to indirect gap in multilayers. The edges of WS2 monolayers exhibit PL signals with extraordinary intensity, around 25 times stronger than that at the platelet's center. The structure and chemical composition of the platelet edges appear to be critical for PL enhancement.

  11. Surface characterization of InP using photoluminescence

    NASA Technical Reports Server (NTRS)

    Chang, R. R.; Iyer, R.; Lile, D. L.

    1987-01-01

    Photoluminescence (PL) measurements have been performed on InP samples in situ during various surface treatments including chemical etching, wet anodization, and low-pressure chemical vapor deposition. It was found, in agreement with previously published results, that the magnitude of the PL signal varies markedly with surface treatment due presumably to changes in either surface-state density, and/or surface potential. In an attempt to assess the effectiveness of this noninvasive method as a tool for characterizing and monitoring the progressive development of a semiconductor surface during processing, a number of experiments on InP have been performed. The results indicate that although some uncertainty may exist in assigning a mechanism for the PL change in any given experiment, the general trend appears to be that surface degradation results in a reduced signal. As a result, process steps which enhance the PL intensity are likely to be beneficial in the preparation of a high-quality interface.

  12. Photoluminescence properties of Mg-doped InN nanowires

    SciTech Connect

    Zhao, Songrui; Liu, Xuedong; Mi, Zetian

    2013-11-11

    In this work, photoluminescence (PL) properties of nearly defect-free Mg-doped InN nanowires were investigated in detail. The low-doped sample exhibits two PL emission peaks up to 152 K, which can be ascribed to the band-to-band recombination and the Mg-acceptor energy level related recombination, respectively. For the high-doped sample, the Mg-acceptor energy level related transition dominates. Detailed power dependent PL studies further indicate that the Mg-acceptor energy level related PL emission is due to the donor-acceptor pair recombination process, which subsequently evolves into the free-to-acceptor recombination with increasing temperature.

  13. Using quantum dot photoluminescence for load detection

    NASA Astrophysics Data System (ADS)

    Moebius, M.; Martin, J.; Hartwig, M.; Baumann, R. R.; Otto, T.; Gessner, T.

    2016-08-01

    We propose a novel concept for an integrable and flexible sensor capable to visualize mechanical impacts on lightweight structures by quenching the photoluminescence (PL) of CdSe quantum dots. Considering the requirements such as visibility, storage time and high optical contrast of PL quenching with low power consumption, we have investigated a symmetrical and an asymmetrical layer stack consisting of semiconductor organic N,N,N',N'-Tetrakis(3-methylphenyl)-3,3'-dimethylbenzidine (HMTPD) and CdSe quantum dots with elongated CdS shell. Time-resolved series of PL spectra from layer stacks with applied voltages of different polarity and simultaneous observation of power consumption have shown that a variety of mechanisms such as photo-induced charge separation and charge injection, cause PL quenching. However, mechanisms such as screening of external field as well as Auger-assisted charge ejection is working contrary to that. Investigations regarding the influence of illumination revealed that the positive biased asymmetrical layer stack is the preferred sensor configuration, due to a charge carrier injection at voltages of 10 V without the need of coincident illumination.

  14. Experimental and theoretical photoluminescence studies in nucleic acid assembled gold-upconverting nanoparticle clusters.

    PubMed

    He, Liangcan; Mao, Chenchen; Cho, Suehyun; Ma, Ke; Xi, Weixian; Bowman, Christopher N; Park, Wounjhang; Cha, Jennifer N

    2015-11-01

    Combinations of rare earth doped upconverting nanoparticles (UCNPs) and gold nanostructures are sought as nanoscale theranostics due to their ability to convert near infrared (NIR) photons into visible light and heat, respectively. However, because the large NIR absorption cross-section of the gold coupled with their thermo-optical properties can significantly hamper the photoluminescence of UCNPs, methods to optimize the ratio of gold nanostructures to UCNPs must be developed and studied. We demonstrate here nucleic acid assembly methods to conjugate spherical gold nanoparticles (AuNPs) and gold nanostars (AuNSs) to silica-coated UCNPs and probe the effect on photoluminescence. These studies showed that while UCNP fluorescence enhancement was observed from the AuNPs conjugated UCNPs, AuNSs tended to quench fluorescence. However, conjugating lower ratios of AuNSs to UCNPs led to reduced quenching. Simulation studies both confirmed the experimental results and demonstrated that the orientation and distance of the UCNP with respect to the core and arms of the gold nanostructures played a significant role in PL. In addition, the AuNS-UCNP assemblies were able to cause rapid gains in temperature of the surrounding medium enabling their potential use as a photoimaging-photodynamic-photothermal agent. PMID:26427014

  15. Experimental and theoretical photoluminescence studies in nucleic acid assembled gold-upconverting nanoparticle clusters.

    PubMed

    He, Liangcan; Mao, Chenchen; Cho, Suehyun; Ma, Ke; Xi, Weixian; Bowman, Christopher N; Park, Wounjhang; Cha, Jennifer N

    2015-11-01

    Combinations of rare earth doped upconverting nanoparticles (UCNPs) and gold nanostructures are sought as nanoscale theranostics due to their ability to convert near infrared (NIR) photons into visible light and heat, respectively. However, because the large NIR absorption cross-section of the gold coupled with their thermo-optical properties can significantly hamper the photoluminescence of UCNPs, methods to optimize the ratio of gold nanostructures to UCNPs must be developed and studied. We demonstrate here nucleic acid assembly methods to conjugate spherical gold nanoparticles (AuNPs) and gold nanostars (AuNSs) to silica-coated UCNPs and probe the effect on photoluminescence. These studies showed that while UCNP fluorescence enhancement was observed from the AuNPs conjugated UCNPs, AuNSs tended to quench fluorescence. However, conjugating lower ratios of AuNSs to UCNPs led to reduced quenching. Simulation studies both confirmed the experimental results and demonstrated that the orientation and distance of the UCNP with respect to the core and arms of the gold nanostructures played a significant role in PL. In addition, the AuNS-UCNP assemblies were able to cause rapid gains in temperature of the surrounding medium enabling their potential use as a photoimaging-photodynamic-photothermal agent.

  16. In-dopants effect on the photoluminescence properties of YVO4 nanophosphors.

    PubMed

    Peng, Zifei; Du, Yanyun; Wang, Yuan; Peng, Donghong

    2010-03-01

    The powders of Yttrium vanadate (YVO4) with In-dopants were synthesized by solid-state reactions, and X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption spectra, photoluminescence (PL) spectra, and the luminescence intensity change were used to characterize the samples. The results of XRD indicated that the YVO4:In3+ samples remained in pure cubic phase. TEM illustrated that the powders mainly consisted of grains with an average size of 100 nm. Under the excitation of 320 nm, the YVO4:In3+ single-crystalline samples exhibited emission ranging from 350 to 700 nm. The emission intensity of YVO4:In3+ increased with increasing indium concentration in the lower indium concentration region until the saturated PL intensity was reached, and the strongest white fluorescence was observed when the In3+ doping concentration was 2% at 900 degrees C. The luminescent intensity of YVO4:In3+ (2%) was 9.6 times as strong as that of non-doped YVO4. The nanophosphors emit white luminescence owing to broad charge transfer in crystal lattice is due to the addition of In3+ to capture the UV radiation. PMID:20355624

  17. Photoluminescence analysis of a polythiophene derivative: Concentration and temperature effects

    NASA Astrophysics Data System (ADS)

    Castrellon-Uribe, J.; Güizado-Rodríguez, M.; Espíndola-Rivera, R.

    2016-08-01

    In this work, the photoluminescence properties of a PA copolymer, which is a polythiophene derived from 3-OT and (S)-(-)-1-(4-nitrophenyl) pyrrolidin-2-il) methyl 2-(thiophen-3-yl) acetate, were investigated. The optical response of the copolymer dissolved in a toluene solution and of the copolymer film under the optical excitation was analyzed. Besides, the temperature dependence of photoluminescence (PL) of the PA copolymer (solution and film) was examined. The PL behavior of the solution-phase copolymer (diluted and concentrated solutions) under 365 nm (UV light) excitation is reported. Moreover, the copolymer films were obtained using the spin coating technique. The PL of the copolymer films under 488 nm (blue light) irradiation was studied at different excitation powers. Finally, we examined the PL signal temperature dependence of the copolymer film. We determined that the maximum PL signal peak of the copolymer corresponds to 626 nm and has a temperature sensitivity of approximately 11 × 10-3/°C, with a minimum ascending and descending temperature hysteresis between 22 °C and 50 °C.

  18. Photoluminescence of europium in silicon/silicon dioxide thin films

    NASA Astrophysics Data System (ADS)

    Nery Gomez, Guillermo Alejandro

    Thin film samples of co-sputtered Si, SiO2, Eu 2O3, and H2 were synthesized, in different combinations and with a variety of percentage compositions and at various substrate temperatures. The films were annealed in a N2-rich atmosphere or in Ar at various temperatures. Thickness, photoluminescence (PL), photoluminescence excitation (PLE), transmission, lifetime, time-resolved spectroscopy, transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and energy dispersive X-ray spectroscopy (EDX) measurements were made to characterize the samples. Evidence for the formation of nanocrystalline Si (nc-Si) was found in some of the samples. The presence of Eu3+ ions was detected is some samples, while Eu2+ ions were detected in others. Non-bridging oxygen hole centers (NBOHC) were also detected. While Eu2O3 contains Eu3+ ions, the Eu2+ ions appeared due to chemical reactions with the Si when sufficient amounts of Eu2O3 and free Si were present as to allow them to interact, under the appropriate deposition temperature or annealing temperatures. The Eu3+ ion PL was only visible when the Eu did not interact with the Si, and drew its energy from its SiO2 host. Where Eu2+ PL was present, NBOHC PL was greatly enhanced, compared to Si/SiO2-only samples, or samples where only Eu3+ was present. The PLE and PL measurements suggest the NBOHC receive energy from the Eu2+ ions.

  19. Optical absorption and emission characterization of P3HT: graphene composite for its prospective photovoltaic application

    NASA Astrophysics Data System (ADS)

    Singh, Joginder; Prasad, Neetu; Nirwal, Varun Singh; Gautam, Khyati; Peta, Koteswara Rao; Bhatnagar, P. K.

    2016-05-01

    In the present work, regioregular P3HT (Poly (3-hexylthiophene-2, 5-diyl) was blended with graphene nanopowder and the optical spectroscopic characterization of the composite has been performed. It was observed that at low concentration of graphene (up to 0.1 wt %) there is no significant variation in absorption intensity or wavelength range. But at higher concentration (> 0.1 wt %) the absorption intensity starts reducing. Whereas, the photoluminescence of the composite solution quenches as we increase the concentration of graphene. It reveals that charge recombination decreases with increase in concentration (0.05 to 0.5 wt %) of graphene. Therefore 0.1 wt % seems to be the optimized concentration of graphene in the composite for which appropriate quenching of PL was observed without any significant reduction in absorption of photons. Thus maximum efficiency in P3HT: graphene composite photovoltaic cell is expected for 0.1 wt % of graphene concentration in our typical case.

  20. Monitoring of photoluminescence decay by alkali and alkaline earth metal cations using a photoluminescent bolaamphiphile self-assembly as an optical probe.

    PubMed

    Kim, Sunhyung; Kwak, Jinyoung; Lee, Sang-Yup

    2014-05-01

    Photoluminescence (PL) decay induced by the displacement of an ionic fluorescence component, Tb(3+), with alkali and alkaline earth metal cations was investigated using photoluminescent spherical self-assemblies as optical probes. The photoluminescent spherical self-assembly was prepared by the self-organization of a tyrosine-containing bolaamphiphile molecule with a photosensitizer and Tb(3+) ion. The lanthanide ion, Tb(3+), electrically bound to the carboxyl group of the bolaamphiphile molecule, was displaced by alkali and alkaline earth metal cations that had stronger electrophilicity. The PL of the self-assembly decayed remarkably due to the substitution of lanthanide ions with alkali and alkaline earth metal cations. The PL decay showed a positive correlation with cation concentration and was sensitive to the cation valency. Generally, the PL decay was enhanced by the electrophilicity of the cations. However, Ca(2+) showed greater PL decay than Mg(2+) because Ca(2+) could create various complexes with the carboxyl groups of the bolaamphiphile molecule. Microscopic and spectroscopic investigations were conducted to study the photon energy transfer and displacement of Tb(3+) by the cation exchange. This study demonstrated that the PL decay by the displacement of the ionic fluorescent compound was applied to the detection of various cations in aqueous media and is applicable to the development of future optical sensors.

  1. Photoluminescence properties of new Zn(II) complexes with 8-hydroxyquinoline ligands: Dependence on volume and electronic effect of substituents

    NASA Astrophysics Data System (ADS)

    Huo, Yanping; Lu, Jiguo; Hu, Sheng; Zhang, Liming; Zhao, Fenghua; Huang, Huarong; Huang, Baohua; Zhang, Li

    2015-03-01

    A series of 2-arylethenyl-8-hydroxyquinoline ligands (A1-A4) with a trimethoxyphenyl, naphthyl, 2-fluoro-4-bromophenyl and anthracenyl group and their corresponding Zn(II) complexes (B1-B4) were synthesized and characterized by means of 1H NMR, ESI-MS, FT-IR and elemental analysis. A1 and A4 were characterized by single-crystal X-ray crystallography. The aggregation behavior of zinc salt and ligands in solution was investigated by several techniques, containing 1H NMR, UV-vis and photoluminescence (PL). The electronic nature and volume of arylethenyl substituents affect the absorption wavelength, the emission color, fluorescence lifetime, fluorescence quantum yield and thermostability of Zn(II) complexes. The experiments corroborated that the properties of Zinc(II) complexes can be tuned by introducing different functional substituents.

  2. Spectral tunability of cerium photoluminescence in nano sized LaF{sub 3}:Ce{sup 3+}

    SciTech Connect

    Srinivasan, T. K.; Suriyamurthy, N. Panigrahi, B. S.; Venkatraman, B.; Sukumar, A. A.

    2015-06-24

    Nano sized LaF{sub 3}:Ce{sup 3+} was synthesized by adopting co-precipitation technique with nominal composition as well as with different molar ratio of reactants La{sup 3+} (Lanthanum) and F{sup −} (Fluoride). All the samples were subjected to X-ray diffraction (XRD), XRF, UV-Vis absorption, and PL characterizations. XRD analysis did not reveal any significant change in the diffraction profile. Particle size variations were observed with respect to change in lanthanum to fluoride molar ratio. An interesting and intense photoluminescence excitation peaks were observed for the samples prepared non-stoichiometrically. The effect of varying nominal reactant composition demonstrates a possibility of introducing tunability in cerium emission in the same host. Life time of cerium has been measured to be in the order of nano seconds.

  3. Evidence for near-infrared photoluminescence of nitrogen vacancy centers in 4 H -SiC

    NASA Astrophysics Data System (ADS)

    Zargaleh, S. A.; Eble, B.; Hameau, S.; Cantin, J.-L.; Legrand, L.; Bernard, M.; Margaillan, F.; Lauret, J.-S.; Roch, J.-F.; von Bardeleben, H. J.; Rauls, E.; Gerstmann, U.; Treussart, F.

    2016-08-01

    We present evidence of near-infrared photoluminescence (PL) signature of nitrogen vacancy centers (NCVSi) - in silicon carbide (SiC). This center exhibits an S =1 ground state spin similar to the NV- center in diamond. We have performed photoluminescence excitation measurements at cryogenic temperature and demonstrated efficient photoexcitation of distinct photoluminescence from (NCVSi)- in 4 H -SiC. Furthermore, by correlating the energies of measured zero phonon lines (ZPLs) with theoretical values derived from hybrid density functional theory each of the ZPLs has been associated to the respective occupation of hexagonal (h ) and quasicubic (k ) lattice sites in close analogy to neutral divacancy centers (VCVSi) 0 in the same material. Finally, with the appropriate choice of excitation energy we demonstrated the selective excitation of (NCVSi) - PL with no contamination by (VCVSi) 0 PL, thereby opening the way towards the optical detection of (NCVSi) - electron spin resonance.

  4. Thermal dissolution of Eu 2+ Suzuki phase nanostructures in KBr crystals monitored by pulsed photoacoustic and photoluminescence techniques

    NASA Astrophysics Data System (ADS)

    Mejía-Uriarte, E. V.; Camarillo, E.; A, J. Hernández; Navarrete, M.; Villagrán-Muniz, M.; S, H. Murrieta

    2005-04-01

    Suzuki-type precipitated phases are nanostructures that change the optical and mechanical properties of the crystal in which they have been formed. The dissolution process of the Europium Suzuki phase (SP) nanostructures was induced by continuous heating (1 °C/min) of KBr:Eu2+ single crystals and it was simultaneously monitored by two techniques: photoacoustic (PA) and photoluminescence (PL). Each sample was heated from room temperature to 205 °C; meanwhile a focused laser pulse (355 nm) impinged on one crystal face to excite the low energy Europium absorption band and generate the photoacoustic signal. The correlation coefficients between subsequent PA signals were used to build a thermal profile and its behaviour was found to be directly related with the absorption coefficient of Eu2+ ion in its crystalline environment. From correlation analysis and Fourier fast transform (FFT) applied to the PA signal data, the dynamical thermal dissolution process has been studied and compared with simultaneous emission spectrum data obtained by the PL technique. The results show good agreement with the literature.

  5. Photoluminescence of cellulose acetate and silica sphere composite

    NASA Astrophysics Data System (ADS)

    Kang, Kwang-Sun

    2014-08-01

    Strong blue and green light emission has been observed from the cellulose acetate (CA) and silica sphere composite. Two different amounts of silica spheres were mixed in the CA solution to fabricate large area super-hydrophobic films. The silica spheres and CA solution ratios were 0.07:4.0 (SSCA-A) and 0.14:4.0 (SSCA-B). The milky color solution of SSCA-A and SSCA-B slowly turned to light yellow and red, respectively, with the time passed. The colors became intense yellow and red for the SSCA-A and SSCA-B, respectively, after 38 days. FTIR spectra show more absorption at 3478 cm-1 corresponding sbnd OH stretching vibration, at 2963 cm-1 caused by sbnd CH stretching vibration, at 1746 and 1713 cm-1 representing the Cdbnd O stretching vibration, and at 1100 cm-1 corresponding sbnd Rsbnd OH and Sisbnd Osbnd Si stretching vibration for CA and silica. Therefore, aged SSCA-A and SSCA-B have more sbnd OH, sbnd CH, sbnd Cdbnd O, and Sisbnd Osbnd Si groups than pure CA. UV-visible spectra show the absorption peaks at 410 nm for both SSCA-A and SSCA-B. Photoluminescence (PL) peaks were shifted toward longer wavelength with the increase of the excitation wavelength and became maximum at approximately 470 nm with excitation wavelength at 400 nm for the SSCA-A. There were two maximum luminescence peaks at 470 and 530 nm with the excitation wavelength at 400 and 470 nm, respectively, for the SSCA-B. The luminescence peak shift was due to the multiple emission center proved by the different excitation energy.

  6. Photoluminescence Imaging of Large-Grain CdTe for Grain Boundary Characterization

    SciTech Connect

    Johnston, Steve; Allende Motz, Alyssa; Reese, Matthew O.; Burst, James M.; Metzger, Wyatt K.

    2015-06-14

    In this work, we use photoluminescence (PL) imaging to characterize CdTe grain boundary recombination. We use a silicon megapixel camera and green (532 nm) laser diodes for excitation. A microscope objective lens system is used for high spatial resolution and a field of view down to 190 um x 190 um. PL images of large-grain (5 to 50 um) CdTe samples show grain boundary and grain interior features that vary with processing conditions. PL images of samples in the as-deposited state show distinct dark grain boundaries that suggest high excess carrier recombination. A CdCl2 treatment leads to PL images with very little distinction at the grain boundaries, which illustrates the grain boundary passivation properties. Other process conditions are also shown, along with comparisons of PL images to high spatial resolution time-resolved PL carrier lifetime maps.

  7. Comparison of photoluminescence quantum yield of single gold nanobipyramids and gold nanorods.

    PubMed

    Rao, Wenye; Li, Qiang; Wang, Yuanzhao; Li, Tao; Wu, Lijun

    2015-03-24

    Fluorescent gold nanoparticles with high quantum yield are highly desirable for optical imaging in the fields of biology and materials science. We investigate the one-photon photoluminescence (PL) properties of individual gold nanobipyramids (GNBs) and find they are analogous to those of the extensively studied gold nanorods (GNRs). By combining PL and atomic force microscopy (AFM) measurements with discrete dipole approximation (DDA) simulations, we obtain the PL quantum yield of single GNRs and GNBs. Compared to GNRs in the similar surface plasmon resonance range, the PL quantum yield of GNBs is found to be doubled. The stronger field intensity around GNBs can explain their higher PL quantum yields. Our research would provide deeper understanding of the mechanism of PL from gold nanoparticles as well as be beneficial for finding out optical imaging labels with high contrast.

  8. Photoluminescence Imaging Characterization of Thin-Film InP

    SciTech Connect

    Johnston, Steve; Allende Motz, Alyssa; Moore, James; Zheng, Maxwell; Javey, Ali; Bermel, Peter

    2015-06-14

    Indium phosphide grown using a novel vapor-liquid-solid method is a promising low-cost material for III-V single-junction photovoltaics. In this work, we characterize the properties of these materials using photoluminescence (PL) imaging, time-resolved photoluminescence (TRPL), and microwave-reflection photoconductive decay (u-PCD). PL image data clearly shows the emergence of a self-similar dendritic growth network from nucleation sites, while zoomed-in images show grain structure and grain boundaries. Single photon TRPL data shows initial surface-dominated recombination, while two-photon excitation TRPL shows a lifetime of 10 ns. Bulk carrier lifetime may be as long as 35 ns as measured by u-PCD, which can be less sensitive to surface recombination.

  9. Effect of TEA on photoluminescence properties of PbS nanocrystalline thin films

    NASA Astrophysics Data System (ADS)

    Tohidi, Tavakkol; Jamshidi-Ghaleh, Kazem

    2015-03-01

    In this work, the PbS nanocrystalline thin films were prepared by chemical bath deposition method on the glass and unpolished Si(100) substrates. Triethanolamine was used as additive in the aqueous solution, which resulted in the enhancement of the luminescence of nanocrystalline PbS thin films. The introduction of triethanolamine reduced the grain size and increased the optical band gap of the PbS nanoparticles. The crystalline size of PbS films deposited at two different bath temperatures of 25 °C (PbS-25) and 40 °C (PbS-40) and at different deposition times was estimated to be around 5-50 nm by XRD analyses. The films at 60 °C (PbS-60) were prepared and studied. The structural, morphological and optical properties of the obtained films were investigated. The energy-dispersive X-ray of the typical PbS film was presented, which confirmed the formation of PbS. The mechanism of growth of the PbS crystallites at different bath temperatures was described. The confinement was reflected in absorption and photoluminescence spectra. The variation of the photoluminescence intensity of PbS nanocrystals with triethanolamine molarity, deposition time and bath temperature was investigated. The PbS thin films were found to exhibit PL in both the ultraviolet and visible regions via quantum size effects, surface states and excitation wavelength variation. The luminescence of Si(100) substrate and PbS nanocrystalline films deposited on Si(100) were compared, and the results revealed that the PbS nanocrystals altered and notably enhanced the emission features of the Si(100) substrate. The multi-peak fitting using Gaussian function was employed for the photoluminescence spectrum of PbS on Si(100) substrate.

  10. [Preparation and Photoluminescent Properties of Ce³⁺-Activated LaPO₄ Nanocrystals and Core/Shell Structure].

    PubMed

    Li, Zhen-ya; Huang, Shi-ming; Gu, Mu; Liu, Xiao-lin

    2015-11-01

    Hydrophobic, monodisperse LaPO₄: Ce³⁺ nanoparticles, LaPO₄:Ce³⁺/LaPO₄ and LaPO₄:Ce³⁺/LaPO₄: Ce³⁺/ LaPO₄ core/shell structure nanocrystals were synthesized via a high-temperature organic solution approach. The as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy (PL). The results show that: all the samples are a monoclinic phase, Because of the size small nanoparticles, the diffraction peaks of the sample occurs width phenomenon. The LaPO₄:Ce³⁺ nano- crystals exhibits the characteristic emission of Ce³⁺ ions, the photoluminescence intensity increases first and then decreases with the increasing doping concentration of Ce³⁺ ions, and the best doping amount is 6 at %, with the increasing doping amount, the photoluminescence intensity decreases which may caused by the concentration quenching. Compared to LaPO₄:Ce³⁺ nanoparti- cles, the photoluminescence intensity of LaPO₄:Ce³⁺/LaPO₄ and LaPO₄: Ce³⁺/LaPO₄: Ce³⁺/LaPO₄ core/shell structure nanocrystals improves about 41% and 95% respectively, this may be a synergy of larger particle size of nanocrystals and surface passivation effect. FTIR spectra data shows that the absorption peak at 1545 and 1461 cm⁻¹ corresponded to the asymmetric and symmetric stretching vibration of --COO⁻, the separation, Δ, between the two peaks is 84 cm⁻¹, The mechanism of the sample surface modification by the organics might be that the oxygen atoms of the carboxyl are coordinated with the lanthunum ions by a bidentate mode.

  11. Layer-dependent modulation of tungsten disulfide photoluminescence by lateral electric fields.

    PubMed

    He, Zhengyu; Sheng, Yuewen; Rong, Youmin; Lee, Gun-Do; Li, Ju; Warner, Jamie H

    2015-03-24

    Large single-crystal domains of WS2 are grown by chemical vapor deposition, and their photoluminescent properties under a lateral electric field are studied. We demonstrate that monolayer and bilayer WS2 have opposite responses to lateral electric fields, with WS2 photoluminescence (PL) substantially reduced in monolayer and increased in bilayers with increasing lateral electric field strength. Temperature-dependent PL measurements are also undertaken and show behavior distinctly different than that of the lateral electric field effects, ruling out heating as the cause of the PL changes. The PL variation in both monolayer and bilayer WS2 is attributed to the transfer of photoexcited electrons from one conduction band extremum to another, modifying the resultant recombination pathways. This effect is observed in 2D transition metal dichalcogenides due to their large exciton binding energy and small energy difference between the two conduction band extrema.

  12. Red photoluminescence BCNO synthesized from graphene oxide nanosheets

    NASA Astrophysics Data System (ADS)

    Kang, Yue; Chu, Zeng-yong; Ma, Tian; Li, Wei-ping; Zhang, Dong-jiu; Tang, Xiao-yu

    2016-01-01

    In this paper, we demonstrate the conversion of graphene oxide (GO) into boron carbon oxynitride (BCNO) hybrid nanosheets via a reaction with boric acid and urea, during which the boron and nitrogen atoms are incorporated into graphene nanosheets. The experimental results reveal that GO is important for the photoluminescence (PL) BCNO phosphor particles. More importantly, in this system, the prepared BCNO phosphors can be used to prepare the materials needed for red light emitting diodes (LEDs).

  13. Intense photoluminescence from dried double-stranded DNA and single-walled carbon nanotube hybrid

    SciTech Connect

    Ito, M.; Kobayashi, T.; Ito, Y.; Hayashida, T.; Nii, D.; Umemura, K.; Homma, Y.

    2014-01-27

    Semiconducting single-walled carbon nanotubes (SWNTs) show near-infrared photoluminescence (PL) when they are individually isolated. This was an obstacle to use photonic properties of SWNTs on a solid surface. We show that SWNTs wrapped with DNA maintain intense PL under the dry conditions. SWNTs are well isolated individually by DNA even when the DNA-SWNT hybrids are agglomerated. This finding opens up application of SWNTs to photonic devices.

  14. Photoluminescence of P3HT nanoparticles

    NASA Astrophysics Data System (ADS)

    Dujovne, Irene; Labastide, Joelle; Baghgar, Mina; McKenna, Aidan; Barnes, Austin M.; Venkataraman, D.; Barnes, Michael D.

    2012-02-01

    Polythiophenes are semiconducting polymers that have been designed to crystallize. The photophysics of semicrystalline polythiophene and polythiophene-blends are the focus of intense research efforts across different disciplines. In these systems there is a competition between charge separation and recombination. Exciton diffusion length in organic-semiconductors is a major road-block for efficient solar energy harvesting devices since, for direct bandgap organic materials, this distance is about 10 nanometers. Thus, efficient extraction of photogenerated electrons and holes requires engineering polymer domain dimensions in this size range. In our initial investigations of the photophysics of isolated P3HT nanoparticles (15 - 130 nm), we have observed several intriguing size-dependent features in the single-particle photoluminescence (PL) connected with exciton diffusion and dissociation dynamics. In addition to the short-time behavior, we also observe size-dependent differences in PL decay at long times. In the 10 - 100 ns time regime, the PL originates not from radiative transitions of bound excitons, but rather from charge-separation followed by bi-polaron recombination--and thus provides an interesting measure of exciton fission probability within the nanoparticle.

  15. Raman and Photoluminescence Studies of In-plane Anisotropic Layered Materials

    NASA Astrophysics Data System (ADS)

    Pant, Anupum

    This thesis presents systematic studies on angle dependent Raman and Photoluminescence (PL) of a new class of layered materials, Transition Metal Trichalcogenides (TMTCs), which are made up of layers possessing anisotropic structure within the van-der-Waals plane. The crystal structure of individual layer of MX3 compounds consists of aligned nanowire like 1D chains running along the b-axis direction. The work focuses on the growth of two members of this family - ZrS3 and TiS3 - through Chemical Vapor Transport Method (CVT), with consequent angle dependent Raman and PL studies which highlight their in-plane optically anisotropic properties. Results highlight that the optical properties of few-layer flakes are highly anisotropic as evidenced by large PL intensity variation with polarization direction (in ZrS3) and an intense variation in Raman intensity with variation in polarization direction (in both ZrS3 and TiS3). Results suggest that light is efficiently absorbed when E-field of the polarized incident excitation laser is polarized along the chain (b-axis). It is greatly attenuated and absorption is reduced when field is polarized perpendicular to the length of 1D-like chains, as wavelength of the exciting light is much longer than the width of each 1D chain. Observed PL variation with respect to the azimuthal flake angle is similar to what has been previously observed in 1D materials like nanowires. However, in TMTCs, since the 1D chains interact with each other, it gives rise to a unique linear dichroism response that falls between 2D and 1D like behavior. These results not only mark the very first demonstration of high PL polarization anisotropy in 2D systems, but also provide a novel insight into how interaction between adjacent 1D-like chains and the 2D nature of each layer influences the overall optical anisotropy of Quasi-1D materials. The presented results are anticipated to have impact in technologies involving polarized detection, near-field imaging

  16. Structure and Composition of Cu Doped CdSe Nanocrystals Using Soft X-ray Absorption Spectroscopy

    SciTech Connect

    Meulenberg, R W; van Buuren, T; Hanif, K M; Willey, T M; Strouse, G F; Terminello, L J

    2004-06-04

    The local structure and composition of Cu ions dispersed in CdSe nanocrystals is examined using soft x-ray absorption near edge spectroscopy (XANES). Using Cu L-edge XANES and X-ray photoelectron measurements (XPS), we find that the Cu ions exist in the Cu(I) oxidation state. We also find that the observed Cu L-edge XANES signal is directly proportional to the molar percent of Cu present in our final material. Se L-edge XANES indicates changes in the Se density of states with Cu doping, due to a chemical bonding effect, and supports a statistical doping mechanism. Photoluminescence (PL) measurements indicate the Cu ions may act as deep electron traps. We show that XANES, XPS, and PL are a powerful combination of methods to study the electronic and chemical structure of dopants in nanostructured materials.

  17. Higher than 60% internal quantum efficiency of photoluminescence from amorphous silicon oxynitride thin films at wavelength of 470 nm

    SciTech Connect

    Zhang, Pengzhan; Chen, Kunji Zhang, Pei; Fang, Zhonghui; Li, Wei; Xu, Jun; Huang, Xinfan; Dong, Hengping

    2014-07-07

    We reported the study on the photoluminescence internal quantum efficiency (PL IQE) and external quantum efficiency (PL EQE) from the amorphous silicon oxynitride (a-SiNO) films, which were fabricated by plasma-enhanced chemical vapor deposition followed by in situ plasma oxidation. We employed the direct measurement of absolute quantum efficiency within a calibrated integration sphere to obtain the PL EQE. Then, we calculated the PL IQE by combing the measured EQE and optical parameters of light extraction factor, reflectivity, and transmittance of the a-SiNO thin films. We also derived the PL QE through investigating the characteristic of the temperature dependent PL. These results show that the PL IQE as high as 60% has been achieved at peak wavelength of about 470 nm, which is much higher than that of Si nanocrystal embedded thin films.

  18. Tunable photoluminescence and spectrum split from fluorinated to hydroxylated graphene

    NASA Astrophysics Data System (ADS)

    Gong, Peiwei; Wang, Jinqing; Sun, Weiming; Wu, Di; Wang, Zhaofeng; Fan, Zengjie; Wang, Honggang; Han, Xiuxun; Yang, Shengrong

    2014-02-01

    Tunable control over the functionalization of graphene is significantly important to manipulate its structure and optoelectronic properties. Yet the chemical inertness of this noble carbon material poses a particular challenge for its decoration without forcing reaction conditions. Here, a mild, operationally simple and controllable protocol is developed to synthesize hydroxylated graphene (HOG) from fluorinated graphene (FG). We successfully demonstrate that under designed alkali environment, fluorine atoms on graphene framework are programmably replaced by hydroxyl groups via a straightforward substitution reaction pathway. Element constituent analyses confirm that homogeneous C-O bonds are successfully grafted on graphene. Rather different from graphene oxide, the photoluminescence (PL) emission spectrum of the obtained HOG becomes split when excited with UV radiation. More interestingly, such transformation from FG facilitates highly tunable PL emission ranging from greenish white (0.343, 0.392) to deep blue (0.156, 0.094). Additionally, both experimental data and density function theory calculation indicate that the chemical functionalization induced structural rearrangement is more important than the chemical decoration itself in tuning the PL emission band tail and splitting energy gaps. This work not only presents a new way to effectively fabricate graphene derivatives with tunable PL performance, but also provides an enlightening insight into the PL origin of graphene related materials.Tunable control over the functionalization of graphene is significantly important to manipulate its structure and optoelectronic properties. Yet the chemical inertness of this noble carbon material poses a particular challenge for its decoration without forcing reaction conditions. Here, a mild, operationally simple and controllable protocol is developed to synthesize hydroxylated graphene (HOG) from fluorinated graphene (FG). We successfully demonstrate that under designed

  19. Cell imaging using GaInAsP semiconductor photoluminescence.

    PubMed

    Sakemoto, Mai; Kishi, Yoji; Watanabe, Keisuke; Abe, Hiroshi; Ota, Satoshi; Takemura, Yasushi; Baba, Toshihiko

    2016-05-16

    We demonstrate label-free imaging of living cells using a GaInAsP semiconductor imaging plate. The photoluminescence (PL) intensity is changed by immersing the semiconductor wafer in different pH solutions and by depositing charged polyelectrolytes on the wafer. Various observations indicate that this phenomenon arises from the radiative and surface recombination rates modified by the Schottky barrier at the charged semiconductor surface. HeLa cancer cells were cultured on the semiconductor, and PL was observed using a near-infrared camera. The semiconductor areas with the cells attached exhibited characteristic PL profiles, which might reflect the attachment and surface condition of the cells, cellular matrix, and other substances. PMID:27409944

  20. Electrospun fluorescein/polymer composite nanofibers and their photoluminescent properties

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi-Hua; Long, Yun-Ze; Yin, Hong-Xin; Sun, Bin; Zheng, Jie; Zhang, Hong-Di; Ji, Xin-Ming; Gu, Chang-Zhi

    2012-09-01

    Fluorescein/polyvinyl pyrrolidone (PVP) composite nanofibers with different fluorescein loadings (with a weight concentration of 0-5.0%) are fabricated via electrospinning. Morphologies, structures and photoluminescent (PL) properties of these straight, helical or wavelike fibers are characterized by scanning electron microscopy (SEM), fluorescence microscopy and a spectrophotometer. It is found that the maximum emission of the as-spun fluorescein/PVP fibers occurs at 510 nm. The PL intensity of the composite fiber increases with fluorescein concentration, then fluorescence quenching appears when the concentration reaches 1.67%. The mechanism of fluorescence quenching of fluorescein is discussed. In addition, the composite fibers exhibit a much stronger PL intensity than fluorescein/PVP bulk film owing to larger specific surface area, which makes them promising materials for biomedical applications such as probes and sensors.

  1. Detection of Human Ig G Using Photoluminescent Porous Silicon Interferometer.

    PubMed

    Cho, Bomin; Kim, Seongwoong; Woo, Hee-Gweon; Kim, Sungsoo; Sohn, Honglae

    2015-02-01

    Photoluminescent porous silicon (PSi) interferometers having dual optical properties, both Fabry-Pérot fringe and photolumincence (PL), have been developed and used as biosensors for detection of Human Immunoglobin G (Ig G). PSi samples were prepared by electrochemical etching of p-type silicon under white light exposure. The surface of PSi was characterized using a cold field emission scanning electron microscope. The sensor system studied consisted of a single layer of porous silicon modified with Protein A. The system was probed with various fragments of aqueous human immunoglobin G (Ig G) analyte. Both reflectivity and PL were simultaneously measured under the exposure of human Ig G. An increase of optical thickness and decrease of PL were obtained under the exposure of human Ig G. Detection limit of 500 fM was observed for the human Ig G.

  2. Effects of natural oxidation on the photoluminescence properties of Si nanocrystals prepared by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Xu, Yanmei; Han, Yinghui

    2014-07-01

    In this work, Si nanocrystals (Si-NCs) have been prepared by pulsed laser ablation technique in dichloromethane, and the microstructure and photoluminescence (PL) properties of the Si-NCs before and after natural oxidation were investigated. Transmission electron microscopy and Raman results show that the average diameter of the Si-NCs is 2.42 nm in the dichloromethane solution. Blue-violet PL with a lifetime of 4.6 ns is observed at room temperature, and the PL peak shifts toward longer wavelength with the red shift of excitation wavelength. The PL excitation spectrum indicates that the bandgap of the Si-NCs in solution is 2.64 eV, which confirms that the blue-violet PL originates from interband transition of Si-NCs caused by quantum confinement effect. The PL peak red shifts to 607 nm after natural oxidation, and the peak lifetime of which is slow down to 13.1 μs. The fixed PL peak excited by different wavelengths and the slow PL decay time indicate that interface defects become the main PL mechanism after natural oxidation. The results will add new information for understanding the PL mechanism of Si-NCs in different environments.

  3. Effect of reaction media on the growth and photoluminescence of colloidal CdSe nanocrystals.

    PubMed

    Yu, Kui; Singh, Shanti; Patrito, Natasha; Chu, Virginia

    2004-12-01

    Using cadium oxide (CdO) as the Cd precursor and tri-n-octylphosphine selenide (TOPSe) as the Se source, TOP-capped and TOP/tri-n-octylphosphine oxide (TOPO)-capped CdSe nanocrystals were synthesized without the use of an acid. The synthetic approach involved the addition of a TOPSe/TOP solution into a CdO/TOP solution with or without TOPO at one temperature and subsequent growth at a lower temperature. The temporal evolution of the optical properties, namely, absorption and luminescence, of the growing nanocrystals was monitored in detail. A comprehensive examination on the control of the photoluminescence (PL) properties was performed by systematically varying the TOP/TOPO weight ratio of the reaction media. Surprisingly, a rational choice of 100% TOP or 80% TOP was found to produce "quality" nanocrystals when monitored under the present experimental conditions and growth-time scale. The term "quality" is mainly based on the sharp features and rich substructure exhibited in the absorption spectra of the growing nanocrystals, as well as the sharp features in the emission spectra with narrow full width at half-maximum (fwhm). There are two distinguishable stages of growth: an early stage (<5 min) and a later stage. TOP plays a major role in the control of a slow growth rate in the early stage, while TOPO controls slow growth in the later stage. The optical sensitivity of the growing nanocrystals when dispersed in nonpolar or polar solvents was studied, including two size-dependent parameters, namely, the solvent sensitivity (PL intensity) and nonresonant Stokes shift (NRSS). The insights gained from the present study enable a synthetic approach in which high-quality CdSe nanocrystals are achieved with high synthetic reproducibility.

  4. Correlation of atomic structure and photoluminescence of the same quantum dot: pinpointing surface and internal defects that inhibit photoluminescence.

    PubMed

    Orfield, Noah J; McBride, James R; Keene, Joseph D; Davis, Lloyd M; Rosenthal, Sandra J

    2015-01-27

    In a size regime where every atom counts, rational design and synthesis of optimal nanostructures demands direct interrogation of the effects of structural divergence of individuals on the ensemble-averaged property. To this end, we have explored the structure-function relationship of single quantum dots (QDs) via precise observation of the impact of atomic arrangement on QD fluorescence. Utilizing wide-field fluorescence microscopy and atomic number contrast scanning transmission electron microscopy (Z-STEM), we have achieved correlation of photoluminescence (PL) data and atomic-level structural information from individual colloidal QDs. This investigation of CdSe/CdS core/shell QDs has enabled exploration of the fine structural factors necessary to control QD PL. Additionally, we have identified specific morphological and structural anomalies, in the form of internal and surface defects, that consistently vitiate QD PL.

  5. Summary of field operations Powerline Wells PL-1, PL-2, PL-3

    SciTech Connect

    Foutz, W.L.

    1996-03-01

    This report summarizes field operations and hydrogeologic data obtained during installation of the Powerline monitoring/test wells near the western boundary of Kirtland Air Force Base. These wells were installed in 1994 as part of the Site-Wide Hydrogeologic Characterization Project saturated zone investigation. The Site-Wide Hydrogeologic Characterization Project is part of Sandia National Laboratories, New Mexico, Environmental Restoration Project. Three wells were drilled and completed at this location, and named PL-1, PL-2, and PL-3. They are located northwest of Tech Area 3, and are named after a high-voltage powerline located just south of the wells. The objectives of the Powerline wells were to determine the depth to water, complete 2 water table wells and a deeper Santa Fe Group well, to determine the geologic provenance of Santa Fe Group sediments at this location, and to obtain background core samples for radiological analysis. During these field operations, important subsurface hydrogeologic data were obtained. These data include drill cuttings and lithologic descriptions, core samples with background analytical data, geophysical logs, water quality parameters, and water levels. Aquifer tests at the Powerline location will generate data that may yield information on anisotropy in the Santa Fe Group and constrain numerical modeling results that indicate that there is a major northward component of groundwater flow from McCormick Ranch and Tech Area 3 test sites toward City of Albuquerque and KAFB well fields.

  6. Photoluminescence from amino-containing polymer in the presence of CO2: carbamato anion formed as a fluorophore.

    PubMed

    Pan, Xiaoyong; Wang, Guan; Lay, Chee Leng; Tan, Beng Hong; He, Chaobin; Liu, Ye

    2013-01-01

    Organic photoluminescent materials are important to many applications especially for diagnosis and detection, and most of organic photoluminescent materials contain fluorophores with extended conjugated structures. Recently some of amino-containing polymers without fluorophores with extended conjugated structure are observed to be photoluminescent, and one possible cause of the photoluminescence is oxidation of the amines. Here we show that photoluminescence can be produced by exposing a typical amino-containing polymer, polyethylenimine, to carbon dioxide. We demonstrate that carbamato anion formed via the reaction between the amine and carbon dioxide is a fluorophore; and the loosely-bound protonated water molecule can increase UV absorption but reduce the photoluminescence emission. Also carbamato anion shows solvent- and excitation wavelength-dependent emission of photoluminescence. The photoluminescence profile of carbamoto anion was discussed. These results will facilitate the understanding of photoluminescence observed from amino-containing materials and the design of new fluorophores. PMID:24067377

  7. Photoluminescence from Amino-Containing Polymer in the Presence of CO2: Carbamato Anion Formed as a Fluorophore

    PubMed Central

    Pan, Xiaoyong; Wang, Guan; Lay, Chee Leng; Tan, Beng Hong; He, Chaobin; Liu, Ye

    2013-01-01

    Organic photoluminescent materials are important to many applications especially for diagnosis and detection, and most of organic photoluminescent materials contain fluorophores with extended conjugated structures. Recently some of amino-containing polymers without fluorophores with extended conjugated structure are observed to be photoluminescent, and one possible cause of the photoluminescence is oxidation of the amines. Here we show that photoluminescence can be produced by exposing a typical amino-containing polymer, polyethylenimine, to carbon dioxide. We demonstrate that carbamato anion formed via the reaction between the amine and carbon dioxide is a fluorophore; and the loosely-bound protonated water molecule can increase UV absorption but reduce the photoluminescence emission. Also carbamato anion shows solvent- and excitation wavelength-dependent emission of photoluminescence. The photoluminescence profile of carbamoto anion was discussed. These results will facilitate the understanding of photoluminescence observed from amino-containing materials and the design of new fluorophores. PMID:24067377

  8. Photoluminescence characteristics of ZnO clusters confined in the micropores of zeolite L

    SciTech Connect

    Wang Fang; Song Hongwei Pan Guohui; Fan Libo; Dai Qilin; Dong Biao; Liu Huihui; Yu Jihong; Wang Xi; Li Li

    2009-03-05

    Sub-nanometric ZnO clusters were prepared in the micropores of zeolite L by the incipient wetness impregnation method. The X-ray patterns (XRD), transmission electron microscope (TEM), N{sub 2} adsorption-desorption isotherms, UV-vis absorption spectra (UV-vis) and photoluminescence spectra (PL) were used to characterize the composite materials. The results indicate that a small amount of sub-nanometric ZnO clusters can be introduced into the channel of zeolite L, however, when the amount of ZnO loading exceeds 20 wt%, macrocrystalline ZnO appears on the external surface of zeolite L. Different from bulk ZnO materials, these sub-nanometric ZnO clusters exhibit their absorption onset below 255 nm and a blue luminescence band in the range of 404-422 nm. The temperature-dependent luminescence demonstrates that the amount of the ZnO loading significantly affects the exciton-phonon interaction between the ZnO clusters and the zeolite host. The ZnO clusters exhibit a picosecond scale emission lifetime at room temperature.

  9. Non-Uniformities in Thin-Film Cadmium Telluride Solar Cells Using Electroluminescence and Photoluminescence: Preprint

    SciTech Connect

    Zaunbrecher, K.; Johnston, S.; Yan, F.; Sites, J.

    2011-07-01

    It is the purpose of this research to develop specific imaging techniques that have the potential to be fast, in-line tools for quality control in thin-film CdTe solar cells. Electroluminescence (EL) and photoluminescence (PL) are two techniques that are currently under investigation on CdTe small area devices made at Colorado State University. It is our hope to significantly advance the understanding of EL and PL measurements as applied to CdTe. Qualitative analysis of defects and non-uniformities is underway on CdTe using EL, PL, and other imaging techniques.

  10. Characterization of semiconductor core shell nanoparticles by resonant Raman scattering and photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Dzhagan, V. M.; Valakh, M. Ya.; Raevskaya, A. E.; Stroyuk, A. L.; Kuchmiy, S. Ya.; Zahn, D. R. T.

    2008-11-01

    Colloidal CdSe nanoparticles (NPs), passivated with CdS and ZnS, were characterized by resonant Raman scattering and photoluminescence (PL). The effect of the passivating shell, its volume and formation procedure on optical and vibrational spectra is discussed. Analyzing the Raman peaks due to optical phonons inside the core and those related to the core-shell interface allows some understanding of the relation between the core-shell structure and its PL properties to be achieved. In particular, a compositional intermixing at the core/shell interface of the NPs was deduced from the Raman spectra, which can noticeably affect their PL intensity.

  11. Transparently wrap-gated semiconductor nanowire arrays for studies of gate-controlled photoluminescence

    SciTech Connect

    Nylund, Gustav; Storm, Kristian; Torstensson, Henrik; Wallentin, Jesper; Borgström, Magnus T.; Hessman, Dan; Samuelson, Lars

    2013-12-04

    We present a technique to measure gate-controlled photoluminescence (PL) on arrays of semiconductor nanowire (NW) capacitors using a transparent film of Indium-Tin-Oxide (ITO) wrapping around the nanowires as the gate electrode. By tuning the wrap-gate voltage, it is possible to increase the PL peak intensity of an array of undoped InP NWs by more than an order of magnitude. The fine structure of the PL spectrum reveals three subpeaks whose relative peak intensities change with gate voltage. We interpret this as gate-controlled state-filling of luminescing quantum dot segments formed by zincblende stacking faults in the mainly wurtzite NW crystal structure.

  12. Influence of doping in InP buffer on photoluminescence behavior of InPBi

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Pan, Wenwu; Cao, Chunfang; Wu, Xiaoyan; Wang, Shumin; Gong, Qian

    2016-11-01

    InP1‑ x Bi x epilayers with 1.0% bismuth concentration were grown on InP(001) substrates by gas-source molecular beam epitaxy. Silicon and beryllium were doped into the InP buffer layer, and their influences on the photoluminescence (PL) emission of InPBi were investigated. The PL emission of InPBi was found to be intensified by beryllium doping into the InP buffer layer. However, there was no influence of silicon doping. To investigate the reason for the PL intensity enhancement of InPBi, the carrier transport behavior at the interface was also discussed.

  13. Temperature dependent photoluminescence and micromapping of multiple stacks InAs quantum dots

    SciTech Connect

    Xu, Ming Jaffré, Alexandre Alvarez, José Kleider, Jean-Paul Boutchich, Mohamed; Jittrong, Apichat; Chokamnuai, Thitipong; Panyakeow, Somsak; Kanjanachuchai, Songphol

    2015-02-27

    We utilized temperature dependent photoluminescence (PL) techniques to investigate 1, 3 and 5 stack InGaAs quantum dots (QDs) grown on cross-hatch patterns. PL mapping can well reproduce the QDs distribution as AFM and position dependency of QD growth. It is possible to observe crystallographic dependent PL. The temperature dependent spectra exhibit the QDs energy distribution which reflects the size and shape. The inter-dot carrier coupling effect is observed and translated as a red shift of 120mV on the [1–10] direction peak is observed at 30K on 1 stack with regards to 3 stacks samples, which is assigned to lateral coupling.

  14. Influence of Au nanoparticles on the photoluminescent and electrical properties of Bi{sub 3.6}Eu{sub 0.4}Ti{sub 3}O{sub 12} ferroelectric thin films

    SciTech Connect

    Su, Li; Qin, Ni E-mail: stsbdh@mail.sysu.edu.cn; Xie, Wei; Fu, Jianhui; Bao, Dinghua E-mail: stsbdh@mail.sysu.edu.cn

    2014-07-21

    Au-doped Bi{sub 3.6}Eu{sub 0.4}Ti{sub 3}O{sub 12} (BET) thin films were prepared on fused silica and Pt/Ti/SiO{sub 2}/Si substrates by a chemical solution deposition method. The existence of Au nanoparticles (NPs) has been confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscope analysis. Enhanced photoluminescence (PL) of Eu{sup 3+} ions was obtained in a wide range of Au doping level. Role of the Au NPs in the PL enhancement was investigated by means of optical absorption, excitation, and emission spectra, as well as decay lifetime measurements. The results indicated that the intra-4f transition of Eu{sup 3+} ions can be intensively activated by the coupling of the charge transfer band of BET with the {sup 5}D{sub 0} state of Eu{sup 3+} ions. The influence of Au NPs on the PL properties of Eu{sup 3+} ions in the present thin films was attributed to the band bending at Au/BET interface and the localized surface plasma resonance absorption of Au NPs in the visible light region. The dielectric and ferroelectric properties of Au-doped BET thin films were investigated as well.

  15. Plasmon enhanced linear and nonlinear photoluminescence in planar nanoparticle arrays (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Walsh, Gary F.; Dal Negro, Luca

    2015-09-01

    Light emission from metal nanoparticles has potential appications as a highly sensitive refractive index detector. In order for this protential to be realized the mechanics of plasmon enhanced photoluminescence (PL) in planar nanoparticle arrays must be understude. We present an experimental exploreation of emission spectra and realitive efficiency of gold PL in nanoplasmonic arrays. We demonstrate tunability of metal PL by nanoparticle size and discover the critical role of near-field interparticle coupling on emission efficiency. We show that direct excition of plasmon resonances by photoexcited electron-hole pairs is the primary contributer to the metalic nanoparticle emission spectrum. We additionally show that emission is quenched by near-field interactions between nanoparticles leading to spectral broading by increased non-radiative plasmon decay. Finally, we show a correlation between plasmon life-time and PL efficiency. We explore this phenominan for both linear and nonlinear PL. Experimental results are supported by numerical simulations of plasmon life-time.

  16. Defect passivation induced strong photoluminescence enhancement of rhombic monolayer MoS2.

    PubMed

    Su, Weitao; Jin, Long; Qu, Xiaodan; Huo, Dexuan; Yang, Li

    2016-05-18

    Growing high quality monolayer MoS2 with strong photoluminescence (PL) is essential to produce light-emitting devices on the atomic scale. In this study we show that rhombic monolayer MoS2 with PL intensity 8 times stronger than those of chemical vapour deposition (CVD)-grown triangular and mechanically exfoliated (ME) monolayer MoS2 can be prepared by using CVD. Both Raman and PL measurements indicate low density of defects in rhombic monolayer MoS2 with enhanced PL intensity. Density functional theory (DFT) calculations show that passivation of defects in MoS2 removes trapping gap states, which may finally result in PL enhancement.

  17. Magneto-photoluminescence of InAs/InGaAs/InAlAs quantum well structures

    SciTech Connect

    Terent'ev, Ya. V.; Danilov, S. N.; Loher, J.; Schuh, D.; Bougeard, D.; Weiss, D.; Ganichev, S. D.; Durnev, M. V.; Tarasenko, S. A.; Mukhin, M. S.; Ivanov, S. V.

    2014-03-10

    Photoluminescence (PL) and highly circularly polarized magneto-PL (up to 50% at 6 T) from two-step bandgap InAs/InGaAs/InAlAs quantum wells (QWs) are studied. Bright PL is observed up to room temperature, indicating a high quantum efficiency of the radiative recombination in these QWs. The sign of the circular polarization indicates that it stems from the spin polarization of heavy holes caused by the Zeeman effect. Although in magnetic field the PL lines are strongly circularly polarized, no energy shift between the counter-polarized PL lines was observed. The results suggest the electron and the hole g-factor to be of the same sign and close magnitudes.

  18. A co-precipitation preparation, crystal structure and photoluminescent properties of Er5%:Gd2O3 nanorods

    NASA Astrophysics Data System (ADS)

    Boopathi, G.; Raj, S. Gokul; Kumar, G. Ramesh; Mohan, R.

    2015-06-01

    An inexpensive preparation method is being reported for obtaining erbium doped gadolinium oxide (Er5%:Gd2O3) nanoscale rods. The elongated nanoscale systems, as-formed through a co-precipitation process, are characterized by using X-ray powder diffraction (XRD) patterns, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) mapping, Ultra Violet-visible (UV-vis.) absorption spectroscopy and photoluminescence (PL) spectroscopy. In addition, the Williamson-Hall (W-H) plot is also performed to distinguish the effect of crystalline size-induced broadening and strain-induced broadening at full-width at half-maximum (FWHM) of the XRD profile. The XRD patterns of as-formed and calcined products show that the phase confirmation. As revealed from the SEM micrographs, the morphology of the products show that the rod-like nanoparticles. The EDX micrographs show that the presence of elements in our samples. The band gap values in calcined samples are found to be in the range of 3.569 eV. Upon 230 nm excitation on calcined samples, three broad emission peaks are observed from PL studies. The possible mechanism for the formation of Er5%:Gd2O3 nanorods is briefly discussed.

  19. Photoluminescence Quenching and Enhanced Optical Conductivity of P3HT-Derived Ho(3+)-Doped ZnO Nanostructures.

    PubMed

    Kabongo, Guy L; Mbule, Pontsho S; Mhlongo, Gugu H; Mothudi, Bakang M; Hillie, Kenneth T; Dhlamini, Mokhotjwa S

    2016-12-01

    In this article, we demonstrate the surface effect and optoelectronic properties of holmium (Ho(3+))-doped ZnO in P3HT polymer nanocomposite. We incorporated ZnO:Ho(3+) (0.5 mol% Ho) nanostructures in the pristine P3HT-conjugated polymer and systematically studied the effect of the nanostructures on the optical characteristics. Detailed UV-Vis spectroscopy analysis revealed enhanced absorption coefficient and optical conductivity in the P3HT-ZnO:Ho(3+) film as compared to the pristine P3HT. Moreover, the obtained photoluminescence (PL) results established the improvement of exciton dissociation as a result of ZnO:Ho(3+) nanostructures inclusion. The occurrence of PL quenching is the result of enhanced charge transfer due to ZnO:Ho(3+) nanostructures in the polymer, whereas energy transfer from ZnO:Ho(3+) to P3HT was verified. Overall, the current investigation revealed a systematic tailoring of the optoelectronic properties of pristine P3HT after inclusion of ZnO:Ho(3+) nanostructures, thus opening brilliant perspectives for applications in various optoelectronic devices. PMID:27650292

  20. Photoluminescence Quenching and Enhanced Optical Conductivity of P3HT-Derived Ho3+-Doped ZnO Nanostructures

    NASA Astrophysics Data System (ADS)

    Kabongo, Guy L.; Mbule, Pontsho S.; Mhlongo, Gugu H.; Mothudi, Bakang M.; Hillie, Kenneth T.; Dhlamini, Mokhotjwa S.

    2016-09-01

    In this article, we demonstrate the surface effect and optoelectronic properties of holmium (Ho3+)-doped ZnO in P3HT polymer nanocomposite. We incorporated ZnO:Ho3+ (0.5 mol% Ho) nanostructures in the pristine P3HT-conjugated polymer and systematically studied the effect of the nanostructures on the optical characteristics. Detailed UV-Vis spectroscopy analysis revealed enhanced absorption coefficient and optical conductivity in the P3HT-ZnO:Ho3+ film as compared to the pristine P3HT. Moreover, the obtained photoluminescence (PL) results established the improvement of exciton dissociation as a result of ZnO:Ho3+ nanostructures inclusion. The occurrence of PL quenching is the result of enhanced charge transfer due to ZnO:Ho3+ nanostructures in the polymer, whereas energy transfer from ZnO:Ho3+ to P3HT was verified. Overall, the current investigation revealed a systematic tailoring of the optoelectronic properties of pristine P3HT after inclusion of ZnO:Ho3+ nanostructures, thus opening brilliant perspectives for applications in various optoelectronic devices.

  1. Absorbance and Photoluminescence of Si, Ge, and MoS{sub 2} Nanoparticles Studied by Liquid Chromatography

    SciTech Connect

    Provencio, P.P.; Samara, G.A.; Wilcoxon, J.P,

    1999-07-12

    The authors have successfully synthesized highly crystalline, size-selected indirect band-gap nanocrystals (NC) of Si, Ge and MoS{sub 2} in the size range 2-10 nm in inverse micelles and studied their optical absorption and photoluminescence (PL) properties using liquid chromatography. Room temperature, visible PL from these nanocrystals was demonstrated in the range 700-350 nm (1.8-3.5 eV). their experimental results are interpreted in terms of the corresponding electronic structure of the bulk materials and it is demonstrated that these nanocrystals retain bulk-like electronic character to sizes as small as 2 nm, but the absorbance energies are strongly blue-shifted by quantum confinement. The experimental results on Si-NCs are also compared to earlier work on Si clusters grown by other techniques and to the predictions of various model calculations. Currently, the wide variations in the theoretical predictions of the various models along with considerable uncertainties in experimental size determination for clusters less than 3-4 nm, make it difficult to select the best model.

  2. A study on annealing effects of AgInS2/GaAs epilayer obtained from photoluminescence measurements

    NASA Astrophysics Data System (ADS)

    Hong, K. J.; Jeong, J. W.; Baek, H. W.; Kim, K. S.; Moon, J. D.; Kim, H. S.; Im, K. H.

    2002-05-01

    The AgInS2 epilayers with a chalcopyrite structure grown using a hot-wall epitaxy (HWE) method have been confirmed to be a high quality crystal. From the optical absorption measurement, the temperature dependence of the energy band gap on AgInS2/GaAs was found to be Eg(T)=2.1365 eV-(9.89×10-3 eV)T2/(2930+T). After the as-grown AgInS2/GaAs was annealed in Ag-, S-, and In-atmospheres, the origin of point defects of AgInS2/GaAs has been investigated by using the photoluminescence (PL) at 10 K. The native defects of VAg, VS, Agint, and Sint obtained from PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the S-atmosphere converted AgInS2/GaAs to an optical p-type. Also, we confirmed that In in AgInS2/GaAs did not form the native defects because In in AgInS2 did exist in the form of stable bonds.

  3. Low-temperature photoluminescence analysis of CdTeSe crystals for radiation-detector applications

    SciTech Connect

    YANG G.; Roy, U. N.; Bolotnikov, A. E.; Cui, Y.; Camarda, G.S.; Hossain, A.; and James, R. B.

    2015-10-05

    Goal: Understanding the changes of material defects in CdTeSe following annealing. Experimental results and discussions: Infrared (IR) transmission microscopy; current-voltage measurements (Highlight: Improvement of resistivity of un-doped crystals after annealing); low-temperature photoluminescence (PL) spectrum of as-grown and annealed samples.

  4. Structural Order-Disorder Transformations Monitored by X-Ray Diffraction and Photoluminescence

    ERIC Educational Resources Information Center

    Lima, R. C.; Paris, E. C.; Leite, E. R.; Espinosa, J. W. M.; Souza, A. G.; Longo, E.

    2007-01-01

    A study was conducted to examine the structural order-disorder transformation promoted by controlled heat treatment using X-ray diffraction technique (XRD) and photoluminescence (PL) techniques as tools to monitor the degree of structural order. The experiment was observed to be versatile and easily achieved with low cost which allowed producing…

  5. Colloidal Organometal Halide Perovskite (MAPbBrxI3−x, 0≤x≤3) Quantum Dots: Controllable Synthesis and Tunable Photoluminescence

    PubMed Central

    Zhao, Ying; Xu, Xiangxing; You, Xiaozeng

    2016-01-01

    Organic-inorganic perovskite materials, typically methylammonium lead trihalide (MAPbX3: MA = methylammonium; X = Br, I), are recently attract enormous attention for their distinguished photo-electronic properties. The control of morphology, composition and dispersability of MAPbX3 perovskite nanocrystals is crucial for the property tailoring and still a major challenge. Here we report the synthesis of colloidal MAPbBrxI3−x(0 ≤ x ≤ 3) nanocrystals at room temperature by using alkyl carboxylate as capping ligands. These nanocrystals exhibit continuously tunable UV-vis absorption and photoluminescence (PL) across the visible spectrum, which is attributed to the quantum confinement effect with certain stoichiometry. Their unique exciton recombination dynamics was investigated and discussed. PMID:27775023

  6. Diffusion limited photoluminescence quantum yields in 1-D semiconductors: single-wall carbon nanotubes.

    PubMed

    Hertel, Tobias; Himmelein, Sabine; Ackermann, Thomas; Stich, Dominik; Crochet, Jared

    2010-12-28

    Photoluminescence quantum yields and nonradiative decay of the excitonic S(1) state in length fractionated (6,5) single-wall carbon nanotubes (SWNTs) are studied by continuous wave and time-resolved fluorescence spectroscopy. The experimental data are modeled by diffusion limited contact quenching of excitons at stationary quenching sites including tube ends. A combined analysis of the time-resolved photoluminescence decay and the length dependence of photoluminescence quantum yields (PL QYs) from SWNTs in sodium cholate suspensions allows to determine the exciton diffusion coefficient D = 10.7 ± 0.4 cm(2)s(-1) and lifetime τ(PL) for long tubes of 20 ± 1 ps. PL quantum yields Φ(PL) are found to scale with the inverse diffusion coefficient and the square of the mean quenching site distance, here l(d) = 120 ± 25 nm. The results suggest that low PL QYs of SWNTs are due to the combination of high-diffusive exciton mobility with the presence of only a few quenching sites.

  7. Exciton-electron dynamics studied by microwave photoconductivity and photoluminescence in undoped GaAs/Al0.3Ga0.7As quantum wells

    NASA Astrophysics Data System (ADS)

    Kozhevnikov, M.; Ashkinadze, B. M.; Cohen, E.; Ron, Arza; Shtrikman, Hadas

    1999-12-01

    We report on a comparative study of the photoinduced microwave absorption (PMA) (contactless photoconductivity) at 35.6 GHz and the photoluminescence (PL) in undoped GaAs/AlxGa1-xAs quantum wells (QW's) having various well widths (50-200 Å). While the PL and its excitation (PLE) spectra probe the excitonic transitions, the PMA intensity and its excitation (PMAE) spectra provide information on unbound electron-hole generation processes. The PMAE spectra show strong (e1:hh1)1S and (e1:1h1)1S excitonic bands. Since these are bound electron-hole transitions that are observed to give rise to free carrier microwave absorption, exciton dissociation processes are involved. A model is presented that explains these bands in terms of Auger-like exciton dissociation at low temperatures and thermal exciton dissociation at high temperatures. We also discuss the effect of carrier and exciton localization in the spatially fluctuating QW potential.

  8. Photoluminescence of defects induced in silicon by SF6/O2 reactive-ion etching

    NASA Astrophysics Data System (ADS)

    Buyanova, I. A.; Henry, A.; Monemar, B.; Lindström, J. L.; Oehrlein, G. S.

    1995-09-01

    Photoluminescence (PL) studies of SF6/O2 plasma-induced defect formation in n-type silicon samples are reported. Ion bombardment of the silicon surface during the SF6 reactive-ion etching (RIE) is shown to introduce defects giving rise to a broad PL band in the 0.70-1.00 eV spectral range and to the carbon-related C and G lines. The role of oxygen during SF6/O2 RIE on the photoluminescence observed is analyzed. It is argued that oxygen contamination enhances the formation of PL centers via the creation of extended defects, such as oxygen precipitates. A lattice contraction nearby these extended defects is suggested to be responsible for the observed splitting of the C and G lines as well as the shift of the phosphorous bound exciton line detected after SF6/O2 RIE.

  9. Photoluminescence study of ZnS and ZnS:Pb nanoparticles

    SciTech Connect

    Virpal, Hastir, Anita; Kaur, Jasmeet; Singh, Gurpreet; Singh, Ravi Chand

    2015-05-15

    Photoluminescence (PL) study of pure and 5wt. % lead doped ZnS prepared by co-precipitation method was conducted at room temperature. The prepared nanoparticles were characterized by X-ray Diffraction (XRD), UV-Visible (UV-Vis) spectrophotometer, Photoluminescence (PL) and Raman spectroscopy. XRD patterns confirm cubic structure of ZnS and PbS in doped sample. The band gap energy value increased in case of Pb doped ZnS nanoparticles. The PL spectrum of pure ZnS was de-convoluted into two peaks centered at 399nm and 441nm which were attributed to defect states of ZnS. In doped sample, a shoulder peak at 389nm and a broad peak centered at 505nm were observed. This broad green emission peak originated due to Pb activated ZnS states.

  10. Blue photoluminescence enhancement in laser-irradiated 6H-SiC at room temperature

    SciTech Connect

    Wu, Yan; Ji, Lingfei Lin, Zhenyuan; Jiang, Yijian; Zhai, Tianrui

    2014-01-27

    Blue photoluminescence (PL) of 6H-SiC irradiated by an ultraviolet laser can be observed at room temperature in dark condition. PL spectra with Gaussian fitting curve of the irradiated SiC show that blue luminescence band (∼440 nm) is more pronounced than other bands. The blue PL enhancement is the combined result of the improved shallow N-donor energy level and the unique surface state with Si nanocrystals and graphene/Si composite due to the effect of photon energy input by the short-wavelength laser irradiation. The study can provide a promising route towards the preparation of well-controlled blue photoluminescence material for light-emitting devices.

  11. Photoluminescence of etched SiC nanowires

    NASA Astrophysics Data System (ADS)

    Stewart, Polite D., Jr.; Rich, Ryan; Zerda, T. W.

    2010-10-01

    SiC nanowires were produced from carbon nanotubes and nanosize silicon powder in a tube furnace at temperatures between 1100^oC and 1350^oC. SiC nanowires had average diameter of 30 nm and very narrow size distribution. The compound possesses a high melting point, high thermal conductivity, and excellent wear resistance. The surface of the SiC nanowires after formation is covered by an amorphous layer. The composition of that layer is not fully understood, but it is believed that in addition to amorphous SiC it contains various carbon and silicon compounds, and SiO2. The objective of the research was to modify the surface structure of these SiC nanowires. Modification of the surface was done using the wet etching method. The etched nanowires were then analyzed using Fourier Transform Infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and photoluminescence (PL). FTIR and TEM analysis provided valid proof that the SiC nanowires were successfully etched. Also, the PL results showed that the SiC nanowire core did possess a fluorescent signal.

  12. Vibronic Structure of Heat-treated Polyparaphenylene Photoluminescence Spectra

    NASA Astrophysics Data System (ADS)

    Matthews, Manyalibo J.; Brown, S. D. M.; Pimenta, M. A.; Dresselhaus, M. S.; Endo, Morinobu

    1998-03-01

    We present the results of detailed photoluminescence (PL) experiments on Kovacic-type PPP prepared at different heat-treatment temperatures. Heat-treated Kovacic-PPP has been shown to produce a structure capable of electrochemically absorbing a large amount of lithium, which has practical interest for applications to lithium-ion batteries. Photoluminescent emissions in the energy range 2.4-3.0 eV show well-defined vibronic levels which are analyzed using Frank-Condon theory, yielding electron-phonon coupled phonon modes with mode frequencies that are in agreement with Raman data. We discuss in detail the anomalous red ( ~ 1.8 eV) emission which is particular to the Kovacic synthesis process, and is sensitive to defect concentration. Ab initio total energy calculations were performed to investigate the influence of both inherent synthesis-dependent defects and thermally-induced defects on the PL spectra. For comparison, we also present PL results and calculations on less-defective Yamamoto-type PPP.

  13. Highly Luminescent Hybrid SiO2-Coated CdTe Quantum Dots Retained Initial Photoluminescence Efficiency in Sol-Gel SiO2 Film.

    PubMed

    Sun, Hongsheng; Xing, Yugui; Wu, Qinan; Yang, Ping

    2015-02-01

    A highly luminescent silica film was fabricated using tetraethyl orthosilicate (TEOS) and 3-aminopropyltrimethoxysilane (APS) through a controlled sol-gel reaction. The pre-hydrolysis of TEOS and APS which resulted in the mixture of TEOS and APS in a molecular level is a key for the formation of homogenous films. The aminopropyl groups in APS play an important role for obtaining homogeneous film with high photoluminescence (PL). Red-emitting hybrid SiO2-coated CdTe nano-crystals (NCs) were fabricated by a two-step synthesis including a thin SiO2 coating via a sol-gel process and a subsequent refluxing using green-emitting CdTe NCs. The hybrid SiO2-coated CdTe NCs were embedded in a functional SiO2 film via a two-step process including adding the NCs in SiO2 sol with a high viscosity and almost without ethanol and a subsequent spinning coating. The hybrid SiO2-coated CdTe NCs retained their initial PL efficiency (54%) in the film. Being encapsulated with the hybrid NCs in the film, no change on the absorption and PL spectra of red-emitting CdTe NCs (632 nm) was observed. This indicates the hybrid NCs is stable enough during preparation. This phenomenon is ascribed to the controlled sol-gel process and a hybrid SiO2 shell on CdTe NCs. Because these films exhibited high PL efficiency and stability, they will be utilizable for potential applications in many fields.

  14. Investigation of Photoluminescence and Photocurrent in InGaAsP/InP Strained Multiple Quantum Well Heterostructures

    NASA Technical Reports Server (NTRS)

    Raisky, O. Y.; Wang, W. B.; Alfano, R. R.; Reynolds, C. L., Jr.; Swaminathan, V.

    1997-01-01

    Multiple quantum well InGaAsP/InP p-i-n laser heterostructures with different barrier thicknesses have been investigated using photoluminescence (PL) and photocurrent (PC) measurements. The observed PL spectrum and peak positions are in good agreement with those obtained from transfer matrix calculations. Comparing the measured quantum well PC with calculated carrier escape rates, the photocurrent changes are found to be governed by the temperature dependence of the electron escape time.

  15. Two-photon absorption in 3-100 nm diameter Silicon nanocrystals in solution

    NASA Astrophysics Data System (ADS)

    Furey, Brandon; Downer, Michael; Yu, Yixuan; Korgel, Brian

    Silicon nanocrystals (nc-Si) exhibit efficient photoluminescence (PL) that has applications in non-toxic bio-imaging. Two-photon absorption (TPA) is an important process for exciting PL in the tissue transparency spectral window, but absolute TPA coefficients have not been measured as a continuous function of nc size or excitation wavelength. Previous TPA studies have focused on nc-Si embedded in an oxide matrix or on porous Si surfaces at selected discrete wavelengths. However, recently free standing, ligand-stabilized nc-Si with diameters ranging from 3 to 100 nm that are soluble in liquids, including water, and suitable for bio-imaging have become available. We will present calibrated TPA spectra for free standing nc-Si over a wide range of nc diameters, based on measurements with tunable femtosecond laser pulses. We will compare indirect TPA measurements based on collection and detection of PL with direct TPA measurements based on attenuation of the incident beam. Department of Physics.

  16. Electron transition pathways of photoluminescence from 3C-SiC nanocrystals unraveled by steady-state, blinking and time-resolved photoluminescence measurements

    NASA Astrophysics Data System (ADS)

    Gan, Zhixing; Wu, Xinglong; Xu, Hao; Zhang, Ning; Nie, Shouping; Fu, Ying

    2016-07-01

    The cubic phase SiC nanocrystals (3C-SiC NCs) have been extensively studied for electronics and photonics applications. In this work we study the electron transition pathways of photoluminescence (PL) from 3C-SiC NCs. It is found through measuring the steady-state, blinking and time-resolved PL spectra that surface passivation by glycerol improved the steady-state PL intensity (it does not modify the emission wavelength) and the NCs fluoresced more steadily. The PL decay lifetimes are shown to be the same when the detection wavelength is modified to scan the broad PL peak, implying that the broad PL peak is originated from the distribution of NCs’ sizes. Furthermore, the PL decay lifetimes are not modified by the surface passivation. It is concluded that for PL, the electron is photoexcited from the ground state in the NC to a high-energy excited state, relaxes to the first excited state then radiatively recombines to the ground state to emit a photon. The photoexcited electron at the high-energy excited state could transit to the surface state, resulting in a reduced PL intensity and a decreased on-state dwell time in the blinking trajectory. The PL decay lifetime data implies that the two principal electron transition pathways of (a) high-energy excited state \\Rightarrow the first excited state \\Rightarrow the ground state, and (b) high-energy excited state \\Rightarrow surface state \\Rightarrow the ground state are independent from each other. We strongly believe that such a deep knowledge about 3C-SiC NCs will open new doors to harness them for novel applications.

  17. Photoluminescence fatigue and inhomogeneous line broadening in semi-insulating Tl6SeI4 single crystals

    NASA Astrophysics Data System (ADS)

    Kostina, S. S.; Peters, J. A.; Lin, W.; Chen, P.; Liu, Z.; Wang, P. L.; Kanatzidis, M. G.; Wessels, B. W.

    2016-06-01

    Photoluminescence (PL) properties of semi-insulating Tl6SeI4 have been investigated. A broad emission band centered at 1.63 ± 0.02 eV was observed in all samples. The PL emission band is excitonic in nature and is tentatively attributed to a bound exciton emission. PL fatigue (a reduction in PL intensity under prolonged laser excitation) was always observed. The amount of PL fatigue depended on excitation power and temperature. PL fatigue kinetics are described by a stretched exponential with nominal lifetimes in the 10–265 s range. The recovery of the PL occurred within a few seconds of light cessation. The magnitude of PL fatigue in different samples correlated with inhomogeneous line broadening of the 1.63 eV emission band, such that broader bands exhibited more fatigue. An additional luminescence band centered at 1.78 eV was observed which increased in intensity under prolonged laser irradiation. The fatigue phenomenon is tentatively attributed to two mechanisms—the formation of photo-induced defects and the formation of quasi-stable particles. Both of these mechanisms introduce additional radiative and non-radiative recombination channels that lead to a decrease in the PL intensity under prolonged laser irradiation. Since inhomogeneous line broadening and PL fatigue are related to the concentration of defects or impurities, the measurement of these two parameters is an effective method to screen sample quality.

  18. Time-resolved photoluminescence properties of ion-beam-synthesized β-FeSi2 and Si-implanted Si

    NASA Astrophysics Data System (ADS)

    Terai, Yoshikazu; Maeda, Yoshihito

    2015-07-01

    Temporal decay characteristics of 1.54 µm photoluminescence (PL) were investigated in β-FeSi2 and Si-implanted Si samples grown by ion-beam-synthesis (IBS). In the samples, the band-edge PL of β-FeSi2 (A-band) and the dislocation-related PL (D1-band) of Si were both observed at ˜0.8 eV. Regarding the dependence of the PL decay curves on excitation power density (P), PL decay curves without extrinsic effects were obtained at a low P of P ≤ 4.3 mW/cm2. The PL decay times obtained at a low P showed clear differences between the A-band and the D1-line. The result showed that the band-edge PL of β-FeSi2 was distinguished from the dislocation-related PL of Si by the PL decay times. The intrinsic PL decay times of β-FeSi2 were determined to be τ1 = 70-100 ns and τ2 = 550-670 ns at 5 K.

  19. Photoluminescence fatigue and inhomogeneous line broadening in semi-insulating Tl6SeI4 single crystals

    NASA Astrophysics Data System (ADS)

    Kostina, S. S.; Peters, J. A.; Lin, W.; Chen, P.; Liu, Z.; Wang, P. L.; Kanatzidis, M. G.; Wessels, B. W.

    2016-06-01

    Photoluminescence (PL) properties of semi-insulating Tl6SeI4 have been investigated. A broad emission band centered at 1.63 ± 0.02 eV was observed in all samples. The PL emission band is excitonic in nature and is tentatively attributed to a bound exciton emission. PL fatigue (a reduction in PL intensity under prolonged laser excitation) was always observed. The amount of PL fatigue depended on excitation power and temperature. PL fatigue kinetics are described by a stretched exponential with nominal lifetimes in the 10-265 s range. The recovery of the PL occurred within a few seconds of light cessation. The magnitude of PL fatigue in different samples correlated with inhomogeneous line broadening of the 1.63 eV emission band, such that broader bands exhibited more fatigue. An additional luminescence band centered at 1.78 eV was observed which increased in intensity under prolonged laser irradiation. The fatigue phenomenon is tentatively attributed to two mechanisms—the formation of photo-induced defects and the formation of quasi-stable particles. Both of these mechanisms introduce additional radiative and non-radiative recombination channels that lead to a decrease in the PL intensity under prolonged laser irradiation. Since inhomogeneous line broadening and PL fatigue are related to the concentration of defects or impurities, the measurement of these two parameters is an effective method to screen sample quality.

  20. Giant photoluminescence emission in crystalline faceted Si grains

    PubMed Central

    Faraci, Giuseppe; Pennisi, Agata R.; Alberti, Alessandra; Ruggeri, Rosa; Mannino, Giovanni

    2013-01-01

    Empowering an indirect band-gap material like Si with optical functionalities, firstly light emission, represents a huge advancement constantly pursued in the realization of any integrated photonic device. We report the demonstration of giant photoluminescence (PL) emission by a newly synthesized material consisting of crystalline faceted Si grains (fg-Si), a hundred nanometer in size, assembled in a porous and columnar configuration, without any post processing. A laser beam with wavelength 632.8 nm locally produce such a high temperature, determined on layers of a given thickness by Raman spectra, to induce giant PL radiation emission. The optical gain reaches the highest value ever, 0.14 cm/W, representing an increase of 3 orders of magnitude with respect to comparable data recently obtained in nanocrystals. Giant emission has been obtained from fg-Si deposited either on glass or on flexible, low cost, polymeric substrate opening the possibility to fabricate new devices. PMID:24056300

  1. Near-infrared photoluminescence in germanium oxide enclosed germanium nano- and micro-crystals.

    PubMed

    Wang, Wenzhong; Wang, Keda; Han, Daxing; Poudel, Bed; Wang, Xiaowei; Wang, D Z; Zeng, Baoqing; Ren, Z F

    2007-02-21

    We have studied the near-infrared photoluminescence properties of free-standing germanium nano-crystals (20 nm on average) and micro-crystals (60 µm on average) at 80-300 K. Two peaks were observed at ∼1.0 and ∼1.4 eV from both the nano- and micro-crystals. The integrated PL (I(PL)) intensity of the nano-crystals is about an order of magnitude stronger than that of the micro-crystals and the I(PL) is also enhanced by ageing in air for both crystals. The ∼1.0 eV peak position does not change with either the crystal size or temperature. We suggest that the deep traps located at the interfacial region between the surface GeO(2) layer and the bulk crystal Ge is responsible for the near-infrared PL.

  2. Nonlinear photoluminescence imaging of isotropic and liquid crystalline dispersions of graphene oxide.

    PubMed

    Senyuk, Bohdan; Behabtu, Natnael; Pacheco, Benjamin G; Lee, Taewoo; Ceriotti, Gabriel; Tour, James M; Pasquali, Matteo; Smalyukh, Ivan I

    2012-09-25

    We report a visible-range nonlinear photoluminescence (PL) from graphene oxide (GO) flakes excited by near-infrared femtosecond laser light. PL intensity has nonlinear dependence on the laser power, implying a multiphoton excitation process, and also strongly depends on a linear polarization orientation of excitation light, being at maximum when it is parallel to flakes. We show that PL can be used for a fully three-dimensional label-free imaging of isotropic, nematic, and lamellar liquid crystalline dispersions of GO flakes in water. This nonlinear PL is of interest for applications in direct label-free imaging of composite materials and study of orientational ordering in mesomorphic phases formed by these flakes, as well as in biomedical and sensing applications utilizing GO.

  3. Nanoplasmonic Photoluminescence Spectroscopy at Single-Particle Level: Sensing for Ethanol Oxidation.

    PubMed

    Zheng, Zhaoke; Majima, Tetsuro

    2016-02-18

    Surface plasmon resonances of metal nanoparticles have shown significant promise for the use of solar energy to drive catalytic chemical reactions. More importantly, understanding and monitoring such catalytic reactions at single-nanoparticle level is crucial for the study of local reaction processes. Herein, using plasmonic photoluminescence (PL) spectroscopy, we describe a novel sensing method for catalytic ethanol oxidation reactions at the single-nanoparticle level. The Au nanorod monitors the interfacial interaction with ethanol during the catalytic reaction through the PL intensity changes in the single-particle PL spectra. The analysis of energy relaxation of excited electron-hole pairs indicates the relationship between the PL quenching and ethanol oxidation reaction on the single Au nanorod.

  4. Correlation of quantum efficiency and photoluminescence lifetime of ZnO tetrapods grown at different temperatures

    NASA Astrophysics Data System (ADS)

    Tam, M. C.; Ng, A. M. C.; Djurišić, A. B.; Wong, K. S.

    2012-07-01

    Absolute external quantum efficiencies (ηs) and photoluminescence (PL) decay lifetimes of ZnO tetrapods grown at different temperatures were measured. All the tetrapods had an UV peak at about 390 nm and a very weak defect emission. Measurements showed that the tetrapods have ηs of 2%-4% at room temperature. The sample, grown at optimal temperature, exhibited the largest absolute η of 4.3% and longest PL decay lifetimes among all the samples. These results showed that precise control of growth temperature plays an important role in making high quality ZnO tetrapods. In time-resolved measurement, the PL decay time constant (τ) versus temperature is well fitted by the theoretical prediction τ =a T3/2. This increase in PL lifetime with increasing temperature shows that the excited state relaxation is dominated by radiative recombination.

  5. Electronic structure and photoluminescence study of silicon doped diamond like carbon (Si:DLC) thin films

    SciTech Connect

    Ray, S.C. . E-mail: raysekhar@rediffmail.com; Okpalugo, T.I.T.; Pao, C.W.; Tsai, H.M.; Chiou, J.W.; Jan, J.C.; Pong, W.F.; Papakonstantinou, P.; McLaughlin, J.A.; Wang, W.J.

    2005-10-06

    We have investigated the electronic and bonding structure using Fourier-transform infra-red (FT-IR) spectra and studied photoluminescence (PL) from micro-Raman spectra analysis of a-C:H:Si (Si:DLC) thin films deposited by plasma enhanced chemical vapour deposition (PECVD) method. Tetramethylsilane [Si(CH{sub 3}){sub 4}, TMS] vapour was used as Silicon precursor and a bias voltage of 400 V was applied during deposition. It is observed from FT-IR spectra that with increasing TMS flow rate, the intensity of Si-H {sub n} and C-H {sub n} modes is increased significantly. PL study indicates that the PL is increased and that the PL peak position is shifted towards lower energy when the TMS flow rate increases gradually during deposition.

  6. Photoluminescence of Single-Walled Carbon Nanotubes: The Role of Stokes Shift and Impurity Levels

    NASA Astrophysics Data System (ADS)

    Mu, Jinglin; Ma, Yuchen; Yin, Huabing; Liu, Chengbu; Rohlfing, Michael

    2013-09-01

    Recent experiments have indicated that dopants and defects can trigger new redshifted photoluminescence (PL) peaks below the E11 peak in single-walled carbon nanotubes (SWCNTs). To understand the origin of the new PL peaks, we study theoretically the excited-state properties of SWCNTs with some typical dopants and defects by ab initio many-body perturbation theory. Our calculations demonstrate that the Stokes shift in doped centers can be as large as 170 meV, which is much larger than that of intact SWCNTs and must be taken into account. We find dipole-allowed transitions from localized midgap and shallow impurity levels, which can give rise to pronounced PL peaks. Dark excitons, on the other hand, seem to have oscillator strengths that are too small to account for the new PL peaks.

  7. Photoluminescence studies of polycrystalline Cu(In,Ga)Se2: Lateral inhomogeneities beyond Abbe's diffraction limit

    NASA Astrophysics Data System (ADS)

    Neumann, Oliver; Brüggemann, Rudolf; Hariskos, Dimitrios; Witte, Wolfram; Bauer, Gottfried H.

    2015-11-01

    We analyze Cu(In,Ga)Se2 absorbers with a scanning near-field optical microscope (SNOM) by photoluminescence (PL). Such measurements allow one to extract local fluctuations of the integral PL yield, the quasi-Fermi level splitting, and the material composition in the submicron range. However, the experimental findings depend strongly on the surface roughness of the absorber: If the surface is rough, artifact-prone correlations between surface contour and PL features measured by SNOM can be found that complicate the study of recombination effects. For smooth surfaces, such correlations no longer exist and the influence of grain boundaries on the integral PL yield and the quasi-Fermi level splitting is revealed. The method also allows a detailed determination of the local band gaps in neighboring grains and their spatial variation inside, and thus of possibly local changes in chemical composition of different grains.

  8. An analysis of temperature dependent photoluminescence line shapes in InGaN

    NASA Astrophysics Data System (ADS)

    Teo, K. L.; Colton, J. S.; Yu, P. Y.; Weber, E. R.; Li, M. F.; Liu, W.; Uchida, K.; Tokunaga, H.; Akutsu, N.; Matsumoto, K.

    1998-09-01

    Photoluminescence (PL) line shapes in InGaN multiple quantum well structures have been studied experimentally and theoretically between 10 and 300 K. The higher temperature PL spectra can be fitted quantitatively with a thermalized carrier distribution and a broadened joint-density-of-states. The low temperature PL line shapes suggest that carriers are not thermalized, as a result of localization by band-gap fluctuations. We deduce a localization energy of ˜7 meV as compared with an activation energy of ˜63 meV from thermal quenching of the PL intensity. We thus conclude that this activation energy and the band-gap fluctuation most likely have different origins.

  9. Maximizing Photoluminescence Extraction in Silicon Photonic Crystal Slabs

    NASA Astrophysics Data System (ADS)

    Mahdavi, Ali; Sarau, George; Xavier, Jolly; Paraïso, Taofiq K.; Christiansen, Silke; Vollmer, Frank

    2016-04-01

    Photonic crystal modes can be tailored for increasing light matter interactions and light extraction efficiencies. These PhC properties have been explored for improving the device performance of LEDs, solar cells and precision biosensors. Tuning the extended band structure of 2D PhC provides a means for increasing light extraction throughout a planar device. This requires careful design and fabrication of PhC with a desirable mode structure overlapping with the spectral region of emission. We show a method for predicting and maximizing light extraction from 2D photonic crystal slabs, exemplified by maximizing silicon photoluminescence (PL). Systematically varying the lattice constant and filling factor, we predict the increases in PL intensity from band structure calculations and confirm predictions in micro-PL experiments. With the near optimal design parameters of PhC, we demonstrate more than 500-fold increase in PL intensity, measured near band edge of silicon at room temperature, an enhancement by an order of magnitude more than what has been reported.

  10. Maximizing Photoluminescence Extraction in Silicon Photonic Crystal Slabs

    PubMed Central

    Mahdavi, Ali; Sarau, George; Xavier, Jolly; Paraïso, Taofiq K.; Christiansen, Silke; Vollmer, Frank

    2016-01-01

    Photonic crystal modes can be tailored for increasing light matter interactions and light extraction efficiencies. These PhC properties have been explored for improving the device performance of LEDs, solar cells and precision biosensors. Tuning the extended band structure of 2D PhC provides a means for increasing light extraction throughout a planar device. This requires careful design and fabrication of PhC with a desirable mode structure overlapping with the spectral region of emission. We show a method for predicting and maximizing light extraction from 2D photonic crystal slabs, exemplified by maximizing silicon photoluminescence (PL). Systematically varying the lattice constant and filling factor, we predict the increases in PL intensity from band structure calculations and confirm predictions in micro-PL experiments. With the near optimal design parameters of PhC, we demonstrate more than 500-fold increase in PL intensity, measured near band edge of silicon at room temperature, an enhancement by an order of magnitude more than what has been reported. PMID:27113674

  11. Maximizing Photoluminescence Extraction in Silicon Photonic Crystal Slabs.

    PubMed

    Mahdavi, Ali; Sarau, George; Xavier, Jolly; Paraïso, Taofiq K; Christiansen, Silke; Vollmer, Frank

    2016-01-01

    Photonic crystal modes can be tailored for increasing light matter interactions and light extraction efficiencies. These PhC properties have been explored for improving the device performance of LEDs, solar cells and precision biosensors. Tuning the extended band structure of 2D PhC provides a means for increasing light extraction throughout a planar device. This requires careful design and fabrication of PhC with a desirable mode structure overlapping with the spectral region of emission. We show a method for predicting and maximizing light extraction from 2D photonic crystal slabs, exemplified by maximizing silicon photoluminescence (PL). Systematically varying the lattice constant and filling factor, we predict the increases in PL intensity from band structure calculations and confirm predictions in micro-PL experiments. With the near optimal design parameters of PhC, we demonstrate more than 500-fold increase in PL intensity, measured near band edge of silicon at room temperature, an enhancement by an order of magnitude more than what has been reported. PMID:27113674

  12. Shaping the photoluminescence from gold nanoshells by cavity plasmons in dielectric-metal core-shell resonators

    NASA Astrophysics Data System (ADS)

    Sun, Ren; Wan, Mingjie; Wu, Wenyang; Gu, Ping; Chen, Zhuo; Wang, Zhenlin

    2016-08-01

    We report experimental investigation of the photoluminescence (PL) generated from the gold nanoshells of the dielectric-metal core-shell resonators (DMCSR) that support multipolar electric and magnetic based cavity plasmon resonances. Significantly enhanced and modulated PL spectrum is observed. By comparing the experimental results with analytical Mie calculations, we are able to demonstrate that the observed reshaping effects are due to the excitations of those narrow-band cavity plasmon resonances. We also present that the variation on the dielectric core size allows for tuning the cavity plasmon resonance wavelengths and thus the peak positions of the PL spectrum.

  13. Recombination Behaviour at the Ultrathin Polypyrrole Film/Silicon Interface Investigated by In-situ Pulsed Photoluminescence

    NASA Astrophysics Data System (ADS)

    Intelmann, Carl Matthias; Hinrichs, Karsten; Syritski, Vitali; Yang, Florent; Rappich, Jörg

    2008-01-01

    We investigated the change in Si surface recombination behaviour during the electrodeposition of ultrathin polypyrrole (PPy) films onto Si surfaces by means of in-situ pulsed photoluminescence (PL) spectroscopy. The quenching of the band-gap related PL is lower (better passivation) when the electrodeposition is performed in a less acidic solution by use of potential pulse sequences. In-situ infrared spectroscopic ellipsometry (IR-SE) was applied for the first time to PPy electrodeposition. IR-SE and PL measurements confirm negligible formation of SiOx species at the Si/PPy interface although aqueous electrolytes were used.

  14. Strange heterogeneous photoluminescence in the Kokchetav metamorphic diamonds

    NASA Astrophysics Data System (ADS)

    Takabe, S.; Ogasawara, Y.

    2013-12-01

    In the laser Raman spectroscopy of the Kokchetav metamorphic diamonds using an Ar+ laser, the bands at 1400 to 1500 cm-1 were reported as "mysterious" Raman bands because those have strange peak positions as Raman shifts and their distributions measuring 1-3 micrometer space in a diamond were so heterogeneous (Igarashi et al., 2011, Ogasawara et al., 2011a, Ogasawara et al., 2011b, Harada et al., 2011). However, in our later examinations, these 'mysterious' bands at 1400-1500 cm-1 by an Ar+ laser (514.5 nm) were confirmed as photoluminescence (PL) bands at ca. 555-557 nm (we named these 'X-bands') because the spectroscopy using a He-Ne laser (632.8 nm) did not show the same bands at the same analyzed positions (Harada and Ogasawara, 2012). These bands were occasionally confirmed in T-type, S-type (core and rim), R-type diamonds in dolomite marble and the diamonds in garnet-biotite gneiss, but not in all grains. In order to understand the detailed characters of these strange PL bands of the Kokchetav diamonds, we conducted laser Raman spectroscopy using both Ar+ and He-Ne lasers with 2D mappings at different depths in a single diamond grain for the same samples and some new samples. The judgment of Raman shift or PL was carried out by comparing two spectra by Ar+ and He-Ne lasers. The laser spot diameter is about 1 μm. In the 2D mappings, diamond grains were scanned with 1 μm X- and Y-intervals at several depths with 2 μm Z-interval. In the Ar+ laser experiments, the PL bands at 637 nm (NV- center) were detected in all types of diamonds in dolomite marble and diamonds in garnet-biotite gneiss. Some grains in dolomite marble showed the PL at 575 nm (NV0 center). These PL were observed throughout whole diamond grains. All intensity maps of PL bands at 637 nm and 575 nm were consistent with the maps of diamond Raman shift at 1332 cm-1. In the 2D maps, however, the 'X-bands' were limited to small domains measuring 1-3 micrometer space in a single diamond grain. In

  15. Effect of hydrogen dilution on photoluminescent properties of nanocrystalline SiC films deposited by helicon wave plasma CVD

    NASA Astrophysics Data System (ADS)

    Yu, Wei; Du, Jie; Zhang, Li; Cui, Shuang Kui; Han, Li; Fu, Guang Sheng

    2007-11-01

    Nanocrystalline silicon carbide (nc-SiC) thin films were deposited by helicon wave plasma enhanced chemical vapor deposition (HW-PECVD) technique at different hydrogen dilution ratio (RH). The PL peak energy and intensity were systemically analyzed using photoluminescent (PL) and photoluminescent excitation (PLE) methods. As a whole, the PL intensity shows an increasing trend and the PL peak energy presents continuous blue shifts with increasing hydrogen dilution ratio. In addition, it is found that the spectra band of samples deposited at low RH are composed of two components, the high energy band comes from quantum confinement effect and the low energy band is related to radiation of surface defect. The low energy band has a decreasing trend with increasing hydrogen dilution ratio and even disappears finally at high RH. We explain dependence of PL properties in terms of the variation of film microstructure induced by hydrogen dilution during film deposition. The increasing of PL intensity and the decreasing of the low energy band can both be accounted by the microstructure improvement. The decrease of PL peak energy is related to the size decrease of SiC nanocrystals.

  16. Exciton Distribution between the Bright and Dark States in Single Carbon Nanotubes Studied by Magneto-Photoluminescence Spectroscopy

    NASA Astrophysics Data System (ADS)

    Matsunaga, Ryusuke; Matsuda, Kazunari; Kanemitsu, Yoshihiko

    2009-03-01

    We have performed micro-photoluminescence (PL) spectroscopy for single carbon nanotubes under magnetic fields at various temperatures. Sharp PL spectra of single carbon nanotubes allow us to directly observe the dark exciton PL peak a few meV below the bright exciton PL peak due to the Aharonov-Bohm effect [1]. From the PL intensity ratio of the dark to the bright excitons under magnetic fields, we found that the non-equilibrium (non-Boltzmann) distribution occurs between the bright and dark states, because phonons cannot scatter excitons between the two states with different parities [2]. Furthermore, we discuss the diameter dependence of the exciton population of the bright and dark states in single carbon nanotubes. [1] R. Matsunaga, K. Matsuda, and Y. Kanemitsu, Phys. Rev. Lett. 101, 147404 (2008). [2] V. Perebeinos, J. Tersoff, and Ph. Avouris, Nano Lett. 5, 2495 (2005).

  17. Photoluminescence polarization anisotropy for studying long-range structural ordering within semiconductor multi-atomic alloys and organic crystals

    SciTech Connect

    Prutskij, T.; Percino, J.; Orlova, T.; Vavilova, L.

    2013-12-04

    Long-range structural ordering within multi-component semiconductor alloys and organic crystals leads to significant optical anisotropy and, in particular, to anisotropy of the photoluminescence (PL) emission. The PL emission of ternary and quaternary semiconductor alloys is polarized if there is some amount of the atomic ordering within the crystal structure. We analyze the polarization of the PL emission from the quaternary GaInAsP semiconductor alloy grown by Liquid Phase Epitaxy (LPE) and conclude that it could be caused by low degree atomic ordering within the crystal structure together with the thermal biaxial strain due to difference between the thermal expansion coefficients of the layer and the substrate. We also study the state of polarization of the PL from organic crystals in order to identify different features of the crystal PL spectrum.

  18. Role of C-N Configurations in the Photoluminescence of Graphene Quantum Dots Synthesized by a Hydrothermal Route

    NASA Astrophysics Data System (ADS)

    Permatasari, Fitri Aulia; Aimon, Akfiny Hasdi; Iskandar, Ferry; Ogi, Takashi; Okuyama, Kikuo

    2016-02-01

    Graphene quantum dots (GQDs) containing N atoms were successfully synthesized using a facile, inexpensive, and environmentally friendly hydrothermal reaction of urea and citric acid, and the effect of the GQDs’ C-N configurations on their photoluminescence (PL) properties were investigated. High-resolution transmission electron microscopy (HR-TEM) images confirmed that the dots were spherical, with an average diameter of 2.17 nm. X-ray photoelectron spectroscopy (XPS) analysis indicated that the C-N configurations of the GQDs substantially affected their PL intensity. Increased PL intensity was obtained in areas with greater percentages of pyridinic-N and lower percentages of pyrrolic-N. This enhanced PL was attributed to delocalized π electrons from pyridinic-N contributing to the C system of the GQDs. On the basis of energy electron loss spectroscopy (EELS) and UV-Vis spectroscopy analyses, we propose a PL mechanism for hydrothermally synthesized GQDs.

  19. Role of C–N Configurations in the Photoluminescence of Graphene Quantum Dots Synthesized by a Hydrothermal Route

    PubMed Central

    Permatasari, Fitri Aulia; Aimon, Akfiny Hasdi; Iskandar, Ferry; Ogi, Takashi; Okuyama, Kikuo

    2016-01-01

    Graphene quantum dots (GQDs) containing N atoms were successfully synthesized using a facile, inexpensive, and environmentally friendly hydrothermal reaction of urea and citric acid, and the effect of the GQDs’ C–N configurations on their photoluminescence (PL) properties were investigated. High-resolution transmission electron microscopy (HR-TEM) images confirmed that the dots were spherical, with an average diameter of 2.17 nm. X-ray photoelectron spectroscopy (XPS) analysis indicated that the C–N configurations of the GQDs substantially affected their PL intensity. Increased PL intensity was obtained in areas with greater percentages of pyridinic-N and lower percentages of pyrrolic-N. This enhanced PL was attributed to delocalized π electrons from pyridinic-N contributing to the C system of the GQDs. On the basis of energy electron loss spectroscopy (EELS) and UV-Vis spectroscopy analyses, we propose a PL mechanism for hydrothermally synthesized GQDs. PMID:26876153

  20. Biexciton state causes photoluminescence fluctuations in CdSe/ZnS core/shell quantum dots at high photoexcitation densities

    NASA Astrophysics Data System (ADS)

    Yoshikawa, N.; Hirori, H.; Watanabe, H.; Aoki, T.; Ihara, T.; Kusuda, R.; Wolpert, C.; Fujiwara, T. K.; Kusumi, A.; Kanemitsu, Y.; Tanaka, K.

    2013-10-01

    The excitation density dependence of photoluminescence (PL) blinking of single CdSe/ZnS quantum dots was studied by means of single-dot PL spectroscopy. As the excitation density increases, an intermediate state appears in addition to the highly emissive (ON) and nonemissive (OFF) states. The systematic study of the excitation density dependence of PL blinking behavior (PL intensity, probabilities of finding these states, time probability distributions, and PL spectra and lifetimes) suggests that the intermediate state can be attributed to a charged exciton (trion) state generated through biexciton generation and charging (ionization) of a quantum dot under a high-density excitation regime. Our results indicate that the biexciton generation is a precursor of the trion state and not of the OFF state.

  1. Structure and infrared photoluminescence of GeSi nanocrystals formed by high temperature annealing of GeOx/SiO2 multilayers

    NASA Astrophysics Data System (ADS)

    Volodin, V. A.; Gambaryan, M. P.; Cherkov, A. G.; Stoffel, M.; Rinnert, H.; Vergnat, M.

    2016-08-01

    Germanium and GeSi nanocrystals were synthesized in SiGeO2 glass by high temperature annealings of GeOx(5 nm)/SiO2(5 nm) multilayers. According to electron microscopy data, the size distribution and stoichiometry of the nanocrystals depend on the annealing temperature (700, 800, or 900 °C). Spatial redistribution of Ge with the formation of large faceted nanocrystals located near the Si substrate and GeSi intermixing at the substrate/film interface were observed. In the case of the 900 °C annealed sample, we note that some nanocrystals have a pyramid-like shape. Infrared absorption spectroscopy demonstrates that intermixing takes place between the GeOx and SiO2 layers leading to the formation of SiGeO2 glass. Raman spectroscopy confirms the formation of Ge nanocrystals after annealing at 700 °C and GeSi nanocrystals after annealing at 800 and 900 °C. For all annealed samples, we report the observation of infrared photoluminescence (PL) at low temperatures in the spectral range 1300-2100 nm. The observation of PL at wavelengths close to 2000 nm may be due to defect-induced radiative transitions in the nanocrystals.

  2. Optical properties study of In.08Ga.92As/GaAs using spectral reflectance, photoreflectance and near-infrared Photoluminescence

    NASA Astrophysics Data System (ADS)

    Tounsi, N.; Habchi, M. M.; Chine, Z.; Rebey, A.; El Jani, B.

    2013-07-01

    Optical properties of In.08Ga.92As/GaAs structure grown by metalorganic vapor phase epitaxy have been investigated. Spectral reflectance (SR) and photoreflectance (PR) as well as near-infrared Photoluminescence (PL) were performed in this study. In fact, SR signals in the range 200-1700 nm provided specific parameters of materials such as optical constant spectra, sensitivity to wavelength and critical point energies. In addition, band gap energy was determined by both PR and optical absorption measurements at room temperature. Spin-orbit splitting, internal electric field and electro-optical energy were also calculated. Results provided by previous techniques present a good correlation and complementarities and agree well with the literature. On the other hand, the origins of 12 K PL peaks at 1.42, 1.38 and 1.29 eV, have been identified by performing excitation power (Pex) study. Finally, the peak at 1.38 eV has two regimes of variation with Pex separated by a critical power around 50 mW.

  3. A co-precipitation preparation, crystal structure and photoluminescent properties of Er5%:Gd{sub 2}O{sub 3} nanorods

    SciTech Connect

    Boopathi, G. Mohan, R.; Raj, S. Gokul; Kumar, G. Ramesh

    2015-06-24

    An inexpensive preparation method is being reported for obtaining erbium doped gadolinium oxide (Er5%:Gd{sub 2}O{sub 3}) nanoscale rods. The elongated nanoscale systems, as-formed through a co-precipitation process, are characterized by using X-ray powder diffraction (XRD) patterns, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) mapping, Ultra Violet-visible (UV-vis.) absorption spectroscopy and photoluminescence (PL) spectroscopy. In addition, the Williamson–Hall (W–H) plot is also performed to distinguish the effect of crystalline size-induced broadening and strain-induced broadening at full-width at half-maximum (FWHM) of the XRD profile. The XRD patterns of as-formed and calcined products show that the phase confirmation. As revealed from the SEM micrographs, the morphology of the products show that the rod-like nanoparticles. The EDX micrographs show that the presence of elements in our samples. The band gap values in calcined samples are found to be in the range of 3.569 eV. Upon 230 nm excitation on calcined samples, three broad emission peaks are observed from PL studies. The possible mechanism for the formation of Er5%:Gd{sub 2}O{sub 3} nanorods is briefly discussed.

  4. Quenching of semiconductor quantum dot photoluminescence by a pi-conjugated polymer.

    PubMed

    Selmarten, Donald; Jones, Marcus; Rumbles, Garry; Yu, Pingrong; Nedeljkovic, Jovan; Shaheen, Sean

    2005-08-25

    In this communication we discuss the possibility of hole transfer between a photoexcited semiconductor quantum dot and a pi-conjugated polymer. This charge-transfer event will be investigated (exploited) on the basis of its implication toward a solar energy conversion scheme. Experimentally, we show that the steady-state photoluminescence (PL) of a solution of InP quantum dots is quenched by the introduction of solvated poly(3-hexylthiophene). Time-resolved PL experiments on these solutions are also presented. It was observed that the PL transients did not significantly change upon the addition of the conductive polymer. These new results indicate that said PL quenching is static in nature. This suggests that in solution, the quantum dot and the polymer exhibit a strong intermolecular interaction. As the two species encounter each other through diffusion, the polymer quenches the quantum dot photoluminescence without altering the population's PL lifetime. This new evidence suggests that the polymer and the quantum dot form a relatively stable complex.

  5. Effect of annealing temperature on PL spectrum and surface morphology of zinc oxide thin films

    NASA Astrophysics Data System (ADS)

    Zendehnam, A.; Mirzaee, M.; Miri, S.

    2013-04-01

    Zinc oxide (ZnO) thin films were produced by thermal oxidation of Zn layers (200 nm thickness) which were coated on Si (1 0 0) substrate by DC magnetron sputtering. In order to study the effect of annealing temperature on photoluminescence (PL) properties and the surface morphology of the ZnO samples, the annealing temperature range of 500-700 °C was employed. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) for investigation of surface morphology of the ZnO samples were carried out. The surface statistical characteristics of these ZnO thin films are then evaluated against data which outcome from AFM. SEM and AFM results indicated that the annealing temperature produces larger grains and rough surfaces at higher temperatures. The results of PL spectra represent an increase in interstitial zinc with increasing annealing temperature.

  6. Thermal quenching of photoluminescence of Eu3+ ions in an Eu(fod)3 complex

    NASA Astrophysics Data System (ADS)

    Gerasimova, V. I.; Zavorotnyi, Yu. S.; Rybaltovskii, A. O.; Taraeva, A. Yu.

    2006-05-01

    We have studied the photoluminescence (PL) spectra of Eu3+ ions in the complex Eu(fod)3 (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadione) and also in polymers doped with Eu(fod)3 with the help of supercritical carbon dioxide. We have established that in the temperature range 20°C 100°C, we observe thermal quenching of the photoluminescence of Eu3+ ions, and this quenching is most efficient in polycrystalline Eu(fod)3 powder and Eu(fod)3-doped polypropylene.

  7. A new activator strontium for magnesium tetraborate: PL and TL studies.

    PubMed

    Evis, D; Yucel, A; Kizilkaya, N; Depci, T; Kafadar, V E; Öztürk, E; Yildirim, R G

    2016-10-01

    Strontium was used for the first time as an activator agent for magnesium tetraborate (MBO) and photoluminescence (PL) and thermoluminescence (TL) properties were determined using a spectrophotometer and a TL reader, respectively. The results proved that 0.25wt% Sr ratio played an important role in prolonging the afterglow and the phosphor gave the main TL peak with the highest intensity at 200°C like an ideal case. Therefore, it is worthwhile to carry out continuous and systematic research on it. PMID:27526351

  8. Spectral Behavior of Bias-Dependent Photocurrent and Photoluminescence in Sputtered ZnO Layers

    NASA Astrophysics Data System (ADS)

    Hong, K. J.; Jeong, T. S.; Kim, T. S.; Choi, C. J.; Youn, C. J.

    2016-08-01

    The bias-dependent behavior of the photocurrent (PC) and photoluminescence (PL) of sputtered ZnO layers has been investigated. Based on PC spectroscopy results, the PC intensity of the observed free exciton increased strongly up to electric field of 60 V/cm, after which its rate of increase slightly reduced due to disturbance of field-assisted dissociation of radical ion pairs, which leads to photocarrier generation. Thus, the energy of excitonic PC peaks showed a tendency to red-shift with increasing electric field, being attributed to the induced Stark effect. Therefore, it is concluded that the strong interaction between free excitons and photogenerated PC carriers leads to displacement or widening of the spectrum. In the PL measurements, near-band-edge (NBE) and violet emissions were observed. With increasing electric field, two PL emissions were progressively quenched. The combined PL/PC results reveal that the PL ions associated with the NBE and violet emissions readily interact with the PC carriers of photogenerated electrons and holes. This behavior reduces the recombination ratio and the lifetime of PL ions. So, the PL intensity quenching originates from a decrease in the number of carriers participating in recombination. Consequently, we find that the quenching mechanism of the NBE and violet emissions is strongly related to low external electric field.

  9. Impact of the hydrogen content on the photoluminescence efficiency of amorphous silicon alloys

    SciTech Connect

    Kistner, J.; Schubert, M. B.

    2013-12-07

    This paper analyzes the impact of hydrogen on the photoluminescence (PL) efficiency of the three wide gap silicon alloys: silicon carbide (a-SiC{sub x}), silicon nitride (a-SiN{sub x}): silicon oxide (a-SiO{sub x}). All three materials behave similarly. The progression of the PL efficiency over the Si content splits into two regions. With decreasing Si content, the PL efficiency increases until a maximum is reached. With a further decrease of the Si content, the PL efficiency declines again. A comprehensive analysis of the sample structure reveals that the PL efficiency depends on the degree of passivation of Si and Y atoms (Y = C, N, O) with hydrogen. For samples with a high Si content, an effective passivation of incorporated Y atoms gives rise to an increasing PL efficiency. The PL efficiency of samples with a low Si content is limited due to a rising amount of unpassivated Si defect states. We find that a minimum amount of 0.2 H atoms per Si atom is required to maintain effective luminescence.

  10. Structural phase transition causing anomalous photoluminescence behavior in perovskite (C{sub 6}H{sub 11}NH{sub 3}){sub 2}[PbI{sub 4}

    SciTech Connect

    Yangui, A.; Pillet, S.; Mlayah, A.; Lusson, A.; Bouchez, G.; Boukheddaden, K. E-mail: kbo@physique.uvsq.fr; Triki, S.; Abid, Y. E-mail: kbo@physique.uvsq.fr

    2015-12-14

    Optical and structural properties of the organic-inorganic hybrid perovskite-type (C{sub 6}H{sub 11}NH{sub 3}){sub 2}[PbI{sub 4}] (abbreviated as C{sub 6}PbI{sub 4}) were investigated using optical absorption, photoluminescence (PL), and x-ray diffraction measurements. Room temperature, optical absorption measurements, performed on spin-coated films of C{sub 6}PbI{sub 4}, revealed two absorption bands at 2.44 and 3.21 eV. Upon 325 nm (3.815 eV) laser irradiation, strong green PL emission peaks were observed at 2.41 eV (P1) and 2.24 eV (P2) and assigned to free and localized excitons, respectively. The exciton binding energy was estimated at 356 meV. At low temperature, two additional emission bands were detected at 2.366 eV (P3) and a large band (LB) at 1.97 eV. The former appeared only below 40 K and the latter emerged below 130 K. The thermal dependence of the PL spectra revealed an abnormal behavior accompanied by singularities in the peak positions and intensities at 40 and 130 K. X-ray diffraction studies performed on powder and single crystals as a function of temperature evidenced significant changes of the interlayer spacing at 50 K and ∼138 K. Around 138 K, a commensurate to incommensurate structural phase transition occurred on cooling. It involves a symmetry breaking leading to a distortion of the PbI{sub 6} octahedron. The resulting incommensurate spatial modulation of the Pb–I distances (and Pb–I–Pb angles) causes a spatial modulation of the band gap, which is at the origin of the emergence of the LB below ∼130 K and the anomalous behavior of the position of P1 below 130 K. The change of the interlayer spacing in the 40-50 K range may in turn be related to the significant decrease of the intensity of P2 and the maximum emission of the LB. These results underline the intricate character of the structural and the PL properties of the hybrid perovskites; understanding such properties should benefit to the design of optoelectronic devices with

  11. Structural phase transition causing anomalous photoluminescence behavior in perovskite (C6H11NH3)2[PbI4

    NASA Astrophysics Data System (ADS)

    Yangui, A.; Pillet, S.; Mlayah, A.; Lusson, A.; Bouchez, G.; Triki, S.; Abid, Y.; Boukheddaden, K.

    2015-12-01

    Optical and structural properties of the organic-inorganic hybrid perovskite-type (C6H11NH3)2[PbI4] (abbreviated as C6PbI4) were investigated using optical absorption, photoluminescence (PL), and x-ray diffraction measurements. Room temperature, optical absorption measurements, performed on spin-coated films of C6PbI4, revealed two absorption bands at 2.44 and 3.21 eV. Upon 325 nm (3.815 eV) laser irradiation, strong green PL emission peaks were observed at 2.41 eV (P1) and 2.24 eV (P2) and assigned to free and localized excitons, respectively. The exciton binding energy was estimated at 356 meV. At low temperature, two additional emission bands were detected at 2.366 eV (P3) and a large band (LB) at 1.97 eV. The former appeared only below 40 K and the latter emerged below 130 K. The thermal dependence of the PL spectra revealed an abnormal behavior accompanied by singularities in the peak positions and intensities at 40 and 130 K. X-ray diffraction studies performed on powder and single crystals as a function of temperature evidenced significant changes of the interlayer spacing at 50 K and ˜138 K. Around 138 K, a commensurate to incommensurate structural phase transition occurred on cooling. It involves a symmetry breaking leading to a distortion of the PbI6 octahedron. The resulting incommensurate spatial modulation of the Pb-I distances (and Pb-I-Pb angles) causes a spatial modulation of the band gap, which is at the origin of the emergence of the LB below ˜130 K and the anomalous behavior of the position of P1 below 130 K. The change of the interlayer spacing in the 40-50 K range may in turn be related to the significant decrease of the intensity of P2 and the maximum emission of the LB. These results underline the intricate character of the structural and the PL properties of the hybrid perovskites; understanding such properties should benefit to the design of optoelectronic devices with targeted properties.

  12. Calibration of the photoluminescence technique for measuring concentrations of shallow dopants in Ge

    NASA Astrophysics Data System (ADS)

    Allardt, M.; Kolkovsky, Vl.; Irmscher, K.; Weber, J.

    2012-11-01

    A systematic study of the photoluminescence (PL) from excitons bound to shallow donors or acceptors in Al-, As-, B-, Ga-, In-, P-, and Sb-doped Ge is presented. The results of the PL measurements are correlated with those from photothermal ionization spectroscopy and Hall effect measurements. The dissociation energy of the excitons is shown to satisfy Haynes rule. A calibration is presented, which allows a determination of the donor and acceptor concentrations from their respective bound exciton intensities related to the free exciton intensity.

  13. Experimental (FTIR, Raman, UV-visible and PL) and theoretical (DFT and TDDFT) studies on bis(8-hydroxyquinolinium) tetrachlorocobaltate(II) compound

    NASA Astrophysics Data System (ADS)

    Chaouachi, Soumaya; Elleuch, Slim; Hamdi, Besma; Zouari, Ridha

    2016-12-01

    The purpose of this paper is to present the chemical preparation, crystal structure, vibrational study and optical features for new organic-inorganic compound [C9H8NO]2CoCl4 abbreviated [8-HQ]2CoCl4. The structural study by X-ray diffraction prove that this compound crystallize in a monoclinic unit-cell with space group C2/c (point group 2/m = C2h). It is built of tetrahedra [CoCl4]2- anions and (C9H8NO)+ cations in the 1/2 ratio. The crystal structure is stabilized by network three-dimensional of Nsbnd H⋯Cl, Nsbnd H⋯O, Osbnd H⋯Cl, Csbnd H⋯Cl hydrogen bonds, and offset π-π stacking interactions. Also, the Hirshfeld Surface projections and Fingerprint plots were elucidated the relative contribution of the type, nature and explore the H⋯Cl, C⋯H, C⋯C, C⋯N, H⋯O intermolecular contacts in the crystal in a visual manner. Furthermore, vibrational analysis of the structural groups in the compound was carried out by both Fourier transforms infrared (FT-IR) and Raman spectra. The spectral data are complemented by good information at the region characteristic of metal-ligand, which evidences coordination through the compound. The optical properties of the crystal were studied by using optical absorption UV-visible and photoluminescence (PL) spectroscopy studies. Theoretical calculations were performed using density functional theory (DFT) at (DFT/B3LYP/LanL2DZ) level in the aim of aiding in studying structural, vibrational and optical properties of the investigated compound. Good relationship consistency is found between the experimental and theoretical studies. Inspection of the optical properties has lead to confirm the exhibition of a green photoluminescence and the occurrence of charge transfer phenomenon in this material.

  14. Synthesis of ZnO flowers and their photoluminescence properties

    SciTech Connect

    Wu Changle; Qiao Xueliang Luo Langli; Li Haijun

    2008-07-01

    Flower-like ZnO nano/microstructures have been synthesized by thermal treatment of Zn(NH{sub 3}){sub 4}{sup 2+} precursor in aqueous solvent, using ammonia as the structure directing agent. A number of techniques, including X-ray diffraction (XRD), field emission scan electron microscopy (FESEM), transmission electron microscopy (TEM), thermal analysis, and photoluminescence (PL) were used to characterize the obtained ZnO structures. The photoluminescence (PL) measurements indicated that the as-synthesized ZnO structures showed UV ({approx}375 nm), blue ({approx}465 nm), and yellow ({approx}585 nm) emission bands when they were excited by a He-Gd laser using 320 nm as the excitation source. Furthermore, it has been interestingly found that the intensity of light emission at {approx}585 nm remarkably decreased when the obtained ZnO nanocrystals were annealed at 600 deg. C for 3 h in air. The reason might be the possible oxygen vacancies and interstitials in the sample decreased at high temperature.

  15. Spontaneous circular polarization of photoluminescence from WS2 single layers

    NASA Astrophysics Data System (ADS)

    Scrace, Thomas; Tsai, Yutsung; Barman, Biplob; Zhang, Peiyao; Petrou, Athos; Kioseoglou, George; Korkusinski, Marek; Ozfidan, Isil; Hawrylak, Pawel

    2015-03-01

    We have carried out a magnetoluminescence study of WS2 single layer crystals excited with linearly polarized light. The photoluminescence (PL) contains two features. The first is associated with the neutral exciton (X0) ; the second feature is due to the recombination of negatively charged excitons (X-) in the presence of a two-dimensional electron gas (2DEG). The X- - 2 DEG feature has a non-zero circular polarization up to 19% at zero magnetic field even though the PL excitation light is linearly polarized. The circular polarization is effected by an external magnetic field applied perpendicular to the crystal plane at 2 % / Tesla . The zero field circular polarization of the X- - 2 DEG photoluminescence feature is interpreted as due to the existence of a spontaneously valley polarized 2DEG. This is a new state possible in WS2 due to valley and spin locking and a strong electron-electron interaction. Work at SUNY Buffalo has been supported by ONR. I.O., M.K. and P.H. acknowledge support of NRC QPSS program and of NSERC.

  16. A biomimetic tongue by photoluminescent metal-organic frameworks.

    PubMed

    Lee, Tu; Lin Lee, Hung; Hsun Tsai, Meng; Cheng, Shao-Liang; Lee, Sheng-Wei; Hu, Jung-Chih; Chen, Lien-Tai

    2013-05-15

    The taste sensing capabilities of a "biomimetic tongue" based on the photoluminescence (PL) responses of metal-organic frameworks (MOFs), [In(OH)(bdc)]n (bdc=1,4-benzenedicarboxylate), [Tb(btc)]n (MOF-76, btc=benzene-1,3,5-tricarboxylate), and [Ca3(btc)2(DMF)2(H2O)2]·3H2O are proven on aqueous solutions of five basic tastants: sucrose (sweet), caffeine (bitter), citric acid (sour), sodium chloride (salty) and monosodium glutamate (umami). For [In(OH)(bdc)]n, the tastant interacts stereochemically with poly(acrylic acid) (PAA) and alters its conformations. The frequency and magnitude of chelation between COO(-) pendant groups of PAA and In(3+) nodes of [In(OH)(bdc)]n framework influence the corresponding PL reponses. For MOF-76, the tastant interacts with incorporated water in MOF-76 through hydrogen bonding. The limitation of O-H bond stretching of water results in the enhancement of the PL intensity. For [Ca3(BTC)2(DMF)2(H2O)2]·3H2O, it is added as a third MOF component to increase the precision on taste discrimination. The significance of MOF-based "biomimetic tongue" includes: (1) PAA on [In(OH)(bdc)]n mimics the taste receptor cells (TRCs) for their structural flexibility, (2) the Weber-Fechner law of human sensing that sensation is proportional to the logarithm of the stimulus intensity is observed between the PL emission response of MOF-76 and the concentration of tastant, (3) the strength of taste is quantified by the τ scale and the PL emission intensity of MOF-76, which are dependent on the logarithmic tastant concentration, (4) the tastant is identified by the shape of the 3D principal component analysis contour map (i.e., pattern recognition method), and (5) the fabrication of [In(OH)(bdc)]n/PAA film by brushing is illustrated. PMID:23277340

  17. Structural and photoluminescence properties of Ce, Dy, Er-doped ZnO nanoparticles

    SciTech Connect

    Jayachandraiah, C.; Kumar, K. Siva; Krishnaiah, G.

    2015-06-24

    Undoped ZnO and rare earth elements (Ce, Dy and Er with 2 at. %) doped nanoparticles were synthesized by wet chemical co-precipitation method at 90°C with Polyvinylpyrrolidone (PVP) as capping agent. The structural, morphological, compositional and photoluminescence studies were performed with X-ray diffraction (XRD), Transmission electron microscopy (TEM), Energy dispersive spectroscopy (EDS), FTIR spectroscopy and Photoluminescence (PL) respectively. XRD results revealed hexagonal wurtzite structure with average particle size around 18 nm - 14 nm and are compatible with TEM results. EDS confirm the incorporation of Ce, Dy and Er elements into the host ZnO matrix and is validated by FTIR analysis. PL studies showed a broad intensive emission peak at 558 nm in all the samples. The intensity for Er- doped ZnO found maximum with additional Er shoulder peaks at 516nm and 538 nm. No Ce, Dy emission centers were found in spectra.

  18. The correlation of blue shift of photoluminescence and morphology of silicon nanoporous

    NASA Astrophysics Data System (ADS)

    Al-Jumaili, Batool E. B.; Talib, Zainal A.; Josephine L., Y.; Paiman, Suriati B.; Ahmed, Naser M.; Al-Jumaily, Abdulmajeed H. J.; Ramizy, Asmiet; Abdulateef, Sinan A.; Muh'd, Ibrahim B.; Mofdal, Manahil E. E.

    2016-07-01

    Porous silicon with diameters ranging from 6.41 to 7.12 nm were synthesized via electrochemical etching by varied anodization current density in ethanoic solutions containing aqueous hydrofluoric acid up to 65mA/cm2.The luminescence properties of the nanoporous at room temperature were analyzed via photoluminescence spectroscopy. Photoluminescence PL spectra exhibit a broad emission band in the range of 360-700 nm photon energy. The PL spectrum has a blue shift in varied anodization current density; the blue shift incremented as the existing of anodization although the intensity decreased. The current blue shift is owning to alteration of silicon nanocrystal structure at the superficies. The superficial morphology of the PS layers consists of unified and orderly distribution of nanocrystalline Si structures, have high porosity around (93.75%) and high thickness 39.52 µm.

  19. On the origin of the spatial inhomogeneity of photoluminescence in thin-film CIGS solar devices

    NASA Astrophysics Data System (ADS)

    El-Hajje, Gilbert; Ory, Daniel; Guillemoles, Jean-François; Lombez, Laurent

    2016-07-01

    In this letter, we investigate the origin of the spatial inhomogeneity of the photoluminescence (PL) intensity maps obtained on thin-film solar cells. Based on a hyperspectral imager setup, we record an absolute map of the quasi-Fermi level splitting Δμ by applying the generalized Planck's law. Then, using scanning confocal microscopy, we perform spatially and time-resolved photoluminescence measurements. This allowed us to quantify and map the micrometric fluctuations of the trapping defect density within these solar cells. Finally, we demonstrate the existence of a direct correlation between the spatial fluctuations of the quasi-Fermi level splitting and the trapping defect density. The latter was found to be correlated with the frequently reported spatially inhomogeneous PL maps of thin-film solar cells. Based on the observed correlation, we can quantify the local losses in quasi-Fermi level splitting induced by the spatial distribution of the trapping defects.

  20. Electric Field Dependent Photoluminescence in Atomically Thin Transition Metal Dichalcogenides van der Waals Heterostructures

    NASA Astrophysics Data System (ADS)

    Jauregui, Luis A.; High, Alex A.; Dibos, Alan; Joe, Andrew; Gulpinar, Elgin; Park, Hongkun; Kim, Philip

    uregui, Alex A. High, Alan Dibos, Andrew Joe, Elgin Gulpinar, Hongkun Park, Philip Kim Harvard University, Physics Department -abstract- Single layer transition metal dichalcogenides (TMDC) are 2-dimensional (2D) semiconductors characterized by a direct optical bandgap and large exciton binding energies (>100 meV). We fabricate CQW heterostructures made of 2D TMDCs with hexagonal Boron nitride (BN) as atomically thin barrier and gate dielectric, with top and bottom gate electrodes. We study the evolution of photoluminescence (PL) spectrum with varying BN barrier thickness, electric field, temperature and polarization. Our measured low-temperature (T = 3K) PL peaks show full width at half maxima on the order of ~3meV. We identify the photoluminescence peaks, corresponding to the charged exciton emission, which red shifts and its brightness increases while the neutral exciton emission becomes darker for increasing electric field.

  1. Formation of photoluminescent n-type macroporous silicon: Effect of magnetic field and lateral electric potential

    NASA Astrophysics Data System (ADS)

    Antunez, E. E.; Estevez, J. O.; Campos, J.; Basurto-Pensado, M. A.; Agarwal, V.

    2014-11-01

    Metal electrode-free electrochemical etching of low doped n-type silicon substrates, under the combined effect of magnetic and lateral electric field, is used to fabricate photoluminescent n-type porous silicon structures in dark conditions. A lateral gradient in terms of structural characteristics (i.e. thickness and pore dimensions) along the electric field direction is formed. Enhancement of electric and magnetic field resulted in the increase of pore density and a change in the shape of the macropore structure, from circular to square morphology. Broad photoluminescence (PL) emission from 500 to 800 nm, with a PL peak wavelength ranging from 571 to 642 nm, is attributed to the wide range of microporous features present on the porous silicon layer.

  2. Investigation on the structural and photoluminescent properties of chromium-doped ceramics cordierite

    NASA Astrophysics Data System (ADS)

    da Silva, M. A. F. M.; Pedro, S. S.; López, A.; Sosman, L. P.

    2016-10-01

    This work presents the investigation about the structural and optical properties of a doped-chromium system containing cordierite (Mg2Al4Si5O18) as main phase. The sample composition and the structural data were obtained from X-ray diffraction (XRD) measurements and the results were analyzed by Rietveld method. Photoluminescence (PL) spectra under several excitation wavelengths and photoluminescence excitation (PLE) measurements were performed. The obtained results from PL and PLE experiments are evidences that Cr3+ occupies octahedral sites in this ceramic system. By correlating the optical results, the crystal field parameter (Dq) and Racah interelectronic repulsion parameters (B and C) were calculated and discussed according to the Tanabe-Sugano (TS) theory for d3 transition metals in octahedral sites.

  3. Photoluminescence and thermoluminescence studies of CaAl2O4:Dy(3+) phosphor.

    PubMed

    Ziyauddin, Mohammad; Tigga, Shalinta; Brahme, Nameeta; Bisen, D P

    2016-02-01

    Calcium aluminate phosphors activated by Dy(3+) have been prepared by a combustion method at a temperature of 600°C. Photoluminescence (PL) and thermoluminescence (TL) properties of gamma-irradiated Dy-doped calcium aluminate were investigated. The PL spectrum shows a broad peak around 488 nm and 573 nm, under 347 nm excitation. Thermoluminescence studies were performed for different concentrations of Dy. Optimum intensity of photoluminescence was found for 0.02 mol% concentration of Dy. It was found that initially the peak TL intensity increases with increasing concentration of Dy in the CaAl2O4 host, attains a maximum value for 0.05 mol% concentration and decreases with further increase in the doping concentration due to concentration quenching.

  4. Photoluminescence in disordered Zn{sub 2}TiO{sub 4}

    SciTech Connect

    Chaves, Alexsandra C.; Lima, Severino J.G.; Araujo, Regiane C.M.U.; Maurera, Maria Aldeiza M.A.; Longo, Elson; Pizani, Paulo S.; Simoes, Luiz G.P.; Soledade, Luiz E.B.; Souza, Antonio G.; Santos, Ieda Maria Garcia dos . E-mail: ieda@quimica.ufpb.br

    2006-04-15

    In this work, the polymeric precursor method was used to obtain disordered Zn{sub 2}TiO{sub 4} powders, either undoped or doped with Sn{sup 4+}, Cr{sup 3+} and V{sup 5+}, to be applied as photoluminescent material. The characterization was undertaken by means of thermal analysis (TG and DTA), X-ray diffraction (XRD), infrared spectroscopy (IR) and photoluminescence (PL). Previous works stated that titanate octahedra containing a short Ti-O distance show efficient luminescence at room temperature if these octahedra are isolated from each other. In the present work, the phenomenon was observed in condensed octahedra, sharing edges. The room temperature PL noticed in undoped Zn{sub 2}TiO{sub 4} had its intensity increased by the dopant addition-the increase was of about 300% for V{sup 5+} doping, 400% for Cr{sup 3+} and 800% for Sn{sup 4+}.

  5. High Performance Photoluminescent Carbon Dots for In Vitro and In Vivo Bioimaging: Effect of Nitrogen Doping Ratios.

    PubMed

    Wang, Junqing; Zhang, Pengfei; Huang, Chao; Liu, Gang; Leung, Ken Cham-Fai; Wáng, Yì Xiáng J

    2015-07-28

    Photoluminescent carbon dots (CDs) have received ever-increasing attention in the application of optical bioimaging because of their low toxicity, tunable fluorescent properties, and ultracompact size. We report for the first time on enhanced photoluminescence (PL) performance influenced by structure effects among the various types of nitrogen doped (N-doped) PL CDs. These CDs were facilely synthesized from condensation carbonization of linear polyethylenic amine (PEA) analogues and citric acid (CA) of different ratios. Detailed structural and property studies demonstrated that either the structures or the molar ratio of PEAs altered the PL properties of the CDs. The content of conjugated π-domains with C═N in the carbon backbone was correlated with their PL Quantum Yield (QY) (up to 69%). The hybridization between the surface/molecule state and the carbon backbone synergistically affected the chemical/physical properties. Also, long-chain polyethylenic amine (PEA) molecule-doped CDs exhibit increasing photostability, but at the expense of PL efficiency, proving that the PL emission of high QY CDs arise not only from the sp(2)/sp(3) carbon core and surface passivation of CDs, but also from the molecular fluorophores integrated in the CDs. In vitro and in vivo bioimaging of these N-doped CDs showed strong photoluminescence signals. Good biocompatibility demonstrates their potential feasibility for bioimaging applications. In addition, the overall size profile of the as-prepared CDs is comparable to the average size of capillary pores in normal living tissues (∼5 nm). Our study provides valuable insights into the effects of the PEA doping ratios on photoluminescence efficiency, biocompatibility, cellular uptake, and optical bioimaging of CDs. PMID:26135003

  6. Enhancement of photoluminescence of different quantum dots by Ag@SiO{sub 2} core–shell nanoparticles

    SciTech Connect

    Chang, Ya-Hsing; Lu, Yu-Chieh; Chou, Kan-Sen

    2013-06-01

    Highlights: ► Enhancement effects of CdS/ZnS, Cd{sub 0.3}Pb{sub 0.7}S and ZnS QDs linked to Ag@SiO{sub 2} nanoparticles were studied. ► There existed an optimal thickness of SiO{sub 2} shell on the enhancement. ► The enhancement factor was in the range of 2.5–3 for CdS/ZnS and Cd{sub 0.3}Pb{sub 0.7}S QDs. ► The PL intensity of ZnS QD was totally quenched due to absorption by silver particles. - Abstract: The enhancement of photoluminescence of several quantum dots, namely CdS/ZnS, Cd{sub 0.3}Pb{sub 0.7}S and pure ZnS, by Ag@SiO{sub 2} core–shell nanoparticles is studied and reported in this work. 3-Aminopropyltriethoxysilane (APS) was used to link QDs to the core–shell nanoparticles. For CdS/ZnS, the Ag@SiO{sub 2} nanoparticles showed a maximum enhancement of about 2.5 due to surface plasmon resonance of silver particles when the shell thickness was 16 nm. When the shell thickness increased to 30 nm, the enhancement effect became negligible. Conversely, when the thickness decreased to 6 nm, the effect was also smaller due to possible capture of excited electrons by silver particles. For Cd{sub 0.3}Pb{sub 0.7}S, a similar enhancement effect was observed. However when pure ZnS was the QD, the photoluminescence went zero after the QD was linked to Ag@SiO{sub 2} nanoparticles. This was caused by the fact that for ZnS QDs, the emission wavelength was 415 nm, which also corresponds to the absorbance peak of silver particles.

  7. Self-assembly and photoluminescence evolution of hydrophilic and hydrophobic quantum dots in sol–gel processes

    SciTech Connect

    Yang, Ping; Matras-Postolek, Katarzyna; Song, Xueling; Zheng, Yan; Liu, Yumeng; Ding, Kun; Nie, Shijie

    2015-10-15

    Graphical abstract: Highly luminescent quantum dots (QDs) with tunable photoluminescence (PL) wavelength were assembled into various morphologies including chain, hollow spheres, fibers, and ring structures through sol–gel processes. The PL properties during assembly as investigated. - Highlights: • Highly luminescent quantum dots (QDs) were synthesized from several ligands. • The evolution of PL in self-assembly via sol–gel processes was investigated. • CdTe QDs were assembled into a chain by controlling hydrolysis and condensation reactions. • Hollow spheres, fibers, and ring structures were created via CdSe/ZnS QDs in sol–gel processes. - Abstract: Highly luminescent quantum dots (QDs) with tunable photoluminescence (PL) wavelength were synthesized from several ligands to investigate the PL evolution in QD self-assembly via sol–gel processes. After ligand exchange, CdTe QDs were assembled into a chain by controlling the hydrolysis and condensation reaction of 3-mercaptopropyl-trimethoxysilane. The chain was then coated with a SiO{sub 2} shell from tetraethyl orthosilicate (TEOS). Hollow spheres, fibers, and ring structures were created from CdSe/ZnS QDs via various sol–gel processes. CdTe QDs revealed red-shifted and narrowed PL spectrum after assembly compared with their initial one. In contrast, the red-shift of PL spectra of CdSe/ZnS QDs is small. By optimizing experimental conditions, SiO{sub 2} spheres with multiple CdSe/ZnS QDs were fabricated using TEOS and MPS. The QDs in these SiO{sub 2} spheres retained their initial PL properties. This result is useful for application because of their high stability and high PL efficiency of 33%.

  8. Preparation and photoluminescence study of mesoporous indium hydroxide nanorods

    SciTech Connect

    Li, Changyu; Lian, Suoyuan; Liu, Yang; Liu, Shouxin; Kang, Zhenhui

    2010-02-15

    Mesoporous indium hydroxide nanorods were successfully synthesized by a mild one-step one-pot method. The obtained samples were characterized by X-ray diffraction, transmission electron microscopy with selected area electron diffraction, N{sub 2} adsorption, ultraviolet-visible absorption and photoluminescence, respectively. Transmission electron microscopy showed that there were some pores in the samples, which were mainly composed of rod-like shapes with length of 300 nm and diameter of 90 nm. N{sub 2} adsorption/desorption measurements confirmed that the prepared powder was mesoporous with average pore diameter of 3.1 nm. The ultraviolet-visible absorption spectroscopy analysis indicated that the band gap energy of the samples was 5.15 eV. Photoluminescence spectrum showed that there were two strong emissions under ultraviolet light irradiation. The growth mechanism of indium hydroxide nanorods and the role of cetyltrimethyl ammonium bromide were also discussed.

  9. Thermal conductivity and photoluminescence of light-emitting silicon nitride films

    NASA Astrophysics Data System (ADS)

    Marconnet, Amy; Panzer, Matt; Yerci, Selçuk; Minissale, Salvatore; Wang, X.; Zhang, X.; Dal Negro, Luca; Goodson, K. E.

    2012-01-01

    Silicon-rich and rare-earth-doped nitride materials are promising candidates for silicon-compatible photonic sources. This work investigates the thermal conductivity and photoluminescence (PL) of light emitting samples fabricated with a range of excess silicon concentrations and annealing temperatures using time-domain picosecond thermoreflectance and time-resolved photoluminescence. A direct correlation between the thermal conductivity and photoluminescence dynamics is demonstrated, as well as a significant reduction of thermal conductivity upon incorporation of erbium ions. These findings highlight the role of annealing and stoichiometry control in the optimization of light emitting microstructures suitable for the demonstration of efficient Si-compatible light sources based on the silicon nitride platform.

  10. Role of plastic deformation mechanisms in the formation of nanostructured silicon and its photoluminescent properties

    NASA Astrophysics Data System (ADS)

    Kulinich, O. A.

    2012-06-01

    The role of plastic deformation mechanisms in the process of obtaining nanostructured silicon layers is demonstrated. The process of obtaining nanostructured silicon consists in growing of silicon oxide layers of various thicknesses on the silicon wafer surface, their subsequent removal, and treatment by selective chemical etchants (SE) before the formation of defectless silicon islands possessing the photoluminescent properties typical of nanostructured silicon. Based on analysis of the photoluminescence intensity spectra of nanostructured silicon islands, the conclusion is drawn on different plastic deformation mechanisms at different thicknesses of thermally grown silicon oxide. Possible mechanisms of displacement of the intensity maximum in the photoluminescence (PL) spectrum toward shorter wavelengths with decreasing nanostructured silicon island sizes are discussed.

  11. Photoluminescence Spectroscopy of Mass-Selected Electrosprayed Ions Embedded in Cryogenic Rare-Gas Matrixes.

    PubMed

    Kern, Bastian; Greisch, Jean-François; Strelnikov, Dmitry; Weis, Patrick; Böttcher, Artur; Ruben, Mario; Schäfer, Bernhard; Schooss, Detlef; Kappes, Manfred M

    2015-12-01

    An apparatus is presented which combines nanoelectrospray ionization for isolation of large molecular ions from solution, mass-to-charge ratio selection in gas-phase, low-energy-ion-beam deposition into a (co-condensed) inert gas matrix and UV laser-induced visible-region photoluminescence (PL) of the matrix isolated ions. Performance is tested by depositing three different types of lanthanoid diketonate cations including also a dissociation product species not directly accessible by chemical synthesis. For these strongly photoluminescent ions, accumulation of some femto- to picomoles in a neon matrix (over a time scale of tens of minutes to several hours) is sufficient to obtain well-resolved dispersed emission spectra. We have ruled out contributions to these spectra due to charge neutralization or fragmentation during deposition by also acquiring photoluminescence spectra of the same ionic species in the gas phase. PMID:26553589

  12. Composition-dependent photoluminescence properties of CuInS2/ZnS core/shell quantum dots

    NASA Astrophysics Data System (ADS)

    Hua, Jie; Du, Yuwei; Wei, Qi; Yuan, Xi; Wang, Jin; Zhao, Jialong; Li, Haibo

    2016-06-01

    CuInS2/ZnS (CIS/ZnS) core/shell quantum dots (QDs) with various Cu/In ratios were synthesized using the hot-injection method, and their photoluminescence (PL) properties were investigated by measuring steady-state and time-resolved PL spectroscopy. The emission peak of the CIS/ZnS QDs were tuned from 680 to 580 nm by decreasing the Cu/In precursor ratio from 1/1 to 1/9. As the Cu/In ratio decreases, the PL lifetimes and PL quantum yields (QYs) of CIS/ZnS core/shell QDs increased firstly and then decreased. Two dominant radiative recombination processes were postulated to analyze composition-dependent PL properties, including the recombination from a quantized conduction band to deep defects state and donor-acceptor pair (DAP) recombination. The decrease of PL efficiency resulted from high density defects and traps, which formed at the interface between CIS core and ZnS shell due to the large off-stoichiometry composition. The PL intensity and peak energy for CIS/ZnS core/shell QDs as a function of temperature were also provided. The thermal quenching further confirmed that the PL emission of CIS/ZnS QDs did not come from the recombination of excitons but from the recombination of many kinds of intrinsic defects inside the QDs as emission centers.

  13. Photochemical Reaction in Monolayer MoS2 via Correlated Photoluminescence, Raman Spectroscopy, and Atomic Force Microscopy.

    PubMed

    Oh, Hye Min; Han, Gang Hee; Kim, Hyun; Bae, Jung Jun; Jeong, Mun Seok; Lee, Young Hee

    2016-05-24

    Photoluminescence (PL) from monolayer MoS2 has been modulated using plasma treatment or thermal annealing. However, a systematic way of understanding the underlying PL modulation mechanism has not yet been achieved. By introducing PL and Raman spectroscopy, we analyze that the PL modulation by laser irradiation is associated with structural damage and associated oxygen adsorption on the sample in ambient conditions. Three distinct behaviors were observed according to the laser irradiation time: (i) slow photo-oxidation at the initial stage, where the physisorption of ambient gases gradually increases the PL intensity; (ii) fast photo-oxidation at a later stage, where chemisorption increases the PL intensity abruptly; and (iii) photoquenching, with complete reduction of PL intensity. The correlated confocal Raman spectroscopy confirms that no structural deformation is involved in slow photo-oxidation stage; however, the structural disorder is invoked during the fast photo-oxidation stage, and severe structural degradation is generated during the photoquenching stage. The effect of oxidation is further verified by repeating experiments in vacuum, where the PL intensity is simply degraded with laser irradiation in a vacuum due to a simple structural degradation without involving oxygen functional groups. The charge scattering by oxidation is further explained by the emergence/disappearance of neutral excitons and multiexcitons during each stage. PMID:27110722

  14. A Label-Free Photoluminescence Genosensor Using Nanostructured Magnesium Oxide for Cholera Detection

    PubMed Central

    Patel, Manoj Kumar; Ali, Md. Azahar; Krishnan, Sadagopan; Agrawal, Ved Varun; Al Kheraif, AbdulAziz A.; Fouad, H.; Ansari, Z.A.; Ansari, S. G.; Malhotra, Bansi D.

    2015-01-01

    Nanomaterial-based photoluminescence (PL) diagnostic devices offer fast and highly sensitive detection of pesticides, DNA, and toxic agents. Here we report a label-free PL genosensor for sensitive detection of Vibrio cholerae that is based on a DNA hybridization strategy utilizing nanostructured magnesium oxide (nMgO; size >30 nm) particles. The morphology and size of the synthesized nMgO were determined by transmission electron microscopic (TEM) studies. The probe DNA (pDNA) was conjugated with nMgO and characterized by X-ray photoelectron and Fourier transform infrared spectroscopic techniques. The target complementary genomic DNA (cDNA) isolated from clinical samples of V. cholerae was subjected to DNA hybridization studies using the pDNA-nMgO complex and detection of the cDNA was accomplished by measuring changes in PL intensity. The PL peak intensity measured at 700 nm (red emission) increases with the increase in cDNA concentration. A linear range of response in the developed PL genosensor was observed from 100 to 500 ng/μL with a sensitivity of 1.306 emi/ng, detection limit of 3.133 ng/μL and a regression coefficient (R2) of 0.987. These results show that this ultrasensitive PL genosensor has the potential for applications in the clinical diagnosis of cholera. PMID:26611737

  15. A Label-Free Photoluminescence Genosensor Using Nanostructured Magnesium Oxide for Cholera Detection

    NASA Astrophysics Data System (ADS)

    Patel, Manoj Kumar; Ali, Md. Azahar; Krishnan, Sadagopan; Agrawal, Ved Varun; Al Kheraif, Abdulaziz A.; Fouad, H.; Ansari, Z. A.; Ansari, S. G.; Malhotra, Bansi D.

    2015-11-01

    Nanomaterial-based photoluminescence (PL) diagnostic devices offer fast and highly sensitive detection of pesticides, DNA, and toxic agents. Here we report a label-free PL genosensor for sensitive detection of Vibrio cholerae that is based on a DNA hybridization strategy utilizing nanostructured magnesium oxide (nMgO; size >30 nm) particles. The morphology and size of the synthesized nMgO were determined by transmission electron microscopic (TEM) studies. The probe DNA (pDNA) was conjugated with nMgO and characterized by X-ray photoelectron and Fourier transform infrared spectroscopic techniques. The target complementary genomic DNA (cDNA) isolated from clinical samples of V. cholerae was subjected to DNA hybridization studies using the pDNA-nMgO complex and detection of the cDNA was accomplished by measuring changes in PL intensity. The PL peak intensity measured at 700 nm (red emission) increases with the increase in cDNA concentration. A linear range of response in the developed PL genosensor was observed from 100 to 500 ng/μL with a sensitivity of 1.306 emi/ng, detection limit of 3.133 ng/μL and a regression coefficient (R2) of 0.987. These results show that this ultrasensitive PL genosensor has the potential for applications in the clinical diagnosis of cholera.

  16. Photoluminescence study of self-interstitial clusters and extended defects in ion-implanted silicon

    NASA Astrophysics Data System (ADS)

    Giri, P. K.

    2003-12-01

    We report on the photoluminescence (PL) studies of self-interstitial (I) clustering in ion-implanted Si at various stages of post-implantation annealing. Low-temperature PL measurements on as-implanted and low-temperature annealed (up to 450°C) samples show sharp X and W bands at 1200 and 1218 nm which are attributed to I4 and I3 clusters, respectively. Annealing at 600°C shows a drastic change in the PL spectra. In case of high-energy self-ion-implanted samples, 600°C annealing produces several peaks in the range 1250-1400 nm. For longer duration annealing, two broad bands form at 1322 and 1392 nm irrespective of the ion fluence. These PL signatures are attributed to I8 clusters and/or (1 0 0) I-chains, and they are believed to be the precursor of {3 1 1} rod-like defects. For annealing above 600°C and for fluence ⩾1×1013 cm-2, a sharp PL band is observed at 1376 nm and it is attributed to {3 1 1} rod-like defects. At higher fluences, an additional broad band appears in the PL spectrum at ∼1576 nm which is related to residual ion-damage or extended defect formation. These results illustrate the potential of silicon I-clusters as a possible source of light emission from Si.

  17. Emergence of new red-shifted carbon nanotube photoluminescence based on proximal doped-site design

    NASA Astrophysics Data System (ADS)

    Shiraki, Tomohiro; Shiraishi, Tomonari; Juhász, Gergely; Nakashima, Naotoshi

    2016-06-01

    Single-walled carbon nanotubes (SWNTs) show unique photoluminescence (PL) in the near-infrared (NIR) region. Here we propose a concept based on the proximal modification in local covalent functionalization of SWNTs. Quantum mechanical simulations reveal that the SWNT band gap changes specifically based on the proximal doped-site design. Thus, we synthesize newly-designed bisdiazonium molecules and conduct local fucntionalisation of SWNTs. Consequently, new red-shifted PL (E112*) from the bisdiazonium-modified SWNTs with (6, 5) chirality is recognized around 1250 nm with over ~270 nm Stokes shift from the PL of the pristine SWNTs and the PL wavelengths are shifted depending on the methylene spacer lengths of the modifiers. The present study revealed that SWNT PL modulation is enable by close-proximity-local covalent modification, which is highly important for fundamental understanding of intrinsic SWNT PL properties as well as exciton engineering-based applications including photonic devices and (bio)imaging/sensing.

  18. Emergence of new red-shifted carbon nanotube photoluminescence based on proximal doped-site design

    NASA Astrophysics Data System (ADS)

    Shiraki, Tomohiro; Shiraishi, Tomonari; Juhász, Gergely; Nakashima, Naotoshi

    2016-06-01

    Single-walled carbon nanotubes (SWNTs) show unique photoluminescence (PL) in the near-infrared (NIR) region. Here we propose a concept based on the proximal modification in local covalent functionalization of SWNTs. Quantum mechanical simulations reveal that the SWNT band gap changes specifically based on the proximal doped-site design. Thus, we synthesize newly-designed bisdiazonium molecules and conduct local fucntionalisation of SWNTs. Consequently, new red-shifted PL (E112*) from the bisdiazonium-modified SWNTs with (6, 5) chirality is recognized around 1250 nm with over ~270 nm Stokes shift from the PL of the pristine SWNTs and the PL wavelengths are shifted depending on the methylene spacer lengths of the modifiers. The present study revealed that SWNT PL modulation is enable by close-proximity-local covalent modification, which is highly important for fundamental understanding of intrinsic SWNT PL properties as well as exciton engineering–based applications including photonic devices and (bio)imaging/sensing.

  19. Electrochemical control of photoluminescence in two-dimensional MoS(2) nanoflakes.

    PubMed

    Wang, Yichao; Ou, Jian Zhen; Balendhran, Sivacarendran; Chrimes, Adam F; Mortazavi, Majid; Yao, David D; Field, Matthew R; Latham, Kay; Bansal, Vipul; Friend, James R; Zhuiykov, Serge; Medhekar, Nikhil V; Strano, Michael S; Kalantar-Zadeh, Kourosh

    2013-11-26

    Two-dimensional (2D) transition metal dichalcogenide semiconductors offer unique electronic and optical properties, which are significantly different from their bulk counterparts. It is known that the electronic structure of 2D MoS2, which is the most popular member of the family, depends on the number of layers. Its electronic structure alters dramatically at near atomically thin morphologies, producing strong photoluminescence (PL). Developing processes for controlling the 2D MoS2 PL is essential to efficiently harness many of its optical capabilities. So far, it has been shown that this PL can be electrically or mechanically gated. Here, we introduce an electrochemical approach to actively control the PL of liquid-phase-exfoliated 2D MoS2 nanoflakes by manipulating the amount of intercalated ions including Li(+), Na(+), and K(+) into and out of the 2D crystal structure. These ions are selected as they are crucial components in many bioprocesses. We show that this controlled intercalation allows for large PL modulations. The introduced electrochemically controlled PL will find significant applications in future chemical and bio-optical sensors as well as optical modulators/switches. PMID:24148149

  20. Unique photoluminescence degradation/recovery phenomena in trivalent ion-activated phosphors

    SciTech Connect

    Sawada, Kenji; Adachi, Sadao

    2015-09-14

    Photo-induced luminescence intensity degradation in red-emitting Tb{sub 3}Ga{sub 5}O{sub 12}:Eu{sup 3+} (TGG:Eu{sup 3+}) phosphor is observed and studied using x-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation spectroscopy, and PL decay analysis. The red-emitting TGG:Eu{sup 3+} phosphor exhibits remarkable degradation in the PL intensity under weak UV light (λ < 350 nm) exposure in the seconds time scale. The PL degradation characteristics can be well expressed by the exponential formulation with respect to exposure time. Interestingly, the PL intensity recovers after a few minutes when the phosphor is stored in a dark room or exposed to the long-wavelength (λ > 350 nm) light. The luminescence decay dynamics measured by excitation at λ{sub ex} = 355 and 266 nm suggest that the present degradation/recovery processes are caused by the electron traps formed in the TGG:Eu{sup 3+} phosphor. The Tb{sup 3+} emission in TGG shows the essentially same degradation characteristics as those observed in the TGG:Eu{sup 3+} phosphor. The present luminescence degradation/recovery phenomena of the trivalent ions (4f → 4f transitions) may universally occur in various oxide phosphors such as TGG (Tb{sup 3+} emission) and CaTiO{sub 3}:Eu{sup 3+}.

  1. Emergence of new red-shifted carbon nanotube photoluminescence based on proximal doped-site design

    PubMed Central

    Shiraki, Tomohiro; Shiraishi, Tomonari; Juhász, Gergely; Nakashima, Naotoshi

    2016-01-01

    Single-walled carbon nanotubes (SWNTs) show unique photoluminescence (PL) in the near-infrared (NIR) region. Here we propose a concept based on the proximal modification in local covalent functionalization of SWNTs. Quantum mechanical simulations reveal that the SWNT band gap changes specifically based on the proximal doped-site design. Thus, we synthesize newly-designed bisdiazonium molecules and conduct local fucntionalisation of SWNTs. Consequently, new red-shifted PL (E112*) from the bisdiazonium-modified SWNTs with (6, 5) chirality is recognized around 1250 nm with over ~270 nm Stokes shift from the PL of the pristine SWNTs and the PL wavelengths are shifted depending on the methylene spacer lengths of the modifiers. The present study revealed that SWNT PL modulation is enable by close-proximity-local covalent modification, which is highly important for fundamental understanding of intrinsic SWNT PL properties as well as exciton engineering–based applications including photonic devices and (bio)imaging/sensing. PMID:27345862

  2. Photoluminescence of localized excitons in ZnCdO thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wu, T. Y.; Huang, Y. S.; Hu, S. Y.; Lee, Y. C.; Tiong, K. K.; Chang, C. C.; Shen, J. L.; Chou, W. C.

    2016-07-01

    We have investigated the luminescence characteristics of Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system. The temperature-dependent photoluminescence (PL) and excitation power-dependent PL spectra were measured to clarify the luminescence mechanisms of the Zn1-xCdxO thin films. The peak energy of the Zn1-xCdxO thin films with increasing the Cd concentration is observed as redshift and can be fitted by the quadratic function of alloy content. The broadened full-width at half-maximum (FWHM) estimated from the 15 K PL spectra as a function of Cd content shows a larger deviation between the experimental values and theoretical curve, which indicates that experimental FWHM values are affected not only by alloy compositional disorder but also by localized excitons occupying states in the tail of the density of states. The Urbach energy determined from an analysis of the lineshape of the low-energy side of the PL spectrum and the degree of localization effect estimated from the temperature-induced S-shaped PL peak position described an increasing mean exciton-localization effects in ZnCdO films with increasing the Cd content. In addition, the PL intensity and peak position as a function of excitation power are carried out to clarify the types of radiative recombination and the effects of localized exciton in the ZnCdO films with different Cd contents.

  3. Photoluminescence Blinking of Single-Crystal Methylammonium Lead Iodide Perovskite Nanorods Induced by Surface Traps

    PubMed Central

    2016-01-01

    Photoluminescence (PL) of organometal halide perovskite materials reflects the charge dynamics inside of the material and thus contains important information for understanding the electro-optical properties of the material. Interpretation of PL blinking of methylammonium lead iodide (MAPbI3) nanostructures observed on polycrystalline samples remains puzzling owing to their intrinsic disordered nature. Here, we report a novel method for the synthesis of high-quality single-crystal MAPbI3 nanorods and demonstrate a single-crystal study on MAPbI3 PL blinking. At low excitation power densities, two-state blinking was found on individual nanorods with dimensions of several hundred nanometers. A super-resolution localization study on the blinking of individual nanorods showed that single crystals of several hundred nanometers emit and blink as a whole, without showing changes in the localization center over the crystal. Moreover, both the blinking ON and OFF times showed power-law distributions, indicating trapping–detrapping processes. This is further supported by the PL decay times of the individual nanorods, which were found to correlate with the ON/OFF states. Furthermore, a strong environmental dependence of the nanorod PL blinking was revealed by comparing the measurements in vacuum, nitrogen, and air, implying that traps locate close to crystal surfaces. We explain our observations by proposing surface charge traps that are likely related to under-coordinated lead ions and methylammonium vacancies to result in the PL blinking observed here. PMID:27617323

  4. Changing interfaces: Photoluminescent ZnO nanoparticle powders in different aqueous environments

    NASA Astrophysics Data System (ADS)

    Kocsis, Krisztina; Niedermaier, Matthias; Bernardi, Johannes; Berger, Thomas; Diwald, Oliver

    2016-10-01

    We transformed vapor phase grown ZnO nanoparticle powders into aqueous ZnO nanoparticle dispersions and studied the impact of associated microstructure and interface property changes on their spectroscopic properties. With photoluminescence (PL) spectroscopy, we probed oxygen interstitials Oi2 - in the near surface region and tracked their specific PL emission response at hvEM = 2.1 eV during the controlled conversion of the solid-vacuum into the solid-liquid interface. While oxygen adsorption via the gas phase does affect the intensity of the PL emission bands, the O2 contact with ZnO nanoparticles across the solid-liquid interface does not. Moreover, we found that the near band edge emission feature at hvEM = 3.2 eV gains relative intensity with regard to the PL emission features in the visible light region. Searching for potential PL indicators that are specific to early stages of particle dissolution, we addressed for aqueous ZnO nanoparticle dispersions the effect of formic acid adsorption. In the absence of related spectroscopic features, we were able to consistently track ZnO nanoparticle dissolution and the concomitant formation of solvated Zinc formate species by means of PL and FT-IR spectroscopy, dynamic light scattering, and zeta potential measurements. For a more consistent and robust assessment of nanoparticle properties in different continuous phases, we discuss characterization challenges and potential pitfalls that arise upon replacing the solid-gas with the solid-liquid interface.

  5. Scanning room temperature photoluminescence in SiN{textbf{text x}}:H layers

    NASA Astrophysics Data System (ADS)

    Tarasov, I.; Dybiec, M.; Ostapenko, S.; Rohatgi, A.; Yelundur, V.; Gabor, A. M.

    2004-07-01

    We report on spectroscopic photoluminescence (PL) mapping of solar-cell-grade mc-Si ribbon wafers. We observe under UV excitation a broad visible emission from the SiNx:H layer. The samples covered with SiNx:H were subjected to rapid thermal processing at different temperatures, and PL maps were measured before and after treatment. We observed that after RTP treatment the intensity of the PL band was significantly increased, which indicates further reduction of non-radiative defects. The magnitude of these increases depends on the RTP conditions. The visible PL band exhibits a reversible photo quenching of the intensity under 325 nm HeCd laser excitation. The PL intensity can be recovered by annealing with the rate exhibiting a thermally activated behavior. The observed PL photo quenching reveals a metastable process in the SiNx:H film under UV excitation. We demonstrate the possibility of creating a reversible luminescence micro-pattern on the SiNx:H layer using a focused UV laser beam.

  6. Photoluminescence Blinking of Single-Crystal Methylammonium Lead Iodide Perovskite Nanorods Induced by Surface Traps

    PubMed Central

    2016-01-01

    Photoluminescence (PL) of organometal halide perovskite materials reflects the charge dynamics inside of the material and thus contains important information for understanding the electro-optical properties of the material. Interpretation of PL blinking of methylammonium lead iodide (MAPbI3) nanostructures observed on polycrystalline samples remains puzzling owing to their intrinsic disordered nature. Here, we report a novel method for the synthesis of high-quality single-crystal MAPbI3 nanorods and demonstrate a single-crystal study on MAPbI3 PL blinking. At low excitation power densities, two-state blinking was found on individual nanorods with dimensions of several hundred nanometers. A super-resolution localization study on the blinking of individual nanorods showed that single crystals of several hundred nanometers emit and blink as a whole, without showing changes in the localization center over the crystal. Moreover, both the blinking ON and OFF times showed power-law distributions, indicating trapping–detrapping processes. This is further supported by the PL decay times of the individual nanorods, which were found to correlate with the ON/OFF states. Furthermore, a strong environmental dependence of the nanorod PL blinking was revealed by comparing the measurements in vacuum, nitrogen, and air, implying that traps locate close to crystal surfaces. We explain our observations by proposing surface charge traps that are likely related to under-coordinated lead ions and methylammonium vacancies to result in the PL blinking observed here.

  7. Tuning photoluminescence and surface properties of carbon nanodots for chemical sensing

    NASA Astrophysics Data System (ADS)

    Zhang, Zhaomin; Pan, Yi; Fang, Yaning; Zhang, Lulu; Chen, Junying; Yi, Changqing

    2015-12-01

    Obtaining tunable photoluminescence (PL) with improved emission properties is crucial for successfully implementing fluorescent carbon nanodots (fCDs) in all practical applications such as multicolour imaging and multiplexed detection by a single excitation wavelength. In this study, we report a facile hydrothermal approach to adjust the PL peaks of fCDs from blue, green to orange by controlling the surface passivation reaction during the synthesis. This is achieved by tuning the passivating reagents in a step-by-step manner. The as-prepared fCDs with narrow size distribution show improved PL properties with different emission wavelengths. Detailed characterization of fCDs using elemental analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy suggested that the surface chemical composition results in this tunable PL emission. Surface passivation significantly alters the surface status, resulting in fCDs with either stronger surface oxidation or N element doping that ultimately determine their PL properties. Further experiments suggested that the as-prepared orange luminescent fCDs (O-fCDs) were sensitive and specific nanosensing platforms towards Fe3+ determination in a complex biological environment, emphasizing their potential practical applications in clinical and biological fields.Obtaining tunable photoluminescence (PL) with improved emission properties is crucial for successfully implementing fluorescent carbon nanodots (fCDs) in all practical applications such as multicolour imaging and multiplexed detection by a single excitation wavelength. In this study, we report a facile hydrothermal approach to adjust the PL peaks of fCDs from blue, green to orange by controlling the surface passivation reaction during the synthesis. This is achieved by tuning the passivating reagents in a step-by-step manner. The as-prepared fCDs with narrow size distribution show improved PL properties with different emission wavelengths. Detailed

  8. Facile route to highly photoluminescent carbon nanodots for ion detection, pH sensors and bioimaging

    NASA Astrophysics Data System (ADS)

    Shen, Chen; Sun, Yupeng; Wang, Jing; Lu, Yun

    2014-07-01

    Carbon nanodots (CDs) of uniform size were prepared simply by the hydrothermal decomposition of folic acid (FA) precursor at various reaction temperatures. The CDs formed via dehydration of FA at 260 °C contributed the strongest photoluminescence (PL) signal and the highest quantum yield at about 68%, without assistance of any passivation agent. The effects of preparation conditions on PL behavior of CDs have been investigated in detail, and the quantum yield of the CDs was found to be associated strongly with sample crystallinity. Moreover, because the obtained CDs also exhibited high luminescence stability, abundant surface functional groups and good biocompatibility, there are many promising applications in printing ink, ion detection, pH sensors and cell imaging.Carbon nanodots (CDs) of uniform size were prepared simply by the hydrothermal decomposition of folic acid (FA) precursor at various reaction temperatures. The CDs formed via dehydration of FA at 260 °C contributed the strongest photoluminescence (PL) signal and the highest quantum yield at about 68%, without assistance of any passivation agent. The effects of preparation conditions on PL behavior of CDs have been investigated in detail, and the quantum yield of the CDs was found to be associated strongly with sample crystallinity. Moreover, because the obtained CDs also exhibited high luminescence stability, abundant surface functional groups and good biocompatibility, there are many promising applications in printing ink, ion detection, pH sensors and cell imaging. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr02154a

  9. Quality Characterization of Silicon Bricks using Photoluminescence Imaging and Photoconductive Decay: Preprint

    SciTech Connect

    Johnston, S.; Yan, F.; Zaunbrecher, K.; Al-Jassim, M.; Sidelkheir, O.; Ounadjela, K.

    2012-06-01

    Imaging techniques can be applied to multicrystalline silicon solar cells throughout the production process, which includes as early as when the bricks are cut from the cast ingot. Photoluminescence (PL) imaging of the band-to-band radiative recombination is used to characterize silicon quality and defects regions within the brick. PL images of the brick surfaces are compared to minority-carrier lifetimes measured by resonant-coupled photoconductive decay (RCPCD). Photoluminescence images on silicon bricks can be correlated to lifetime measured by photoconductive decay and could be used for high-resolution characterization of material before wafers are cut. The RCPCD technique has shown the longest lifetimes of any of the lifetime measurement techniques we have applied to the bricks. RCPCD benefits from the low-frequency and long-excitation wavelengths used. In addition, RCPCD is a transient technique that directly monitors the decay rate of photoconductivity and does not rely on models or calculations for lifetime. The measured lifetimes over brick surfaces have shown strong correlations to the PL image intensities; therefore, this correlation could then be used to transform the PL image into a high-resolution lifetime map.

  10. Origin of tunable photoluminescence from graphene quantum dots synthesized via pulsed laser ablation.

    PubMed

    Santiago, S R M; Lin, T N; Yuan, C T; Shen, J L; Huang, H Y; Lin, C A J

    2016-08-10

    A one-step synthesis of graphene quantum dots (GQDs) has been implemented using pulsed laser ablation (PLA) with carboxyl-functionalized multiwalled carbon nanotubes (MWCNTs). The synthesized GQDs with an average size smaller than 3 nm were obtained by the fragmentation of MWCNTs via oxidative cutting. The GQDs can generate tunable photoluminescence (PL) ranging from green to blue by controlling the PLA time. The PL spectrum (decay time) of the green GQDs remains unchanged under different excitation energies (emission energies), while that of the blue GQDs correlates with the excitation energy (emission energy). On the basis of the pH and temperature dependence of PL, we suggest that the localized intrinsic states associated with the sp(2) nanodomains and delocalized extrinsic states embedded on the GQD surface are responsible for blue and green emission in GQDs, respectively. PMID:27476476

  11. Tip enhancement of upconversion photoluminescence from rare earth ion doped nanocrystals.

    PubMed

    Mauser, Nina; Piatkowski, Dawid; Mancabelli, Tobia; Nyk, Marcin; Mackowski, Sebastian; Hartschuh, Achim

    2015-04-28

    We present tip-enhanced upconversion photoluminescence (PL) images of Er(3+)- and Yb(3+)-doped NaYF4 nanocrystals on glass substrates with subdiffraction spatial resolution. Tip-sample distance dependent measurements clearly demonstrate the near-field origin of the image contrast. Time-resolved PL measurements show that the tip increases the spontaneous emission rate of the two emission channels of Er(3+) in the visible region. Very efficient enhancement of upconversion PL is discussed in the context of the two-photon nature of the excitation process and homoenergy transfer between the ions within the nanocrystals. Comparison between different nanocrystals and tips shows a strong influence of the tip shape on the image contrast that becomes particularly relevant for the larger dimensions of the investigated nanocrystals.

  12. Dopant effects on the photoluminescence of interstitial-related centers in ion implanted silicon

    NASA Astrophysics Data System (ADS)

    Johnson, B. C.; Villis, B. J.; Burgess, J. E.; Stavrias, N.; McCallum, J. C.; Charnvanichborikarn, S.; Wong-Leung, J.; Jagadish, C.; Williams, J. S.

    2012-05-01

    The dopant dependence of photoluminescence (PL) from interstitial-related centers formed by ion implantation and a subsequent anneal in the range 175-525 °C is presented. The evolution of these centers is strongly effected by interstitial-dopant clustering even in the low temperature regime. There is a significant decrease in the W line (1018.2 meV) PL intensity with increasing B concentration. However, an enhancement is also observed in a narrow fabrication window in samples implanted with either P or Ga. The anneal temperature at which the W line intensity is optimized is sensitive to the dopant concentration and type. Furthermore, dopants which are implanted but not activated prior to low temperature thermal processing are found to have a more detrimental effect on the resulting PL. Splitting of the X line (1039.8 meV) arising from implantation damage induced strain is also observed.

  13. Silver nanoparticles enhanced photoluminescence of Nd3+ doped germanate glasses at 1064 nm

    NASA Astrophysics Data System (ADS)

    Kassab, Luciana R. P.; Silva, Davinson M.; Garcia, José A. M.; da Silva, Diego S.; de Araújo, Cid B.

    2016-10-01

    Infrared photoluminescence (PL) properties of PbO-GeO2 glasses containing neodymium ions (Nd3+) and silver nanoparticles (NPs) were investigated. The excitation was made with a continuous-wave diode laser operating at 805 nm, in resonance with the Nd3+ transition 4I9/2 → 4F5/2. Growth of ∼160% in the PL intensity at 1064 nm, was observed in comparison with a reference sample without silver NPs. The PL enhancement is attributed to the increased local-field in the Nd3+ locations nearby the NPs. The present results indicate that PbO-GeO2 glasses containing Nd3+ and silver NPs have good prospect to be used in optical amplifiers at 1064 nm.

  14. Photoluminescence studies of type-II CdSe/CdTe superlattices

    SciTech Connect

    Li Jingjing; Johnson, Shane R.; Wang Shumin; Ding Ding; Ning Cunzheng; Zhang Yonghang; Yin Leijun; Skromme, B. J.; Liu Xinyu; Furdyna, Jacek K.

    2012-08-06

    CdSe/CdTe type-II superlattices grown on GaSb substrates by molecular beam epitaxy are studied using time-resolved and steady-state photoluminescence (PL) spectroscopy at 10 K. The relatively long carrier lifetime of 188 ns observed in time-resolved PL measurements shows good material quality. The steady-state PL peak position exhibits a blue shift with increasing excess carrier concentration. Self-consistent solutions of the Schroedinger and Poisson equations show that this effect can be explained by band bending as a result of the spatial separation of electrons and holes, which is critical confirmation of a strong type-II band edge alignment between CdSe and CdTe.

  15. Green Photoluminescence Suppression in ZnO Embedded in Porous Opal

    NASA Astrophysics Data System (ADS)

    Abrarov, Sanjar M.; Yuldashev, Shavkat U.; Lee, Sergey B.; Kang, Tae Won

    2004-09-01

    The photoluminescence (PL) and transmittance characteristics of zinc oxide (ZnO) embedded in voids of silicon dioxide synthetic opal by the technologically simple sol-gel method are reported. The uniform formation of ZnO nanoparticles inside of the opal matrix can be obtained after its infiltration in an aqueous solution containing a zinc nitrite hexahydride precursor followed by thermal annealing. The green-PL suppression is observed due to the inhibition of spontaneous emission through oxygen vacancies in ZnO. The strong redshift of the transmittance characteristics signifies the essential filling of voids in the fcc packed structure. The infiltration of nanocrystals into synthetic opal may be used as an inexpensive method for the fabrication of polycrystalline ZnO with dominant ultraviolet-blue PL. This technology may also be promising for the fabrication of color light sources, such as RGB pixels in secondary-electron-emission or field-emission displays.

  16. Visible to infrared low temperature photoluminescence of rare earth doped bismuth germanate crystals.

    PubMed

    Canimoglu, A; Ayvacikli, M; Karabulut, Y; Karali, T; Can, N

    2016-05-01

    In this paper, the influence of a series of rare earth (Eu, Tm, Nd) and Cr ion doping on the optical properties of BGO was investigated by means of photoluminescence (PL) from visible to IR region in the 10-300K temperature range using different types of detectors, namely, photomultiplier tube (PMT), InGaAs (IGA), and Si. Several samples were investigated having dopants concentrations of 0.3wt%Nd, 0.4wt%Tm, 0.06wt% Cr and 3ppm Eu. The PL spectra of the samples showed different luminescence behaviour which is assigned to the 4f intra shell transition from rare earth ions. The temperature dependence of the PL from rare earth doped BGO crystals is also examined. PMID:26943903

  17. Hysteresis compensation of photoluminescence in ZnS:Cu for noncontact shaft torque sensing.

    PubMed

    Cho, Min-Young; Kim, Ji-Sik; Kim, Gi-Woo

    2016-03-01

    This paper presents a preliminary investigation of loading rate-dependent hysteresis of photoluminescence (PL) by phosphorescence quenching of copper-doped zinc sulfide (ZnS:Cu) microparticles in response to dynamic torsional loading. Precision sinusoidal torque waveforms in the frequency range of 0.5-3 Hz are used to identify the loading rate-dependent (i.e., frequency-dependent) nonlinear hysteresis phenomenon. The potential of the application of PL is demonstrated by successfully measuring the sinusoidal torque applied to a rotational shaft by evaluating the loading rate-dependent PL intensity signature using a photomultiplier tube. In addition, the potential of noncontact shaft torque sensing is demonstrated successfully by the simple compensation derived from ad hoc heuristic characterization. PMID:26974628

  18. Light-emitting device with organic electroluminescent material and photoluminescent materials

    DOEpatents

    McNulty, Thomas Francis; Duggal, Anil Raj; Turner, Larry Gene; Shiang, Joseph John

    2005-06-07

    A light-emitting device comprises a light-emitting member, which comprises two electrodes and an organic electroluminescent material disposed between the electrodes, and at least one organic photoluminescent ("PL") material. The light-emitting member emits light having a first spectrum in response to a voltage applied across the two electrodes. The organic PL material absorbs a portion of the light emitted by the light-emitting member and emits light having second spectrum different than the first spectrum. The light-emitting device can include an inorganic PL material that absorbs another portion of the light emitted from the light-emitting member and emits light having a third spectrum different than both the first and the second spectra.

  19. Photoluminescent Si/SiOx nanoparticle network by near atmospheric plasma-enhanced chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Yang, Q. Y.; Wang, D. X.; Guo, Y.; Ding, K.; Xu, J. Z.; Shi, J. J.; Zhang, J.

    2011-11-01

    A very fast and simple near atmospheric plasma-enhanced chemical vapour deposition method modulated by a pulsed negative bias voltage is newly developed to yield a Si/SiOx nanoparticle-linked network structure, which emitted enhanced 410 nm photoluminescence (PL) at room temperature. Hydrogen dissociation, oxidation and polarization of the silane plasma-generated active particles could be tuned by the magnitude of bias voltage. The porosity and oxidation of this network structure and the intensity of its PL spectrum at 410 nm were observed to increase with the bias voltage. The large surface area of the Si/SiOx nanoparticle-linked network intensified the radiative recombination centre effect and caused the PL emission enhancement.

  20. Temperature dependence of photoluminescence properties in a thermally activated delayed fluorescence emitter

    SciTech Connect

    Niwa, Akitsugu; Kobayashi, Takashi Nagase, Takashi; Naito, Hiroyoshi; Goushi, Kenichi; Adachi, Chihaya

    2014-05-26

    Using steady-state and time-resolved photoluminescence (PL) spectroscopy, we have investigated the temperature dependence of PL properties of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyano-benzene (4CzIPN), which have a small energy gap between its singlet and triplet excited states and thus exhibits efficient thermally activated delayed fluorescence [H. Uoyama et al., Nature 492, 235 (2012)]. Below around 100 K, PL quantum efficiency of 4CzIPN thin films is largely suppressed and strong photoexcitation intensity dependence appears. These features can be explained by using rate equations for the densities of singlet and triplet excited states considering a triplet-triplet annihilation process.

  1. Photoluminescence of SiO2 nanocomposite films implanted with Si+ and C+ ions

    NASA Astrophysics Data System (ADS)

    Buntov, E. A.; Zatsepin, A. F.; Bokizoda, D. A.

    2016-09-01

    The article is devoted to the photoluminescence (PL) of quantum dots in ion-beam synthesized SiO2:Si, SiO2:C and SiO2:Si:C thin film systems and its sensitization problem. Within the shape of the broad PL spectra for ion-modified films the bands corresponding to silicon and carbon-containing nanoclusters are detected, both with elementary (Si, C) and binary (SiC) composition. Various luminescence decay times of such components point to differences in the nature of the disorder and the local environment of the corresponding luminescence centers. The results indicate the possibility of controlling the spectral composition of the PL by varying the heat treatment conditions, and the dose of ion implantation. Possible ways are proposed for sensitization of the luminescence by means of molecular ions.

  2. Revealing Defect-State Photoluminescence in Monolayer WS2 by Cryogenic Laser Processing.

    PubMed

    He, Zhengyu; Wang, Xiaochen; Xu, Wenshuo; Zhou, Yingqiu; Sheng, Yuewen; Rong, Youmin; Smith, Jason M; Warner, Jamie H

    2016-06-28

    Understanding the stability of monolayer transition metal dichalcogenides in atmospheric conditions has important consequences for their handling, life-span, and utilization in applications. We show that cryogenic photoluminescence spectroscopy (PL) is a highly sensitive technique to the detection of oxidation induced degradation of monolayer tungsten disulfide (WS2) caused by exposure to ambient conditions. Although long-term exposure to atmospheric conditions causes massive degradation from oxidation that is optically visible, short-term exposure produces no obvious changes to the PL or Raman spectra measured at either room temperature or even cryogenic environment. Laser processing was employed to remove the surface adsorbents, which enables the defect states to be detected via cryogenic PL spectroscopy. Thermal cycling to room temperature and back down to 77 K shows the process is reversible. We also monitor the degradation process of WS2 using this method, which shows that the defect related peak can be observed after one month aging in ambient conditions. PMID:27295362

  3. Deep ultraviolet photoluminescence of Tm-doped AlGaN alloys

    SciTech Connect

    Nepal, N.; Zavada, J. M.; Lee, D. S.; Steckl, A. J.; Sedhain, A.; Lin, J. Y.; Jiang, H. X.

    2009-03-16

    The ultraviolet (UV) photoluminescence (PL) properties of Tm-doped Al{sub x}Ga{sub 1-x}N (0.39{<=}x{<=}1) alloys grown by solid-source molecular beam epitaxy were probed using above-bandgap excitation from a laser source at 197 nm. The PL spectra show dominant UV emissions at 298 and 358 nm only for samples with x=1 and 0.81. Temperature dependence of the PL intensities of these emission lines reveals exciton binding energies of 150 and 57 meV, respectively. The quenching of these UV emissions appears related to the thermal activation of the excitons bound to rare-earth structured isovalent (RESI) charge traps, which transfer excitonic energy to Tm{sup 3+} ions resulting in the UV emissions. A model of the RESI trap levels in AlGaN alloys is presented.

  4. Photoluminescence efficiency of BGaN epitaxial layers with high boron content

    NASA Astrophysics Data System (ADS)

    Jurkevičius, J.; Mickevičius, J.; Kadys, A.; Kolenda, M.; Tamulaitis, G.

    2016-07-01

    High-boron-content epitaxial layers of BGaN intended for lattice-matching with AlGaN in UV light emitters were grown on SiC substrate and GaN and AlN templates on sapphire. Photoluminescence (PL) of these layers was studied under quasi-steady-state conditions by varying temperature and excitation intensity. The PL spectra in the samples with different boron content and their dynamics evidence formation of boron-rich regions occupying a small fraction of the total layer volume and acting as the emission killers. The room-temperature PL efficiency of the BGaN epilayers was estimated and shown to drastically decrease at increasing boron content with no significant correlation with either the type of substrate/template or technological conditions of the layer deposition.

  5. The effect of SiO2 on TiO2 up-conversion photoluminescence film

    NASA Astrophysics Data System (ADS)

    Meng, Xiaoqi; Li, Lianqiang; Zou, Kaishun; Liu, Juncheng

    2014-11-01

    In order to increase the photoelectric conversion efficiency of silicon solar cell, the up-conversion film has been tried to enhance the response of the solar cells to the infrared band. Yb3+, Er3+ co-doped SiO2/TiO2 composite films with different Ti/Si molar ratio were deposited on the glass substrate with sol-gel method and spin-coating technique. The effect of different molar ratio of Ti/Si on the film's morphology and optical properties was investigated. The morphology, the absorption spectra and photoluminescence (PL) spectra of the film were tested and analyzed. After the film was annealed at 900 °C, the XRD diffraction pattern indicated that rare earths ions have evenly dispersed into the matrix lattice. The FT-IR showed that Si ions entered into the lattice of titanium dioxide, and the Ti-O-Si bonds came into being. When the film pumped with a laser of 980 nm, there were a dominant red emission and several weak green peaks. In addition, with the increase of the mole ratio of Si/Ti, the intensity of the film's up-conversion luminescence increases at first and then decreases. When the molar ratio of Si/Ti is 1/8, the sample had the highest intensity of up-conversion luminescence.

  6. Simulation of J-aggregate microcavity photoluminescence

    NASA Astrophysics Data System (ADS)

    Michetti, Paolo; La Rocca, Giuseppe C.

    2008-05-01

    We have developed a model in order to account for the photoexcitation dynamics of J-aggregate films and strongly coupled J-aggregate microcavities. The J aggregates are described as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. The correspondence between the photophysics in J-aggregate films and that in J-aggregate microcavities is obtained by introducing a model polariton wave function mixing cavity photon modes and J-aggregate super-radiant excitons. With the same description of the material properties, we have calculated both absorption and luminescence spectra for the J-aggregate film and the photoluminescence of strongly coupled organic microcavities. The model is able to account for the fast relaxation dynamics in organic microcavities following nonresonant pumping and explains the temperature dependence of the ratio between the upper polariton and the lower polariton luminescence.

  7. Systematic safety evaluation on photoluminescent carbon dots

    NASA Astrophysics Data System (ADS)

    Wang, Kan; Gao, Zhongcai; Gao, Guo; Wo, Yan; Wang, Yuxia; Shen, Guangxia; Cui, Daxiang

    2013-03-01

    Photoluminescent carbon dots (C-dots) were prepared using the improved nitric acid oxidation method. The C-dots were characterized by tapping-mode atomic force microscopy, and UV-vis absorption spectroscopy. The C-dots were subjected to systematic safety evaluation via acute toxicity, subacute toxicity, and genotoxicity experiments (including mouse bone marrow micronuclear test and Salmonella typhimurium mutagenicity test). The results showed that the C-dots were successfully prepared with good stability, high dispersibility, and water solubility. At all studied C-dot dosages, no significant toxic effect, i.e., no abnormality or lesion, was observed in the organs of the animals. Therefore, the C-dots are non-toxic to mice under any dose and have potential use in fluorescence imaging in vivo, tumor cell tracking, and others.

  8. Synthesis and photoluminescence of Tb{sup 3+} Activated NaY(WO{sub 4}){sub 2} phosphors

    SciTech Connect

    Liu, Xiaohua; Xiang, Wendou; Chen, Fengming; Zhang, Wei; Hu, Zhengfa

    2012-11-15

    Graphical abstract: The phosphor powders of NaY(WO{sub 4}){sub 2}:Tb{sup 3+} were prepared by solid state reaction. The dependence of luminescence intensity on the Tb{sup 3+} concentration was investigated. Highlights: ► We synthesize NaY(WO{sub 4}){sub 2}:Tb{sup 3+} phosphors by the solid-state reaction technique. ► We observe and explain the blue shifting of excitation peak positions of CTBs. ► The PL from {sup 5}D{sub 3} level become less probable with increasing the Tb{sup 3+} content. ► The PL intensity increases with Tb{sup 3+} content without concentration quenching. ► NaY(WO{sub 4}){sub 2}:Tb{sup 3+} has potential application as a green emitting phosphor in lamps. -- Abstract: The novel yellowish green phosphor powders of NaY(WO{sub 4}){sub 2} doped with Tb{sup 3+} were prepared by solid-state reaction. The powder samples were characterized by X-ray diffraction and photoluminescence. X-ray diffraction analysis showed that the phosphors sintered at 900 °C for 6 h were a pure NaY(WO{sub 4}){sub 2} phase for all the Tb{sup 3+} doping concentrations. The room temperature excitation spectra vary with the Tb{sup 3+} concentration and consist of an intense charge transfer band of WO{sub 4}{sup 2−} group and weak intra-4f{sup 8} transition absorption peaks of Tb{sup 3+} ions. The photoluminescence spectra, excited at the peak wavelengths of charge transfer bands, consist of the characteristic Tb{sup 3+} emission transitions from {sup 5}D{sub 3} and {sup 5}D{sub 4} excited levels to {sup 7}F{sub J} (J = 3–6) levels. The dependence of luminescence intensity on the Tb{sup 3+} concentration in NaY(WO{sub 4}){sub 2}:Tb phosphors was investigated.

  9. Photoluminescence enhancement of carbon dots by gold nanoparticles conjugated via PAMAM dendrimers

    NASA Astrophysics Data System (ADS)

    Zong, Jie; Yang, Xiaoling; Trinchi, Adrian; Hardin, Simon; Cole, Ivan; Zhu, Yihua; Li, Chunzhong; Muster, Tim; Wei, Gang

    2013-10-01

    Carbon dots (CDs) have many fascinating fluorescent properties, however, their low quantum yield limits their applications. In this study, the photoluminescence (PL) of CDs in the vicinity of gold nanoparticles (Au NPs) is enhanced significantly due to the surface plasmon resonance (SPR) of the Au NPs. This is achieved by conjugating Au NPs and CDs to dendrimers (PAMAM) through an amidation reaction, resulting in the formation of the Au-PAMAM-CD conjugates. The maximum 62-fold enhancement was obtained with an optimized molar ratio between Au NPs, PAMAM, and CDs. In this process, PAMAM, which serves as a spacer, can keep Au NPs and CDs at an appropriate distance for PL enhancement. The adjustment of the amount of Au NPs or CDs linked to PAMAM can induce the optimum PL enhancement. This strategy can be easily applied to different metal-space-fluorophore systems to enhance the fluorescence of fluorophores.Carbon dots (CDs) have many fascinating fluorescent properties, however, their low quantum yield limits their applications. In this study, the photoluminescence (PL) of CDs in the vicinity of gold nanoparticles (Au NPs) is enhanced significantly due to the surface plasmon resonance (SPR) of the Au NPs. This is achieved by conjugating Au NPs and CDs to dendrimers (PAMAM) through an amidation reaction, resulting in the formation of the Au-PAMAM-CD conjugates. The maximum 62-fold enhancement was obtained with an optimized molar ratio between Au NPs, PAMAM, and CDs. In this process, PAMAM, which serves as a spacer, can keep Au NPs and CDs at an appropriate distance for PL enhancement. The adjustment of the amount of Au NPs or CDs linked to PAMAM can induce the optimum PL enhancement. This strategy can be easily applied to different metal-space-fluorophore systems to enhance the fluorescence of fluorophores. Electronic supplementary information (ESI) available: Estimate of the density of CDs, calculation of the amount of Au, PAMAM, and CDs. See DOI: 10.1039/c3nr02527f

  10. Effects of thickness layer on the photoluminescence properties of InAlAs/GaAlAs quantum dots

    NASA Astrophysics Data System (ADS)

    Daly, A. Ben; Bernardot, F.; Barisien, T.; Galopin, E.; Lemaître, A.; Maaref, M. A.; Testelin, C.

    2016-09-01

    We investigated the effect of InAlAs layer thickness on exciton-spin relaxation and optical properties of In0.62Al0.38As/Al0.67Ga0.33As QDs. The luminescence properties and carrier dynamics of QDs were studied by the temperature-dependent photoluminescence (PL) and pump-probe measurements. As the total amount of deposited In0.62Al0.38As alloy increased, the central position of the low-energy PL signal decreases, while its full width at half maximum (FWHM) increases. A monotonous redshift of the PL peak was observed with increasing temperature due to the electron-phonon scattering. From the pump-probe measurement, the spin relaxation time decreases with the monolayers at higher temperatures, in agreement with the phonon energy determinate by PL measurements.

  11. Charge separation in subcells of triple-junction solar cells revealed by time-resolved photoluminescence spectroscopy.

    PubMed

    Tex, David M; Imaizumi, Mitsuru; Kanemitsu, Yoshihiko

    2015-11-30

    We measure the excitation-wavelength and power dependence of time-resolved photoluminescence (PL) from the top InGaP subcell in a InGaP/GaAs/Ge triple-junction solar cell. The wavelength-dependent data reveals that the PL decays are governed by charge separation. A fast single-exponential PL decay is observed at low excitation power densities, which is the charge separation under short-circuit condition. Under strong excitation a bi-exponential PL decay is observed. Its slow component appears at early times, followed by a faster component at late times. The slow decay is the carrier recombination of the subcell. The following fast component is the charge separation process under reduced built-in potential near the operating point. The subcells electrical conversion efficiency close to the operating point is evaluated using this decay time constant.

  12. Temperature-dependent photoluminescence emission and Raman scattering from Mo1-x W x S2 monolayers

    NASA Astrophysics Data System (ADS)

    Chen, Yanfeng; Wen, Wen; Zhu, Yiming; Mao, Nannan; Feng, Qingliang; Zhang, Mei; Hsu, Hung-Pin; Zhang, Jin; Huang, Ying-Sheng; Xie, Liming

    2016-11-01

    2D transition metal dichalcogenide (TMD) alloys with tunable band gaps have recently gained wide interest due to their potential applications in future nanoelectronics and optoelectronics. Here, we report the temperature-dependent photoluminescence (PL) and Raman spectra of Mo1-x W x S2 monolayers with W composition x = 0, 0.29, 0.53, 0.66 and 1 in the temperature range 93-493 K. We observed a linear temperature dependence of PL emission energy and Raman frequency. The PL intensity is enhanced at high temperature (>393 K). The temperature coefficients are negative for both PL and Raman bands, which may result from anharmonicity, thermal expansion and composition disorder.

  13. Temperature-dependent photoluminescence emission and Raman scattering from Mo1-x W x S2 monolayers.

    PubMed

    Chen, Yanfeng; Wen, Wen; Zhu, Yiming; Mao, Nannan; Feng, Qingliang; Zhang, Mei; Hsu, Hung-Pin; Zhang, Jin; Huang, Ying-Sheng; Xie, Liming

    2016-11-01

    2D transition metal dichalcogenide (TMD) alloys with tunable band gaps have recently gained wide interest due to their potential applications in future nanoelectronics and optoelectronics. Here, we report the temperature-dependent photoluminescence (PL) and Raman spectra of Mo1-x W x S2 monolayers with W composition x = 0, 0.29, 0.53, 0.66 and 1 in the temperature range 93-493 K. We observed a linear temperature dependence of PL emission energy and Raman frequency. The PL intensity is enhanced at high temperature (>393 K). The temperature coefficients are negative for both PL and Raman bands, which may result from anharmonicity, thermal expansion and composition disorder. PMID:27670929

  14. Distinct photoluminescence and Raman spectroscopy signatures for identifying highly crystalline WS2 monolayers produced by different growth methods

    DOE PAGES

    McCreary, Amber; Berkdemir, Ayse; Wang, Junjie; Nguyen, Minh An; Elías, Ana Laura; Perea-López, Néstor; Fujisawa, Kazunori; Kabius, Bernd; Carozo, Victor; Cullen, David A.; et al

    2016-03-08

    We report that transition metal dichalcogenides (TMDs) such as WS2 show exciting promise in electronic and optoelectronic applications. Significant variations in the transport, Raman, and photoluminescence (PL) can be found in the literature, yet it is rarely addressed why this is. In this report, Raman and PL of monolayered WS2 produced via different methods are studied and distinct features that indicate the degree of crystallinity of the material are observed. While the intensity of the LA(M) Raman mode is found to be a useful indicator to assess the crystallinity, PL is drastically more sensitive to the quality of the materialmore » than Raman spectroscopy. We also show that even exfoliated crystals, which are usually regarded as the most pristine material, can contain large amounts of defects that would not be apparent without Raman and PL measurements. Ultimately, these findings can be applied to the understanding of other two-dimensional heterostructured systems.« less

  15. Strain effect of cellulose-wrapped single-walled carbon nanotubes measured by photoluminescence and Raman scattering spectroscopy

    NASA Astrophysics Data System (ADS)

    Ito, Masahiro; Yajima, Hirofumi; Homma, Yoshikazu

    2016-07-01

    The photoluminescence (PL) of single-walled carbon nanotubes (SWNTs) can be obtained even under the dry condition when SWNTs are dispersed in biochemical polymers. We fabricated transparent films composed of SWNTs and a large amount of carboxymethyl cellulose (CMC), and evaluated the effects of CMC wrapping on PL properties. The PL peaks from the transparent CMC-SWNT film showed SWNT-type-dependent peak shifts, indicating that SWNTs were under uniaxial compression strain in the CMC film. Raman scattering spectra also suggested uniaxial compression strain. The rate of strain was estimated to be 0.3-0.4% by PL and Raman scattering spectroscopies. Furthermore, the release of strain was demonstrated by stretching the CMC film.

  16. Strain effect of cellulose-wrapped single-walled carbon nanotubes measured by photoluminescence and Raman scattering spectroscopy

    NASA Astrophysics Data System (ADS)

    Ito, Masahiro; Yajima, Hirofumi; Homma, Yoshikazu

    2016-07-01

    The photoluminescence (PL) of single-walled carbon nanotubes (SWNTs) can be obtained even under the dry condition when SWNTs are dispersed in biochemical polymers. We fabricated transparent films composed of SWNTs and a large amount of carboxymethyl cellulose (CMC), and evaluated the effects of CMC wrapping on PL properties. The PL peaks from the transparent CMC–SWNT film showed SWNT-type-dependent peak shifts, indicating that SWNTs were under uniaxial compression strain in the CMC film. Raman scattering spectra also suggested uniaxial compression strain. The rate of strain was estimated to be 0.3–0.4% by PL and Raman scattering spectroscopies. Furthermore, the release of strain was demonstrated by stretching the CMC film.

  17. Photoluminescence studies of polycrystalline Cu(In,Ga)Se{sub 2}: Lateral inhomogeneities beyond Abbe's diffraction limit

    SciTech Connect

    Neumann, Oliver; Brüggemann, Rudolf Bauer, Gottfried H.; Hariskos, Dimitrios; Witte, Wolfram

    2015-11-14

    We analyze Cu(In,Ga)Se{sub 2} absorbers with a scanning near-field optical microscope (SNOM) by photoluminescence (PL). Such measurements allow one to extract local fluctuations of the integral PL yield, the quasi-Fermi level splitting, and the material composition in the submicron range. However, the experimental findings depend strongly on the surface roughness of the absorber: If the surface is rough, artifact-prone correlations between surface contour and PL features measured by SNOM can be found that complicate the study of recombination effects. For smooth surfaces, such correlations no longer exist and the influence of grain boundaries on the integral PL yield and the quasi-Fermi level splitting is revealed. The method also allows a detailed determination of the local band gaps in neighboring grains and their spatial variation inside, and thus of possibly local changes in chemical composition of different grains.

  18. Photoluminescence related to the 2-dimensional electron gas in modulation doped GaN/AlGaN structures

    SciTech Connect

    Bergman, J.P.; Lundstroem, T.; Monemar, B.; Amano, H.; Akasaki, I.

    1996-11-01

    The authors report low temperature photoluminescence (PL) spectra related to a two-dimensional electron gas confined at a GaN/AlGaN heterointerface. The recombination between electrons confined in the bottom of the interface potential and photoexcited holes causes a broad PL emission about 50 meV below the bulk GaN exciton emission. A second emission, attributed to the recombination of electrons in the first excited level at the interface, is also observed close to the excitonic band gap in GaN. The data agrees with a self consistent calculation of the energy levels and the electron concentration at the interface. Similar PL data from a modulation doped AlGaN/GaN quantum well exhibit three PL emissions related to the 2D electron gas.

  19. The photoluminescence and structural properties of (Ce, Yb) co-doped silicon oxides after high temperature annealing

    SciTech Connect

    Heng, C. L. Li, J. T.; Su, W. Y.; Yin, P. G.; Finstad, T. G.

    2015-01-28

    We studied the photoluminescence (PL) and structural properties of Ce and Yb co-doped silicon oxide films after high temperature annealing. The PL spectra of Ce{sup 3+} and Yb{sup 3+} ions were sensitive to the structural variation of the films, and the Yb PL intensities were significantly enhanced especially upon 1200 °C annealing. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, indicated that rare earth silicates and the CeO{sub 2} phase had formed in the oxides. The proportions of the phases varied with the “nominal Si-richness” of the films. Energy transfer from the excited Ce{sup 3+} to Yb{sup 3+} can be inferred from both PL excitation and decay spectra.

  20. Temperature-dependent photoluminescence emission and Raman scattering from Mo1-x W x S2 monolayers.

    PubMed

    Chen, Yanfeng; Wen, Wen; Zhu, Yiming; Mao, Nannan; Feng, Qingliang; Zhang, Mei; Hsu, Hung-Pin; Zhang, Jin; Huang, Ying-Sheng; Xie, Liming

    2016-11-01

    2D transition metal dichalcogenide (TMD) alloys with tunable band gaps have recently gained wide interest due to their potential applications in future nanoelectronics and optoelectronics. Here, we report the temperature-dependent photoluminescence (PL) and Raman spectra of Mo1-x W x S2 monolayers with W composition x = 0, 0.29, 0.53, 0.66 and 1 in the temperature range 93-493 K. We observed a linear temperature dependence of PL emission energy and Raman frequency. The PL intensity is enhanced at high temperature (>393 K). The temperature coefficients are negative for both PL and Raman bands, which may result from anharmonicity, thermal expansion and composition disorder.

  1. Electric Field Modulation of Semiconductor Quantum Dot Photoluminescence: Insights Into the Design of Robust Voltage-Sensitive Cellular Imaging Probes.

    PubMed

    Rowland, Clare E; Susumu, Kimihiro; Stewart, Michael H; Oh, Eunkeu; Mäkinen, Antti J; O'Shaughnessy, Thomas J; Kushto, Gary; Wolak, Mason A; Erickson, Jeffrey S; Efros, Alexander L; Huston, Alan L; Delehanty, James B

    2015-10-14

    The intrinsic properties of quantum dots (QDs) and the growing ability to interface them controllably with living cells has far-reaching potential applications in probing cellular processes such as membrane action potential. We demonstrate that an electric field typical of those found in neuronal membranes results in suppression of the QD photoluminescence (PL) and, for the first time, that QD PL is able to track the action potential profile of a firing neuron with millisecond time resolution. This effect is shown to be connected with electric-field-driven QD ionization and consequent QD PL quenching, in contradiction with conventional wisdom that suppression of the QD PL is attributable to the quantum confined Stark effect.

  2. Thermoluminescence and photoluminescence studies on γ-ray-irradiated Ce³⁺,Tb³⁺-doped potassium chloride single crystals.

    PubMed

    Bangaru, S; Saradha, K; Muralidharan, G

    2016-05-01

    Single crystals of KCl doped with Ce(3+),Tb(3+) were grown using the Bridgeman-Stockbarger technique. Thermoluminescence (TL), optical absorption, photoluminescence (PL), photo-stimulated luminescence (PSL), and thermal-stimulated luminescence (TSL) properties were studied after γ-ray irradiation at room temperature. The glow curve of the γ-ray-irradiated crystal exhibits three peaks at 420, 470 and 525 K. F-Light bleaching (560 nm) leads to a drastic change in the TL glow curve. The optical absorption measurements indicate that F- and V-centres are formed in the crystal during γ-ray irradiation. It was attempted to incorporate a broad band of cerium activator into the narrow band of terbium in the KCl host without a reduction in the emission intensity. Cerium co-doped KCl:Tb crystals showed broad band emission due to the d-f transition of cerium and a reduction in the intensity of the emission peak due to (5)D3 -(7)F(j) (j = 3, 4) transition of terbium, when excited at 330 nm. These results support that energy transfer occurs from cerium to terbium in the KCl host. Co-doping Ce(3+) ions greatly intensified the excitation peak at 339 nm for the emission at 400 nm of Tb(3+). The emission due to Tb(3+) ions was confirmed by PSL and TSL spectra. PMID:26381612

  3. Thermoluminescence and photoluminescence studies on γ-ray-irradiated Ce³⁺,Tb³⁺-doped potassium chloride single crystals.

    PubMed

    Bangaru, S; Saradha, K; Muralidharan, G

    2016-05-01

    Single crystals of KCl doped with Ce(3+),Tb(3+) were grown using the Bridgeman-Stockbarger technique. Thermoluminescence (TL), optical absorption, photoluminescence (PL), photo-stimulated luminescence (PSL), and thermal-stimulated luminescence (TSL) properties were studied after γ-ray irradiation at room temperature. The glow curve of the γ-ray-irradiated crystal exhibits three peaks at 420, 470 and 525 K. F-Light bleaching (560 nm) leads to a drastic change in the TL glow curve. The optical absorption measurements indicate that F- and V-centres are formed in the crystal during γ-ray irradiation. It was attempted to incorporate a broad band of cerium activator into the narrow band of terbium in the KCl host without a reduction in the emission intensity. Cerium co-doped KCl:Tb crystals showed broad band emission due to the d-f transition of cerium and a reduction in the intensity of the emission peak due to (5)D3 -(7)F(j) (j = 3, 4) transition of terbium, when excited at 330 nm. These results support that energy transfer occurs from cerium to terbium in the KCl host. Co-doping Ce(3+) ions greatly intensified the excitation peak at 339 nm for the emission at 400 nm of Tb(3+). The emission due to Tb(3+) ions was confirmed by PSL and TSL spectra.

  4. Rapid thermal annealing and modulation-doping effects on InAs/GaAs quantum dots photoluminescence dependence on excitation power

    NASA Astrophysics Data System (ADS)

    Chaâbani, W.; Melliti, A.; Maaref, M. A.; Testelin, C.; Lemaître, A.

    2016-07-01

    The optical properties of p-doped and annealed InAs/GaAs quantum dots (QDs) was investigated by photoluminescence (PL) as a function of temperature and excitation power density (Pexc). At low-T, PL spectra of rapid thermal annealing (RTA) and p-modulation doped QDs show an energy blueshift and redshift, respectively. A superlinear dependence of integrated PL intensity on Pexc at high-T was found only for undoped QD. The superlinearity was suppressed by modulation-doping and RTA effects. A linear dependence of IPL at all temperatures and a decrease of the carrier-carrier Coulomb interaction at high-T was found after RTA.

  5. Carrier redistribution between different potential sites in semipolar (202{sup ¯}1) InGaN quantum wells studied by near-field photoluminescence

    SciTech Connect

    Marcinkevičius, S.; Gelžinytė, K.; Zhao, Y.; Nakamura, S.; DenBaars, S. P.; Speck, J. S.

    2014-09-15

    Scanning near-field photoluminescence (PL) spectroscopy at different excitation powers was applied to study nanoscale properties of carrier localization and recombination in semipolar (202{sup ¯}1) InGaN quantum wells (QWs) emitting in violet, blue, and green-yellow spectral regions. With increased excitation power, an untypical PL peak energy shift to lower energies was observed. The shift was attributed to carrier density dependent carrier redistribution between nm-scale sites of different potentials. Near-field PL scans showed that in (202{sup ¯}1) QWs the in-plane carrier diffusion is modest, and the recombination properties are uniform, which is advantageous for photonic applications.

  6. Thermally enhanced photoluminescence for heat harvesting in photovoltaics

    PubMed Central

    Manor, Assaf; Kruger, Nimrod; Sabapathy, Tamilarasan; Rotschild, Carmel

    2016-01-01

    The maximal Shockley–Queisser efficiency limit of 41% for single-junction photovoltaics is primarily caused by heat dissipation following energetic-photon absorption. Solar-thermophotovoltaics concepts attempt to harvest this heat loss, but the required high temperatures (T>2,000 K) hinder device realization. Conversely, we have recently demonstrated how thermally enhanced photoluminescence is an efficient optical heat-pump that operates in comparably low temperatures. Here we theoretically and experimentally demonstrate such a thermally enhanced photoluminescence based solar-energy converter. Here heat is harvested by a low bandgap photoluminescent absorber that emits thermally enhanced photoluminescence towards a higher bandgap photovoltaic cell, resulting in a maximum theoretical efficiency of 70% at a temperature of 1,140 K. We experimentally demonstrate the key feature of sub-bandgap photon thermal upconversion with an efficiency of 1.4% at only 600 K. Experiments on white light excitation of a tailored Cr:Nd:Yb glass absorber suggest that conversion efficiencies as high as 48% at 1,500 K are in reach. PMID:27762271

  7. Impurity mediated large three photon absorption in ZnS:Cu nanophosphors

    NASA Astrophysics Data System (ADS)

    Sreeja, R.; Sridharan, Kishore; Philip, Reji; Jayaraj, M. K.

    2014-03-01

    Copper doped ZnS nanophosphors with the cubic zinc blende (Sphalerite) structure have been prepared through the wet chemical route in aqueous media. The ZnS:Cu nanoparticles display a widening in the band gap with increase in Cu dopant concentration. The observed green photoluminescence (PL) in ZnS:Cu originates from the transition between the conduction band and the copper acceptor levels. The open aperture Z-scan traces of the ZnS:Cu nanoparticles embedded in PVA matrix, excited at 800 nm using 100 fs laser pulses, show an optical limiting type nonlinearity which is attributed to three photon absorption. An increase in the value of the three photon absorption coefficient is observed with increase in the Cu doping concentration. The increase in the density of intermediate defect levels plays a significant role in the enhancement of three photon absorption in Cu doped ZnS. These studies reveal that Cu doped ZnS nanoparticles in polymer matrices are potential candidates for ultra fast optical limiting applications.

  8. Studying of photoluminescence characteristics of CdTe/ZnS QDs manipulated by TiO2 inverse opal photonic crystals

    NASA Astrophysics Data System (ADS)

    Chi, Xiao-Chun; Yang, Ying-Shu; Wang, Ying-Hui; Gao, Jie-Chao; Sui, Ning; Yang, Hai-Gui; Zou, Lu; Kang, Zhi-Hui; Zhang, Han-Zhuang

    2015-08-01

    The photoluminescence (PL) characteristics of CdTe/ZnS quantum dots (QDs) infiltrated in TiO2 inverse opal photonic crystals (PCs) are studied in detail. The PL dynamics of QDs show that the PCs could accelerate the PL relaxation rate of QDs as the PL peak of QDs is overlapped with the photonic stop band of PCs. Besides, the PCs could decrease the activation energy of QDs due to its porous structure and suppress the exciton annihilation process of QDs at high excitation intensity, owing to the light scattering effect. The final results are beneficial for people in further understanding the role of inverse opal PCs on manipulating the PL characteristics of QDs.

  9. Absolute Photoluminescence Quantum Yields of IR-26 Dye, PbS, and PbSe Quantum Dots

    SciTech Connect

    Semonin, Octavi Escala; Johnson, Justin C; Luther, Joseph M; Midgett, Aaron G; Nozik, Arthur J; Beard, Matthew C

    2010-08-19

    In this study, we have directly measured the photoluminescence quantum yield (Φ{sub PL}) of IR-26 at a range of concentrations and the Φ{sub PL} of PbS and PbSe QDs for a range of sizes. We find that the Φ{sub PL} of IR-26 has a weak concentration dependence due to reabsorption, with a Φ{sub PL} of 0.048 ± 0.002% for low concentrations, lower than previous reports by a full order of magnitude. We also find that there is a dramatic size dependence for both PbS and PbSe QDs, with the smallest dots exhibiting a Φ{sub PL} in excess of 60%, while larger dots fall below 3%. A model, including nonradiative transition between electronic states and energy transfer to ligand vibrations, appears to explain this size dependence. These findings provide both a better characterization of photoluminescence for near-infrared emitters and some insight into how improved QDs can be developed.

  10. Caution for monitoring the surface modification of dually emitted ZnSe quantum dots by time-resolved photoluminescence

    NASA Astrophysics Data System (ADS)

    Wang, Chunlei; Hu, Zhiyang; Xu, Shuhong; Zhou, Shujie; Wang, Zhuyuan; Cui, Yiping

    2015-03-01

    This work wants to give a caution for monitoring the surface modification of dually emitted ZnSe quantum dots (QDs) by using time-resolved photoluminescence (PL). Aqueous ZnSe QDs have two emission bands: namely ZnSe band gap emission centered at 395 nm and ZnSe trap emission centered at 470 nm. By fitting the measured PL spectra by two peaks, serious overlapping of two emission bands can be found in the range of 360-430 nm. As a result, the measured PL lifetimes at 395 nm (the peak position of ZnSe band gap emission) is just an apparent value, composing of both ZnSe band emission (contribution proportion about 80%) and ZnSe trap emission (contribution proportion about 20%). Due to the much smaller PL lifetime of ZnSe band gap emission (less than 20 ns) than that of ZnSe trap emission (about 50-70 ns), the elevated contribution proportion of ZnSe band gap emission at improved QD surface modification will lead to the decreased average PL lifetime at 395 nm. This result is completely opposite to the traditional result where improved QD surface modification leads to increased PL lifetimes on the basis of single emitted QDs. Hence, when time-resolved PL is used for monitoring the surface modification of dually emitted QDs, the emission bands overlapping should be taken into consideration with caution.

  11. Photoluminescence and Cathodoluminescence Characterization of Ge/GeO2 Nanostructure Synthesized by Thermal Evaporation of Ge Powder

    NASA Astrophysics Data System (ADS)

    Pham, V. H.; Trung, D. Q.; Kien, N. D. T.; Tam, P. D.; Huy, P. T.

    2016-09-01

    This paper reports the first attempt to characterize the light-emission from Ge/GeO2 nanostructure synthesized by thermal evaporation. The synthesized Ge/GeO2 was observed to have a nanowire structure. Photoluminescence (PL) results show that the emission center of the PL peak at about 410 and 485 nm depends on the excitation wavelength. Experimental XRD, EDS and spectral analyses suggest that the 410 nm emission can be attributed to the Ge core; however, 485 nm is attributed to the GeO2 sheath.

  12. Interfacial refractive index sensing using visible-excited intrinsic zinc oxide photoluminescence coupled to whispering gallery modes

    NASA Astrophysics Data System (ADS)

    Moirangthem, Rakesh Singh; Erbe, Andreas

    2013-07-01

    Whispering gallery modes (WGMs) excited by the intrinsic photoluminescence (PL) in zinc oxide microspherical resonators are investigated in this work. The microspheres were synthesized via a one-pot hydrothermal technique. A polymer was applied after the synthesis to fill remaining pores in the oxide particle. Defect-related ZnO PL was excited in the visible, coupling to WGMs. The observed WGMs red-shift with increasing refractive index of the surrounding medium with a sensitivity of 90-100 nm/refractive index unit. The spherical microresonators may be used to investigate binding to and structure at the particle/solution interface.

  13. Analysis of oxyluciferin photoluminescence pathways in aqueous solutions.

    PubMed

    Hiyama, Miyabi; Mochizuki, Toshimitsu; Akiyama, Hidefumi; Koga, Nobuaki

    2015-01-01

    We evaluated the pK(a) values of oxyluciferin and its conjugate acids and bases theoretically with the help of experimental correction values, from which free energies for the first excited and the ground states of all the species were estimated. On the basis of these results, we calculated pH-dependent absorption spectra, where the relative absorption intensities of various species strongly depend on photoexcitation energy, and we further analyzed the photoluminescence pathways of oxyluciferin in aqueous solutions with various pH. In the case of 350 nm photoexcitation, in particular, experiments have shown that dominant emission color is green and it attenuates with pH decreasing, while blue (3 < pH < 8) and red (pH < 3) emissions appear. Our present results clarify the pathways of these photoluminescence depending on the pH values and thus should be useful in further analyses of photoluminescence pathways for other photoexcitation wavelength in comparison with experiments. PMID:25334091

  14. Enhanced Organo-Metal Halide Perovskite Photoluminescence from Nanosized Defect-Free Crystallites and Emitting Sites.

    PubMed

    Tian, Yuxi; Merdasa, Aboma; Unger, Eva; Abdellah, Mohamed; Zheng, Kaibo; McKibbin, Sarah; Mikkelsen, Anders; Pullerits, Tõnu; Yartsev, Arkady; Sundström, Villy; Scheblykin, Ivan G

    2015-10-15

    Photoluminescence (PL) of organo-metal halide perovskite semiconductors can be enhanced by several orders of magnitude by exposure to visible light. We applied PL microscopy and super-resolution optical imaging to investigate this phenomenon with spatial resolution better than 10 nm using films of CH3NH3PbI3 prepared by the equimolar solution-deposition method, resulting in crystals of different sizes. We found that PL of ∼100 nm crystals enhances much faster than that of larger, micrometer-sized ones. This crystal-size dependence of the photochemical light passivation of charge traps responsible for PL quenching allowed us to conclude that traps are present in the entire crystal volume rather than at the surface only. Because of this effect, "dark" micrometer-sized perovskite crystals can be converted into highly luminescent smaller ones just by mechanical grinding. Super-resolution optical imaging shows spatial inhomogeneity of the PL intensity within perovskite crystals and the existence of <100 nm-sized localized emitting sites. The possible origin of these sites is discussed. PMID:26722793

  15. Photoluminescence characteristics of polariton condensation in a CuBr microcavity

    SciTech Connect

    Nakayama, Masaaki Murakami, Katsuya; Furukawa, Yoshiaki; Kim, DaeGwi

    2014-07-14

    We have investigated the photoluminescence (PL) properties of a CuBr microcavity at 10 K, including the temporal profiles, from the viewpoint of cavity-polariton condensation. The excitation energy density dependence of the PL intensity (band width) of the lower polariton branch at an in-plane wave vector of k{sub //} = 0 exhibits a threshold-like increase (decrease). A large blueshift in the PL energy of ∼10 meV caused by the cavity-polariton renormalization is correlated with the excitation energy density dependence of the PL intensity. The estimated density of photogenerated electron-hole pairs at the threshold is two orders lower than the Mott transition density. These results consistently demonstrate the occurrence of cavity-polariton condensation. In addition, we found that the PL rise and decay times are shortened dramatically by the cavity-polariton condensation, which reflects the bosonic final state stimulation in the relaxation process and the intrinsic cavity-polariton lifetime in the decay process.

  16. Studies of low temperature photoluminescence spectra and excitonic valley polarization in monolayer MoTe2

    NASA Astrophysics Data System (ADS)

    Koirala, Sandhaya; Mouri, Shinichiro; Miyauchi, Yuhei; Matsuda, Kazunari; Kyoto University Team

    Recently, atomically thin layered transition-metal dichalcogenide (TMDs) in the form MX2 (M = Mo, W, X = S, Se, Te) have attracted much interest from the viewpoints of their fundamental physics and potential applications. The characteristic optical features of semiconducting TMDs arise from excitons confined in their atomically thin layers. Molybdenum ditelluride MoTe2 has attracted emerging research interest because of optical gap energy (lowest exciton transition) of 1.09 eV, and large spin-orbit coupling of 250 meV. Temperature-dependent photoluminescence (PL) and polarization-resolved PL measurement were performed for mechanically exfoliated monolayer MoTe2 from 4.4 to 300 K. At a low temperature, the PL spectra from MoTe2 show two sharp peaks for excitons and charged excitons (trions). The systematic temperature-dependent PL measurements revel that the homogeneous linewidth of the exciton peak broadens linearly as the temperature increased due to exciton-acoustic-phonon interactions. From polarization-resolved PL measurements, the valley polarization of above 40 % in the exciton state has been observed at low temperatures. In this meeting, we will discuss about exciton dephasing and valley polarization in monolayer MoTe2.

  17. Laser-induced Greenish-Blue Photoluminescence of Mesoporous Silicon Nanowires

    NASA Astrophysics Data System (ADS)

    Choi, Yan-Ru; Zheng, Minrui; Bai, Fan; Liu, Junjun; Tok, Eng-Soon; Huang, Zhifeng; Sow, Chorng-Haur

    2014-05-01

    Solid silicon nanowires and their luminescent properties have been widely studied, but lesser is known about the optical properties of mesoporous silicon nanowires (mp-SiNWs). In this work, we present a facile method to generate greenish-blue photoluminescence (GB-PL) by fast scanning a focused green laser beam (wavelength of 532 nm) on a close-packed array of mp-SiNWs to carry out photo-induced chemical modification. The threshold of laser power is 5 mW to excite the GB-PL, whose intensity increases with laser power in the range of 5-105 mW. The quenching of GB-PL comes to occur beyond 105 mW. The in-vacuum annealing effectively excites the GB-PL in the pristine mp-SiNWs and enhances the GB-PL of the laser-modified mp-SiNWs. A complex model of the laser-induced surface modification is proposed to account for the laser-power and post-annealing effect. Moreover, the fast scanning of focused laser beam enables us to locally tailor mp-SiNWs en route to a wide variety of micropatterns with different optical functionality, and we demonstrate the feasibility in the application of creating hidden images.

  18. CLASSICAL AREAS OF PHENOMENOLOGY: Photoluminescence evolution in self-ion-implanted and annealed silicon

    NASA Astrophysics Data System (ADS)

    Yang, Yu; Wang, Chong; Yang, Rui-Dong; Li, Liang; Xiong, Fei; Bao, Ji-Ming

    2009-11-01

    Si+ ion-implanted silicon wafers are annealed at different temperatures from room temperature to 950 °C and then characterized by using the photoluminescence (PL) technique at different recorded temperatures (RETs). Plentiful optical features are observed and identified clearly in these PL curves. The PL spectra of these samples annealed in different temperature ranges are correspondingly dominated by different emission peaks. Several characteristic features, such as an R line, S bands, a W line, the phonon-assistant WTA and SiTO peaks, can be detected in the PL spectra of samples annealed at different temperatures. For the samples annealed at 800 °C, emission peaks from the dislocations bounded at the deep energy levels of the forbidden band, such as D1 and D2 bands, can be observed at a temperature as high as 280 K. These data strongly indicate that a severe transformation of defect structures could be manipulated by the annealing and recorded temperatures. The deactivation energies of the main optical features are extracted from the PL data at different temperatures.

  19. Photoluminescence of gallium ion irradiated hexagonal and cubic GaN quantum dots

    NASA Astrophysics Data System (ADS)

    Rothfuchs, Charlotte; Kukharchyk, Nadezhda; Koppe, Tristan; Semond, Fabrice; Blumenthal, Sarah; Becker, Hans-Werner; As, Donat J.; Hofsäss, Hans C.; Wieck, Andreas D.; Ludwig, Arne

    2016-09-01

    We report on ion implantation into GaN QDs and investigate their radiation hardness. The experimental study is carried out by photoluminescence (PL) measurements on molecular beam epitaxy-grown GaN quantum dots after ion implantation. Both quantum dots grown in the hexagonal (H) and the cubic (C) crystal structure were subjected to gallium ions with an energy of 400 kV (H) and 75 kV (C) with fluences ranging from 5 ×1010 cm-2 to 1 ×1014 cm-2 (H) and to 1 ×1015 cm-2 (C), respectively. Low-temperature PL measurements reveal a PL quenching for which a quantitative model as a function of the ion fluence is developed. A high degradation resistance is concluded. A non-radiative trap with one main activation energy is found for all QD structures by temperature-dependent PL measurements. Further analysis of fluence-dependent PL energy shifts shows ion-induced intermixing and strain effects. Particular for the hexagonal quantum dots, a strong influence of the quantum confined Stark effect is present.

  20. Influence of C or In buffer layer on photoluminescence behaviour of ultrathin ZnO film

    NASA Astrophysics Data System (ADS)

    Saravanan, K.; Jayalakshmi, G.; Krishnan, R.; Sundaravel, B.; Panigrahi, B. K.

    2016-09-01

    We study the effect of the indium or carbon buffer layer on the photoluminescence (PL) property of ZnO ultrathin films deposited on a Si(100) substrate. The surface morphology of the films obtained using scanning tunnelling microscopy shows spherical shaped ZnO nanoparticles of size ˜8 nm in ZnO/C/Si and ˜22 nm in ZnO/Si samples, while the ZnO/In/Si sample shows elliptical shaped ZnO particles. Further, the ZnO/C/Si sample shows densely packed ZnO nanoparticles in comparison with other samples. Strong band edge emission has been observed in the presence of In or C buffer layer, whereas the ZnO/Si sample exhibits poor PL emission. The influence of C and In buffer layers on the PL behaviour of ZnO films is studied in detail using temperature dependent PL measurements in the range of 4 K-300 K. The ZnO/C/Si sample exhibits a multi-fold enhancement in the PL emission intensity with well-resolved free and bound exciton emission lines. Our experimental results imply that the ZnO films deposited on the C buffer layer showed higher particle density and better exciton emission desired for optoelectronic applications.

  1. Laser-induced greenish-blue photoluminescence of mesoporous silicon nanowires.

    PubMed

    Choi, Yan-Ru; Zheng, Minrui; Bai, Fan; Liu, Junjun; Tok, Eng-Soon; Huang, Zhifeng; Sow, Chorng-Haur

    2014-05-13

    Solid silicon nanowires and their luminescent properties have been widely studied, but lesser is known about the optical properties of mesoporous silicon nanowires (mp-SiNWs). In this work, we present a facile method to generate greenish-blue photoluminescence (GB-PL) by fast scanning a focused green laser beam (wavelength of 532 nm) on a close-packed array of mp-SiNWs to carry out photo-induced chemical modification. The threshold of laser power is 5 mW to excite the GB-PL, whose intensity increases with laser power in the range of 5-105 mW. The quenching of GB-PL comes to occur beyond 105 mW. The in-vacuum annealing effectively excites the GB-PL in the pristine mp-SiNWs and enhances the GB-PL of the laser-modified mp-SiNWs. A complex model of the laser-induced surface modification is proposed to account for the laser-power and post-annealing effect. Moreover, the fast scanning of focused laser beam enables us to locally tailor mp-SiNWs en route to a wide variety of micropatterns with different optical functionality, and we demonstrate the feasibility in the application of creating hidden images.

  2. Redox-mediated reversible modulation of the photoluminescence of single quantum dots

    NASA Astrophysics Data System (ADS)

    Li, Ying; Liu, Ren-Wei; Ma, Li; Fan, Su-Na; Li, Hui; Hu, Shu-Xin; Li, Ming

    2015-07-01

    Precise control over the photoluminescence (PL) of single quantum dots (QDs) is important for their practical applications. We show that the PL of individual CdSe/ZnS core/shell QDs can be effectively enhanced and continuously modulated by electrochemically manipulating the electron transfer (ET) between the QDs and the attached redox-active ligands such as 2-mercaptoethanol (BME). We found that i) the ET from BME to the QDs’ surface trap states suppresses the blinking of the QDs, ii) the ET from the QDs’ conduction band to the oxidization product results in dimmed PL when BME is oxidized, and iii) further oxidization of BME results in a significant PL brightening. The single particle measurements help us unveil the important features hidden in ensemble measurements and understand the underlying mechanism of the PL modulation. The results also suggest a simple yet efficient method to produce bright and non-blinking QDs and offer opportunities for further development of high resolution fluorescent bioimaging and nanodevices. Project supported by the National Natural Science Foundation of China (Grant Nos. 10904164, 61275192, and 11104328).

  3. Mechanism of photoluminescence investigation of Si nano-crystals embedded in SiOx

    NASA Astrophysics Data System (ADS)

    Vivas Hernández, A.; Torchynska, T. V.; Guerrero Moreno, I.

    2010-05-01

    Nanoscaled Si (Ge) systems continue to be of interest for their potential application as Si (Ge) based light emiting materials and photonic structures. Optical properties of such systems are sensitive to nanocrystallite (NC) size fluctuations as well as to defects effects due to large surface to volume ratio in small NCs. Intensive research of Si (Ge) NCs is focused on the elucidation of the mechanism of radiative recombination with the aim to provide high efficient emission at room temperature in different spectral range. The bright visible photoluminescence (PL) of the Si (Ge)-SiOX system was investigated during last 15 years and several models were proposed. It was shown that blue (~2.64 eV) and green (~2.25 eV) PL are caused by various emitting centers in silicon oxide [1], while the nature of the more intensive red (1.70-2.00 eV) and infrared (0.80-1.60 eV) PL bands steel is no clear. These include PL model connected whit quantum confinement effects in Si (Ge) nanocrystallites [2-4], surface states on Si (Ge) nanocrystallites, as well as defects at the Si/SiOX (Ge/SiOX) interface and in the SiO2 layer [5-11]. It should be noted, that even investigation of PL on single Si quantum dots [12] cannot undoubtedly confirm the quantum confinement nature of red emission.

  4. Amino-functionalized graphene quantum dots: origin of tunable heterogeneous photoluminescence

    NASA Astrophysics Data System (ADS)

    Sandeep KumarThese Authors Contributed Equally To The Present Work., G.; Roy, Rajarshi; Sen, Dipayan; Ghorai, Uttam Kumar; Thapa, Ranjit; Mazumder, Nilesh; Saha, Subhajit; Chattopadhyay, Kalyan K.

    2014-02-01

    Graphene quantum dots are known to exhibit tunable photoluminescence (PL) through manipulation of edge functionality under various synthesis conditions. Here, we report observation of excitation dependent anomalous m-n type fingerprint PL transition in synthesized amino functionalized graphene quantum dots (5-7 nm). The effect of band-to-band π*-π and interstate to band n-π induced transitions led to effective multicolor emission under changeable excitation wavelength in the functionalized system. A reasonable assertion that equi-coupling of π*-π and n-π transitions activated the heterogeneous dual mode cyan emission was made upon observation of the PL spectra. Furthermore, investigation of incremented dimensional scaling through facile synthesis of amino functionalized quantum graphene flakes (20-30 nm) revealed it had negligible effect on the modulated PL pattern. Moreover, an effort was made to trace the origin of excitation dependent tunable heterogeneous photoluminescence through the framework of energy band diagram hypothesis and first principles analysis. Ab initio results suggested formation of an interband state as a manifestation of p orbital hybridization between C-N atoms at the edge sites. Therefore comprehensive theoretical and experimental analysis revealed that newly created energy levels can exist as an interband within the energy gap in functionalized graphene quantum structures yielding excitation dependent tunable PL for optoelectronic applications.Graphene quantum dots are known to exhibit tunable photoluminescence (PL) through manipulation of edge functionality under various synthesis conditions. Here, we report observation of excitation dependent anomalous m-n type fingerprint PL transition in synthesized amino functionalized graphene quantum dots (5-7 nm). The effect of band-to-band π*-π and interstate to band n-π induced transitions led to effective multicolor emission under changeable excitation wavelength in the functionalized

  5. Time-integrated photoluminescence and pump-probe reflection spectroscopy of Si doped InN thin films

    SciTech Connect

    Mohanta, Antaryami; Jang, Der-Jun Wang, Ming-Sung; Tu, L. W.

    2014-01-28

    Temperature and excitation power dependent time-integrated photoluminescence of Si doped InN thin films are investigated. Photoluminescence (PL) spectra at low temperatures are described by single emission peak ensued due to “free-to-bound” recombination; whereas PL spectra at higher temperatures above 150 K are characterized by both “band-to-band” and “free-to-bound” transition. Carrier dynamics of Si doped InN thin films is studied using pump-probe reflection spectroscopy at room temperature. The hot electron cooling process is well described by electron-electron scattering. The dependence of the hot electron cooling rate on total electron density shows sublinear to linear behavior with increase of background electron density. The variation of the carrier recombination lifetime with total electron density implicates the dominance of the defect-related nonradiative recombination channel over other recombination processes.

  6. Time-resolved photoluminescence of type-II quantum dots and isoelectronic centers in Zn-Se-Te superlattice structures

    NASA Astrophysics Data System (ADS)

    Cheung, M. C.-K.; Cartwright, A. N.; Sellers, I. R.; McCombe, B. D.; Kuskovsky, I. L.

    2008-01-01

    Spectrally and time-resolved photoluminescence of a ZnTe /ZnSe superlattice reveals a smooth transition of the photoluminescence (PL) lifetime from ˜100ns at 2.35eV to less than a few nanoseconds at 2.8eV. The significant increase of the lifetime in the low energy region is strong evidence to support the formation of type-II quantum dots (QDs), since in these nanostructures the spatial separation of carriers is increased. The shorter lived emission above 2.5eV is attributed to excitons bound to Te isoelectronic centers in the ZnSe matrix. The smooth transition of the PL lifetime confirms that clusters of these Te atoms evolve into type-II ZnTe /ZnSe QDs.

  7. Examination of electronic structure differences between CIGSSe and CZTSSe by photoluminescence study

    SciTech Connect

    Tai, Kong Fai; Huan, Cheng Hon Alfred; Gershon, Talia; Gunawan, Oki

    2015-06-21

    In this paper, we elaborate on the interpretation and use of photoluminescence (PL) measurements as they relate to the “donor/acceptor” and “electrostatic potential fluctuations” models for compensated semiconductors. Low-temperature (7 K) PL measurements were performed on high-efficiency Cu(In,Ga)(S,Se){sub 2} and two Cu{sub 2}ZnSn(S,Se){sub 4} solar cells with high- and low-S/(S + Se) ratio, all fabricated by a hydrazine solution-processing method. From excitation-dependent PL, the total defect density (which include radiative and non-radiative defects) within the band gap (E{sub g}) was estimated for each material and the consequent depth of the electrostatic potential fluctuation (γ) was calculated. The quasi-donor-acceptor pair (QDAP) density was estimated from the blue-shift magnitude of the QDAP PL peak position in power-dependent PL spectra. As a further verification, we show that the slope of the lifetime as a function of photon energies (dτ/dE) is consistent with our estimate for the magnitude of γ. Lastly, the energetic depth of the QDAP defects is examined by studying the spectral evolution of the PL as a function of temperature. The shallow defect levels in CIGSSe resulted in a significant blue-shift of the PL peak with temperature, whereas no obvious shift was observed for either CZTSSe sample, indicating an increase in the depth of the defects. Further improvement on Cu{sub 2}ZnSn(S,Se){sub 4} solar cell should focus on reducing the sub-E{sub g} defect density and avoiding the formation of deep defects.

  8. Photoluminescence in the Ca{sub x}Sr{sub 1-x}WO{sub 4} system at room temperature

    SciTech Connect

    Porto, S.L.; Longo, E.; Simoes, L.G.P.; Lima, S.J.G.; Ferreira, J.M.; Soledade, L.E.B.; Espinoza, J.W.M.; Cassia-Santos, M.R.; Maurera, M.A.M.A.; Paskocimas, C.A.; Santos, I.M.G. Souza, A.G.

    2008-08-15

    In this work, a study was undertaken about the structural and photoluminescent properties, at room temperature, of powder samples from the Ca{sub x}Sr{sub 1-x}WO{sub 4} (x=0-1.0) system, synthesized by a soft chemical method and heat treated between 400 and 700 deg. C. The material was characterized using Infrared, UV-vis and Raman spectroscopy and XRD. The most intense PL emission was obtained for the sample calcined at 600 deg. C, which is neither highly disordered (400-500 deg. C), nor completely ordered (700 deg. C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO{sub 4} or SrWO{sub 4}, but for Ca{sub 0.6}Sr{sub 0.4}WO{sub 4}. The PL emission spectra could be separated into two Gaussian curves. The lower wavelength peak is placed around 530 nm, and the higher wavelength peak at about 690 nm. Similar results were reported in the literature for both CaWO{sub 4} and SrWO{sub 4}. - Graphical abstract: The structural and room temperature photoluminescence of Ca{sub x}Sr{sub 1-x}WO4 synthesized by a soft chemical method was studied. The most intense PL emission was obtained for the sample calcined at 600 deg. C, that is neither highly disordered (400-500 deg. C), nor completely ordered (700 deg. C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO{sub 4} or SrWO{sub 4}, but for Ca{sub 0.6}Sr{sub 0.4}WO{sub 4}.

  9. Competition between auger recombination and hot-carrier trapping in PL intensity fluctuations of type II nanocrystals.

    PubMed

    Mangum, Benjamin D; Wang, Feng; Dennis, Allison M; Gao, Yongqian; Ma, Xuedan; Hollingsworth, Jennifer A; Htoon, Han

    2014-07-23

    Performing time-tagged, time-correlated, single-photon-counting studies on individual colloidal nanocrystal quantum dots (NQDs), the evolution of photoluminescence (PL) intensity-fluctuation behaviors in near-infrared (NIR) emitting type II, InP/CdS core-shell NQDs is investigated as a function of shell thickness. It is observed that Auger recombination and hot-carrier trapping compete in defining the PL intensity-fluctuation behavior for NQDs with thin shells, whereas the role of hot-carrier trapping dominates for NQDs with thick shells. These studies further reveal the distinct ramifications of altering either the excitation fluence or repetition rate. Specifically, an increase in laser pump fluence results in the creation of additional hot-carrier traps. Alternately, higher repetition rates cause a saturation in hot-carrier traps, thus activating Auger-related PL fluctuations. Furthermore, it is shown that Auger recombination of negatively charged excitons is suppressed more strongly than that of positively charged excitons because of the asymmetry in the electron-hole confinement in type II NQDs. Thus, this study provides new understanding of how both NQD structure (shell thickness and carrier-separation characteristics) and excitation conditions can be used to tune the PL stability, with important implications for room-temperature single-photon generation. Specifically, the first non-blinking NQD capable of single-photon emission in the near-infrared spectral regime is described. PMID:24715631

  10. Syntax-directed documentation for PL360

    NASA Technical Reports Server (NTRS)

    Mills, H. D.

    1970-01-01

    PL360 is a phrase-structured programming language which provides the facilities of a symbolic machine language for the IBM 360 computers. An automatic process, syntax-directed documentation, is described which acquires programming documentation through the syntactical analysis of a program, followed by the interrogation of the originating programmer. This documentation can be dispensed through reports of file query replies when other programmers later need to know the program structure and its details. A key principle of the programming documentation process is that it is managed solely on the basis of the syntax of programs.

  11. Enhanced photoluminescence from CdS with SiO2 nanopillar arrays

    PubMed Central

    Li, Wei; Wang, Shaolei; He, Sufeng; Wang, Jing; Guo, Yanyan; Guo, Yufeng

    2015-01-01

    In this paper, the enhanced photoluminescence from CdS thin film with SiO2 nanopillar array (NPA) was demonstrated. The CdS was prepared using chemical bath deposition in a solution bath containing CdSO4, SC(NH2)2, and NH4OH. The SiO2 NPA was fabricated by the nanosphere lithography (NSL) techniques. The nanopillar is about 50 nm in diameter, and the height is 150 nm. As a result, the sample with NPA shows an obvious improvement of photoluminescence (PL), compared with the one without NPA. In addition, we also observed that the PL intensity is increased ~5 times if the active layer is deposited on the nanopillar arrays and covered by a thin metal film of Al. It is noteworthy that the enhancement of photoluminescence could be attributed to the roughness of the surface, the 2D photonic band gap (PBG) effect and the surface plasmon resonance (SPR) effects. PMID:26077552

  12. Enhanced photoluminescence from CdS with SiO2 nanopillar arrays

    NASA Astrophysics Data System (ADS)

    Li, Wei; Wang, Shaolei; He, Sufeng; Wang, Jing; Guo, Yanyan; Guo, Yufeng

    2015-06-01

    In this paper, the enhanced photoluminescence from CdS thin film with SiO2 nanopillar array (NPA) was demonstrated. The CdS was prepared using chemical bath deposition in a solution bath containing CdSO4, SC(NH2)2, and NH4OH. The SiO2 NPA was fabricated by the nanosphere lithography (NSL) techniques. The nanopillar is about 50 nm in diameter, and the height is 150 nm. As a result, the sample with NPA shows an obvious improvement of photoluminescence (PL), compared with the one without NPA. In addition, we also observed that the PL intensity is increased ~5 times if the active layer is deposited on the nanopillar arrays and covered by a thin metal film of Al. It is noteworthy that the enhancement of photoluminescence could be attributed to the roughness of the surface, the 2D photonic band gap (PBG) effect and the surface plasmon resonance (SPR) effects.

  13. The role of N-Si-O bonding configurations in tunable photoluminescence of oxygenated amorphous silicon nitride films

    SciTech Connect

    Zhang, Pengzhan; Chen, Kunji Lin, Zewen; Li, Wei; Xu, Jun; Huang, Xinfan; Dong, Hengping

    2015-06-08

    Last year, we have reported that the internal quantum efficiency of photoluminescence (PL) from amorphous silicon oxynitride (a-SiN{sub x}O{sub y}) films has been achieved as high as 60%. The present work intensively investigated the mechanisms for tunable PL in the 2.05–2.95 eV range from our a-SiN{sub x}:O films, by using a combination of optical characterizations, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) measurements. The results of XPS, EPR, and photoluminescence excited measurements indicated that the incorporation of oxygen atoms into silicon nitride (a-SiN{sub x}) networks not only reduced the band tail structure disorder (Urbach tail width E{sub U}) but also created N-Si-O (N{sub x}) defect states in the band gap. We have discovered the distinctive PL characteristics from a-SiN{sub x}:O films with various NH{sub 3/}SiH{sub 4} ratios. The PL peak energy (E{sub PL}) is independent of the excitation energy (E{sub exc}) and the PL intensity (I{sub PL}) is regardless of the optical band gap (E{sub opt}) but is proportional to the N{sub x} defects concentration, both of which are completely different from the PL characteristics by band tail states recombination mechanism, in which the E{sub PL} is proportional to E{sub exc} (when E{sub exc} ≤ E{sub opt}) and the I{sub PL} is dependent on the relative position of E{sub exc} and E{sub opt}. Based on the N-Si-O bonding configurations and the distinctive PL characteristics, the radiative recombination mechanism through the N-Si-O defect states has been proposed, by which the performance of stimulated emission may be realized in this kind of a-SiN{sub x}:O films.

  14. Photoluminescence from silicon nanoparticles embedded in ammonium silicon hexafluoride.

    PubMed

    Kalem, Seref; Werner, Peter; Talalaev, Vadim; Becker, Michael; Arthursson, Orjan; Zakharov, Nikolai

    2010-10-29

    Silicon (Si) nanoparticles (NPs) were synthesized by transforming a Si wafer surface to ammonium silicon hexafluoride (ASH) or (NH(4))(2)SiF(6) under acid vapor treatment. Si-NPs which were found to be embedded within the polycrystalline (ASH) layer exhibit a strong green-orange photoluminescence (PL). Differential PL measurements revealed a major double component spectrum consisting of a broad band associated with the ASH-Si wafer interfacial porous oxide layer and a high energy band attributable to Si-NPs embedded in the ASH. The origin of the latter emission can be explained in terms of quantum/spatial confinement effects probably mediated by oxygen related defects in or around Si-NPs. Although Si-NPs are derived from the interface they are much smaller in size than those embedded within the interfacial porous oxide layer (SiO(x), x > 1.5). Transmission electron microscopy (TEM) combined with Raman scattering and Fourier transformed infrared (FTIR) analysis confirmed the presence of Si-NP and Si-O bondings pointing to the role of oxygen related defects in a porous/amorphous structure. The presence of oxygen of up to 4.5 at.% in the (NH(4))(2)SiF(6) layer was confirmed by energy dispersive spectroscopy (EDS) analysis.

  15. Enhanced photoluminescence of porous silicon nanoparticles coated by bioresorbable polymers

    PubMed Central

    2012-01-01

    A significant enhancement of the photoluminescence (PL) efficiency is observed for aqueous suspensions of porous silicon nanoparticles (PSiNPs) coated by bioresorbable polymers, i.e., polylactic-co-glycolic acid (PLGA) and polyvinyl alcohol (PVA). PSiNPs with average size about 100 nm prepared by mechanical grinding of electrochemically etched porous silicon were dispersed in water to prepare the stable suspension. The inner hydrophobic PLGA layer prevents the PSiNPs from the dissolution in water, while the outer PVA layer makes the PSiNPs hydrophilic. The PL quantum yield of PLGA/PVA-coated PSiNPs was found to increase by three times for 2 weeks of the storage in water. The observed effect is explained by taking into account both suppression of the dissolution of PSiNPs in water and a process of the passivation of nonradiative defects in PSiNPs. The obtained results are interesting in view of the potential applications of PSiNPs in bioimaging. PMID:22873790

  16. Modulation of porphyrin photoluminescence by nanoscale spacers on silicon substrates

    NASA Astrophysics Data System (ADS)

    Fang, Y. C.; Zhang, Y.; Gao, H. Y.; Chen, L. G.; Gao, B.; He, W. Z.; Meng, Q. S.; Zhang, C.; Dong, Z. C.

    2013-11-01

    We investigate photoluminescence (PL) properties of quasi-monolayered tetraphenyl porphyrin (TPP) molecules on silicon substrates modulated by three different nanoscale spacers: native oxide layer (NOL), hydrogen (H)-passivated layer, and Ag nanoparticle (AgNP) thin film, respectively. In comparison with the PL intensity from the TPP molecules on the NOL-covered silicon, the fluorescence intensity from the molecules on the AgNP-covered surface was greatly enhanced while that for the H-passivated surface was found dramatically suppressed. Time-resolved fluorescence spectra indicated shortened lifetimes for TPP molecules in both cases, but the decay kinetics is believed to be different. The suppressed emission for the H-passivated sample was attributed to the weaker decoupling effect of the monolayer of hydrogen atoms as compared to the NOL, leading to increased nonradiative decay rate; whereas the enhanced fluorescence with shortened lifetime for the AgNP-covered sample is attributed not only to the resonant excitation by local surface plasmons, but also to the increased radiative decay rate originating from the emission enhancement in plasmonic "hot-spots".

  17. Photoluminescence decay rate of silicon nanoparticles modified with gold nanoislands

    NASA Astrophysics Data System (ADS)

    Dan'ko, Viktor; Michailovska, Katerina; Indutnyi, Ivan; Shepeliavyi, Petro

    2014-04-01

    We investigated plasmon-assisted enhancement of emission from silicon nanoparticles (ncs-Si) embedded into porous SiO x matrix in the 500- to 820-nm wavelength range. In the presence in the near-surface region of gold nanoisland film, ncs-Si exhibited up to twofold luminescence enhancement at emission frequencies that correspond to the plasmon resonance frequency of Au nanoparticles. Enhancement of the photoluminescence (PL) intensity was attributed to coupling with the localized surface plasmons (LSPs) excited in Au nanoparticles and to increase in the radiative decay rate of ncs-Si . It has been shown that spontaneous emission decay rate of ncs-Si modified by thin Au film over the wide emission spectral range was accelerated. The emission decay rate distribution was determined by fitting the experimental decay curves to the stretched exponential model. The observed increase of the PL decay rate distribution width for the Au-coated nc-Si-SiO x sample in comparison with the uncoated one was explained by fluctuations in the surface-plasmon excitation rate .

  18. Tuning photoluminescence of organic rubrene nanoparticles through a hydrothermal process

    PubMed Central

    2011-01-01

    Light-emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) nanoparticles (NPs) prepared by a reprecipitation method were treated hydrothermally. The diameters of hydrothermally treated rubrene NPs were changed from 100 nm to 2 μm, depending on hydrothermal temperature. Photoluminescence (PL) characteristics of rubrene NPs varied with hydrothermal temperatures. Luminescence of pristine rubrene NPs was yellow-orange, and it changed to blue as the hydrothermal temperature increased to 180°C. The light-emitting color distribution of the NPs was confirmed using confocal laser spectrum microscope. As the hydrothermal temperature increased from 110°C to 160°C, the blue light emission at 464 to approximately 516 nm from filtered-down NPs was enhanced by H-type aggregation. Filtered-up rubrene NPs treated at 170°C and 180°C exhibited blue luminescence due to the decrease of intermolecular excimer densities with the rapid increase in size. Variations in PL of hydrothermally treated rubrene NPs resulted from different size distributions of the NPs. PMID:21711925

  19. Photoluminescence properties of rare earths (Eu{sup 3+}, Tb{sup 3+}, Dy{sup 3+} and Tm{sup 3+}) activated NaInW{sub 2}O{sub 8} wolframite host lattice

    SciTech Connect

    Asiri Naidu, S.; Boudin, S.; Varadaraju, U.V.; Raveau, B.

    2012-01-15

    The photoluminescence (PL) studies on NaIn{sub 1-x}RE{sub x}W{sub 2}O{sub 8}, with RE=Eu{sup 3+}, Tb{sup 3+}, Dy{sup 3+} and Tm{sup 3+} phases have shown that the relative contribution of the host lattice and of the intra-f-f emission of the activators to the PL varies with the nature of the rare earth cation. In the case of Dy{sup 3+} and Tm{sup 3+} activators, with yellow and blue emission, respectively, the energy transfer from host to the activator plays a major role. In contrast for Eu{sup 3+}, with intense red emission, the host absorption is less pronounced and the intra-f-f transitions of the Eu{sup 3+} ions play a major role, whereas for Tb{sup 3+} intra-f-f transitions are only observed, giving rise to green emission. - Graphical abstract: NaInW{sub 2}O{sub 8} double tungstate doped with Eu{sup 3+}, Dy{sup 3+}, Tb{sup 3+}and Tm{sup 3+} shows characteristic emission of intense red for Eu{sup 3+}, yellow for Dy{sup 3+}, green for Tb{sup 3+} and blue for Tm{sup 3+}. Highlights: Black-Right-Pointing-Pointer Characteristic emissions of rare earths (Eu{sup 3+}, Tb{sup 3+}, Dy{sup 3+} and Tm{sup 3+}) are observed NaInW{sub 2}O{sub 8} wolframite. Black-Right-Pointing-Pointer Energy transfer from host to the activators (Eu{sup 3+} Dy{sup 3+} Tm{sup 3+} is observed. Black-Right-Pointing-Pointer PL properties of rare earth ions depend on minor structural variations in the host lattice.

  20. Synthesis and characterization of a new photoluminescent material tris (2-methyl-8-hydroxy quinoline) lanthanum La(mq)3

    NASA Astrophysics Data System (ADS)

    Kumar, Rahul; Bhargava, Parag

    2016-05-01

    A new photoluminescence material, tris (2-methyl-8-hydroxy quinoline) lanthanum has been synthesized and characterized by different techniques. The prepared material La(mq)3 was characterized for structural, thermal and photoluminescence analysis. Structural analysis of this material was done by fourier transformed infrared spectroscopy (FTIR) and mass spectroscopy. Thermal analysis of this material was done by thermal gravimetric analysis (TGA) shows the thermal stability up to 400°C. Absorption and emission spectra of the material was measured by UV-visible spectroscopy and photoluminescence spectroscopy. Solution of this material La(mq)3 in ethanol showed absorption peak at 385nm respectively which may be attributed due to (π - π*) transitions. The photoluminescence spectra of La(mq)3 in ethanol solution showed intense peak at 430 nm.

  1. An unambiguous identification of 2D electron gas features in the photoluminescence spectrum of AlGaN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Jana, Dipankar; Sharma, T. K.

    2016-07-01

    A fast and non-destructive method for probing the true signatures of 2D electron gas (2DEG) states in AlGaN/GaN heterostructures is presented. Two broad features superimposed with interference oscillations are observed in the low temperature photoluminescence (PL) spectrum. The two features are identified as the ground and excited 2DEG states which are confirmed by comparing the PL spectra of as-grown and top barrier layer etched samples. Broad PL features disappear at a certain temperature along with the associated interference oscillations. Furthermore, the two broad PL features depicts specific temperature and excitation intensity dependencies which make them easily distinguishable from the bandedge excitonic or defect related PL features. The presence of strong interference oscillations associated with the 2DEG PL features is explained by considering the localized generation of PL signal at the AlGaN/GaN heterointerface. Finally, a large value of the polarization induced electric field of ~1.01 MV cm-1 is reported from PL measurements for AlGaN/GaN HEMT structures. It became possible only when the true identification of 2DEG features was made possible by the proposed method.

  2. Time-resolved analysis of the white photoluminescence from chemically synthesized SiCxOy thin films and nanowires

    NASA Astrophysics Data System (ADS)

    Tabassum, Natasha; Nikas, Vasileios; Ford, Brian; Huang, Mengbing; Kaloyeros, Alain E.; Gallis, Spyros

    2016-07-01

    The study reported herein presents results on the room-temperature photoluminescence (PL) dynamics of chemically synthesized SiCxOy≤1.6 (0.19 < x < 0.6) thin films and corresponding nanowire (NW) arrays. The PL decay transients of the SiCxOy films/NWs are characterized by fast luminescence decay lifetimes that span in the range of 350-950 ps, as determined from their deconvoluted PL decay spectra and their stretched-exponential recombination behavior. Complementary steady-state PL emission peak position studies for SiCxOy thin films with varying C content showed similar characteristics pertaining to the variation of their emission peak position with respect to the excitation photon energy. A nearly monotonic increase in the PL energy emission peak, before reaching an energy plateau, was observed with increasing excitation energy. This behavior suggests that band-tail states, related to C-Si/Si-O-C bonding, play a prominent role in the recombination of photo-generated carriers in SiCxOy. Furthermore, the PL lifetime behavior of the SiCxOy thin films and their NWs was analyzed with respect to their luminescence emission energy. An emission-energy-dependent lifetime was observed, as a result of the modulation of their band-tail states statistics with varying C content and with the reduced dimensionality of the NWs.

  3. Structure and photoluminescent properties of a ZnS/Si nanoheterostructure based on a silicon nanoporous pillar array

    NASA Astrophysics Data System (ADS)

    Xu, Hai Jun; Li, Xin Jian

    2009-07-01

    A silicon nanoporous pillar array (Si-NPA) is a silicon hierarchical structure with regularly patterned surface morphology. Through a heterogeneous reaction process, the nanocrystallites of zinc sulfide (nc-ZnS) were grown onto the Si-NPA and a uniquely patterned core/shell nanoheterostructure array (ZnS/Si-NPA) was obtained. The pillars of the ZnS/Si-NPA were constructed by an outermost shell of a nc-ZnS membrane, an innermost core of a nanoporous silicon pillar and an interface with nc-ZnS embedded into an amorphous SiO2 matrix. The photoluminescence (PL) spectrum of the ZnS/Si-NPA showed that in addition to the two blue PL bands peaked at ~412 and ~491 nm observed in the Si-NPA, a green PL band at ~537 nm was observed in the ZnS/Si-NPA when it was excited by 300 nm ultraviolet light. Based on these experimental results, the two blue PL bands of the ZnS/Si-NPA came from a Si-NPA substrate, while the green PL band was attributed to the emission from the surface states of sulfur vacancies of nc-ZnS. The broad PL from blue to red in the visible region realized in the ZnS/Si-NPA might be applied in solid-state lighting devices with white light emission.

  4. In situ and nonvolatile photoluminescence tuning and nanodomain writing demonstrated by all-solid-state devices based on graphene oxide.

    PubMed

    Tsuchiya, Takashi; Tsuruoka, Tohru; Terabe, Kazuya; Aono, Masakazu

    2015-02-24

    In situ and nonvolatile tuning of photoluminescence (PL) has been achieved based on graphene oxide (GO), the PL of which is receiving much attention because of various potential applications of the oxide (e.g., display, lighting, and nano-biosensor). The technique is based on in situ and nonvolatile tuning of the sp(2) domain fraction to the sp(3) domain fraction (sp(2)/sp(3) fraction) in GO through an electrochemical redox reaction achieved by solid electrolyte thin films. The all-solid-state variable PL device was fabricated by GO and proton-conducting mesoporous SiO2 thin films, which showed an extremely low PL background. The device successfully tuned the PL peak wavelength in a very wide range from 393 to 712 nm, covering that for chemically tuned GO, by adjusting the applied DC voltage within several hundred seconds. We also demonstrate the sp(2)/sp(3) fraction tuning using a conductive atomic force microscope. The device achieved not only writing, but also erasing of the sp(2)/sp(3)-fraction-tuned nanodomain (both directions operation). The combination of these techniques is applicable to a wide range of nano-optoelectronic devices including nonvolatile PL memory devices and on-demand rewritable biosensors that can be integrated into nano- and microtips which are transparent, ultrathin, flexible, and inexpensive.

  5. Auger ionization beats photo-oxidation of semiconductor quantum dots: extended stability of single-molecule photoluminescence.

    PubMed

    Yamashita, Shin-Ichi; Hamada, Morihiko; Nakanishi, Shunsuke; Saito, Hironobu; Nosaka, Yoshio; Wakida, Shin-Ichi; Biju, Vasudevanpillai

    2015-03-23

    Despite the bright and tuneable photoluminescence (PL) of semiconductor quantum dots (QDs), the PL instability induced by Auger recombination and oxidation poses a major challenge in single-molecule applications of QDs. The incomplete information about Auger recombination and oxidation is an obstacle in the resolution of this challenge. Here, we report for the first time that Auger-ionized QDs beat self-sensitized oxidation and the non-digitized PL intensity loss. Although high-intensity photoactivation insistently induces PL blinking, the transient escape of QDs into the ultrafast Auger recombination cycle prevents generation of singlet oxygen ((1) O2 ) and preserves the PL intensity. By the detection of the NIR phosphorescence of (1) O2 and evaluation of the photostability of single QDs in aerobic, anaerobic, and (1) O2 scavenger-enriched environments, we disclose relations of Auger ionization and (1) O2 -mediated oxidation to the PL stability of single QDs, which will be useful during the formulation of QD-based single-molecule imaging tools and single-photon devices.

  6. Highly enhanced photoluminescence of AgInS2/ZnS quantum dots by hot-injection method

    NASA Astrophysics Data System (ADS)

    Liao, Shenghua; Huang, Yu; Zhang, Ying; Shan, Xiaohui; Yan, Zhengyu; Shen, Weiyang

    2015-01-01

    Highly photoluminescent and air-stable AgInS2 quantum dots (AIS QDs) were synthesized by a hot-injection route in N2 atmosphere and dark environment. The as-synthesized AIS QDs were further capped with ZnS shell by one-pot method in order to enhance the photoluminescence (PL) intensity. The photo-electronic property and the morphology of AIS QDs and AIS/ZnS QDs were characterized by ultraviolet-visible spectroscopy (UV), PL spectroscopy and transmission electronic microscopy (TEM). The results indicated that the narrow and symmetrical PL spectra of AIS QDs was time-dependent, and the emission wavelength of AIS QDs could be tunable within 436-610 nm by altering the initial Ag/In ratios. After being capped with ZnS shell, the AIS QDs showed excellent optical characteristics, including PL QYs up to 15%. The TEM results indicated that the spherical AIS/ZnS QDs were nearly monodispersed and homogeneous with an average particle size of 8 nm. The heavy metal free and high luminous AIS/ZnS QDs have great potential in biological application.

  7. Impurity Studies of Cd(0.8)Zn(0.2)Te Crystals Using Photoluminescence and Glow Discharge Mass Spectroscopy

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Lehoczky, Sandor L.; Scripa, Rosalie N.

    2005-01-01

    Cd(1-x)Zn(x)Te semiconductor crystal is a highly promising material for room temperature x- and gamma-ray detector applications because of its high resistivity, long carrier lifetime, and relatively high hole and electron mobilities. This paper reports the investigation of the impurities in several Cd(1-x)Zn(x)Te (x = 0.20) crystals grown using the vertical Bridgman method under a Cd overpressure. The impurity concentrations were measured using glow discharge mass spectroscopy (GDMS). The energy states of the impurities were studied using photoluminescence (PL) spectroscopy at liquid helium temperature. The PL spectra showed a series of sharp high energy lines which are associated with free excitons and excitons bound to impurities as donors and acceptors in the crystals. The impurities also contributed to donor-acceptor pair recombination. The correlation between the GDMS and PL results will be reported.

  8. Investigation to the deep center related properties of low temperature grown InPBi with Hall and photoluminescence

    SciTech Connect

    Wang, Peng; Pan, Wenwu; Wu, Xiaoyan; Wang, Kai; Yue, Li; Gong, Qian; Wang, Shumin

    2015-12-15

    InP{sub 1-x}Bi{sub x} epilayers with bismuth (Bi) concentration x= 1.0% were grown on InP by gas source molecular beam epitaxy (GS-MBE) at low temperature (LT). Bi incorporation decreased the intrinsic free electron concentration of low temperature grown InP indicated by hall analysis. It is concluded that deep level center was introduced by Bi. Influence of Si doping on the InP{sub 1-x}Bi{sub x} films Photoluminescence (PL) was investigated. N-type doping in the InP{sub 1-x}Bi{sub x} epilayers was found to be effective at PL enhancement. Blue shift of InPBi PL emission wavelength was observed as the Si doping concentration increasing. Two independent peaks were fitted and their temperature dependence behavior was observed to be distinct obviously. Two individual radiative recombination processes were expected to be involved.

  9. Time- and locally resolved photoluminescence of semipolar GaInN /GaN facet light emitting diodes

    NASA Astrophysics Data System (ADS)

    Wunderer, Thomas; Brückner, Peter; Hertkorn, Joachim; Scholz, Ferdinand; Beirne, Gareth J.; Jetter, Michael; Michler, Peter; Feneberg, Martin; Thonke, Klaus

    2007-04-01

    The authors investigate the carrier lifetime and photoluminescence (PL) intensity of a semipolar GaInN /GaN sample which was realized by growing five GaInN /GaN quantum wells on the {11¯01} side facets of selectively grown n-GaN stripes that have a triangular shape running along the ⟨112¯0⟩ direction. Time- and locally resolved PL measurements show drastically reduced lifetimes for the semipolar sample of only 650ps at 4K whereas lifetimes exceeding 50ns were found for a polar reference sample. Furthermore, more than a doubling of the luminescence intensity and a significantly reduced blueshift of the PL peak wavelength with increasing excitation power density provide further evidence for the presence of reduced piezoelectric fields in the semipolar sample.

  10. Composition dependence of photoluminescence properties of In x Al1‑x N/AlGaN quantum wells

    NASA Astrophysics Data System (ADS)

    Zubialevich, V. Z.; Alam, S. N.; Li, H. N.; Parbrook, P. J.

    2016-09-01

    A series of InAlN/AlGaN five quantum well (QW) heterostructures was prepared by metal-organic vapour phase epitaxy to investigate their photoluminescence (PL) properties as a function of indium content in QWs at aluminium content in barriers fixed at 59%. In addition to the expected redshift of the emission spectrum, a strong rise of PL efficiency was observed with increasing indium content from 12.5 to 18%. Use of a higher indium content leads to a further redshift but also to a sudden and sharp degradation of PL efficiency. Reasons for the observed behaviour are discussed in detail, which raise the possibility of a transition to a type II band lineup in the InAlN–AlGaN system.

  11. Tunable photoluminescence of self-assembled GeSi quantum dots by B{sup +} implantation and rapid thermal annealing

    SciTech Connect

    Chen, Yulu; Wu, Shan; Ma, Yinjie; Fan, Yongliang; Yang, Xinju; Zhong, Zhenyang; Jiang, Zuimin

    2014-06-21

    The layered GeSi quantum dots (QDs) are grown on (001) Si substrate by molecular beam epitaxy. The photoluminescence (PL) peak of the as-grown GeSi quantum dots has obvious blue shift and enhancement after processed by ion implantation and rapid thermal annealing. It is indicated that the blue shift is originated from the interdiffusion of Ge and Si at the interface between QDs and the surrounding matrix. The dependence of PL intensity on the excitation power shows that there are the nonradiative centers of shallow local energy levels from the point defects caused by the ion implantation, but not removed by the rapid thermal annealing. The tunable blue shift of the PL position from the 1300 nm to 1500 nm region may have significant application value in the optical communication.

  12. Photoinduced magnetization effect in a p -type Hg1 -xMnxTe single crystal investigated by infrared photoluminescence

    NASA Astrophysics Data System (ADS)

    Zhu, Liangqing; Shao, Jun; Chen, Xiren; Li, Yanqiu; Zhu, Liang; Qi, Zhen; Lin, Tie; Bai, Wei; Tang, Xiaodong; Chu, Junhao

    2016-10-01

    Photoinduced magnetization (PIM) effect of Hg1 -xMnxTe provides an attractive solution for realizing the quantum anomalous Hall effect in quantum wells with a light field. In this paper, the PIM effect of p -type Hg0.74Mn0.26Te single crystal was investigated by power-, polarization- and temperature-dependent photoluminescence (PL) measurements in both reflection and transmission geometries. Giant Zeeman splitting and polarization of PL spectra were observed without an external magnetic field evolving with excitation-power density of the pumping laser and temperature, which were accounted for by the PIM effect. The occurrence of the PIM was qualitatively understandable by the carrier-mediated mean-field theory known as the Zener model. The results indicate that infrared PL measurements with enhanced sensitivity and signal-to-noise ratio can serve as a convenient pathway for clarifying the PIM effect of semimagnetic semiconductors.

  13. Aryl-modified graphene quantum dots with enhanced photoluminescence and improved pH tolerance

    NASA Astrophysics Data System (ADS)

    Luo, Peihui; Ji, Zhe; Li, Chun; Shi, Gaoquan

    2013-07-01

    Chemical modification is an important technique to modulate the chemical and optical properties of graphene quantum dots (GQDs). In this paper, we report a versatile diazonium chemistry method to graft aryl groups including phenyl, 4-carboxyphenyl, 4-sulfophenyl and 5-sulfonaphthyl to GQDs via Gomberg-Bachmann reaction. The aryl-modified GQDs are nanocrystals with lateral dimensions in the range of 2-4 nm and an average thickness lower than 1 nm. Upon chemical modification with aryl groups, the photoluminescence (PL) bands of GQDs were tuned in the range of 418 and 447 nm, and their fluorescence quantum yields (QYs) were increased for up to about 6 times. Furthermore, the aryl-modified GQDs exhibited stable PL (both intensity and peak position) in a wide pH window of 1-11. The mechanism of improving the PL properties of GQDs by aryl-modification was also discussed.Chemical modification is an important technique to modulate the chemical and optical properties of graphene quantum dots (GQDs). In this paper, we report a versatile diazonium chemistry method to graft aryl groups including phenyl, 4-carboxyphenyl, 4-sulfophenyl and 5-sulfonaphthyl to GQDs via Gomberg-Bachmann reaction. The aryl-modified GQDs are nanocrystals with lateral dimensions in the range of 2-4 nm and an average thickness lower than 1 nm. Upon chemical modification with aryl groups, the photoluminescence (PL) bands of GQDs were tuned in the range of 418 and 447 nm, and their fluorescence quantum yields (QYs) were increased for up to about 6 times. Furthermore, the aryl-modified GQDs exhibited stable PL (both intensity and peak position) in a wide pH window of 1-11. The mechanism of improving the PL properties of GQDs by aryl-modification was also discussed. Electronic supplementary information (ESI) available: Fluorescence quantum yield measurements, estimation of grafting ratio, TEM images, FTIR spectra, PL spectra and zeta potentials. See DOI: 10.1039/c3nr02156d

  14. Origin of photoluminescence from silicon nanowires prepared by metal induced etching (MIE)

    SciTech Connect

    Saxena, Shailendra K. Rai, Hari. M.; Late, Ravikiran; Sagdeo, Pankaj R.; Kumar, Rajesh

    2015-05-15

    In this present study the origin of luminescence from silicon nanowires (SiNws) has been studied. SiNWs are fabricated on Si substrate by metal induced chemical etching (MIE). Here it is found that the band gap of SiNWs is higher than the gap of luminescent states in SiNWs which leads to the effect of Si=O bond. The band gap is estimated from diffuse reflectance analysis. Here we observe that band gap can be tailored depending on size (quantum confinement) but photoluminescence (PL) from all the sample is found to be fixed at 1.91 eV. This study is important for the understanding of origin of photoluminescence.

  15. Spectrally resolved modulated infrared radiometry of photothermal, photocarrier, and photoluminescence response of CdSe crystals: Determination of optical, thermal, and electronic transport parameters

    NASA Astrophysics Data System (ADS)

    Pawlak, M.; Chirtoc, M.; Horny, N.; Pelzl, J.

    2016-03-01

    Spectrally resolved modulated infrared radiometry (SR-MIRR) with super-band gap photoexcitation is introduced as a self-consistent method for semiconductor characterization (CdSe crystals grown under different conditions). Starting from a theoretical model combining the contributions of the photothermal (PT) and photocarrier (PC) signal components, an expression is derived for the thermal-to-plasma wave transition frequency ftc which is found to be wavelength-independent. The deviation of the PC component from the model at high frequency is quantitatively explained by a quasi-continuous distribution of carrier recombination lifetimes. The integral, broad frequency band (0.1 Hz-1 MHz) MIRR measurements simultaneously yielded the thermal diffusivity a, the effective IR optical absorption coefficient βeff, and the bulk carrier lifetime τc. Spectrally resolved frequency scans were conducted with interchangeable IR bandpass filters (2.2-11.3 μm) in front of the detector. The perfect spectral match of the PT and PC components is the direct experimental evidence of the key assumption in MIRR that de-exciting carriers are equivalent to blackbody (Planck) radiators. The exploitation of the β spectrum measured by MIRR allowed determining the background (equilibrium) free carrier concentration n0. At the shortest wavelength (3.3 μm), the photoluminescence (PL) component supersedes the PC one and has distinct features. The average sample temperature influences the PC component but not the PT one.

  16. Photoassisted photoluminescence fine-tuning of gold nanodots through free radical-mediated ligand-assembly

    NASA Astrophysics Data System (ADS)

    Tseng, Yu-Ting; Cherng, Rochelle; Harroun, Scott G.; Yuan, Zhiqin; Lin, Tai-Yuan; Wu, Chien-Wei; Chang, Huan-Tsung; Huang, Chih-Ching

    2016-05-01

    In this study, we have developed a simple photoassisted ligand assembly to fine-tune the photoluminescence (PL) of (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide-capped gold nanodots (11-MUTAB-Au NDs). The 11-MUTAB-Au NDs (size: ca. 1.8 nm), obtained from the reaction of gold nanoparticles (ca. 3 nm) and 11-MUTAB, exhibited weak, near-infrared (NIR) PL at 700 nm with a quantum yield (QY) of 0.37% upon excitation at 365 nm. The PL QY of the Au NDs increased to 11.43% after reaction with 11-mercaptoundecanoic acid (11-MUA) for 30 min under ultraviolet (UV) light, which was accompanied by a PL wavelength shift to the green region (~520 nm). UV-light irradiation accelerates 11-MUA assembly on the 11-MUTABAu NDs (11-MUA/11-MUTAB-Au NDs) through a radical-mediated reaction. Furthermore, the PL wavelength of the 11-MUA/11-MUTAB-Au NDs can be switched to 640 nm via cysteamine under UV-light irradiation. We propose that the PL of the Au NDs with NIR and visible emissions was originally from the surface thiol-Au complexes and the Au core, respectively. These dramatically different optical properties of the Au NDs were due to variation in the surface ligands, as well as the densities and surface oxidant states of the surface Au atoms/ions. These effects can be controlled by assembling surface thiol ligands and accelerated by UV irradiation.In this study, we have developed a simple photoassisted ligand assembly to fine-tune the photoluminescence (PL) of (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide-capped gold nanodots (11-MUTAB-Au NDs). The 11-MUTAB-Au NDs (size: ca. 1.8 nm), obtained from the reaction of gold nanoparticles (ca. 3 nm) and 11-MUTAB, exhibited weak, near-infrared (NIR) PL at 700 nm with a quantum yield (QY) of 0.37% upon excitation at 365 nm. The PL QY of the Au NDs increased to 11.43% after reaction with 11-mercaptoundecanoic acid (11-MUA) for 30 min under ultraviolet (UV) light, which was accompanied by a PL wavelength shift to the green region

  17. Nonlinear photoluminescence spectrum of single gold nanostructures.

    PubMed

    Knittel, Vanessa; Fischer, Marco P; de Roo, Tjaard; Mecking, Stefan; Leitenstorfer, Alfred; Brida, Daniele

    2015-01-27

    We investigate the multiphoton photoluminescence characteristics of gold nanoantennas fabricated from single crystals and polycrystalline films. By exciting these nanostructures with ultrashort pulses tunable in the near-infrared range, we observe distinct features in the broadband photoluminescence spectrum. By comparing antennas of different crystallinity and shape, we demonstrate that the nanoscopic geometry of plasmonic devices determines the shape of the emission spectra. Our findings rule out the contribution of the gold band structure in shaping the photoluminescence.

  18. Observations of unusual temperature dependent photoluminescence anti-quenching in two-dimensional nanosheets of ZnS/ZnO composites and polarization dependent photoluminescence enhancement in fungi-like ZnO nanostructures

    NASA Astrophysics Data System (ADS)

    Kole, A. K.; Kumbhakar, P.; Ganguly, T.

    2014-06-01

    Hybrid semiconductor nanostructures which integrate the favourable characteristics of both the component materials are found recently to be attractive candidate materials for research investigations having interesting optical properties. Considering the fact that the temperature of the materials used in photo-luminescent devices may vary while using them in a real device, it is essential to study the performances of such materials at variable temperatures. But the photoluminescence (PL) emission capabilities of such materials above room temperatures have not been well investigated, yet. However, in this work we have reported temperature dependent unusual PL emission characteristics of 2D nanosheets of ZnS/ZnO composite in the temperature range of 273-333 K. The composite sample has been produced by annealing the organic-inorganic ZnS(ethylenediamine)0.5 nanosheets, which are obtained by solvothermal technique. The as-synthesized nanosheets and another thermally annealed product of ZnO nanostructures showed usual thermally quenched PL emissions, whereas luminescence temperature anti-quenching (LTAQ) effect has been found in the ZnS/ZnO composite nanosheets. The PL emission intensity has been enhanced up to 242% with a small temperature variation of 60 K. The LTAQ effect has been explained by using the Berthelot-type model. It has been found that the diffused oxygen present in the composite nanostructures is acting as trap centre and played the major role in LTAQ effect. The analyses of time resolved PL emission spectroscopy data also confirmed the presence of oxygen trap level within the band gap of the material. Further, enhanced PL emission from the synthesized fungi-like ZnO samples has also been reported under the excitation of polarised ultraviolet light.

  19. Photoluminescence of CdTe Crystals Grown by Physical-Vapor Transport

    NASA Technical Reports Server (NTRS)

    Palosz, W.; Grasza, K.; Boyd, P. R.; Cui, Y.; Wright, G.; Roy, U. N.; Burger, A.

    2003-01-01

    High-quality CdTe crystals with resistivities higher than 10(exp 8) omega cm were grown by the physical-vapor transport (PVT) technique. Indium, aluminum, and the transition-metal scandium were introduced at the nominal level of about 6 ppm to the source material. Low-temperature photoluminescence (PL) has been employed to identify the origins of PL emissions of the crystals. The emission peaks at 1.584 eV and 1.581 eV were found only in the In-doped crystal. The result suggests that the luminescence line at 1.584 eV is associated with Cd-vacancy/In complex. The intensity of the broadband centered at 1.43 eV decreases strongly with introduction of Sc.

  20. Photoluminescence of CdTe Crystals Grown by Physical Vapor Transport

    NASA Technical Reports Server (NTRS)

    Palosz, W.; Grasza, K.; Boyd, P. R.; Cui, Y.; Wright, G.; Roy, U. N.; Burger, A.

    2002-01-01

    High quality CdTe crystals with resistivities higher than 10(exp 8) omega cm were grown by the physical vapor transport technique. Indium, Aluminum, and the transition metal Scandium were introduced at the nominal level of about 6 ppm to the source material. Low-temperature photoluminescence (PL) has been employed to identify the origins of PL emissions of the crystals. The emission peaks at 1.584 eV and 1.581 eV were found only in the In-doped crystal. The result suggests that the luminescence line at 1.584 eV is associated with Cd-vacancy/indium complex. The intensity of the broadband centered at 1.43 eV decreases strongly with introduction of Sc.

  1. Photoluminescence quantum yield of PbS nanocrystals in colloidal suspensions

    SciTech Connect

    Greben, M.; Fucikova, A.; Valenta, J.

    2015-04-14

    The absolute photoluminescence (PL) quantum yield (QY) of oleic acid-capped colloidal PbS quantum dots (QDs) in toluene is thoroughly investigated as function of QD size, concentration, excitation photon energy, and conditions of storage. We observed anomalous decrease of QY with decreasing concentration for highly diluted suspensions. The ligand desorption and QD-oxidation are demonstrated to be responsible for this phenomenon. Excess of oleic acid in suspensions makes the QY values concentration-independent over the entire reabsorption-free range. The PL emission is shown to be dominated by surface-related recombinations with some contribution from QD-core transitions. We demonstrate that QD colloidal suspension stability improves with increasing the concentration and size of PbS QDs.

  2. The synthesis of size-controlled 3C-SiC nanoflakes and their photoluminescent properties

    NASA Astrophysics Data System (ADS)

    Fan, Xiujun; Ye, Ruquan; Peng, Zhiwei; Wang, Juanjuan; Fan, Ailing; Guo, Xia

    2016-06-01

    Size-controlled and high-purity 3C-SiC nanoflakes (NFs) are synthesized on the tips of vertically aligned carbon nanotube (VA-CNT) carpets with a hot-filament chemical vapor deposition (HF-CVD) method. The average diameter and height of SiC NFs can be tuned by changing the thickness of per-deposited Si and growth conditions. The growth process of the SiC NFs is suggested to be dominated by a vapor-solid (VS) mechanism. The prepared SiC NFs exhibit quantum-confinement effects, emitting strong violet-blue photoluminescence (PL) under ultraviolet excitation. The PL peak position changes from 410 to 416 nm as the excitation line increases from 290 to 400 nm. This result opens the possibility for the application of the luminescent solid-state freestanding 3C-SiC NFs in photonics as well as photonics/electronics integration.

  3. Convenient synthesis of stable silver quantum dots with enhanced photoluminescence emission by laser fragmentation

    NASA Astrophysics Data System (ADS)

    Shuang, Li; Ming, Chen

    2016-04-01

    A new strategy for the facile synthesis of very stable and mono-dispersed silver (Ag) quantum dots (QDs) is developed by laser fragmentation of bulk Ag in water using polysorbate 80 as a dispersing and stabilizing agent. The surfactant plays an important role in the formation of size-controlled Ag nano-structures. The Ag QDs have excellent photo-stability of ∼500 h and enhanced photoluminescence (PL) at 510 nm. This has significant implications for selective and ultrasensitive PL probes. Based on laser fragmentation in the biocompatible surfactant solution, our results have opened up a novel paradigm to obtain stable metal QDs directly from bulk targets. This is a breakthrough in the toxicity problems that arise from standard chemical fabrication. Project supported by the National Natural Science Foundation of China (Grant Nos. 11575102, 11105085, 11275116, and 11375108) and the Fundamental Research Funds of Shandong University, China (Grant No. 2015JC007).

  4. Photoluminescence studies of growth-sector dependence of nitrogen distribution in synthetic Ib diamond

    SciTech Connect

    Wang, Kaiyue; Steeds, John W.; Li, Zhihong; Tian, Yuming

    2014-08-15

    The photoluminescence technology previously employed to investigate the boron distribution of type IIb diamond has now been applied to study the nitrogen distribution of type Ib diamond. All growth sectors were clearly distinguished by the characteristic colors and the brightness of the synthetic Ib diamond's cathodoluminescence topography. As a measure of the concentration of nitrogen impurity, the nitrogen-vacancy luminescence gave relative concentrations in different growth sectors as: the (111) sector was the highest, followed by the (311), (100) and (511) sectors. The results were reconfirmed by the evidence of the broadened and strengthened zero phonon lines of nitrogen-vacancy center with the increase of nitrogen concentration of type Ib diamond. - Highlights: • The growth sectors were clearly distinguished by CL technology. • The N distribution was investigated by the examination of PL spectroscopy. • Results showed that (111) has the highest N, followed by (311), (100) and (511). • The conclusion was reconfirmed by the PL results of NV center.

  5. Photoluminescence and thermoluminescence properties of Y3(Al,Ga)5O12:Tb3+ phosphor

    NASA Astrophysics Data System (ADS)

    Yousif, A.; Som, S.; Swart, H. C.

    2016-01-01

    A comparative study of the structural, photoluminescence (PL) and thermoluminescence (TL) properties of Y3(Al,Ga)5O12:Tb3+ phosphor powder was performed. The scanning electron microscope images showed that the phosphor particles were agglomerated and irregular in shape. The bigger particles consisted of smaller spherically shaped agglomerated particles ranging in size between 0.5 and 1 μm. The UV-VUV synchrotron radiation was used to study the luminescence properties of the phosphor. The TL study was performed after the sample was irradiated by γ-rays obtained from a 60Co target in the dose range of 10-50 Gy. The effect of heating rate on the TL glow curves and trapping parameters was also calculated. The correlation between PL and TL was explored.

  6. Using Low Temperature Photoluminescence Spectroscopy to Investigate CH₃NH₃PbI₃ Hybrid Perovskite Degradation.

    PubMed

    Jemli, Khaoula; Diab, Hiba; Lédée, Ferdinand; Trippé-Allard, Gaelle; Garrot, Damien; Geffroy, Bernard; Lauret, Jean-Sébastien; Audebert, Pierre; Deleporte, Emmanuelle

    2016-01-01

    Investigating the stability and evaluating the quality of the CH₃NH₃PbI₃ perovskite structures is quite critical both to the design and fabrication of high-performance perovskite devices and to fundamental studies of the photophysics of the excitons. In particular, it is known that, under ambient conditions, CH₃NH₃PbI₃ degrades producing some PbI₂. We show here that low temperature Photoluminescence (PL) spectroscopy is a powerful tool to detect PbI₂ traces in hybrid perovskite layers and single crystals. Because PL spectroscopy is a signal detection method on a black background, small PbI₂ traces can be detected, when other methods currently used at room temperature fail. Our study highlights the extremely high stability of the single crystals compared to the thin layers and defects and grain boundaries are thought to play an important role in the degradation mechanism. PMID:27399669

  7. Probing the photoluminescence properties of gold nanoclusters by fluorescence lifetime correlation spectroscopy

    SciTech Connect

    Yuan, C. T. Lin, T. N.; Shen, J. L.; Lin, C. A.; Chang, W. H.; Cheng, H. W.; Tang, J.

    2013-12-21

    Gold nanoclusters (Au NCs) have attracted much attention for promising applications in biological imaging owing to their tiny sizes and biocompatibility. So far, most efforts have been focused on the strategies for fabricating high-quality Au NCs and then characterized by conventional ensemble measurement. Here, a fusion single-molecule technique combining fluorescence correlation spectroscopy and time-correlated single-photon counting can be successfully applied to probe the photoluminescence (PL) properties for sparse Au NCs. In this case, the triplet-state dynamics and diffusion process can be observed simultaneously and the relevant time constants can be derived. This work provides a complementary insight into the PL mechanism at the molecular levels for Au NCs in solution.

  8. Photoluminescence study of high density Si quantum dots with Ge core

    NASA Astrophysics Data System (ADS)

    Kondo, K.; Makihara, K.; Ikeda, M.; Miyazaki, S.

    2016-01-01

    Si quantum dots (Si-QDs) with Ge core were self-assembled on thermally grown SiO2 from alternate thermal decomposition of pure SiH4 and GeH4 diluted with He. When the sample was excited by the 979 nm line of a semiconductor laser, fairly broad photoluminescence (PL) spectra in the region of 0.6-0.8 eV were observed at room temperature. The observed PL spectra suggested that radiative recombination of photo-generated carriers through quantized states of Ge core is the dominant pathway for the emission from the dots, reflecting the type II energy band discontinuity between the Si clad and Ge core. We also found that P-δ doping to Ge core plays an important role in recombination through the quantized states in the valence band of Ge core and P donor levels.

  9. Defect-Band Emission Photoluminescence Imaging on Multi-Crystalline Si Solar Cells

    SciTech Connect

    Yan, F.; Johnston, S.; Zaunbrecher, K.; Al-Jassim, M.; Sidelkheir, O.; Blosse, A.

    2011-01-01

    Defect-band photoluminescence (PL) imaging with an InGaAs camera was applied to multicrystalline silicon (mc-Si) wafers, which were taken from different heights of different Si bricks. Neighboring wafers were picked at six different processing steps, from as-cut to post-metallization. By using different cut-off filters, we were able to separate the band-to-band emission images from the defect-band emission images. On the defect-band emission images, the bright regions that originate from the grain boundaries and defect clusters were extracted from the PL images. The area fraction percentage of these regions at various processing stages shows a correlation with the final cell electrical parameters.

  10. Photoluminescence due to impurity-cluster-bound exciton in highly doped and highly compensated Si

    NASA Astrophysics Data System (ADS)

    Tajima, Michio; Tanaka, Koji; Dubois, Sébastien; Veirman, Jordi; Nakagawa, Kei; Ogura, Atsushi

    2015-11-01

    We have investigated photoluminescence (PL) at 4.2 K in highly doped and highly compensated Si with donor and acceptor impurities in the intermediate concentration range from 1 × 1016 to 3 × 1018 cm-3. PL spectra were dominated by the radiative recombination of excitons bound by impurity clusters and the donor-acceptor pair emission. The peak position of the exciton emission shifts to the lower energy side monotonically with an increase in the sum of the donor and acceptor concentrations, where the relationship between the position and the concentration is universal regardless of the species of impurities and is valid also for uncompensated Si. This allowed us to suggest that the cluster consists of multiple species of donor and acceptor impurities and that the difference in the species does not cause a detectable variation in the binding energy of an exciton. A possible method for quantifying the donor and acceptor impurities is proposed.

  11. Electronic excitation and relaxation processes of oxygen vacancies in YSZ and their involvement in photoluminescence

    NASA Astrophysics Data System (ADS)

    Morimoto, Takaaki; Kuroda, Yasuhiro; Ohki, Yoshimichi

    2016-09-01

    Yttria-stabilized zirconia (YSZ) consists of zirconia and yttria and oxygen vacancies appear in accordance with the ratio of yttria. The oxygen vacancy would sometimes give annoyance, but it would be beneficial on other occasions, depending on its applications. Photoluminescence (PL) due to oxygen vacancies induced by photons with energies around 5.5 eV exhibits two decay time constants. As a possible reason for this, an oxygen vacancy changes its charging state from neutral to positive monovalent by losing an electron when YSZ is irradiated by ultraviolet photons. The PL decays either in a ms range or in a ns range, depending on whether the oxygen vacancies are neutral or positive monovalent.

  12. Photoluminescence of zinc selenide single crystals annealed in zinc or selenium atmosphere

    SciTech Connect

    Yoshino, Kenji; Matsushima, Yasushi; Kinoshita, Hiroyoshi; Hiramatsu, Makoto

    1994-12-31

    Zinc selenide single crystals grown by the sublimation method are annealed in Zn or Se atmosphere. The annealing effects are examined by means of photoluminescence (PL) and reflection spectroscopy at 4.2 K. In the PL spectrum for the as-grown crystal, bound exciton lines (I{sub 2}, I{sub 1}) are observed. For the Zn-annealed crystal, the free exciton line is clearly observed. For the Se-annealed crystal, peak positions of all lines shift to the higher energies and all lines become sharp, compared with the spectra for the as-grown crystal. It is concluded that Sc-vacancies affect the bandgap energy more than Zn-vacancies do.

  13. Defect-Band Emission Photoluminescence Imaging on Multi-Crystalline Si Solar Cells: Preprint

    SciTech Connect

    Yan, F.; Johnston, S.; Zaunbrecher, K.; Al-Jassim, M.; Sidelkheir, O.; Blosse, A.

    2011-07-01

    Defect-band photoluminescence (PL) imaging with an InGaAs camera was applied to multicrystalline silicon (mc-Si) wafers, which were taken from different heights of different Si bricks. Neighboring wafers were picked at six different processing steps, from as-cut to post-metallization. By using different cut-off filters, we were able to separate the band-to-band emission images from the defect-band emission images. On the defect-band emission images, the bright regions that originate from the grain boundaries and defect clusters were extracted from the PL images. The area fraction percentage of these regions at various processing stages shows a correlation with the final cell electrical parameters.

  14. Characteristics and photoluminescence of nanotubes and nanowires of poly (3-methylthiophene)

    NASA Astrophysics Data System (ADS)

    Park, D. H.; Kim, B. H.; Jang, M. G.; Bae, K. Y.; Joo, J.

    2005-03-01

    We synthesized nanotubes and nanowires of π-conjugated poly (3-methylthiophene) (P3MT) by using nanoporous anodic aluminum oxide (Al2O3) template through electrochemical polymerization method. From scanning electron microscope and transmission electron microscope photographs, we observed the formation of nanotubes with diameters of 100-200 nm and wall thicknesses of 5-10 nm. Relatively long nanotubes and nanowires of P3MT (about 40μm in length) were obtained. To discern the structural and optical properties of the systems, we measured ultraviolet and visible absorbance and Fourier transform-infrared spectroscopy. We observed that the doping level, the π-π* transition peak, and bipolaron peaks in P3MT nanotubes varied with synthetic temperature. The photoluminescence (PL) spectra of the P3MT nanotubes solution were observed at ˜490nm. For the P3MT nanotubes synthesized at lower temperatures, the PL peaks became sharper and the resistance decreased.

  15. Improved photoluminescence property of CTAB assisted polyaniline-AlZnO nanocomposite

    SciTech Connect

    Mitra, Mousumi; Banerjee, Dipali; Kargupta, Kajari; Ganguly, Saibal

    2015-06-24

    Polyaniline-Al doped ZnO ((PANI-AlZnO:: 70:30) nanocomposite was prepared via in situ chemical oxidative polymerization, while the hexagonal powder of AlZnO was synthesized via sol-gel technique, using Hexadecyltrimethylammonium bromide (CTAB) as a capping agent. The prepared nanocomposite was characterized by High resolution transmission electron microscopy (HRTEM), EDAX, X-ray diffraction (XRD) and Fourier transforms infrared (FTIR) spectra. The optical property of the nanomaterials is examined by photoluminescence (PL) spectra analysis. The XRD pattern confirms the formation of Al doped ZnO as well as PANI. The HRTEM images of the composite showed the formation of hexagonal AlZnO embedded in polyaniline matrix. EDAX spectrum shows the compositional analysis of the nanocomposite. FTIR spectra confirm the formation of nanocomposite of PANI and hexagonal AlZnO. The PL intensity of the nanocomposite is improved as compared to pure AlZnO.

  16. Heterogeneous core/shell fluoride nanocrystals with enhanced upconversion photoluminescence for in vivo bioimaging.

    PubMed

    Hao, Shuwei; Yang, Liming; Qiu, Hailong; Fan, Rongwei; Yang, Chunhui; Chen, Guanying

    2015-06-28

    We report on heterogeneous core/shell CaF2:Yb(3+)/Ho(3+)@NaGdF4 nanocrystals of 17 nm with efficient upconversion (UC) photoluminescence (PL) for in vivo bioimaging. Monodisperse core/shell nanostructures were synthesized using a seed-mediated growth process involving two quite different approaches of liquid-solid-solution and thermal decomposition. They exhibit green emission with a sharp band around 540 nm when excited at ∼980 nm, which is about 39 times brighter than the core CaF2:Yb(3+)/Ho(3+) nanoparticles. PL decays at 540 nm revealed that such an enhancement arises from efficient suppression of surface-related deactivation from the core nanocrystals. In vivo bioimaging employing water-dispersed core/shell nanoparticles displayed high contrast against the background. PMID:26035440

  17. Enhanced photoluminescence of Si nanocrystals-doped cellulose nanofibers by plasmonic light scattering

    NASA Astrophysics Data System (ADS)

    Sugimoto, Hiroshi; Zhang, Ran; Reinhard, Björn M.; Fujii, Minoru; Perotto, Giovanni; Marelli, Benedetto; Omenetto, Fiorenzo G.; Dal Negro, Luca

    2015-07-01

    We report the development of bio-compatible cellulose nanofibers doped with light emitting silicon nanocrystals and Au nanoparticles via facile electrospinning. By performing photoluminescence (PL) spectroscopy as a function of excitation wavelength, we demonstrate plasmon-enhanced PL by a factor of 2.2 with negligible non-radiative quenching due to plasmon-enhanced scattering of excitation light from Au nanoparticles to silicon nanocrystals inside the nanofibers. These findings provide an alternative approach for the development of plasmon-enhanced active systems integrated within the compact nanofiber geometry. Furthermore, bio-compatible light-emitting nanofibers prepared by a cost-effective solution-based processing are very promising platforms for biophotonic applications such as fluorescence sensing and imaging.

  18. Sharp and bright photoluminescence emission of single-crystalline diacetylene nanoparticles

    NASA Astrophysics Data System (ADS)

    Kim, Seokho; Kim, Hyeong Tae; Park, Dong Hyuk; Xianling, Piao; Cui, Chunzhi

    2016-08-01

    Amorphous nanoparticles (NPs) of diacetylene (DA) molecules were prepared by using a reprecipitation method. After crystallization through a solvent-vapor annealing process, the highly crystalline DA NPs show different structural and optical characteristics compared with the amorphous DA NPs. The single crystal structure of DA NPs was confirmed by using high-resolution transmission electron microscopy (HR-TEM) and wide angle X-ray scattering (WAXS). The luminescence color and the photoluminescence (PL) characteristics of the DA NPs were measured using color charge-coupled device (CCD) images and high-resolution laser confocal microscope (LCM). The crystalline DA NPs, emit bright green light compared with amorphous DA NPs and the main PL peak of the crystalline DA NPs exhibits relatively narrow, blue-shift phenomena due to enhanced interactions between the DA molecules in the nano-size crystal structure.

  19. Enhanced photoluminescence of Si nanocrystals-doped cellulose nanofibers by plasmonic light scattering

    SciTech Connect

    Sugimoto, Hiroshi; Zhang, Ran; Reinhard, Björn M.; Fujii, Minoru; Perotto, Giovanni; Marelli, Benedetto; Omenetto, Fiorenzo G.; Dal Negro, Luca

    2015-07-27

    We report the development of bio-compatible cellulose nanofibers doped with light emitting silicon nanocrystals and Au nanoparticles via facile electrospinning. By performing photoluminescence (PL) spectroscopy as a function of excitation wavelength, we demonstrate plasmon-enhanced PL by a factor of 2.2 with negligible non-radiative quenching due to plasmon-enhanced scattering of excitation light from Au nanoparticles to silicon nanocrystals inside the nanofibers. These findings provide an alternative approach for the development of plasmon-enhanced active systems integrated within the compact nanofiber geometry. Furthermore, bio-compatible light-emitting nanofibers prepared by a cost-effective solution-based processing are very promising platforms for biophotonic applications such as fluorescence sensing and imaging.

  20. Fabrication of visibly photoluminescent Si microstructures by focused ion beam implantation and wet etching

    NASA Astrophysics Data System (ADS)

    Xu, J.; Steckl, A. J.

    1994-10-01

    A technique is reported for the fabrication of optically active Si microstructures embedded in a crystalline Si (c-Si) substrate. The process combines Si microstructure fabrication by localized high dose Ga+ (1016/cm2) focused ion beam (FIB) implantation at 30 kV into n-type (100) Si followed by anisotropic etching in KOH:H2O (1:5 by volume). Self-selective porous Si (PoSi) formation of the microstructures is obtained by stain etching in HF:HNO3:H2O (1:3:5 by volume). Upon UV 365 nm or Ar+ 488 nm excitation, selective visible room-temperature photoluminescence (PL) was observed from the Si microstructures only. The PL, peaked at ˜670 nm with a full width at half-magnitude (FWHM) of ˜130 nm, is similar to that of PoSi obtained from c-Si substrate.

  1. Formation and dynamics of "waterproof" photoluminescent complexes of rare earth ions in crowded environment.

    PubMed

    Ignatova, Tetyana; Blades, Michael; Duque, Juan G; Doorn, Stephen K; Biaggio, Ivan; Rotkin, Slava V

    2014-12-28

    Understanding behavior of rare-earth ions (REI) in crowded environments is crucial for several nano- and bio-technological applications. Evolution of REI photoluminescence (PL) in small compartments inside a silica hydrogel, mimic to a soft matter bio-environment, has been studied and explained within a solvation model. The model uncovered the origin of high PL efficiency to be the formation of REI complexes, surrounded by bile salt (DOC) molecules. Comparative study of these REI-DOC complexes in bulk water solution and those enclosed inside the hydrogel revealed a strong correlation between an up to 5×-longer lifetime of REIs and appearance of the DOC ordered phase, further confirmed by dynamics of REI solvation shells, REI diffusion experiments and morphological characterization of microstructure of the hydrogel. PMID:25379879

  2. Modification of Photoluminescence Properties of ZnO Island Films by Localized Surface Plasmons

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Li, Xue-Hong; Peng, Cheng-Xiao

    2012-10-01

    The modification of localised surface plasmons of photoluminescence properties of ZnO is studied. It is found that the ultraviolet emission is drastically enhanced, and the visible emission related to the defects is almost completely suppressed, after an Au layer of nanoparticles is deposited on the surface of ZnO island films. This pronounced change in PL spectra is attributed to the efficient electron transfer via the coupling of localised surface plasmons at the interface between the Au nanoparticle layer and ZnO films.

  3. Synthesis, structure and photoluminescence properties of Sm3+-doped BiOBr phosphor

    NASA Astrophysics Data System (ADS)

    Halappa, Pramod; Shivakumara, C.; Saraf, Rohit; Nagabhushana, H.

    2016-05-01

    Well-crystallized tetragonal layered BiOBr and Bi0.95Sm0.05OBr phosphors were prepared by the solid state method. These compounds were characterized using powder X-Ray diffraction and photoluminescence technique. In PL spectra, the electric dipole transitions dominate than other transitions which indicate that the Sm3+ ions occupy a site with an inversion center of BiOBr. CIE chromaticity diagram confirmed that these phosphors can be useful in the fabrication of red component in white light emitting diodes (WLEDs) for display device applications.

  4. Diameter Control and Photoluminescence of ZnO Nanorods from Trialkylamines

    DOE PAGES

    Andelman, Tamar; Gong, Yinyan; Neumark, Gertrude; O'Brien, Stephen

    2007-01-01

    A novel solution method to control the diameter of ZnO nanorods is reported. Small diameter (2-3 nm) nanorods were synthesized from trihexylamine, and large diameter (50–80 nm) nanorods were synthesized by increasing the alkyl chain length to tridodecylamine. The defect (green) emission of the photoluminescence (PL) spectra of the nanorods varies with diameter, and can thus be controlled by the diameter control. The small ZnO nanorods have strong green emission, while the large diameter nanorods exhibit a remarkably suppressed green band. We show that this observation supports surface oxygen vacancies as the defect that gives rise to the green emission.

  5. DNA detection using plasmonic enhanced near-infrared photoluminescence of gallium arsenide.

    PubMed

    Tang, Longhua; Chun, Ik Su; Wang, Zidong; Li, Jinghong; Li, Xiuling; Lu, Yi

    2013-10-15

    Efficient near-infrared detection of specific DNA with single nucleotide polymorphism selectivity is important for diagnostics and biomedical research. Herein, we report the use of gallium arsenide (GaAs) as a sensing platform for probing DNA immobilization and targeting DNA hybridization, resulting in ∼8-fold enhanced GaAs photoluminescence (PL) at ∼875 nm. The new signal amplification strategy, further coupled with the plasmonic effect of Au nanoparticles, is capable of detecting DNA molecules with a detection limit of 0.8 pM and selectivity against single base mismatches. Such an ultrasensitive near-infrared sensor can find a wide range of biochemical and biomedical applications.

  6. Synthesis and Photoluminescent Properties of Eu²⁺-Doped BaSiF₆ Nanoparticles.

    PubMed

    Zhao, Xin; Hua, Ruinian; Zhang, Wei; Zhao, Jun; Tang, Dongxin; Sun, Zhengang

    2016-01-01

    By adjusting the molar ratio of oleic acid (OA), oleylamine (OM), and 1-octadecene (OD) ligands in reaction solution, Eu²⁺-doped BaSiF₆ nanoparticles were synthesized using a thermal decomposition synthesis route. Eu²⁺ ions have been successfully doped into BaSiF₆ host lattice and strong 4f-4f line emission of the Eu²⁺ in BaSiF₆ matrix is observed. Meanwhile, the photoluminescent (PL) properties of BaSiF₆:Eu²⁺ nanoparticles doping Eu²⁺ ions at different concentrations were also studied. PMID:27398531

  7. Charge-tunnelling and self-trapping: common origins for blinking, grey-state emission and photoluminescence enhancement in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Osborne, M. A.; Fisher, A. A. E.

    2016-04-01

    Understanding instabilities in the photoluminescence (PL) from light emitting materials is crucial to optimizing their performance for different applications. Semiconductor quantum dots (QDs) offer bright, size tunable emission, properties that are now being exploited in a broad range of developing technologies from displays and solar cells to biomaging and optical storage. However, instabilities such as photoluminescence intermittency, enhancement and bleaching of emission in these materials can be detrimental to their utility. Here, we report dielectric dependent blinking, intensity-``spikes'' and low-level, ``grey''-state emission, as well as PL enhancement in ZnS capped CdSe QDs; observations that we found consistent with a charge-tunnelling and self-trapping (CTST) description of exciton-dynamics on the QD-host system. In particular, modulation of PL in grey-states and PL enhancement are found to have a common origin in the equilibrium between exciton charge carrier core and surface-states within the CTST framework. Parameterized in terms of size and electrostatic properties of the QD and its nanoenvironment, the CTST offers predictive insight into exciton-dynamics in these nanomaterials.Understanding instabilities in the photoluminescence (PL) from light emitting materials is crucial to optimizing their performance for different applications. Semiconductor quantum dots (QDs) offer bright, size tunable emission, properties that are now being exploited in a broad range of developing technologies from displays and solar cells to biomaging and optical storage. However, instabilities such as photoluminescence intermittency, enhancement and bleaching of emission in these materials can be detrimental to their utility. Here, we report dielectric dependent blinking, intensity-``spikes'' and low-level, ``grey''-state emission, as well as PL enhancement in ZnS capped CdSe QDs; observations that we found consistent with a charge-tunnelling and self-trapping (CTST

  8. Synthesis, characterization and photoluminescence studies of Mn doped ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Chandrakar, Raju Kumar; Baghel, R. N.; Chandra, V. K.; Chandra, B. P.

    2015-10-01

    The present paper reports the synthesis, characterization and photoluminescence (PL) studies of Mn doped ZnS nanoparticles prepared by chemical precipitation method using mercaptoethanol as a capping agent. The nanoparticles were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscope (FEGSEM), and high resolution transmission electron microscope (HRTEM). When the concentrations of capping agent (merceptoethanol) used are 0 M, 0.01 M, 0.025 M, 0.040 M, and 0.060 M, the sizes of the nanoparticles are 2.98 nm, 2.80 nm, 2.61 nm, 2.20 nm and 2.10 nm, respectively. Two peaks are obtained in the PL spectra of ZnS:Mn nanoparticles for the excitation wavelength of 220 nm, in which the first peak shifts from 400 nm to 388 nm with decreasing size of nanocrystals, and the second peak lies at 583 nm and it does not shift with reducing size of nanocrystals. The PL spectra of ZnS:Mn nanoparticles were measured for different concentrations of merceptoethanol used. The concentration of Mn was kept 1.2%, in which two peaks were found for each sample of ZnS:Mn nanocrystals. The intensities of both the PL peaks increase with reducing size of the nanoparticles. The PL emission centered at 583 nm is the characteristics emission of Mn-ion which can be attributed to a 4T1 → 6A1 transition. However, the blue emission around 400 nm is very broad and originates from the radiative recombination involving defect states in the ZnS nanocrystals. Expressions derived for the dependence of PL intensities of peak-I and peak-II on the size of nanoparticles are in good agreement with experimental results.

  9. Photoluminescence and structure of sputter-deposited Zn2SiO4:Mn thin films

    NASA Astrophysics Data System (ADS)

    Lee, Yeon Oh; Kim, Joo Han

    2016-01-01

    Mn-doped Zn2SiO4 thin films were deposited on Si (100) substrates by radio-frequency (RF) magnetron sputtering. The deposited films were then annealed at temperatures ranging from 600 to 1200 °C in an air ambient for 1 hour. The as-deposited Zn2SiO4:Mn films exhibited an amorphous structure having a smooth surface and showed no photoluminescence (PL). Annealing at 600 °C was found to have little effect on the properties of the films. The films still remained amorphous with no PL. After annealing at 800 °C, the films were crystallized in a mixture of orthorhombic β-Zn2SiO4 and rhombohedral α-Zn2SiO4 phases. These films showed a PL emission spectrum that could be resolved into two bands, one centered at 520 nm in the green region and the other at 571 nm in the yellow region. The green PL emission originated from the 4T1 → 6A1 intrashell transition of Mn2+ ions in the α-Zn2SiO4 phase while the yellow emission was attributed to Mn2+ ions in β-Zn2SiO4. The films annealed at and above a temperature of 900 °C exhibited only the α-Zn2SiO4 phase, and the PL spectra of these films showed only the green emission band with a peak maximum at around 523 nm. The PL emission intensity increased with increasing annealing temperature, which was due to the better crystalline quality and the rougher surface morphology of the Zn2SiO4:Mn films annealed at higher temperatures.

  10. Functional Exploration of the Polysaccharide Lyase Family PL6

    PubMed Central

    Mathieu, Sophie; Henrissat, Bernard; Labre, Flavien; Skjåk-Bræk, Gudmund; Helbert, William

    2016-01-01

    Alginate, the main cell-wall polysaccharide of brown algae, is composed of two residues: mannuronic acid (M-residues) and, its C5-epimer, guluronic acid (G-residues). Alginate lyases define a class of enzymes that cleave the glycosidic bond of alginate by β-elimination. They are classified according to their ability to recognize the distribution of M- and G-residues and are named M-, G- or MG-lyases. In the CAZy database, alginate lyases have been grouped by sequence similarity into seven distinct polysaccharide lyase families. The polysaccharide lyase family PL6 is subdivided into three subfamilies. Subfamily PL6_1 includes three biochemically characterized enzymes (two alginate lyases and one dermatan sulfatase lyase). No characterized enzymes have been described in the two other subfamilies (PL6_2 and PL6_3). To improve the prediction of polysaccharide-lyase activity in the PL6 family, we re-examined the classification of the PL6 family and biochemically characterized a set of enzymes reflecting the diversity of the protein sequences. Our results show that subfamily PL6_1 includes two dermatan sulfates lyases and several alginate lyases that have various substrate specificities and modes of action. In contrast, subfamilies PL6_2 and PL6_3 were found to contain only endo-poly-MG-lyases. PMID:27438604

  11. Magneto-Optical Study of Defect Induced Sharp Photoluminescence in LaAlO3 and SrTiO3

    PubMed Central

    Sarkar, Soumya; Saha, Surajit; Motapothula, M. R.; Patra, Abhijeet; Cao, Bing-Chen; Prakash, Saurav; Cong, Chun Xiao; Mathew, Sinu; Ghosh, Siddhartha; Yu, Ting; Venkatesan, T.

    2016-01-01

    Strongly correlated electronic systems such as Transition Metal Oxides often possess various mid-gap states originating from intrinsic defects in these materials. In this paper, we investigate an extremely sharp Photoluminescence (PL) transition originating from such defect states in two widely used perovskites, LaAlO3 and SrTiO3. A detailed study of the PL as a function of temperature and magnetic field has been conducted to understand the behavior and origin of the transition involved. The temperature dependence of the PL peak position for SrTiO3 is observed to be opposite to that in LaAlO3. Our results reveal the presence of a spin/orbital character in these transitions which is evident from the splitting of these defect energy levels under a high magnetic field. These PL transitions have the potential for enabling non-contact thermal and field sensors. PMID:27619076

  12. Magneto-Optical Study of Defect Induced Sharp Photoluminescence in LaAlO3 and SrTiO3

    NASA Astrophysics Data System (ADS)

    Sarkar, Soumya; Saha, Surajit; Motapothula, M. R.; Patra, Abhijeet; Cao, Bing-Chen; Prakash, Saurav; Cong, Chun Xiao; Mathew, Sinu; Ghosh, Siddhartha; Yu, Ting; Venkatesan, T.

    2016-09-01

    Strongly correlated electronic systems such as Transition Metal Oxides often possess various mid-gap states originating from intrinsic defects in these materials. In this paper, we investigate an extremely sharp Photoluminescence (PL) transition originating from such defect states in two widely used perovskites, LaAlO3 and SrTiO3. A detailed study of the PL as a function of temperature and magnetic field has been conducted to understand the behavior and origin of the transition involved. The temperature dependence of the PL peak position for SrTiO3 is observed to be opposite to that in LaAlO3. Our results reveal the presence of a spin/orbital character in these transitions which is evident from the splitting of these defect energy levels under a high magnetic field. These PL transitions have the potential for enabling non-contact thermal and field sensors.

  13. Hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot structure with enhanced photoluminescence

    SciTech Connect

    Ji, Hai-Ming; Liang, Baolai Simmonds, Paul J.; Juang, Bor-Chau; Yang, Tao; Young, Robert J.; Huffaker, Diana L.

    2015-03-09

    We investigate the photoluminescence (PL) properties of a hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot (QD) structure grown in a GaAs matrix by molecular beam epitaxy. This hybrid QD structure exhibits more intense PL with a broader spectral range, compared with control samples that contain only InAs or GaSb QDs. This enhanced PL performance is attributed to additional electron and hole injection from the type-I InAs QDs into the adjacent type-II GaSb QDs. We confirm this mechanism using time-resolved and power-dependent PL. These hybrid QD structures show potential for high efficiency QD solar cell applications.

  14. Magneto-Optical Study of Defect Induced Sharp Photoluminescence in LaAlO3 and SrTiO3.

    PubMed

    Sarkar, Soumya; Saha, Surajit; Motapothula, M R; Patra, Abhijeet; Cao, Bing-Chen; Prakash, Saurav; Cong, Chun Xiao; Mathew, Sinu; Ghosh, Siddhartha; Yu, Ting; Venkatesan, T

    2016-01-01

    Strongly correlated electronic systems such as Transition Metal Oxides often possess various mid-gap states originating from intrinsic defects in these materials. In this paper, we investigate an extremely sharp Photoluminescence (PL) transition originating from such defect states in two widely used perovskites, LaAlO3 and SrTiO3. A detailed study of the PL as a function of temperature and magnetic field has been conducted to understand the behavior and origin of the transition involved. The temperature dependence of the PL peak position for SrTiO3 is observed to be opposite to that in LaAlO3. Our results reveal the presence of a spin/orbital character in these transitions which is evident from the splitting of these defect energy levels under a high magnetic field. These PL transitions have the potential for enabling non-contact thermal and field sensors. PMID:27619076

  15. Temperature-dependent photoluminescence of CuAlO2 single crystals fabricated by using a flux self-removal method

    NASA Astrophysics Data System (ADS)

    Nam, Y. S.; Yoon, J. S.; Ju, H. L.; Chang, S. K.; Baek, K. S.

    2014-10-01

    The temperature-dependent behavior of p-type transparent semiconducting oxide CuAlO2 single crystals prepared by using a flux self-removal method in alumina crucibles was investigated through transmittance and photoluminescence (PL) measurements at temperatures from 12 K to room temperature. The low-temperature (12 K) PL spectrum shows two weak, broad emission peaks, one at 3.52 eV and the other at 3.08 eV, which we assign to excitonic emission and to defectrelated emission originating from copper vacancies. The positions of the PL peaks as functions of temperature exhibit a normal behavior satisfying the standard Varshini law, and the Debye temperature is found to be θ D = 610 ± 80 K. The exciton-binding energy of the CuAlO2 single crystal is estimated to be 49 meV from the PL intensity change with temperature.

  16. Change point analysis of matrix dependent photoluminescence intermittency of single CdSe/ZnS quantum dots with intermediate intensity levels

    NASA Astrophysics Data System (ADS)

    Schmidt, Robert; Krasselt, Cornelius; von Borczyskowski, Christian

    2012-10-01

    Blinking dynamics of single CdSe/ZnS quantum dots are analyzed by change point analysis, which gives access to intermediate photoluminescence (PL) intensities observed during PL intermittency. The on-times show systematic deviations from a (truncated) power law. This deviation is manifested in variations of the PL intensity distribution and is related with well defined PL intensity jumps. Varying the matrix from polystyrene (PS) to polyvinyl alcohol (PVA) changes the on-time blinking dynamics and reveals coupling of the QDs either to OH-groups of the SiOx interface or to OH-groups of PVA. Analysis of dwell times in respective intensity correlated traps reveals that OH-related traps are strongly stabilized with much longer dwell times as compared to otherwise broadly distributed trap states.

  17. Delocalized and localized charged excitons in single CdSe/CdS dot-in-rods revealed by polarized photoluminescence blinking

    NASA Astrophysics Data System (ADS)

    Ihara, Toshiyuki; Sato, Ryota; Teranishi, Toshiharu; Kanemitsu, Yoshihiko

    2014-07-01

    CdSe/CdS heterostructured nanocrystals with quasi-type-II band alignments provide an interesting platform for studying the photoluminescence (PL) blinking associated with their unique morphologies. By using simultaneous measurements of the PL intensity, lifetime, and polarization anisotropy, we reveal the role of the electron delocalization during the blinking of single CdSe/CdS dot-in-rods. We found that a significant change in the PL polarization anisotropy distinguishes between two kinds of charged excitons with different electron delocalizations. We report our observation of unique polarized PL blinking governed by the band alignments and the Coulomb interactions between the charges inside and outside the dot-in-rod.

  18. Carrier-density dependence of photoluminescence from localized states in InGaN/GaN quantum wells in nanocolumns and a thin film

    SciTech Connect

    Shimosako, N. Inose, Y.; Satoh, H.; Kinjo, K.; Nakaoka, T.; Oto, T.; Kishino, K.; Ema, K.

    2015-11-07

    We have measured and analyzed the carrier-density dependence of photoluminescence (PL) spectra and the PL efficiency of InGaN/GaN multiple quantum wells in nanocolumns and in a thin film over a wide excitation range. The localized states parameters, such as the tailing parameter, density and size of the localized states, and the mobility edge density are estimated. The spectral change and reduction of PL efficiency are explained by filling of the localized states and population into the extended states around the mobility edge density. We have also found that the nanocolumns have a narrower distribution of the localized states and a higher PL efficiency than those of the film sample although the In composition of the nanocolumns is higher than that of the film.

  19. Photoluminescence of polydiacetylene membranes on porous silicon utilized for chemical sensors

    NASA Astrophysics Data System (ADS)

    Sabatani, Eyal; Kalisky, Yehoshua; Berman, Amir; Golan, Yuval; Gutman, Nadav; Urbach, Benayahu; Sa'ar, Amir

    2008-07-01

    Langmuir-Blodgett (LB) films of the conjugated polydiacetylene (PDA) exhibit spectroscopic behavior, which is dependent on the type of the supporting substrate. While on polished silicon surfaces the photoluminescence (PL) of PDA is quenched, it is preserved on top of 2D patterned macro-porous silicon (2D-MPS). 2D-MPS, prepared by electrochemical etching of photo-lithographically pre-patterned silicon, is a 2D array of ca. 10 μm deep pores with lateral 2-4 μm repeating unit cells in orthogonal or hexagonal arrangements. LB films of PDA on such surfaces form membranes with continuous domains of the size sufficient to cover laterally many cell units. Apparently, the PL from this film results exclusively from the portion of the PDA membrane which is suspended over pore openings, while portions of the film which are attached to the silicon on top of the pores walls does not exhibit PL at all. We have used these membranes in different configurations and exposed them to different chemical and biological agents and followed the PL intensity change. This report demonstrates the effectiveness of the combined system: LB films of PDA on top of 2D-MPS as sensing probe for a variety of chemicals including, Cd ions and TNT explosives. In addition, the use of films of PDA, in which glycol-lipid were embedded, for binding and recognition of lectin protein, mimicking the cell membrane interaction with its environment, is also demonstrated.

  20. Hydrogen plasma induced modification of photoluminescence from a-SiNx:H thin films

    NASA Astrophysics Data System (ADS)

    Bommali, R. K.; Ghosh, S.; Vijaya Prakash, G.; Gao, K.; Zhou, S.; Khan, S. A.; Srivastava, P.

    2014-02-01

    Low temperature (250-350 °C) hydrogen plasma annealing (HPA) treatments have been performed on amorphous hydrogenated silicon nitride (a-SiNx:H) thin films having a range of compositions and subsequent modification of photoluminescence (PL) is investigated. The PL spectral shape and peak positions for the as deposited films could be tuned with composition and excitation energies. HPA induced modification of PL of these films is found to depend on the N/Si ratio (x). Upon HPA, the PL spectra show an emergence of a red emission band for x ≤ 1, whereas an overall increase of intensity without change in the spectral shape is observed for x > 1. The emission observed in the Si rich films is attributed to nanoscale a-Si:H inclusions. The enhancement is maximum for off-stoichiometric films (x ˜ 1) and decreases as the compositions of a-Si (x = 0) and a-Si3N4 (x = 1.33) are approached, implying high density of non-radiative defects around x = 1. The diffusion of hydrogen in these films is also analyzed by Elastic Recoil Detection Analysis technique.

  1. Efficient Excitonic Photoluminescence in Direct and Indirect Band Gap Monolayer MoS2.

    PubMed

    Steinhoff, A; Kim, J-H; Jahnke, F; Rösner, M; Kim, D-S; Lee, C; Han, G H; Jeong, M S; Wehling, T O; Gies, C

    2015-10-14

    We discuss the photoluminescence (PL) of semiconducting transition metal dichalcogenides on the basis of experiments and a microscopic theory. The latter connects ab initio calculations of the single-particle states and Coulomb matrix elements with a many-body description of optical emission spectra. For monolayer MoS2, we study the PL efficiency at the excitonic A and B transitions in terms of carrier populations in the band structure and provide a quantitative comparison to an (In)GaAs quantum well-structure. Suppression and enhancement of PL under biaxial strain is quantified in terms of changes in the local extrema of the conduction and valence bands. The large exciton binding energy in MoS2 enables two distinctly different excitation methods: above-band gap excitation and quasi-resonant excitation of excitonic resonances below the single-particle band gap. The latter case creates a nonequilibrium distribution of carriers predominantly in the K-valleys, which leads to strong emission from the A-exciton transition and a visible B-peak even if the band gap is indirect. For above-band gap excitation, we predict a strongly reduced emission intensity at comparable carrier densities and the absence of B-exciton emission. The results agree well with PL measurements performed on monolayer MoS2 at excitation wavelengths of 405 nm (above) and 532 nm (below the band gap). PMID:26322814

  2. Phosphorus and boron codoping of silicon nanocrystals by ion implantation: Photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Nakamura, Toshihiro; Adachi, Sadao; Fujii, Minoru; Miura, Kenta; Yamamoto, Shunya

    2012-01-01

    The photoluminescence (PL) properties of P or B single-doped Si nanocrystals (Si-nc's) and P and B co-doped Si-nc's are studied. In the single-doped Si-nc samples, PL quenching occurs as a result of the Auger nonradiative recombination process between the photoexcited excitons and free carriers supplied by doped impurities. In the (P, B) co-doped sample, on the other hand, the donor-acceptor (D-A)-pair recombination emission is clearly observed on the long-wavelength side of the intrinsic Si-nc emission peak at ˜900 nm. The D-A-pair recombination energy is found to be smaller than the band-gap energy of bulk Si and is strongly dependent on the number of P and B impurities doped in a Si-nc. PL spectra are measured at 50 and 300 K and found to indicate that strong thermal quenching occurs in a (P, B) co-doped sample at 300 K. This quenching effect is probably because of carrier migration among the donor and acceptor states. The PL decay rate is determined as a function of the emitted-light wavelength for the pure and (P, B) co-doped Si-nc samples.

  3. Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures

    PubMed Central

    Chen, Yulu; Wu, Qiong; Ma, Yingjie; Liu, Tao; Fan, Yongliang; Yang, Xinju; Zhong, Zhenyang; Xu, Fei; Lu, Jianping; Jiang, Zuimin

    2015-01-01

    The ability to control light-matter interaction is central to several potential applications in lasing, sensing, and communication. Graphene plasmons provide a way of strongly enhancing the interaction and realizing ultrathin optoelectronic devices. Here, we find that photoluminescence (PL) intensities of the graphene/GeSi quantum dots hybrid structures are saturated and quenched under positive and negative voltages at the excitation of 325 nm, respectively. A mechanism called plasmon-gating effect is proposed to reveal the PL dependence of the hybrid structures on the external electric field. On the contrary, the PL intensities at the excitation of 405 and 795 nm of the hybrid structures are quenched due to the charge transfer by tuning the Fermi level of graphene or the blocking of the excitons recombination by excitons separation effect. The results also provide an evidence for the charge transfer mechanism. The plasmon gating effect on the PL provides a new way to control the optical properties of graphene/QD hybrid structures. PMID:26631498

  4. Photoluminescence and contactless electroreflectance characterization of BexCd1-xSe alloys

    NASA Astrophysics Data System (ADS)

    Huang, P. J.; Huang, Y. S.; Firszt, F.; Meczynska, H.; Maksimov, O.; Tamargo, M. C.; Tiong, K. K.

    2007-01-01

    A detailed optical characterization of a Bridgman-grown wurtzite- (WZ-) type Be0.075Cd0.925Se mixed crystal and three zinc-blende (ZB) BexCd1-xSe epilayers grown by MBE on InP substrates has been carried out via photoluminescence (PL) and contactless electroreflectance (CER) in the temperature range of 15-400 K. The PL spectrum of the WZ-BeCdSe at low temperature consists of an exciton line, an edge emission feature due to recombination of donor-acceptor pairs, and a broad band related to recombination through deep-level defects, while the PL emission peaks of the ZB-BeCdSe epilayers show an asymmetric shape with a tail on the low-energy side. Various interband transitions, originating from the band edge and spin-orbit splitting critical points, of the samples have been observed in the CER spectra. The peak positions of the exciton emission lines in the PL spectra correspond quite well to the energies of the fundamental transitions determined from electromodulation data. The parameters that describe the temperature dependence of the fundamental and spin split-off bandgaps and the broadening function of the band-edge exciton are evaluated and discussed.

  5. Photoluminescence study of epitaxially grown ZnSnAs2:Mn thin films

    NASA Astrophysics Data System (ADS)

    Mammadov, E.; Haneta, M.; Toyota, H.; Uchitomi, N.

    2011-03-01

    The photoluminescence (PL) properties of heavily Mn-doped ZnSnAs2 layers epitaxially grown on nearly lattice-matched semi-insulating InP substrates are studied. PL spectra are obtained for samples with Mn concentrations of 5, 12 and 24 mol% relative to the combined concentrations of Zn and Sn. A broad emission band centered at ~ 1 eV is detected for Mn-doped layers at room temperature. The emission is a intense broad asymmetric line at low temperatures. The line is reconstructed by superposition of two bands with peak energies of ~ 0.99 and 1.07 eV, similar to those reported for InP. These bands are superimposed onto a 1.14 eV band with well-resolved phonon structure for the layer doped with 12 % Mn. Recombination mechanism involving the split-off band of the ZnSnAs2 is suggested. Temperature dependence of integrated intensities of the PL bands indicates to thermally activated emission with activation energies somewhat different from those found for InP. Mn substitution at cationic sites increases the concentration of holes which may act as recombination centers. Recombination to the holes bound to Mn ions with the ground state located below the top of the valence band has been proposed as a possible PL mechanism.

  6. Structural and photoluminescence properties of terbium-doped zinc oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Ningthoujam Surajkumar, Singh; Shougaijam Dorendrajit, Singh; Sanoujam Dhiren, Meetei

    2014-05-01

    We present in this paper a study of the structural and photoluminescence (PL) properties of terbium (Tb) doped zinc oxide (ZnO) nanoparticles synthesized by a simple low temperature chemical precipitation method, using zinc acetate and terbium nitrate in an isopropanol medium with diethanolamine (DEA) as the capping agent at 60 °C. The as-prepared samples were heat treated and the PL of the annealed samples were studied. The prepared nanoparticles were characterized with X-ray diffraction (XRD). The XRD patterns show the pattern of typical ZnO nanoparticles and correspond with the standard XRD pattern given by JCPDS card No. 36-1451, showing the hexagonal phase structure. The PL intensity was enhanced due to Tb3+ doping, and it decreased at higher concentrations of Tb3+ doping after reaching a certain optimum concentration. The PL spectra of Tb3+ doped samples exhibited blue, bluish green, and green emissions at 460 nm (5D3 - 7F3), 484 nm (5D4 - 7F6), and 530 nm (5D4 - 7F5), respectively, which were more intense than the emissions for the undoped ZnO sample. Based on the results, an energy level schematic diagram was proposed to explain the possible electron transition processes.

  7. Photoluminescence of Si nanocrystal memory devices obtained by ion beam synthesis

    SciTech Connect

    Carrada, Marzia; Wellner, Anja; Paillard, Vincent; Bonafos, Caroline; Coffin, Hubert; Claverie, Alain

    2005-12-19

    In this letter, we propose an original method to investigate Si nanocrystal-based nonvolatile memory devices, taking benefit of the photoluminescence (PL) spectroscopy and the specific optoelectronic properties of Si nanocrystals (Si-NCs). Ordered two-dimensional-arrays of Si-NCs were synthesized by ultralow-energy ion implantation in 7-nm-thick SiO{sub 2} and subsequent annealing. The Si-NCs population characteristics (size and density) were adjusted by different oxidizing annealing. This allowed, at the same time, the progressive healing of the oxide matrix. The analysis of the spectra revealed the presence of two PL bands, one due to quantum confinement effects in Si-NCs, and the other one attributed to silicon-rich oxide. Therefore, the evolution in energy and intensity of the PL bands was correlated to the oxidizing conditions, thus to the change of the Si-NCs size and density, and to the formation of stoichiometric SiO{sub 2}. These results are of great interest as being the first step in using PL spectroscopy as a nondestructive method to assess or monitor the electrical performances of the future memory devices, before any step of contact fabrication.

  8. Optical properties of GaSb measured using photoluminescence and photoreflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Jo, Hyun-Jun; So, Mo Geun; Kim, Jong Su; Lee, Sang Jun

    2016-09-01

    The optical properties of a GaSb layer were investigated using temperature-dependent photoluminescence (PL) and photoreflectance (PR) measurements. The defect-related transitions were observed at 0.714 and 0.728 eV in the PL measurements at 10 K. The band-to-band transition was observed at 0.712 eV in the PL measurement at 300 K. With decreasing temperature, the behavior of the defect-related transition changed slowly compared to the band-to-band transition. The PR spectrum at 300 K showed four signals of E 0 (0.72 eV), E 0 + Δ0 (1.52 eV), E 1 (2.07 eV) and E 1 + Δ1 (2.53 eV). The behavior of the E 1 transition was similar to that of the E 0 transition because the two transitions are band-to-band transitions. The behaviors of the eh transitions from the PL spectra were similar to the results for the E 0 of the PR spectra. The two PR signals of the E 1 transitions using below and above pumping were in good agreement across all temperatures. We confirmed that the below pumping technique was useful in the PR measurement.

  9. Photoluminescence from a Tb-doped photonic crystal microcavity for white light generation

    NASA Astrophysics Data System (ADS)

    Li, Yigang; Almeida, Rui M.

    2010-11-01

    Terbium-doped one-dimensional triple microcavities have been prepared by sol-gel processing. The photoluminescence (PL) of Tb3+ ions outside a microcavity structure, when excited by blue laser light at 488 nm, consisted of three distinct peaks at 542, 587 and 619 nm. When embedded in the microcavities, the three Tb3+ PL peaks were enhanced, balanced and broadened by the photonic crystal structure and combined into a continuous broad band. An analysis in the CIE colour space showed that white light can be obtained by mixing the modified Tb3+ PL with the blue exciting light, while this is impossible with the original PL profile. This novel technique may improve white light generation by enhancing and modifying the spontaneous emission of current phosphors. It may also lead to the development of new rare-earth phosphor materials based on 4f-4f transitions, able to generate white light more efficiently, via simpler and cheaper alternatives to the current phosphor compositions. A novel configuration to combine this kind of structure with a white light-emitting-diode (LED) is also proposed.

  10. Visible photoluminescence of porous Si(1-x)Ge(x) obtained by stain etching

    NASA Technical Reports Server (NTRS)

    Ksendzov, A.; Fathauer, R. W.; George, T.; Pike, W. T.; Vasquez, R. P.; Taylor, A. P.

    1993-01-01

    We have investigated visible photoluminescence (PL) from thin porous Si(1-x)Ge(x) alloy layers prepared by stain etching of molecular-beam-epitaxy-grown material. Seven samples with nominal Ge fraction x varying from 0.04 to 0.41 were studied at room temperature and 80 K. Samples of bulk stain etched Si and Ge were also investigated. The composition of the porous material was determined using X-ray photoemission spectroscopy and Rutherford backscattering techniques to be considerably more Ge-rich than the starting epitaxial layers. While the luminescence intensity drops significantly with the increasing Ge fraction, we observe no significant variation in the PL wavelength at room temperature. This is clearly in contradiction to the popular model based on quantum confinement in crystalline silicon which predicts that the PL energy should follow the bandgap variation of the starting material. However, our data are consistent with small active units containing only a few Si atoms that are responsible for the light emission. Such units are present in many compounds proposed in the literature as the cause of the visible PL in porous Si.

  11. Photoluminescence Dynamics of Aryl sp(3) Defect States in Single-Walled Carbon Nanotubes.

    PubMed

    Hartmann, Nicolai F; Velizhanin, Kirill A; Haroz, Erik H; Kim, Mijin; Ma, Xuedan; Wang, YuHuang; Htoon, Han; Doorn, Stephen K

    2016-09-27

    Photoluminescent defect states introduced by sp(3) functionalization of semiconducting carbon nanotubes are rapidly emerging as important routes for boosting emission quantum yields and introducing new functionality. Knowledge of the relaxation dynamics of these states is required for understanding how functionalizing agents (molecular dopants) may be designed to access specific behaviors. We measure photoluminescence (PL) decay dynamics of sp(3) defect states introduced by aryl functionalization of the carbon nanotube surface. Results are given for five different nanotube chiralities, each doped with a range of aryl functionality. We find that the PL decays of these sp(3) defect states are biexponential, with both components relaxing on time scales of ∼100 ps. Exciton trapping at defects is found to increases PL lifetimes by a factor of 5-10, in comparison to those for the free exciton. A significant chirality dependence is observed in the decay times, ranging from 77 ps for (7,5) nanotubes to >600 ps for (5,4) structures. The strong correlation of time constants with emission energy indicates relaxation occurs via multiphonon decay processes, with close agreement to theoretical expectations. Variation of the aryl dopant further modulates decay times by 10-15%. The aryl defects also affect PL lifetimes of the free E11 exciton. Shortening of the E11 bright state lifetime as defect density increases provides further confirmation that defects act as exciton traps. A similar shortening of the E11 dark exciton lifetime is found as defect density increases, providing strong experimental evidence that dark excitons are also trapped at such defect sites.

  12. Design And Ground Testing For The Expert PL4/PL5 'Natural And Roughness Induced Transition'

    NASA Astrophysics Data System (ADS)

    Masutti, Davie; Chazot, Olivier; Donelli, Raffaele; de Rosa, Donato

    2011-05-01

    Unpredicted boundary layer transition can impact dramatically the stability of the vehicle, its aerodynamic coefficients and reduce the efficiency of the thermal protection system. In this frame, ESA started the EXPERT (European eXPErimental Reentry Testbed) program to pro- vide and perform in-flight experiments in order to obtain aerothermodynamic data for the validation of numerical models and of ground-to-flight extrapolation methodologies. Considering the boundary layer transition investigation, the EXPERT vehicle is equipped with two specific payloads, PL4 and PL5, concerning respectively the study of the natural and roughness induced transition. The paper is a survey on the design process of these two in-flight experiments and it covers the major analyses and findings encountered during the development of the payloads. A large amount of transition criteria have been investigated and used to estimate either the dangerousness of the height of the distributed roughness, arising due to nose erosion, or the effectiveness of height of the isolated roughness element forcing the boundary layer transition. Supporting the PL4 design, linear stability computations and CFD analyses have been performed by CIRA on the EXPERT flight vehicle to determine the amplification factor of the boundary layer instabilities at different point of the re-entry trajectory. Ground test experiments regarding the PL5 are carried on in the Mach 6 VKI H3 Hypersonic Wind Tunnel with a Reynolds numbers ranging from 18E6/m to 26E6/m. Infrared measurements (Stanton number) and flow visualization are used on a 1/16 scaled model of the EXPERT vehicle and a flat plate to validate the Potter and Whitfield criterion as a suitable methodology for ground-to-flight extrapolation and the payload design.

  13. Effect of high energy proton irradiation on InAs/GaAs quantum dots: Enhancement of photoluminescence efficiency (up to {approx}7 times) with minimum spectral signature shift

    SciTech Connect

    Sreekumar, R.; Mandal, A.; Gupta, S.K.; Chakrabarti, S.

    2011-11-15

    Graphical abstract: Authors demonstrate enhancement in photoluminescence efficiency (7 times) in single layer InAs/GaAs quantum dots using proton irradiation without any post-annealing treatment via either varying proton energy (a) or fluence (b). The increase in PL efficiency is explained by a proposed model before (c) and after irradiation (d). Highlights: {yields} Proton irradiation improved PL efficiency in InAs/GaAs quantum dots (QDs). {yields} Proton irradiation favoured defect and strain annihilation in InAs/GaAs QDs. {yields} Reduction in defects/non-radiative recombination improved PL efficiency. {yields} Protons could be used to improve PL efficiency without spectral shift. {yields} QD based devices will be benefited by this technique to improve device performance. -- Abstract: We demonstrate 7-fold increase of photoluminescence efficiency in GaAs/(InAs/GaAs) quantum dot hetero-structure, employing high energy proton irradiation, without any post-annealing treatment. Protons of energy 3-5 MeV with fluence in the range (1.2-7.04) x 10{sup 12} ions/cm{sup 2} were used for irradiation. X-ray diffraction analysis revealed crystalline quality of the GaAs cap layer improves on proton irradiation. Photoluminescence study conducted at low temperature and low laser excitation density proved the presence of non-radiative recombination centers in the system which gets eliminated on proton irradiation. Shift in photoluminescence emission towards higher wavelength upon irradiation substantiated the reduction in strain field existed between GaAs cap layer and InAs/GaAs quantum dots. The enhancement in PL efficiency is thus attributed to the annihilation of defects/non-radiative recombination centers present in GaAs cap layer as well as in InAs/GaAs quantum dots induced by proton irradiation.

  14. Effects of Hydrogen in the Annealing Environment on Photoluminescence from Si Nanoparticles in SiO(2)

    SciTech Connect

    Barbour, J.C.; Budai, J.D.; Hembree, D.M.; Meldrum, A.; White, C.W.; Withrow, S.P.

    1999-03-23

    The role of hydrogen in enhancing the photoluminescence (PL) yield observed from Si nanocrystals embedded in SiO{sub 2} has been studied. SiO{sub 2} thermal oxides and bulk fused silica samples have been implanted with Si and subsequently annealed in various ambients including hydrogen or deuterium forming gases (Ar+4%H{sub 2} or Ar+4%D{sub 2}) or pure Ar. Results are presented for annealing at temperatures between 200 and 1100 C. Depth and concentration profiles of H and D at various stages of processing have been measured using elastic recoil detection. Hydrogen or deuterium is observed in the bulk after annealing in forming gas but not after high temperature (1100 C) anneals in Ar. The presence of hydrogen dramatically increases the broad PL band centered in the near-infrared after annealing at 1100 C but has almost no effect on the PL spectral distribution. Hydrogen is found to selectively trap in the region where Si nanocrystals are formed, consistent with a model of H passivating surface states at the Si/SiO{sub 2} interface that leads to enhanced PL. The thermal stability of the trapped H and the PL yield observed after a high temperature anneal have been studied. The hydrogen concentration and PL yield are unchanged for subsequent anneals up to 400 C. However, above 400 C the PL decreases and a more complicated H chemistry is evident. Similar concentrations of H or D are trapped after annealing in H{sub 2} or D{sub 2} forming gas; however, no differences in the PL yield or spectral distribution are observed, indicating that the electronic transitions resulting in luminescence are not dependent on the mass of the hydrogen species.

  15. Photoluminescence probing of interface evolution with annealing in InGa(N)As/GaAs single quantum wells

    SciTech Connect

    Shao, Jun Qi, Zhen; Zhu, Liang; Chen, Xiren; Guo, Shaoling; Zhao, H.; Song, Yuxin; Zha, F.-X.; Wang, S. M.

    2015-10-28

    The effects of thermal annealing on the interfaces of InGa(N)As/GaAs single quantum wells (SQWs) are investigated by excitation-, temperature-, and magnetic field-dependent photoluminescence (PL). The annealing at 750 °C results in more significant blueshift and narrowing to the PL peak than that at 600 °C. Each of the PL spectra can be reproduced with two PL components: (i) the low-energy component (LE) keeps energetically unchanged, while the high-energy component (HE) moves up with excitation and shows at higher energy for the In{sub 0.375}Ga{sub 0.625}As/GaAs but crosses over with the LE at a medium excitation power for the In{sub 0.375}Ga{sub 0.625}N{sub 0.012}As{sub 0.988}/GaAs SQWs. The HE is broader than the corresponding LE, the annealing at 750 °C narrows the LE and HE and shrinks their energetic separation; (ii) the PL components are excitonic, and the InGaNAs shows slightly enhanced excitonic effects relative to the InGaAs SQW; (iii) no typical S-shape evolution of PL energy with temperature is detectable, and similar blueshift and narrowing are identified for the same annealing. The phenomena are mainly from the interfacial processes. Annealing improves the intralayer quality, enhances the interfacial In-Ga interdiffusion, and reduces the interfacial fluctuation. The interfacial interdiffusion does not change obviously by the small N content and hence similar PL-component narrowing and blueshift are observed for the SQWs after a nominally identical annealing. Comparison with previous studies is made and the PL measurements under different conditions are shown to be effective for probing the interfacial evolution in QWs.

  16. Enhanced photoluminescence spectra of Sm3+ Co-doped with Tb3+ in PEO+PVP blended polymer films

    NASA Astrophysics Data System (ADS)

    Kumar, K. Naveen; Buddhudu, S.

    2015-06-01

    Sm3++Tb3+: PEO+PVP blended polymer films have successfully been synthesized by solution casting method. Structural and Optical analysis have been analyzed based on their XRD, optical absorption and photoluminescence spectral profiles. Semicrystalline nature has been confirmed by XRD analysis. Both optical absorption and photoluminescence spectra have been measured in evaluating their optical properties. The Sm3+: PEO+PVP polymer film has displayed a reddish-orange emission at 600 nm under UV lamp and its absorption and emission spectra have also been measured to evaluate its optical characteristics. The photoluminescence efficiency of Sm3+ ion has been enhanced due to the addition of Tb3+ by means of an energy transfer process. The energy transfer mechanism, from Tb3+ to Sm3+ has been explained clearly with Life time decay analysis. From these results, these films could be suggested as potential reddish-orange luminescent optical materials.

  17. Blue Photoluminescence From Silacyclobutene Compounds

    NASA Astrophysics Data System (ADS)

    Pernisz, Udo

    1999-04-01

    Organosilicon compounds in which the Si atom is bound to an aromatic moiety such as a phenyl group, exhibit strong blue photoluminescence when excited with UV light (for example at a wavelength of 337 nm). This phenomenon was investigated quantitatively at room temperature and at the temperature of liquid nitrogen (78 K) by measuring the emission and excitation spectra of the total luminescence, and of the phosphorescence, for a silacyclobutene compound in which two phenyl groups are joined across the C=C double bond of the ring. The effect of a series of organic substituents on the Si atom was investigated as well as the time dependence of the phosphorescence intensity decay for this class of materials. A tentative model of the energy levels in this compound is proposed. The observation of visible blue emission -- in contrast to photoluminescence in the UV from the aromatic groups -- is explained by the Si-C bond lowering the energy of the molecular orbitals, an effect that is currently under study for a range of Si-containing compounds. Synthesis of the silacyclobutene compounds was performed at the laboratory of Prof. N. Auner, now at J.W. Goethe Universität, Frankfurt, Germany. His contributions, and those of his collaborators, to the work reported here are gratefully acknowledged.

  18. Infrared photoluminescence from GeSi nanocrystals embedded in a germanium–silicate matrix

    SciTech Connect

    Volodin, V. A. Gambaryan, M. P.; Cherkov, A. G.; Vdovin, V. I.; Stoffel, M.; Rinnert, H.; Vergnat, M.

    2015-12-15

    We investigate the structural and optical properties of GeO/SiO{sub 2} multilayers obtained by evaporation of GeO{sub 2} and SiO{sub 2} powders under ultrahigh vacuum conditions on Si(001) substrates. Both Raman and infrared absorption spectroscopy measurements indicate the formation of GeSi nanocrystals after postgrowth annealing at 800°C. High-resolution transmission electron microscopy characterizations show that the average size of the nanocrystals is about 5 nm. For samples containing GeSi nanocrystals, photoluminescence is observed at 14 K in the spectral range 1500–1600 nm. The temperature dependence of the photoluminescence is studied.

  19. Giant photoluminescence enhancement in tungsten-diselenide–gold plasmonic hybrid structures

    PubMed Central

    Wang, Zhuo; Dong, Zhaogang; Gu, Yinghong; Chang, Yung-Huang; Zhang, Lei; Li, Lain-Jong; Zhao, Weijie; Eda, Goki; Zhang, Wenjing; Grinblat, Gustavo; Maier, Stefan A.; Yang, Joel K. W.; Qiu, Cheng-Wei; Wee, Andrew T. S.

    2016-01-01

    Impressive properties arise from the atomically thin nature of transition metal dichalcogenide two-dimensional materials. However, being atomically thin limits their optical absorption or emission. Hence, enhancing their photoluminescence by plasmonic nanostructures is critical for integrating these materials in optoelectronic and photonic devices. Typical photoluminescence enhancement from transition metal dichalcogenides is 100-fold, with recent enhancement of 1,000-fold achieved by simultaneously enhancing absorption, emission and directionality of the system. By suspending WSe2 flakes onto sub-20-nm-wide trenches in gold substrate, we report a giant photoluminescence enhancement of ∼20,000-fold. It is attributed to an enhanced absorption of the pump laser due to the lateral gap plasmons confined in the trenches and the enhanced Purcell factor by the plasmonic nanostructure. This work demonstrates the feasibility of giant photoluminescence enhancement in WSe2 with judiciously designed plasmonic nanostructures and paves a way towards the implementation of plasmon-enhanced transition metal dichalcogenide photodetectors, sensors and emitters. PMID:27150276

  20. Giant photoluminescence enhancement in tungsten-diselenide-gold plasmonic hybrid structures

    NASA Astrophysics Data System (ADS)

    Wang, Zhuo; Dong, Zhaogang; Gu, Yinghong; Chang, Yung-Huang; Zhang, Lei; Li, Lain-Jong; Zhao, Weijie; Eda, Goki; Zhang, Wenjing; Grinblat, Gustavo; Maier, Stefan A.; Yang, Joel K. W.; Qiu, Cheng-Wei; Wee, Andrew T. S.

    2016-05-01

    Impressive properties arise from the atomically thin nature of transition metal dichalcogenide two-dimensional materials. However, being atomically thin limits their optical absorption or emission. Hence, enhancing their photoluminescence by plasmonic nanostructures is critical for integrating these materials in optoelectronic and photonic devices. Typical photoluminescence enhancement from transition metal dichalcogenides is 100-fold, with recent enhancement of 1,000-fold achieved by simultaneously enhancing absorption, emission and directionality of the system. By suspending WSe2 flakes onto sub-20-nm-wide trenches in gold substrate, we report a giant photoluminescence enhancement of ~20,000-fold. It is attributed to an enhanced absorption of the pump laser due to the lateral gap plasmons confined in the trenches and the enhanced Purcell factor by the plasmonic nanostructure. This work demonstrates the feasibility of giant photoluminescence enhancement in WSe2 with judiciously designed plasmonic nanostructures and paves a way towards the implementation of plasmon-enhanced transition metal dichalcogenide photodetectors, sensors and emitters.

  1. Precision Landing and Hazard Avoidance (PL&HA) Domain

    NASA Technical Reports Server (NTRS)

    Robertson, Edward A.; Carson, John M., III

    2016-01-01

    The Precision Landing and Hazard Avoidance (PL&HA) domain addresses the development, integration, testing, and spaceflight infusion of sensing, processing, and GN&C (Guidance, Navigation and Control) functions critical to the success and safety of future human and robotic exploration missions. PL&HA sensors also have applications to other mission events, such as rendezvous and docking.

  2. Bright photoluminescent hybrid mesostructured silica nanoparticles.

    PubMed

    Miletto, Ivana; Bottinelli, Emanuela; Caputo, Giuseppe; Coluccia, Salvatore; Gianotti, Enrica

    2012-07-28

    Bright photoluminescent mesostructured silica nanoparticles were synthesized by the incorporation of fluorescent cyanine dyes into the channels of MCM-41 mesoporous silica. Cyanine molecules were introduced into MCM-41 nanoparticles by physical adsorption and covalent grafting. Several photoluminescent nanoparticles with different organic loadings have been synthesized and characterized by X-ray powder diffraction, high resolution transmission electron microscopy and nitrogen physisorption porosimetry. A detailed photoluminescence study with the analysis of fluorescence lifetimes was carried out to elucidate the cyanine molecules distribution within the pores of MCM-41 nanoparticles and the influence of the encapsulation on the photoemission properties of the guests. The results show that highly stable photoluminescent hybrid materials with interesting potential applications as photoluminescent probes for diagnostics and imaging can be prepared by both methods. PMID:22706523

  3. Structural changes and self-activated photoluminescence in reductively annealed Sr{sub 3}AlO{sub 4}F

    SciTech Connect

    Green, Robert; Avdeev, Maxim; Vogt, Thomas

    2015-08-15

    White light emission of self-activated photoluminescence (PL) in Sr{sub 3}AlO{sub 4}F under 254 nm light is only observed after annealing in a reducing atmosphere of 5%H{sub 2}/95%Ar. High-resolution neutron powder diffraction reveals that the FSr{sub 6} octahedrons and AlO{sub 4} tetrahedrons in this anti-perovskite structure are closer packed in reduced than in air-annealed samples which show no PL. Careful analysis of temperature-dependent neutron powder diffraction data establishes smaller isotropic displacement parameters for Sr(1) and O in Sr{sub 3}AlO{sub 4}F annealed in a reducing atmosphere indicating that the denser packing of the polyhedral sub-units leads to a slightly deeper potential for the Sr(1) and O atoms. Both the air- and reductively-annealed samples have identical thermal expansion within the temperature range between 3 and 350 K. The Debye temperatures were calculated using the atomic displacement parameters and show no significant differences between the air and reductively annealed samples making the Debye temperature a bad proxy for self-activated PL. - Graphical abstract: Annealing Sr{sub 3}AlO{sub 4}F under reducing conditions results in an intense self-activated photoluminescence which is correlated with a denser packing of FSr{sub 6} and AlO{sub 4} polyhedra. - Highlights: • Sr{sub 3}AlO{sub 4}F made in air does not show self-activated photoluminescence. • Only when annealing Sr{sub 3}AlO{sub 4}F in a reducing gas is photoluminescence observed. • FSr{sub 6} and AlO{sub 4} polyhedra in reduced Sr{sub 3}AlO{sub 4}F structure are packed more efficient. • Smaller displacement parameters are found for under-bonded Sr(1) and O sites.

  4. Enhancement in photoluminescence from 1 eV GaInNAs epilayers subject to 7 MeV electron irradiation

    NASA Astrophysics Data System (ADS)

    Pavelescu, E.-M.; Kudrawiec, R.; Bălţăţeanu, N.; Spânulescu, S.; Dumitrescu, M.; Guina, M.

    2013-02-01

    We have investigated the influence of 7 MeV electron irradiation (1014-1015 cm-2 range) and subsequent rapid thermal annealing (RTA) on luminescence efficiency of nearly lattice-matched 1 eV GaInNAs-on-GaAs epilayers, grown by molecular beam epitaxy. The study has been done by means of 9 K photoluminescence (PL) and 300 K photoreflectance (PR) spectroscopy. Electron irradiation was found to directly promote a notable increase in PL intensity. A further PL enhancement, remarkable at the higher annealing temperature, has been seen upon two RTA stages (at 800 and 900 °C) applied to irradiated samples as compared to a non-irradiated sample. This irradiation-promoted PL enhancement upon annealing occurred with a small additional blue-shift of PL for the lower temperature-annealed samples but no additional shift in PL was noted for the higher temperature-annealed sample. The additional annealing-induced PL blue-shift was mainly due to an irradiation-promoted enhancement in In-N bonds formation, whose magnitude does not appear to depend on dose within the studied range.

  5. Charge Injection at the Heterointerface in Perovskite CH3NH3PbI3 Solar Cells Studied by Simultaneous Microscopic Photoluminescence and Photocurrent Imaging Spectroscopy.

    PubMed

    Yamashita, Daiki; Handa, Taketo; Ihara, Toshiyuki; Tahara, Hirokazu; Shimazaki, Ai; Wakamiya, Atsushi; Kanemitsu, Yoshihiko

    2016-08-18

    Charge carrier dynamics in perovskite CH3NH3PbI3 solar cells were studied by means of microscopic photoluminescence (PL) and photocurrent (PC) imaging spectroscopy. The PL intensity, PL lifetime, and PC intensity varied spatially on the order of several tens of micrometers. Simultaneous PL and PC image measurements revealed a positive correlation between the PL intensity and PL lifetime, and a negative correlation between PL and PC intensities. These correlations were due to the competition between photocarrier injection from the CH3NH3PbI3 layer into the charge transport layer and photocarrier recombination within the CH3NH3PbI3 layer. Furthermore, we found that the decrease in the carrier injection efficiency under prolonged light illumination leads to a reduction in PC, resulting in light-induced degradation of solar cell devices. Our findings provide important insights for understanding carrier injection at the interface and light-induced degradation in perovskite solar cells. PMID:27482607

  6. Electronic states in Cd{sub 1{minus}x}Zn{sub x}Te/CdTe strained layer coupled double quantum wells and their photoluminescence

    SciTech Connect

    Li, T.; Lozykowski, H.J.; Reno, J.

    1994-12-31

    Experimental and theoretical investigation of electronic states in a strained-layer CdTe/CdZnTe coupled double quantum well structure are presented. The optical properties of this lattice-mismatched heterostructure were characterized with photoluminescence (PL), PL excitation and polarization spectroscopies. Influence of electrical field on exciton states in the strained-layer CdTe/CdZnTe coupled double quantum well structure is experimentally studied. The confined electronic states were calculated in the framework of the envelope function approach, taking into account the strain effect induced by the lattice-mismatch. Experimental results are compared with the calculated transition energies.

  7. Photoluminescence spectra of {ital n}-doped double quantum wells in a parallel magnetic field

    SciTech Connect

    Huang, D.; Lyo, S.K.

    1999-03-01

    We show that the photoluminescence (PL) line shapes from tunnel-split ground sublevels of {ital n}-doped thin double quantum wells (DQW{close_quote}s) are sensitively modulated by an in-plane magnetic field B{sub {parallel}} at low temperatures (T). The modulation is caused by the B{sub {parallel}}-induced distortion of the electronic structure. The latter arises from the relative shift of the energy-dispersion parabolas of the two quantum wells (QW{close_quote}s) in {rvec k} space, both in the conduction and valence bands, and formation of an anticrossing gap in the conduction band. Using a self-consistent density-functional theory, the PL spectra and the band-gap narrowing are calculated as a function of B{sub {parallel}}, {ital T}, and the homogeneous linewidths. The PL spectra from symmetric and asymmetric DQW{close_quote}s are found to show strikingly different behavior. In symmetric DQW{close_quote}s with a high density of electrons, two PL peaks are obtained at B{sub {parallel}}=0, representing the interband transitions between the pair of the upper (i.e., antisymmetric) levels and that of the lower (i.e., symmetric) levels of the ground doublets. As B{sub {parallel}} increases, the upper PL peak develops an N-type kink, namely a maximum followed by a minimum, and merges with the lower peak, which rises monotonically as a function of B{sub {parallel}} due to the diamagnetic energy. When the electron density is low, however, only a single PL peak, arising from the transitions between the lower levels, is obtained. In asymmetric DQW{close_quote}s, the PL spectra show mainly one dominant peak at all B{sub {parallel}}{close_quote}s. In this case, the holes are localized in one of the QW{close_quote}s at low {ital T} and recombine only with the electrons in the same QW. At high electron densities, the upper PL peak shows an N-type kink like in symmetric DQW{close_quote}s. However, the lower peak is absent at low B{sub {parallel}}{close_quote}s because it arises

  8. Photoluminescence of fluoroacrylate polymers impregnated with Eu(bta)3 using supercritical CO2

    NASA Astrophysics Data System (ADS)

    Gerasimova, V. I.; Antoshkov, A. A.; Zavorotny, Yu. S.; Lemenovskii, D. A.

    2012-05-01

    Optical properties (photoluminescence and absorption) of Eu(bta)3(B) n (B = H2O or 1,10-phenanthroline) polycrystalline powders and fluoroacrylate polymers (FAPs) impregnated with these compounds using supercritical CO2 (SC CO2) were investigated. It was established that impregnation of Eu(bta)3phen into the FAPs using an SC CO2 solution was difficult to achieve. The type of B (ancillary ligand) and the polymer matrix were shown to influence the temperature quenching of photoluminescence of Eu3+ ions in the range 25-100°C. A comparative analysis of quantum yields (λex = 300 and 380 nm) and photoluminescence decay times (λex = 337.1 nm) for Eu(bta)3B n and for Eu(bta)3B n -doped FAPs was performed.

  9. Control of Photoluminescence of Carbon Nanodots via Surface Functionalization using Para-substituted Anilines

    PubMed Central

    Kwon, Woosung; Do, Sungan; Kim, Ji-Hee; Seok Jeong, Mun; Rhee, Shi-Woo

    2015-01-01

    Carbon nanodots (C-dots) are a kind of fluorescent carbon nanomaterials, composed of polyaromatic carbon domains surrounded by amorphous carbon frames, and have attracted a great deal of attention because of their interesting properties. There are still, however, challenges ahead such as blue-biased photoluminescence, spectral broadness, undefined energy gaps and etc. In this report, we chemically modify the surface of C-dots with a series of para-substituted anilines to control their photoluminescence. Our surface functionalization endows our C-dots with new energy levels, exhibiting long-wavelength (up to 650 nm) photoluminescence of very narrow spectral widths. The roles of para-substituted anilines and their substituents in developing such energy levels are thoroughly studied by using transient absorption spectroscopy. We finally demonstrate light-emitting devices exploiting our C-dots as a phosphor, converting UV light to a variety of colors with internal quantum yields of ca. 20%. PMID:26218869

  10. Radiative and non-radiative recombinations in tensile strained Ge microstrips: Photoluminescence experiments and modeling

    SciTech Connect

    Virgilio, M.; Schroeder, T.; Yamamoto, Y.; Capellini, G.

    2015-12-21

    Tensile germanium microstrips are candidate as gain material in Si-based light emitting devices due to the beneficial effect of the strain field on the radiative recombination rate. In this work, we thoroughly investigate their radiative recombination spectra by means of micro-photoluminescence experiments at different temperatures and excitation powers carried out on samples featuring different tensile strain values. For sake of comparison, bulk Ge(001) photoluminescence is also discussed. The experimental findings are interpreted in light of a numerical modeling based on a multi-valley effective mass approach, taking in to account the depth dependence of the photo-induced carrier density and of the self-absorption effect. The theoretical modeling allowed us to quantitatively describe the observed increase of the photoluminescence intensity for increasing values of strain, excitation power, and temperature. The temperature dependence of the non-radiative recombination time in this material has been inferred thanks to the model calibration procedure.

  11. Visible to infrared photoluminescence from gold nanoparticles embedded in germano-silicate glass fiber.

    PubMed

    Lin, Aoxiang; Son, Dong Hoon; Ahn, Il Ho; Song, G Hugh; Han, Won-Taek

    2007-05-14

    Germano-silicate glass fiber containing gold nanoparticles was developed by modified chemical vapor deposition and solution doping processes. Pumping with 488 nm Argon ion laser, we firstly report on the visible to infrared photoluminescence of the gold nanoparticles embedded in the core of the germano-silicate fibers. The surface plasmon resonance absorption peak at 498.4 nm and the visible to infrared photoluminescence over the range of 600 nm approximately 1560 nm were found and explained according to the interband and intraband electronic transitions of Au atoms. The averaged quantum efficiencies of the photoluminescence at 833 nm and 1536 nm were estimated to be 5.75 x 10(-8) and 2.01 x 10(-9), respectively.

  12. Radiative and non-radiative recombinations in tensile strained Ge microstrips: Photoluminescence experiments and modeling

    NASA Astrophysics Data System (ADS)

    Virgilio, M.; Schroeder, T.; Yamamoto, Y.; Capellini, G.

    2015-12-01

    Tensile germanium microstrips are candidate as gain material in Si-based light emitting devices due to the beneficial effect of the strain field on the radiative recombination rate. In this work, we thoroughly investigate their radiative recombination spectra by means of micro-photoluminescence experiments at different temperatures and excitation powers carried out on samples featuring different tensile strain values. For sake of comparison, bulk Ge(001) photoluminescence is also discussed. The experimental findings are interpreted in light of a numerical modeling based on a multi-valley effective mass approach, taking in to account the depth dependence of the photo-induced carrier density and of the self-absorption effect. The theoretical modeling allowed us to quantitatively describe the observed increase of the photoluminescence intensity for increasing values of strain, excitation power, and temperature. The temperature dependence of the non-radiative recombination time in this material has been inferred thanks to the model calibration procedure.

  13. Near-infrared photoluminescence and thermally stimulated current in Cu3Ga5Se9 layered crystals: A comparative study

    NASA Astrophysics Data System (ADS)

    Gasanly, N. M.

    2016-07-01

    Near-infrared photoluminescence (PL) and thermally stimulated current (TSC) spectra of Cu3Ga5Se9 layered crystals grown by Bridgman method have been studied in the photon energy region of 1.35-1.46 eV and the temperature range of 15-115 K (PL) and 10-170 K (TSC). An infrared PL band centered at 1.42 eV was revealed at T = 15 K. Radiative transitions from shallow donor level placed at 20 meV to moderately deep acceptor level at 310 meV were suggested to be the reason of the observed PL band. TSC curve of Cu3Ga5Se9 crystal exhibited one broad peak at nearly 88 K. The thermal activation energy of traps was found to be 22 meV. An energy level diagram demonstrating the transitions in the crystal band gap was plotted taking account of results of PL and TSC experiments conducted below room temperature.

  14. Photoluminescence study on heavily donor and acceptor impurity doped GaAs layers grown by molecular-beam epitaxy

    SciTech Connect

    Islam, A. Z. M. Touhidul; Jung, D. W.; Noh, J. P.; Otsuka, N.

    2009-05-01

    Gallium arsenide layers doped with high concentrations of Be and Si by molecular-beam epitaxy are studied by photoluminescence (PL) spectroscopy. PL peaks from doped layers are observed at energies significantly lower than the band-gap of GaAs. The growth and doping conditions suggest that the origin of these peaks is different from that of low energy PL peaks, which were observed in earlier studies and attributed to impurity-vacancy complexes. The dependence of the peak energy on the temperature and the annealing is found to differ from that of the peaks attributed to impurity-vacancy complexes. On the basis of these observations, it is suggested that the low energy peaks are attributed to short range ordered arrangements of impurity ions. This possibility is examined by calculations of the PL spectra with models of pairs of acceptor and donor delta-doped layers and PL experiments of a superlattice of pairs of Be and Si delta-doped layers.

  15. Green synthesis of magnesium ion incorporated nanocrystalline hydroxyapatite and their mechanical, dielectric and photoluminescence properties

    SciTech Connect

    Arul, K. Thanigai; Kolanthai, Elayaraja; Manikandan, E.; Bhalerao, G.M.; Chandra, V. Sarath; Ramya, J. Ramana; Mudali, U. Kamachi; Nair, K.G.M.; Kalkura, S.Narayana

    2015-07-15

    Highlights: • Rapid technique to synthesize nanorods of magnesium ion incorporated hydroxyapatite. • Enhanced electrical and mechanical properties. • Improved photoluminescence and wettability on magnesium incorporation. • Increased in vitro bioactivity. - Abstract: Nanocrystalline hydroxyapatite (HAp-Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2,} 35 nm) and magnesium (Mg{sup 2+}) ion incorporated HAp were synthesized by microwave technique. XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), FE-HRTEM (Field emission high resolution transmission electron microscopy), DLS (dynamic light scattering), EDXRF (energy dispersive X-ray fluorescence spectrometry), microhardness, permittivity and alternating current (ac) conductivity, besides the PL (photoluminescence), wettability and in vitro bioactivity of the samples were analysed. EDXRF revealed the Mg{sup 2+} ion incorporation in HAp. The Mg{sup 2+} ion incorporation did not alter the phase but drastically reduced the crystallite size and particle size respectively by 48% and 32%. There was enhanced microhardness (24%) at low level (<13%) and decreased zeta potential of Mg{sup 2+} ion incorporation. The permittivity, ac conductivity, PL, wettability and in vitro bioactivity were enhanced on Mg{sup 2+} ion incorporation. These properties enable them to be a promising candidate for wound healing, bone replacement applications and also as a biosensor.

  16. Achieving highly-enhanced UV photoluminescence and its origin in ZnO nanocrystalline films

    NASA Astrophysics Data System (ADS)

    Thapa, Dinesh; Huso, Jesse; Morrison, John L.; Corolewski, Caleb D.; McCluskey, Matthew D.; Bergman, Leah

    2016-08-01

    ZnO is an efficient luminescent material in the UV-range ∼3.4 eV with a wide range of applications in optical technologies. Sputtering is a cost-effective and relatively straightforward growth technique for ZnO films; however, most as-grown films are observed to contain intrinsic defects which can significantly diminish the desirable UV-emission. In this research the defect dynamics and optical properties of ZnO sputtered films were studied via post-growth annealing in Ar or O2 ambient, with X-ray diffraction (XRD), imaging, transmission and Urbach analysis, Raman scattering, and photoluminescence (PL). The imaging, XRD, Raman and Urbach analyses indicate significant improvement in crystal morphology and band-edge characteristics upon annealing, which is nearly independent of the annealing environment. The native defects specific to the as-grown films, which were analyzed via PL, are assigned to Zni related centers that luminesce at 2.8 eV. Their presence is attributed to the nature of the sputtering growth technique, which supports Zn-rich growth conditions. After annealing, in either environment the 2.8 eV center diminished accompanied by morphology improvement, and the desirable UV-PL significantly increased. The O2 ambient was found to introduce nominal Oi centers while the Ar ambient was found to be the ideal environment for the enhancement of the UV-light emission: an enhancement of ∼40 times was achieved. The increase in the UV-PL is attributed to the reduction of Zni-related defects, the presence of which in ZnO provides a competing route to the UV emission. Also, the effect of the annealing was to decrease the compressive stress in the films. Finally, the dominant UV-PL at the cold temperature regime is attributed to luminescent centers not associated with the usual excitons of ZnO, but rather to structural defects.

  17. Effects of thermal annealing on photoluminescence of Si+/C+ implanted SiO2 films

    NASA Astrophysics Data System (ADS)

    Chen, Yin-Yu; Chao, Der-Sheng; Tsai, Hsu-Sheng; Liang, Jenq-Horng

    2016-04-01

    The mechanisms of photoluminescence (PL) originating from Si+/C+ implanted SiO2 are still unclear and need to be clarified. Thus, the purpose of this study is to thoroughly investigate the effects of ion implantation and post-annealing temperature on microstructures and PL characteristics of the Si+/C+ implanted SiO2 films. A comparative analysis was also conducted to clarify the different optical properties between the Si+ and Si+/C+ implanted SiO2 films. In this study, thermally-grown SiO2 films on Si substrates were used as the matrix materials. The Si+ ions and C+ ions were separately implanted into the SiO2 films at room temperature. After ion implantation, the post-annealing treatments were carried out using the furnace annealing (FA) method at various temperatures (600-1100 °C) for 1 h in a N2 ambient. The PL characteristics of the implanted SiO2 films were analyzed using a fluorescence spectrophotometer. The results revealed that the distinct PL peaks were observed at approximately 310, 450 and 650 nm in the Si+-implanted SiO2 films, which can be attributed to the defects, the so-called oxygen deficiency centers (ODCs) and non-bridging oxygen hole centers (NBOHCs), in the materials. In contrast to the Si+ ion implantation, the SiO2 films which were sequentially implanted with Si+ and C+ ions and annealed at 1100 °C can emit white light corresponding to the PL peaks located at around 420, 520 and 720 nm, those can be assigned to the Si-C bonding, C-C graphite-like structure (sp2), and Si nanocrystals, respectively. Moreover, a correlation between the optical properties, microstructures, and bonding configurations of the Si+/C+ implanted SiO2 films was also established in this study.

  18. Significant enhancement of optical absorption through nano-structuring of copper based oxide semiconductors: possible future materials for solar energy applications.

    PubMed

    Bhaumik, Anagh; Shearin, Austin M; Patel, Rishi; Ghosh, Kartik

    2014-06-14

    The optical absorption coefficient is a crucial parameter in determining solar cell efficiency under operational conditions. It is well known that inorganic nanocrystals are a benchmark model for solar cell nanotechnology, given that the tunability of optical properties and stabilization of specific phases are uniquely possible at the nanoscale. A hydrothermal method was employed to fabricate nanostructured copper oxides where the shape, size and phase were tailored by altering the growth parameters, namely the base media used, the reaction temperature, and the reaction time. The nano crystalline structures, phases, morphology, molecular vibrational modes, and optical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL), and UV-vis spectroscopy. A significantly large optical absorption coefficient, of the order of twice that of Si in the visible range, was observed in a particular phase mixture of nanostructured copper oxides. An optical absorption coefficient of 7.05 10(+5) cm(-1) at 525 nm was observed in a particular nanostructured phase mixture of copper oxides which is appreciably larger than commercially pure CuO (1.19 10(+5) cm(-1)) and Si (1.72 10(+5) cm(-1)). A possible mechanism of formation of phase mixtures and morphology of copper oxides has also been discussed, which opens up a roadmap in synthesis of similar morphology nanostructures for efficient solar cells.

  19. Synthesis, photoluminescence and magnetic properties of barium vanadate nanoflowers

    SciTech Connect

    Xu, Jing; Hu, Chenguo; Xi, Yi; Peng, Chen; Wan, Buyong; He, Xiaoshan

    2011-06-15

    Graphical abstract: The flower-shaped barium vanadate was obtained for the first time. The photoluminescence and magnetic properties of the barium vanadate nanoflowers were investigated at room temperature. Research highlights: {yields} In the paper, the flower-shaped barium vanadate were obtained for the first time. The CHM method used here is new and simple for preparation of barium vanadate. {yields} The photoluminescence and magnetic properties of the barium vanadate nanoflowers were investigated at room temperature. The strong bluish-green emission was observed. {yields} The ferromagnetic behavior of the barium vanadate nanoflowers was found with saturation magnetization of about 83.50 x 10{sup -3} emu/g, coercivity of 18.89 Oe and remnant magnetization of 4.63 x 10{sup -3} emu/g. {yields} The mechanisms of PL and magnetic property of barium vanadate nanoflowers have been discussed. -- Abstract: The flower-shaped barium vanadate has been obtained by the composite hydroxide mediated (CHM) method from V{sub 2}O{sub 5} and BaCl{sub 2} at 200 {sup o}C for 13 h. XRD and XPS spectrum of the as-synthesized sample indicate it is hexagonal Ba{sub 3}V{sub 2}O{sub 8} with small amount of Ba{sub 3}VO{sub 4.8} coexistence. Scan electron microscope and transmission electron microscope display that the flower-shaped crystals are composed of nanosheets with thickness of {approx}20 nm. The UV-visible spectrum shows that the barium vanadate sample has two optical gaps (3.85 eV and 3.12 eV). Photoluminescence spectrum of the barium vanadate flowers exhibits a visible light emission centered at 492 and 525 nm which might be attributed to VO{sub 4} tetrahedron with T{sub d} symmetry in Ba{sub 3}V{sub 2}O{sub 8}. The ferromagnetic behavior of the barium vanadate nanoflowers has been found with saturation magnetization of about 83.50 x 10{sup -3} emu/g, coercivity of 18.89 Oe and remnant magnetization of 4.63 x 10{sup -3} emu/g, which is mainly due to the presence of a non

  20. Spatially-Resolved Studies of Grain-Boundary Effects in Polycrystalline Solar Cells Using Micro-Photoluminescence and Near-Field Microscopy

    SciTech Connect

    Smith, S.; Dhere, R.; Gessert, T.; Stradins, P.; Mascarenhas, A.

    2005-01-01

    Photoluminescence and photocurrent spectroscopies combined with diffraction-limited and sub- diffraction-limited spatial resolution are achieved via micro-photoluminescence (m-PL) and near-field microscopy (NSOM). These methods are used to examine the photo-response of individual grain boundaries in thin-film, polycrystalline solar cells at room and cryogenic temperatures. A systematic m-PL study of the effect of CdCl2-treatment on recombination in CdTe/CdS solar cell structures of varying thickness directly reveals the grain-boundary and surface passivation action of this important post-growth processing step. We achieve 50nm (l/10) spatial resolution in near-field Optical Beam Induced Current imaging (n-OBIC) of polycrystalline silicon solar cells using NSOM, at varying stages of silicon nitride grain-boundary passivation, and measure lateral variations in photo-response of CdTe/CdS solar cells with subwavelength spatial resolution.

  1. Conjugated polymer network films of poly(p-phenylene vinylene) with hole-transporting carbazole pendants: dual photoluminescence and electrochromic behavior.

    PubMed

    Ponnapati, Ramakrishna; Felipe, Mary Jane; Muthalagu, Vetrichelvan; Puno, Katherine; Wolff, Birte; Advincula, Rigoberto

    2012-03-01

    A series of poly(p-phenylene vinylene) (PPV) copolymers functionalized with hole-transport and electrochemically active carbazole units as pendant moieties is reported. These polymers exhibit photoluminescence properties by virtue of the PPV analogous backbone. They were also designed as precursor polymer bearing the electroactive carbazole group to form conjugated polymer network (CPN) films by electrodeposition. The electrochemical polymerization of the pendant units eventually lead to a dual property electro-optically active thin film - photoluminescence (PL) behavior that can be attenuated with CPN formation, and a reversible doping and dedoping processes at controlled potentials that lead to an electrochromic behavior. This reveals the ability to incorporate complementary optical and electro-optical properties within the same film using the CPN approach. It should be possible to design and synthesize other PPV π-conjugated polymers with efficient pendant hole-transport groups exhibiting tunable PL and electrochromism with cross-linking. PMID:22329863

  2. Conjugated polymer network films of poly(p-phenylene vinylene) with hole-transporting carbazole pendants: dual photoluminescence and electrochromic behavior.

    PubMed

    Ponnapati, Ramakrishna; Felipe, Mary Jane; Muthalagu, Vetrichelvan; Puno, Katherine; Wolff, Birte; Advincula, Rigoberto

    2012-03-01

    A series of poly(p-phenylene vinylene) (PPV) copolymers functionalized with hole-transport and electrochemically active carbazole units as pendant moieties is reported. These polymers exhibit photoluminescence properties by virtue of the PPV analogous backbone. They were also designed as precursor polymer bearing the electroactive carbazole group to form conjugated polymer network (CPN) films by electrodeposition. The electrochemical polymerization of the pendant units eventually lead to a dual property electro-optically active thin film - photoluminescence (PL) behavior that can be attenuated with CPN formation, and a reversible doping and dedoping processes at controlled potentials that lead to an electrochromic behavior. This reveals the ability to incorporate complementary optical and electro-optical properties within the same film using the CPN approach. It should be possible to design and synthesize other PPV π-conjugated polymers with efficient pendant hole-transport groups exhibiting tunable PL and electrochromism with cross-linking.

  3. Tilted dipole model for bias-dependent photoluminescence pattern

    NASA Astrophysics Data System (ADS)

    Fujieda, Ichiro; Suzuki, Daisuke; Masuda, Taishi

    2014-12-01

    In a guest-host system containing elongated dyes and a nematic liquid crystal, both molecules are aligned to each other. An external bias tilts these molecules and the radiation pattern of the system is altered. A model is proposed to describe this bias-dependent photoluminescence patterns. It divides the liquid crystal/dye layer into sub-layers that contain electric dipoles with specific tilt angles. Each sub-layer emits linearly polarized light. Its radiation pattern is toroidal and is determined by the tilt angle. Its intensity is assumed to be proportional to the power of excitation light absorbed by the sub-layer. This is calculated by the Lambert-Beer's Law. The absorption coefficient is assumed to be proportional to the cross-section of the tilted dipole moment, in analogy to the ellipsoid of refractive index, to evaluate the cross-section for each polarized component of the excitation light. Contributions from all the sub-layers are added to give a final expression for the radiation pattern. Self-absorption is neglected. The model is simplified by reducing the number of sub-layers. Analytical expressions are derived for a simple case that consists of a single layer with tilted dipoles sandwiched by two layers with horizontally-aligned dipoles. All the parameters except for the tilt angle can be determined by measuring transmittance of the excitation light. The model roughly reproduces the bias-dependent photoluminescence patterns of a cell containing 0.5 wt. % coumarin 6. It breaks down at large emission angles. Measured spectral changes suggest that the discrepancy is due to self-absorption and re-emission.

  4. Tilted dipole model for bias-dependent photoluminescence pattern

    SciTech Connect

    Fujieda, Ichiro Suzuki, Daisuke; Masuda, Taishi

    2014-12-14

    In a guest-host system containing elongated dyes and a nematic liquid crystal, both molecules are aligned to each other. An external bias tilts these molecules and the radiation pattern of the system is altered. A model is proposed to describe this bias-dependent photoluminescence patterns. It divides the liquid crystal/dye layer into sub-layers that contain electric dipoles with specific tilt angles. Each sub-layer emits linearly polarized light. Its radiation pattern is toroidal and is determined by the tilt angle. Its intensity is assumed to be proportional to the power of excitation light absorbed by the sub-layer. This is calculated by the Lambert-Beer's Law. The absorption coefficient is assumed to be proportional to the cross-section of the tilted dipole moment, in analogy to the ellipsoid of refractive index, to evaluate the cross-section for each polarized component of the excitation light. Contributions from all the sub-layers are added to give a final expression for the radiation pattern. Self-absorption is neglected. The model is simplified by reducing the number of sub-layers. Analytical expressions are derived for a simple case that consists of a single layer with tilted dipoles sandwiched by two layers with horizontally-aligned dipoles. All the parameters except for the tilt angle can be determined by measuring transmittance of the excitation light. The model roughly reproduces the bias-dependent photoluminescence patterns of a cell containing 0.5 wt. % coumarin 6. It breaks down at large emission angles. Measured spectral changes suggest that the discrepancy is due to self-absorption and re-emission.

  5. Tunable photoluminescence from nc-Si/a-SiNx:H quantum dot thin films prepared by ICP-CVD.

    PubMed

    Sain, Basudeb; Das, Debajyoti

    2013-03-21

    Intense visible photoluminescence (PL) tunable within 1.66-2.47 eV, under UV 325 nm excitation, was obtained from nanocrystalline silicon quantum dots (∼5.72-1.67 nm in diameter) embedded in amorphous silicon-nitride matrix (nc-Si/a-SiN(x):H) prepared in RF-ICPCVD (13.56 MHz) at substrate temperatures between 400 to 150 °C. The dominant component of PL, having a narrow band width of ∼0.16-0.45 eV, originates from quasi-direct band-to-band recombination due to quantum confinement effect (QCE) in the nanocrystalline silicon quantum dots (nc-Si QDs) of appropriate size; however, the contribution of defects arose at lower substrate temperatures leading to asymmetric broadening. Intense atomic hydrogen flux in high-density inductively coupled plasmas (ICPs) provides a very high surface coverage, passivates well the nonradiative dangling bonds, and thereby favors the PL intensity. The average size of nc-Si QDs measured by HR-TEM appears consistent with similar estimates from Raman studies. The red shift of the Raman line and corresponding line broadening originates from the confinement of optical phonons within nc-Si QDs. Photoluminescence emerging from nc-Si/a-SiN(x):H quantum dots obtained from the low temperature and single-step plasma processing holds great promise for the fabrication of light-emitting devices and flexible flat panel displays. PMID:23407687

  6. Lymph capillary pressure of rat intestinal villi during fluid absorption.

    PubMed

    Lee, J S

    1979-09-01

    A newly developed intestinal preparation is described for determining lymph capillary pressure (PL) in the villi in vivo and in vitro. Determination of PL provided an estimate of tissue fluid pressure in the villi. PL was related to the fluid absorption rate and increased by lymphatic obstruction. During fluid absorption from isotonic mucosal fluid, PL was 1.4 +/- 0.5 or 1.1 +/- 0.4 cmH2O determined in vivo or in vitro, respectively. Both pressures were essentially in the same range as that (0.7 +/- 0.3--1.3 +/- 0.5 cmH2O) in which the mucosal fluid was isotonic Na2SO4 solution or Na-free solutions from which little fluid absorption occurred. This range of pressures may be taken as the normal tissue fluid pressure in the villi. At a high rate of fluid absorption from hypotonic mucosal fluid, PL increased to 5.2 +/- 1.4 cmH2O and tissue fluid pressure was also similarly increased. It is concluded that the fluid absorptive process by the epithelium could not develop an appreciable hydrostatic pressure in the villus tissue space or in the lymphatics.

  7. Time-Resolved Photoluminescence and Photovoltaics

    SciTech Connect

    Metzger, W. K.; Ahrenkiel, R. K.; Dippo, P.; Geisz, J.; Wanlass, M. W.; Kurtz, S.

    2005-01-01

    The time-resolved photoluminescence (TRPL) technique and its ability to characterize recombination in bulk photovoltaic semiconductor materials are reviewed. Results from a variety of materials and a few recent studies are summarized and compared.

  8. Photoluminescence and Raman behaviors of ZnO nanostructures with different morphologies

    NASA Astrophysics Data System (ADS)

    Chen, S. J.; Liu, Y. C.; Lu, Y. M.; Zhang, J. Y.; Shen, D. Z.; Fan, X. W.

    2006-03-01

    The morphology, structure and photoluminescence properties of ZnO nanostructures synthesized from different zinc precursors by a vapor transport process were investigated. The zinc precursors involved pure zinc powder, zinc powder mixed with graphite and zinc powder mixed with carbon nanotubes. The products were characterized by XRD, FESEM, TEM, Raman and PL techniques. The results indicated that the zinc precursors have a strong effect on the morphology and structural properties of the ZnO nanostructures. For the pure zinc, zinc mixed with graphite and zinc mixed with carbon nanotube, uniform tetrapod-, chrysanthemum- and needle-like morphologies are obtained, respectively. Photoluminescence measurements show that all the products have a strong near-band-edge UV emission accompanied by weak visible emissions. The relatively stronger green-light emission from the tetrapods implies that more defects exist in the tetrapods. A peak at 445 nm is found in the spectrum of the tetrapod-like nanostructures, which may be caused by oxygen-depletion interface traps. Furthermore, products synthesized at 600 °C demonstrate better photoluminescence properties than those synthesized at 450 °C.

  9. Photoluminescent properties of SPAN-80 coated intrinsic and extrinsic ZnO nanostructures

    NASA Astrophysics Data System (ADS)

    Kavita; Kumar, Dinesh; Singh, Karamjit; Kumar, Sunil; Bhatti, H. S.

    2016-05-01

    Semiconductor nanostructures catch the attention due to morphology tunable properties. SPAN-80-Capped intrinsic and extrinsic ZnO nanostructures have been synthesized by the simple wet-chemical synthesis route. Structural behavior (morphology and crystallography) and photoluminescence performance of synthesized nanomaterials have been explored as a function of variable SPAN-80 concentration (0.05-0.125%). Crystallographic studies reveal that the prepared products possess wurtzite structure. Electron microscopy infers that the quantum dots are bunched together to form multifaceted morphology for 0.05% SPAN-80 concentration, whereas rectangular shape has been observed for extreme capping concentration. Photoluminescence properties have affected drastically with the introduction of SPAN-80 during the precipitation reaction. Photoluminescent properties of the synthesized nanostructures are strongly dependent on SPAN-80 concentration. Augmentation of capping concentration from 0.05% to 0.075% diminishes the luminescence quantum yield due to increased surface passivation whereas further addition of capping agent beyond the optimum capping concentration (0.075%) enhances the PL intensity due to increased energy transfer from capping shell to the nanostructure core.

  10. Photoluminescence and electronic transitions in cubic silicon nitride

    PubMed Central

    Museur, Luc; Zerr, Andreas; Kanaev, Andrei

    2016-01-01

    A spectroscopic study of cubic silicon nitride (γ-Si3N4) at cryogenic temperatures of 8 K in the near IR - VUV range of spectra with synchrotron radiation excitation provided the first experimental evidence of direct electronic transitions in this material. The observed photoluminescence (PL) bands were assigned to excitons and excited and centers formed after the electron capture by neutral structural defects. The excitons are weakly quenched on neutral and strongly on charged defects. The fundamental band-gap energy of 5.05 ± 0.05 eV and strong free exciton binding energy ~0.65 eV were determined. The latter value suggests a high efficiency of the electric power transformation in light in defect-free crystals. Combined with a very high hardness and exceptional thermal stability in air, our results indicate that γ-Si3N4 has a potential for fabrication of robust and efficient photonic emitters. PMID:26725937

  11. Photoluminescence enhancement in quaternary III-nitrides alloys grown by molecular beam epitaxy with increasing Al content

    SciTech Connect

    Fernandez-Garrido, S.; Pereiro, J.; Gonzalez-Posada, F.; Munoz, E.; Calleja, E.

    2008-02-15

    Room temperature photoluminescence and optical absorption spectra have been measured in wurtzite In{sub x}Al{sub y}Ga{sub 1-x-y}N (x{approx}0.06, 0.02Photoluminescence spectra show both an enhancement of the integrated intensity and an increasing Stokes shift with the Al content. Both effects arise from an Al-enhanced exciton localization revealed by the S- and W-shaped temperature dependences of the photoluminescence emission energy and bandwidth, respectively. Present results point to these materials as a promising choice for the active region in efficient light emitters. An In-related bowing parameter of 1.6 eV was derived from optical absorption data.

  12. Syndrome in question: antisynthetase syndrome (anti-PL-7)*

    PubMed Central

    Esposito, Ana Cláudia Cavalcante; Gige, Tatiana Cristina; Miot, Hélio Amante

    2016-01-01

    Antisynthetase syndrome is a rare autoimmune disease characterized by interstitial lung disease and/or inflammatory myositis, with positive antisynthetase antibodies (anti-Jo-1, anti-PL-7, anti-PL-12, ZO, OJ, anti-KE or KS). Other symptoms described include: non-erosive arthritis, fever, Raynaud's phenomenon, and "mechanic's hands." The first therapeutic option is corticotherapy, followed by other immunosuppressants. The prognosis of the disease is quite limited when compared to other inflammatory myopathies with negative antisynthetase antibodies.

  13. The down-conversion and up-conversion photoluminescence properties of Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}:Yb{sup 3+}/Pr{sup 3+} ceramics

    SciTech Connect

    Huang, Yinpeng; Luo, Laihui Wang, Jia; Zuo, Qianghui; Yao, Yongjie; Li, Weiping

    2015-07-28

    Na{sub 0.5}Bi{sub 0.5−x−y}Yb{sub x}Pr{sub y}TiO{sub 3} (NBT:xYb/yPr) ceramics with different Yb and Pr contents are prepared. Both the down-conversion (DC) and up-conversion (UC) photoluminescence (PL) of the ceramics via 453 and 980 nm excitation, respectively, are investigated. The effect of Yb{sup 3+} and Pr{sup 3+} doping contents on the DC and UC PL is significantly different from each other. Furthermore, the UC PL of the ceramics as a function of temperatures is measured to investigate the UC process in detail. Based on energy level diagram of Pr{sup 3+} and Yb{sup 3+} ions and the DC and UC PL spectra, the DC and UC PL mechanisms of Pr{sup 3+} and Yb{sup 3+} ions are discussed. Especially, the UC PL mechanism is clarified, which is different from the previously reported literature. Also, the temperature sensing properties of the ceramics are studied based on the photoluminescence ratio technique, using the thermal coupling energy levels of Pr{sup 3+}.

  14. Impact of photoluminescence temperature and growth parameter on the exciton localized in BxGa1-xAs/GaAs epilayers grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Hidouri, Tarek; Saidi, Faouzi; Maaref, Hassen; Rodriguez, Philippe; Auvray, Laurent

    2016-10-01

    In this work, BxGa1-xAs/GaAs epilayers with three different boron compositions were elaborated by metal organic chemical vapor deposition (MOCVD) on GaAs (001) substrate. Structural study using High resolution X-ray diffraction (HRXRD) spectroscopy and Atomic Force Microscopy (AFM) have been used to estimate the boron fraction. The luminescence keys were carried out as functions of temperature in the range 10-300 K, by the techniques of photoluminescence (PL). The low PL temperature has shown an abnormal emission appeared at low energy side witch attributed to the recombination through the deep levels. In all samples, the PL peak energy and the full width at half maximum (FWHM), present an anomalous behavior as a result of the competition process between localized and delocalized carriers. We propose the Localized-state Ensemble model to explain the unusual photoluminescence behaviors. Electrical carriers generation, thermal escape, recapture, radiative and non-radiative lifetime are taken into account. The temperature-dependent photoluminescence measurements were found to be in reasonable agreement with the model of localized states. We controlled the evolution of such parameters versus composition by varying the V/III ratio to have a quantitative and qualitative understanding of the recombination mechanisms. At high temperature, the model can be approximated to the band-tail-state emission.

  15. In situ temperature measurements of reaction spaces under microwave irradiation using photoluminescent probes.

    PubMed

    Ano, Taishi; Kishimoto, Fuminao; Sasaki, Ryo; Tsubaki, Shuntaro; Maitani, Masato M; Suzuki, Eiichi; Wada, Yuji

    2016-05-11

    We demonstrate two novel methods for the measurement of the temperatures of reaction spaces locally heated by microwaves, which have been applied here to two example systems, i.e., BaTiO3 particles covered with a SiO2 shell (BaTiO3-SiO2) and layered tungstate particles. Photoluminescent (PL) probes showing the temperature-sensitivity in their PL lifetimes are located in the nanospaces of the above systems. In the case of BaTiO3-SiO2 core-shell particles, rhodamine B is loaded into the mesopores of the SiO2 shell covering the BaTiO3 core, which generates the heat through the dielectric loss of microwaves. The inner nanospace temperature of the SiO2 shell is determined to be 28 °C higher than the bulk temperature under microwave irradiation at 24 W. On the other hand, Eu(3+) is immobilized in the interlayer space of layered tungstate as the PL probe, showing that the nanospace temperature of the interlayer is only 4 °C higher than the bulk temperature. This method for temperature-measurement is powerful for controlling microwave heating and elucidates the ambiguous mechanisms of microwave special effects often observed in chemical reactions, contributing greatly to the practical application of microwaves in chemistry and materials sciences. PMID:27136754

  16. Photoluminescence of Cu-related states in CdTe and CdS

    NASA Astrophysics Data System (ADS)

    Price, K. J.

    2000-10-01

    We present results of Cu-related photoluminescence (PL) in CdTe and CdS single crystals, and CdS/CdTe polycrystalline devices, doped by diffusion of thermally evaporated Cu. In crystalline CdTe:Cu our results are consistent with some Cu atoms occupying substitutional positions on the Cd sublattice and with others forming pairs involving an interstitial Cu and a Cd vacancy. In addition, we find that Cu-related states in CdTe:Cu samples exhibit a reversible "aging" behavior. In crystalline CdS:Cu, the main effect of Cu diffusion is a quenching of the PL intensity. We also show evidence of an exciton bound to a Cu-related site that is stable under short-term light illumination. In addition, a donor-acceptor pair transition may be observed in CdS:Cu using excitation energies below the transition emission energy. We find that PL from polycrystalline CdS/CdTe solar cells with Cu back contacts is qualitatively similar to that in crystalline CdTe:Cu and CdS:Cu. We relate the results to stability behavior of CdS/CdTe solar cells with Cu contacts. This work is supported by NREL.

  17. Modified Photoluminescence by Silicon-Based One-Dimensional Photonic Crystal Microcavities

    NASA Astrophysics Data System (ADS)

    Chen, San; Qian, Bo; Wei, Jun-Wei; Chen, Kun-Ji; Xu, Jun; Li, Wei; Huang, Xin-Fan

    2005-01-01

    Photoluminescence (PL) from one-dimensional photonic band structures is investigated. The doped photonic crystal with microcavities are fabricated by using alternating hydrogenated amorphous silicon nitride (a-SiNx:H/a-SiNy:H) layers in a plasma enhanced chemical vapour deposition (PECVD) chamber. It is observed that microcavities strongly modify the PL spectra from active hydrogenated amorphous silicon nitride (a-SiNz:H) thin film. By comparison, the wide emission band width 208 nm is strongly narrowed to 11 nm, and the resonant enhancement of the peak PL intensity is about two orders of magnitude with respect to the emission of the λ/2-thick layer of a-SiNz:H. A linewidth of Δλ = 11 nm and a quality factor of Q = 69 are achieved in our one-dimensional a-SiNz photonic crystal microcavities. Measurements of transmittance spectra of the as-grown samples show that the transmittance resonant peak of a cavity mode at 710 nm is introduced into the band gap of one-dimensional photonic crystal distributed Bragg reflector (DBR), which further verifies the microcavity effects.

  18. pH- and Temperature-Sensitive Hydrogel Nanoparticles with Dual Photoluminescence for Bioprobes.

    PubMed

    Zhao, Yue; Shi, Ce; Yang, Xudong; Shen, Bowen; Sun, Yuanqing; Chen, Yang; Xu, Xiaowei; Sun, Hongchen; Yu, Kui; Yang, Bai; Lin, Quan

    2016-06-28

    This study demonstrates high contrast and sensitivity by designing a dual-emissive hydrogel particle system, whose two emissions respond to pH and temperature strongly and independently. It describes the photoluminescence (PL) response of poly(N-isopropylacrylamide) (PNIPAM)-based core/shell hydrogel nanoparticles with dual emission, which is obtained by emulsion polymerization with potassium persulfate, consisting of the thermo- and pH-responsive copolymers of PNIPAM and poly(acrylic acid) (PAA). A red-emission rare-earth complex and a blue-emission quaternary ammonium tetraphenylethylene derivative (d-TPE) with similar excitation wavelengths are inserted into the core and shell of the hydrogel nanoparticles, respectively. The PL intensities of the nanoparticles exhibit a linear temperature response in the range from 10 to 80 °C with a change as large as a factor of 5. In addition, the blue emission from the shell exhibits a linear pH response between pH 6.5 and 7.6 with a resolution of 0.1 unit, while the red emission from the core is pH-independent. These stimuli-responsive PL nanoparticles have potential applications in biology and chemistry, including bio- and chemosensors, biological imaging, cancer diagnosis, and externally activated release of anticancer drugs. PMID:27232534

  19. Low temperature growth and dimension- dependent photoluminescence efficiency of semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Hsu, Y.-J.; Lu, S.-Y.

    2005-08-01

    Low temperature growth and dimension dependent photoluminescence (PL) efficiency of semiconductor nanowires were investigated with CdS as a model system. The CdS nanowires were prepared with a simple, low temperature metal-organic chemical vapor deposition (MOCVD) process via the vapor liquid solid (VLS) mechanism. The low growth temperature of 360 °C was made possible with a newly developed single-source precursor of CdS and by using sputtered Au as the catalyst for the VLS growth. The length and diameter of the nanowires were adjusted by reaction time and sputtering conditions of Au, respectively. Nanowires of up to several μm in length and 20 to 200 nm in diameter were obtained. The PL quantum yield of the nanowires was found to decrease with increasing wire length, but to increase with decreasing wire diameter. This dimension-dependent PL efficiency of one-dimensional nanostructure, unlikely resulting from the quantum size confinement effect, appears to be a new observation that carries application significance.

  20. Enhanced photoluminescence in air-suspended carbon nanotubes by oxygen doping

    NASA Astrophysics Data System (ADS)

    Chen, Jihan; Dhall, Rohan; Hou, Bingya; Yang, Sisi; Wang, Bo; Kang, Daejing; Cronin, Stephen B.

    2016-10-01

    We report photoluminescence (PL) imaging and spectroscopy of air-suspended carbon nanotubes (CNTs) before and after exposure to a brief (20 s) UV/ozone treatment. These spectra show enhanced PL intensities in 10 out of 11 nanotubes that were measured, by as much as 5-fold. This enhancement in the luminescence efficiency is caused by oxygen defects which trap excitons. We also observe an average 3-fold increase in the D-band Raman intensity further indicating the creation of defects. Previous demonstrations of oxygen doping have been carried out on surfactant-coated carbon nanotubes dissolved in solution, thus requiring substantial longer ozone/UV exposure times (˜15 h). Here, the ozone treatment is more efficient because of the surface exposure of the air-suspended CNTs. In addition to enhanced PL intensities, we observe narrowing of the emission linewidth by 3-10 nm. This ability to control and engineer defects in CNTs is important for realizing several optoelectronic applications such as light-emitting diodes and single photon sources.

  1. Two color DNA barcode detection in photoluminescence suppressed silicon nitride nanopores.

    PubMed

    Assad, Ossama N; Di Fiori, Nicolas; Squires, Allison H; Meller, Amit

    2015-01-14

    Optical sensing of solid-state nanopores is a relatively new approach that can enable high-throughput, multicolor readout from a collection of nanopores. It is therefore highly attractive for applications such as nanopore-based DNA sequencing and genotyping using DNA barcodes. However, to date optical readout has been plagued by the need to achieve sufficiently high signal-to-noise ratio (SNR) for single fluorophore sensing, while still maintaining millisecond resolution. One of the main factors degrading the optical SNR in solid-state nanopores is the high photoluminescence (PL) background emanating from the silicon nitride (SiNx) membrane in which pores are commonly fabricated. Focusing on the optical properties of SiNx nanopores we show that the local membrane PL intensity is substantially reduced, and its spectrum is shifted toward shorter wavelengths with increasing e-beam dose. This phenomenon, which is correlated with a marked photocurrent enhancement in these nanopores, is utilized to perform for the first time single molecule fluorescence detection using both green and red laser excitations. Specifically, the reduction in PL and the concurrent measurement of the nanopore photocurrent enhancement allow us to maximize the background suppression and to detect a dual color, five-unit DNA barcode with high SNR levels. PMID:25522780

  2. Polarization memory effect in the photoluminescence of nc-Si-SiOx light-emitting structures.

    PubMed

    Michailovska, Katerina; Indutnyi, Ivan; Shepeliavyi, Petro; Sopinskyy, Mykola

    2016-12-01

    The polarization memory (PM) effect in the photoluminescence (PL) of the porous nc-Si-SiOx light-emitting structures, containing nanoparticles of silicon (nc-Si) in the oxide matrix and passivated in a solution of hydrofluoric acid (HF), has been investigated. The studied nc-Si-SiOx structures were produced by evaporation of Si monoxide (SiO) powder in vacuum and oblique deposition on Si wafer, and then the deposited silicon oxide (SiOx) films were annealed in the vacuum at 975 °C to grow nc-Si. It was found that the PM effect in the PL is observed only after passivation of nanostructures: during etching in HF solution, the initial symmetric nc-Si becomes asymmetric elongated. It was also found that in investigated nanostructures, there is a defined orientational dependence of the PL polarization degree (ρ) in the sample plane which correlates with the orientation of SiOx nanocolumns, forming the structure of the porous layer. The increase of the ρ values in the long-wavelength spectral range with time of HF treatment can be associated with increasing of the anisotropy of large Si nanoparticles. The PM effect for this spectral interval can be described by the dielectric model. In the short-wavelength spectral range, the dependence of the ρ values agrees qualitatively with the quantum confinement effect.

  3. Ultrabroad Photoluminescence and Electroluminescence at New Wavelengths from Doped Organometal Halide Perovskites.

    PubMed

    Zhou, Yang; Yong, Zi-Jun; Zhang, Kai-Cheng; Liu, Bo-Mei; Wang, Zhao-Wei; Hou, Jing-Shan; Fang, Yong-Zheng; Zhou, Yi; Sun, Hong-Tao; Song, Bo

    2016-07-21

    Doping of semiconductors by introducing foreign atoms enables their widespread applications in microelectronics and optoelectronics. We show that this strategy can be applied to direct bandgap lead-halide perovskites, leading to the realization of ultrawide photoluminescence (PL) at new wavelengths enabled by doping bismuth (Bi) into lead-halide perovskites. Structural and photophysical characterization reveals that the PL stems from one class of Bi doping-induced optically active center, which is attributed to distorted [PbI6] units coupled with spatially localized bipolarons. Additionally, we find that compositional engineering of these semiconductors can be employed as an additional way to rationally tune the PL properties of doped perovskites. Finally, we accomplished the electroluminescence at cryogenic temperatures by using this system as an emissive layer, marking the first electrically driven devices using Bi-doped photonic materials. Our results suggest that low-cost, earth-abundant, solution-processable Bi-doped perovskite semiconductors could be promising candidate materials for developing optical sources operating at new wavelengths. PMID:27377481

  4. Synthesis and Photoluminescence of Single-Crystalline Fe(III)-Doped CdS Nanobelts.

    PubMed

    Kamran, Muhammad Arshad; Zou, Bingsuo; Majid, A; Alharbil, Thamer; Saeed, M A; Abdullah, Ali; Javed, Qurat-ul-ain

    2016-04-01

    In this paper, we report the synthesis and optical properties of Fe(III) doped CdS nanobelts (NBs) via simple Chemical Vapor Deposition (CVD) technique to explore their potential in nano-optics. The energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis manifested the presence of Fe(III) ions in the NBs subsequently confirmed by the peak shifting to lower phonon energies as recorded by Raman spectra and shorter lifetime in ns. Photoluminescence (PL) spectrum investigations of the single Fe(III)-doped CdS NBs depicted an additional PL peak centered at 573 nm (orange emission) in addition to the bandedge(BE) emission. The redshift and decrease in the BE intensity of the PL peaks, as compared to the bulk CdS, confirmed the quenching of spectra upon Fe doping. The synthesis and orange emission for Fe-doped CdS NBs have been observed for the first time and point out their potential in nanoscale devices. PMID:27451769

  5. Polarization memory effect in the photoluminescence of nc-Si-SiOx light-emitting structures

    NASA Astrophysics Data System (ADS)

    Michailovska, Katerina; Indutnyi, Ivan; Shepeliavyi, Petro; Sopinskyy, Mykola

    2016-06-01

    The polarization memory (PM) effect in the photoluminescence (PL) of the porous nc-Si-SiOx light-emitting structures, containing nanoparticles of silicon (nc-Si) in the oxide matrix and passivated in a solution of hydrofluoric acid (HF), has been investigated. The studied nc-Si-SiOx structures were produced by evaporation of Si monoxide (SiO) powder in vacuum and oblique deposition on Si wafer, and then the deposited silicon oxide (SiOx) films were annealed in the vacuum at 975 °C to grow nc-Si. It was found that the PM effect in the PL is observed only after passivation of nanostructures: during etching in HF solution, the initial symmetric nc-Si becomes asymmetric elongated. It was also found that in investigated nanostructures, there is a defined orientational dependence of the PL polarization degree ( ρ) in the sample plane which correlates with the orientation of SiOx nanocolumns, forming the structure of the porous layer. The increase of the ρ values in the long-wavelength spectral range with time of HF treatment can be associated with increasing of the anisotropy of large Si nanoparticles. The PM effect for this spectral interval can be described by the dielectric model. In the short-wavelength spectral range, the dependence of the ρ values agrees qualitatively with the quantum confinement effect.

  6. Photoluminescence blinking and carrier dynamics in giant nanocrystals with different electron confinement

    NASA Astrophysics Data System (ADS)

    Sampat, Sid; Guo, Yijun; Vela, Javier; Malko, Anton

    2012-02-01

    Quantum dots have shown great promise as high quantum yield photon sources for applications in bioimaging, LEDs, lasers, etc. However, their photoluminescence (PL) intermittency (blinking) often complicates practical implementations. Recently, a new breed of giant nanocrystal quantum dots (gNQDs) with a large number of shell monolayers (ML) has been developed that show strongly suppressed blinkingootnotetextY. Chen et al., JACS 130, 5026 (2008) and existence of multiexcitons.ootnotetextY.S. Park et al., Phys. Rev. Lett. 106, 187401 (2011)^,ootnotetextA. V. Malko et al., Nano Lett., accepted (2011) So far, their PL emission has been limited to around 630nm. In this work, we broadened this approach and extended gNQD emission to shorter wavelength in the visible spectrum. We investigated photostable CdSe/CdS gNQDs with small (480nm emission) core and compared them to large (625nm emission) core non-blinking gNQDs with similar shell thickness (14-17 ML). The small core dots show increased blinking behavior and shorter PL decay times in comparison to large core dots. The observed difference in blinking behavior is suggestive of different carrier confinement regimes leading to enhanced electron trapping at the dot's surface as well as modifications to non-radiative Auger recombination rates.

  7. Characterization of Highly Efficient CdTe Thin Film Solar Cells by Low-Temperature Photoluminescence

    NASA Astrophysics Data System (ADS)

    Okamoto, Tamotsu; Matsuzaki, Yuichi; Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    1998-07-01

    Highly efficient CdTe thin film solar cells prepared by close-spaced sublimation (CSS) method with a glass/ITO/CdS/CdTe/Cu-doped carbon/Ag structure were characterized by low-temperature photoluminescence (PL) measurement. A broad 1.42 eV band probably due to VCd Cl defect complexes appeared as a result of CdCl2 treatment. CdS/CdTe junction PL revealed that a CdSxTe1-x mixed crystal layer was formed at the CdS/CdTe interface region during the deposition of CdTe by CSS and that CdCl2 treatment promoted the formation of the mixed crystal layer. Furthermore, in the PL spectra of the heat-treated CdTe after screen printing of the Cu-doped carbon electrode, a neutral-acceptor bound exciton (ACu0, X) line at 1.590 eV was observed, suggesting that Cu atoms were incorporated into CdTe as effective acceptors after the heat treatment.

  8. Photoluminescence detection of alpha particle using DAM-ADC nuclear detector

    NASA Astrophysics Data System (ADS)

    Abdalla, Ayman M.; Harraz, Farid A.; Ali, Atif M.; Al-Sayari, S. A.; Al-Hajry, A.

    2016-09-01

    The photoluminescence (PL) and UV-vis spectral analysis of DAM-ADC (diallyl maleate: DAM, polyallyl diglycol carbonate: ADC) nuclear detector are demonstrated for the first time. The DAM-ADC surfaces were exposed to thin 241Am disk source that emits alpha particles with activity 333 kBq. It is found that the track density of the irradiated samples remarkably influences the PL characteristics of the DAM-ADC detector. The spectral peak heights and the integrated intensities under the peaks exhibit linear correlations with correlation coefficient R2=0.9636 and 0.9806, respectively for different alpha particle fluences ranging from 8.16-40.82×107 particles/cm2. Additionally, a correlation coefficient R2=0.9734 was achieved for the UV-vis spectral analysis. The linear fitting functions, along with the corresponding fitting parameters were evaluated in each case. Both the PL and the UV-vis data of the irradiated DAM-ADC samples showed considerable spectral differences, and hence they would be used to offer sensitive approaches for alpha particle detection.

  9. Laser induced micro-photoluminescence of marble and application to authenticity testing of ancient objects

    NASA Astrophysics Data System (ADS)

    Polikreti, K.; Christofides, C.

    2008-02-01

    For the last 70 years, the authenticity of disputable marble objects has been tested by using a black light lamp. According to empirical observations “fresh marbles are purple while ancient ones are blue under the lamp”. This discrimination lacks scientific basis but is very popular because sculptured stone dating is impossible. This work aims to test the reliability of the “UV method” by studying the laser excited photoluminescence (PL) of marble surfaces. An argon ion laser beam was focused through a microscope objective onto the sample, offering a PL spatial resolution of 3 μm. Newly-cut marbles show an intense emission at 610 nm ascribed to Mn2+ and a less intense one at 390 nm. Excavated surfaces show the 610 nm emission and a broadband (380-530 nm) one. Similar broadband emissions due to humic (HAs) and fulvic acids (FAs) are typical in soil PL spectra and were observed in the spectra of samples taken from the soil surrounding the excavated surfaces. Additionally, electron paramagnetic resonance (EPR) spectra of excavated surfaces show a peak at g=2.0045, typical in calcite doped with humic acids. We presume that the 380-550 nm emission originates from HA and FA salts existing in the infiltrated soil or the recrystallised calcite developed in marble patinas. Finally, the application of the “UV method” on twelve ancient and modern surfaces proved that the technique is only partly reliable and should be used together with other analytical techniques.

  10. Structure, nanohardness and photoluminescence of ZnO ceramics based on nanopowders

    NASA Astrophysics Data System (ADS)

    Muktepavela, Faina; Grigorjeva, Larisa; Kundzins, Karlis; Gorokhova, Elena; Rodnyi, Piotr

    2015-09-01

    ZnO ceramics obtained from grained powders with different grain size by hot pressing and ceramics from tetrapods nanopowders obtained by press-less sintering have been investigated under identical conditions. Ceramics obtained by hot pressing were optically transparent but were composed of large inhomogeneous grains (d = 8-35 μm) exhibiting a substructure. Decreased values of elastic modulus within a grain and a wide defect-associated (‘green’) photoluminescence (PL) band at 2.2-2.8 eV in conjunction with a weak excitonic band indicate a high concentration of residual point defects in hot pressed ZnO ceramics. Utilization of more small-grained powders contributes to the formation of more uniform microstructure (d = 5-15 μm) and extraction of point defects. This reflects as a substantially decreased defect PL band and increased excitonic band. Ceramics obtained by press-less sintering from tetrapods had fine-grained structure (d = 1-4 μm) with no signs of a substructure. PL spectrum has a narrow excitonic band with phonon replicas (1LO_ExD0), whereas the defect ‘green’ luminescence is negligible. The effects of powders morphologies have been explained in terms of a hereditary influence of interaction processes between initial particles on the formation of a microstructure and kinetic of defect distribution on the grain growth stages during the sintering of ZnO ceramics.

  11. Facile synthesis and photoluminescence characteristics of blue-emitting nitrogen-doped graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Gu, Jian; Zhang, Xiaoping; Pang, Aimin; Yang, Jun

    2016-04-01

    A one-step hydrothermal method for synthesizing nitrogen-doped graphene quantum dots (N-GQDs) from organic carbon sources is presented in this paper. The high-quality N-GQDs can be obtained via tuning the degree of dehydration/carbonization of citric acid and doping of nitrogen atoms into the graphene lattice. The micromorphology, chemical structure, composition and photoluminescence (PL) characteristics of the N-GQDs were characterized systematically. The size of the obtained N-GQDs is about 5-10 nm with typical topographic heights of 0.8-2.5 nm. There is intense blue emission and excitation-independent PL behavior when the N-GQDs are in aqueous solution. The most remarkable innovation is that the fluorescence quantum yield (FL QY) of our N-GQDs is up to 75.2%, which is much higher than that of most reported GQDs (less than 25%). Thus, it is initially believed that synthesis parameters, hydrothermal process and nitrogen doping may greatly influence the surface state and bandgap of the GQDs, which are important in determining the PL characteristics of the N-GQDs.

  12. Growth mechanism, structure and IR photoluminescence studies of indium nitride nanorods

    NASA Astrophysics Data System (ADS)

    Lan, Z. H.; Wang, W. M.; Sun, C. L.; Shi, S. C.; Hsu, C. W.; Chen, T. T.; Chen, K. H.; Chen, C. C.; Chen, Y. F.; Chen, L. C.

    2004-08-01

    High-quality single crystal indium nitride nanorods were grown on Si substrates by catalytic chemical vapor deposition. Both Raman and high resolution transmission electron microscopic analyses suggested that even a minute amount of oxygen, from the residual oxygen in the growth environment and/or native oxide on the Si, would effectively help the growth of InN nanorods. The In 2O 3 formed on Au nanoparticles helped dissolve nitrogen as a catalyst with the subsequent growth of InN nanorods. Variations in the apparent color and photoluminescence (PL) spectra of the InN nanorods were observed. For the optically brown InN nanorods that exhibited diameters in the range of 30-50 nm, the PL study showed a peak at 1.9 eV, the possible origins of which are discussed. In contrast, for the optically black InN nanorods that exhibited diameters in the range of 50-100 nm, the PL peak at approximately 0.766 eV measured at 20 K was attributed to band edge emission.

  13. Improved photoluminescence efficiency in UV nanopillar light emitting diode structures by recovery of dry etching damage.

    PubMed

    Jeon, Dae-Woo; Jang, Lee-Woon; Jeon, Ju-Won; Park, Jae-Woo; Song, Young Ho; Jeon, Seong-Ran; Ju, Jin-Woo; Baek, Jong Hyeob; Lee, In-Hwan

    2013-05-01

    In this study, we have fabricated 375-nm-wavelength InGaN/AlInGaN nanopillar light emitting diodes (LED) structures on c-plane sapphire. A uniform and highly vertical nanopillar structure was fabricated using self-organized Ni/SiO2 nano-size mask by dry etching method. To minimize the dry etching damage, the samples were subjected to high temperature annealing with subsequent chemical passivation in KOH solution. Prior to annealing and passivation the UV nanopillar LEDs showed the photoluminescence (PL) efficiency about 2.5 times higher than conventional UV LED structures which is attributed to better light extraction efficiency and possibly some improvement of internal quantum efficiency due to partially relieved strain. Annealing alone further increased the PL efficiency by about 4.5 times compared to the conventional UV LEDs, while KOH passivation led to the overall PL efficiency improvement by more than 7 times. Combined results of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) suggest that annealing decreases the number of lattice defects and relieves the strain in the surface region of the nanopillars whereas KOH treatment removes the surface oxide from nanopillar surface. PMID:23858920

  14. Photoluminescence characterization of polythiophene films incorporated with highly functional molecules such as metallophthalocyanine

    SciTech Connect

    Kobe, Hiroaki; Ohnaka, Kazumasa; Kato, Hitoshi; Takemura, Susumu; Shimada, Kazuhiro; Hiramatsu, Tomoyasu; Matsui, Kazunori

    2013-01-15

    The photoluminescence (PL) of conducting polymer polythiophene (PT) films incorporated with metallophthalocyanines (PcMs) such as CuPc, MgPc, FePc, Li{sub 2}Pc, and CoPc was studied by PL and time-correlated single photon counting (TCSPC) measurements. Polymer films were prepared by electrochemical polymerization and PcMs migrated into the polymer films by a diffusion method using acetonitrile or toluene as a solvent to dissolve the PcMs. The wavelength of PL emission peaks changed significantly depending on the solvent used in the doping process. Using acetonitrile, the observed PL emission peaks originated from the Q band, whereas they were assigned to the Soret band in the case of toluene. TCSPC measurements showed that PL emission took place through a ligand-ligand transition process when using acetonitrile because the average lifetimes were comparable and independent of the central metal ions for CoPc-, Li{sub 2}Pc-, and MgPc-doped polymer films. Conversely, using toluene, it was found that ligand-ligand emission occurred for Li{sub 2}Pc-, MgPc-, and FePc-doped films. To identify the cause of the drastic change in PL emission pattern, x-ray photoelectron spectroscopy measurements were obtained. A lower binding energy component appeared in the C 1s core-level spectra of acetonitrile-processed PcM-doped PT films, whereas this component shifted to higher energy and overlapped with the main peak for toluene-processed PcM-doped PT films. The lower binding energy component corresponded to photoelectrons due to the C atoms in the benzene rings of the ligand. Lower binding energy components also appeared in the N 1s core-level spectra of acetonitrile-processed PcM-doped PT films, and this component shifted to higher energy for toluene-processed PcM-doped PT films. These lower energy components were assigned to the core-level peaks due to the N atoms at the meso position bridging between pyrrole rings. This suggests that the electron charge at the N sites of the meso

  15. Synthesis and characterization of a new photoluminescent material (8-hydroxy quinoline) bis (2-2'bipyridine) lanthanum La(Bpy)2q

    NASA Astrophysics Data System (ADS)

    Kumar, Rahul; Bhargava, Parag

    2016-05-01

    A new photoluminescence material, (8-hydroxy quinoline) bis (2-2'bipyridine) lanthanum has been synthesized and characterized by different techniques. The prepared material La(Bpy)2q was characterized for structural, thermal and photoluminescence analysis. Structural analysis of this material was done by Fourier transformed infrared spectroscopy (FTIR) and mass spectroscopy. Thermal analysis of this material was done by thermal gravimetric analysis (TGA) shows the thermal stability up to 190°C.Absorption and emission spectra of the material was measured by UV-visible spectroscopy and photoluminescence spectroscopy. Solution of this material La(Bpy)2q in ethanol showed absorption peak at 385nm, which may be attributed due to (π - π*) transitions. The photoluminescence spectra of La(Bpy)2q in ethanol solution showed intense peak at 490 nm

  16. Raman and Photoluminescence Spectroscopy in Mineral Identification

    NASA Astrophysics Data System (ADS)

    Kuehn, J. W.

    2014-06-01

    Raman spectroscopy is particularly useful for rapid identification of minerals and gemstones. Raman spectrometers also allow PL studies for authentication of samples and geological provenance, diamond type screening and detection of HPHT treatments.

  17. Iodomethane-Mediated Organometal Halide Perovskite with Record Photoluminescence Lifetime.

    PubMed

    Xu, Weidong; McLeod, John A; Yang, Yingguo; Wang, Yimeng; Wu, Zhongwei; Bai, Sai; Yuan, Zhongcheng; Song, Tao; Wang, Yusheng; Si, Junjie; Wang, Rongbin; Gao, Xingyu; Zhang, Xinping; Liu, Lijia; Sun, Baoquan

    2016-09-01

    Organometallic lead halide perovskites are excellent light harvesters for high-efficiency photovoltaic devices. However, as the key component in these devices, a perovskite thin film with good morphology and minimal trap states is still difficult to obtain. Herein we show that by incorporating a low boiling point alkyl halide such as iodomethane (CH3I) into the precursor solution, a perovskite (CH3NH3PbI3-xClx) film with improved grain size and orientation can be easily achieved. More importantly, these films exhibit a significantly reduced amount of trap states. Record photoluminescence lifetimes of more than 4 μs are achieved; these lifetimes are significantly longer than that of pristine CH3NH3PbI3-xClx films. Planar heterojunction solar cells incorporating these CH3I-mediated perovskites have demonstrated a dramatically increased power conversion efficiency compared to the ones using pristine CH3NH3PbI3-xClx. Photoluminescence, transient absorption, and microwave detected photoconductivity measurements all provide consistent evidence that CH3I addition increases the number of excitons generated and their diffusion length, both of which assist efficient carrier transport in the photovoltaic device. The simple incorporation of alkyl halide to enhance perovskite surface passivation introduces an important direction for future progress on high efficiency perovskite optoelectronic devices. PMID:27529636

  18. Observation and tunability of room temperature photoluminescence of GaAs/GaInAs core-multiple-quantum-well shell nanowire structure grown on Si (100) by molecular beam epitaxy

    PubMed Central

    2014-01-01

    We report the observation of room temperature photoluminescence (PL) emission from GaAs/GaInAs core-multiple-quantum-well (MQW) shell nanowires (NWs) surrounded by AlGaAs grown by molecular beam epitaxy (MBE) using a self-catalyzed technique. PL spectra of the sample show two PL peaks, originating from the GaAs core NWs and the GaInAs MQW shells. The PL peak from the shell structure red-shifts with increasing well width, and the peak position can be tuned by adjusting the width of the MQW shell. The GaAs/GaInAs core-MQW shell NW surrounded by AlGaAs also shows an enhanced PL intensity due to the improved carrier confinement owing to the presence of an AlGaAs clad layer. The inclined growth of the GaAs NWs produces a core-MQW shell structure having a different PL peak position than that of planar QWs. The PL emission by MQW shell and the ability to tune the PL peak position by varying the shell width make such core-shell NWs highly attractive for realizing next generation ultrasmall light sources and other optoelectronics devices. PACS 81.07.Gf; 81.15.Hi; 78.55.Cr PMID:25489280

  19. Redox properties of a single (7,5)single-walled carbon nanotube determined by an in situ photoluminescence spectroelectrochemical method.

    PubMed

    Hong, Liu; Mouri, Shinichiro; Miyauchi, Yuhei; Matsuda, Kazunari; Nakashima, Naotoshi

    2014-11-01

    The determination of electronic states of single-walled carbon nanotubes (SWNTs) has been a central issue in science and nanotechnology of carbon nanotubes. We here describe the oxidation and reduction potentials of a single SWNT determined by in situ photoluminescence (PL) spectroelectrochemical measurements. By PL imaging and single SWNT PL spectroscopy, the stepwise quenching behavior of the PL from a single (7,5)SWNT was detected as the outer-applied potentials increased. Based on the analysis of the obtained potential-dependent PL plots using the Nernst equation, the oxidation and reduction potentials of the (7,5) tube are successfully determined as 0.41 V and -0.38 V vs. Ag/AgCl, respectively, which shift from those of the bulk (7,5)SWNTs. We further observed a PL blueshift and narrowing of the line width as the external-applied potential to the single SWNT increases. The present results are important for understanding the electronic properties of a single (n,m)SWNT and its applications.

  20. Charge-tunnelling and self-trapping: common origins for blinking, grey-state emission and photoluminescence enhancement in semiconductor quantum dots.

    PubMed

    Osborne, M A; Fisher, A A E

    2016-04-28

    Understanding instabilities in the photoluminescence (PL) from light emitting materials is crucial to optimizing their performance for different applications. Semiconductor quantum dots (QDs) offer bright, size tunable emission, properties that are now being exploited in a broad range of developing technologies from displays and solar cells to biomaging and optical storage. However, instabilities such as photoluminescence intermittency, enhancement and bleaching of emission in these materials can be detrimental to their utility. Here, we report dielectric dependent blinking, intensity-"spikes" and low-level, "grey"-state emission, as well as PL enhancement in ZnS capped CdSe QDs; observations that we found consistent with a charge-tunnelling and self-trapping (CTST) description of exciton-dynamics on the QD-host system. In particular, modulation of PL in grey-states and PL enhancement are found to have a common origin in the equilibrium between exciton charge carrier core and surface-states within the CTST framework. Parameterized in terms of size and electrostatic properties of the QD and its nanoenvironment, the CTST offers predictive insight into exciton-dynamics in these nanomaterials. PMID:27088542

  1. Mapping of Defects in Large-Area Silicon Carbide Wafers via Photoluminescence and its Correlation with Synchrotron White Beam X-Ray Topography

    SciTech Connect

    Chen, Yi; Balaji, R.; Dudley, Michael; Murthy, Madhu; Maximenko, Serguei I.; Freitas, Jamie A.

    2008-12-12

    Comparative studies of defect microstructure in 4H-SiC wafers have been carried out using photoluminescence (PL) imaging and grazing-incidence Synchrotron White Beam X-ray Topography. Images of low angle grain boundaries on the PL images correlate well with SWBXT observations, and similar correlation can be established for some micropipe images although the latter is complicated by the overall level of distortion and misorientation associated with the low angle grain boundaries and the fact that many of the micropipes are located in or close to the boundaries. This validation indicates that PL imaging may provide a rapid way of imaging such defect structures in large-scale SiC wafers.

  2. Emission mechanisms in Al-rich AlGaN/AlN quantum wells assessed by excitation power dependent photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Iwata, Yoshiya; Banal, Ryan G.; Ichikawa, Shuhei; Funato, Mitsuru; Kawakami, Yoichi

    2015-02-01

    The optical properties of Al-rich AlGaN/AlN quantum wells are assessed by excitation-power-dependent time-integrated (TI) and time-resolved (TR) photoluminescence (PL) measurements. Two excitation sources, an optical parametric oscillator and the 4th harmonics of a Ti:sapphire laser, realize a wide range of excited carrier densities between 1012 and 1021 cm-3. The emission mechanisms change from an exciton to an electron-hole plasma as the excitation power increases. Accordingly, the PL decay time is drastically reduced, and the integrated PL intensities increase in the following order: linearly, super-linearly, linearly again, and sub-linearly. The observed results are well accounted for by rate equations that consider the saturation effect of non-radiative recombination processes. Using both TIPL and TRPL measurements allows the density of non-radiative recombination centers, the internal quantum efficiency, and the radiative recombination coefficient to be reliably extracted.

  3. Optical detection of argon gas flow based on vibration-induced change in photoluminescence of a semiconducting single-walled carbon nanotube bundle.

    PubMed

    Kim, Hong-Seok; Kim, Woo-Jae; Strano, Michael S; Hanl, Jae-Hee

    2014-12-01

    In this work, we demonstrate that Ar gas flow can be optically detected using mechanical vibration of a semiconducting single-walled carbon nanotube (SWCNT) bundle as a platform. A change in the photoluminescence (PL) intensity was induced by out-of-focusing of the SWCNT bundle of interest due to vibration caused by the introduced gas stream, for which a gas flow control system was installed in an optical microscope. The PL intensity was found to change systemically with the Ar flow rates in a range of relatively large flow rate intervals [0.70 to 3.0 standard cubic liters per minute (SLM) with 0.1-0.5 SLM intervals] with a noticeable hysteresis. It was, however, difficult to obtain a detectable PL change in a range of very small flow rate intervals (0.67 to 0.70 SLM with a 0.01 SLM interval). The detailed results and underlying mechanism are discussed in detail.

  4. Photoluminescence study on polar nanoregions and structural variations in Pb(Mg₁/₃Nb₂/₃)O₃ ₋ PbTiO₃ single crystals.

    PubMed

    Zhang, X L; Zhu, J J; Zhang, J Z; Xu, G S; Hu, Z G; Chu, J H

    2014-09-01

    We report polar nanostructure and electronic transitions in relaxor ferroelectric Pb(Mg₁/₃Nb₂/₃)O₃ ₋ PbTiO (PMN-PT) single crystals around morphotropic phase boundary (MPB) region by variable-temperature (80-800 K) photoluminescence (PL) spectra and low-wavenumber Raman scattering (LWRS). The discontinuous evolution from peak positions and intensity of luminescence emissions can be corresponding to formation of polar nanoclusters and phase transitions. Six emissions have been derived from PL spectra and show obvious characteristics near phase transition temperatures, which indicates that PL spectral measurement is promising in understanding the microcosmic mechanism. The Raman mode at 1145 cm(-1) indicates that temperature dependent luminescence phenomena can be modulated by thermal quenching. PMID:25321565

  5. Strong excitation intensity dependence of the photoluminescence line shape in GaAs{sub 1-x}Bi{sub x} single quantum well samples

    SciTech Connect

    Mazur, Yu. I.; Dorogan, V. G.; Ware, M. E.; Salamo, G. J.; Schmidbauer, M.; Tarasov, G. G.; Johnson, S. R.; Lu, X.; Yu, S.-Q.; Tiedje, T.

    2013-04-14

    A set of high quality single quantum well samples of GaAs{sub 1-x}Bi{sub x} with bismuth concentrations not exceeding 6% and well widths ranging from 7.5 to 13 nm grown by molecular beam epitaxy on a GaAs substrate at low temperature is studied by means of photoluminescence (PL). It is shown that the PL line shape changes when the exciton reduced mass behavior changes from an anomalous increase (x < 5%) to a conventional decrease (x > 5%). Strongly non-monotonous PL bandwidth dependence on the excitation intensity is revealed and interpreted in terms of optically unresolved contributions from the saturable emission of bound free excitons.

  6. Nanoscale mapping of excitonic processes in single-layer MoS2 using tip-enhanced photoluminescence microscopy.

    PubMed

    Su, Weitao; Kumar, Naresh; Mignuzzi, Sandro; Crain, Jason; Roy, Debdulal

    2016-05-19

    In two-dimensional (2D) semiconductors, photoluminescence originating from recombination processes involving neutral electron-hole pairs (excitons) and charged complexes (trions) is strongly affected by the localized charge transfer due to inhomogeneous interactions with the local environment and surface defects. Herein, we demonstrate the first nanoscale mapping of excitons and trions in single-layer MoS2 using the full spectral information obtained via tip-enhanced photoluminescence (TEPL) microscopy along with tip-enhanced Raman spectroscopy (TERS) imaging of a 2D flake. Finally, we show the mapping of the PL quenching centre in single-layer MoS2 with an unprecedented spatial resolution of 20 nm. In addition, our research shows that unlike in aperture-scanning near field microscopy, preferential exciton emission mapping at the nanoscale using TEPL and Raman mapping using TERS can be obtained simultaneously using this method that can be used to correlate the structural and excitonic properties. PMID:27152366

  7. Nanoscale mapping of excitonic processes in single-layer MoS2 using tip-enhanced photoluminescence microscopy.

    PubMed

    Su, Weitao; Kumar, Naresh; Mignuzzi, Sandro; Crain, Jason; Roy, Debdulal

    2016-05-19

    In two-dimensional (2D) semiconductors, photoluminescence originating from recombination processes involving neutral electron-hole pairs (excitons) and charged complexes (trions) is strongly affected by the localized charge transfer due to inhomogeneous interactions with the local environment and surface defects. Herein, we demonstrate the first nanoscale mapping of excitons and trions in single-layer MoS2 using the full spectral information obtained via tip-enhanced photoluminescence (TEPL) microscopy along with tip-enhanced Raman spectroscopy (TERS) imaging of a 2D flake. Finally, we show the mapping of the PL quenching centre in single-layer MoS2 with an unprecedented spatial resolution of 20 nm. In addition, our research shows that unlike in aperture-scanning near field microscopy, preferential exciton emission mapping at the nanoscale using TEPL and Raman mapping using TERS can be obtained simultaneously using this method that can be used to correlate the structural and excitonic properties.

  8. Mechanisms behind blue, green, and red photoluminescence emissions in CaWO4 and CaMoO4 powders

    NASA Astrophysics Data System (ADS)

    Campos, A. B.; Simões, A. Z.; Longo, E.; Varela, J. A.; Longo, V. M.; de Figueiredo, A. T.; De Vicente, F. S.; Hernandes, A. C.

    2007-07-01

    A combined experimental and theoretical study was conducted to analyze the photoluminescence (PL) properties of ordered and disordered CaWO4 (CW) and CaMoO4 (CM) powders. Two mechanisms were found to be responsible for photoluminescence emission in CW and CM powders. The first one, in the disordered powders, was caused by oxygen complex vacancies [MO3•VOx], [MO3•VO•] and [MO3•VO••], where M =W or Mo, which leads to additional levels in the band gap. The second mechanism, in ordered powders, was caused by an intrinsic slight distortion of the [WO4] or [MoO4] tetrahedral in the short range.

  9. Sensitive Room Temperature Photoluminescence-Based Sensing of H2S with Novel CuO-ZnO Nanorods.

    PubMed

    Liu, Xiao; Du, Baosheng; Sun, Ye; Yu, Miao; Yin, Yongqi; Tang, Wei; Chen, Chong; Sun, Lei; Yang, Bin; Cao, Wenwu; Ashfold, Michael N R

    2016-06-29

    Novel CuO nanoparticle-capped ZnO nanorods have been produced using a pulsed laser deposition (PLD) method. These nanorods are shown to grow by a CuO-nanoparticle-assisted vapor-solid-solid (V-S-S) mechanism. The photoluminescence (PL) accompanying ultraviolet illumination of these capped nanorod samples shows large variations upon exposure to trace quantities of H2S gas. The present data suggest that both the Cu-doped ZnO stem and the CuO capping nanoparticle contribute to optical H2S sensing with these CuO-ZnO nanorods. This study represents the first demonstration of PL-based H2S gas sensing, at room temperature, with sub-ppm sensitivity. It also opens the way to producing CuO-ZnO nanorods by a V-S-S mechanism using gas-phase methods other than PLD. PMID:27258907

  10. Photoluminescence studies of shock-recovered Y{sub 2}O{sub 3}:Eu{sup 3+}

    SciTech Connect

    Kishimura, Hiroaki Hamada, Sho; Aruga, Atsushi; Matsumoto, Hitoshi

    2015-01-05

    A series of shock-recovery experiments on Y{sub 2}O{sub 3}:Eu{sup 3+} powder were conducted involving the impact of a flyer plate accelerated by a single-stage powder-propellant gun. The recovered samples were characterized by X-ray diffraction (XRD) analysis and photoluminescence (PL) spectroscopy. The XRD and PL results of samples shocked at pressures of 13 GPa indicated that a phase transition from a cubic phase to a monoclinic phase occurred. The recovered samples shocked at 21 and 25 GPa consisted of Y{sub 2}O{sub 3}:Eu{sup 3+} with the cubic phase and the monoclinic phase. These results indicated that the shock-induced phase transition was the partial completion of the phase transition.

  11. Sn-filled Si nanotubes fabricated by the facile DC arc discharge method and their photoluminescence property

    NASA Astrophysics Data System (ADS)

    Feng, J. J.; Yan, P. X.; Yang, Q.; Chen, J. T.; Yan, D.

    2008-10-01

    High-yield preparation of polycrystalline Si nanotubes (SiNTs) filled with single-crystal Sn was achieved by the DC arc discharge method. The Sn/Si nanocables were identified by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and photoluminescence (PL). The results show that the Sn/Si coaxial nanocables have homogeneous diameters of about 20-30 nm and lengths ranging from several ten to several hundred nanometers. Most of them are composed of an oval-shaped tip and a tapered hollow body. The possible growth mechanism is vapor-liquid-solid (VLS) model. The PL spectrum shows two characteristic emissions at 491 nm (blue emission) and 572 nm (yellow emission). The origin of luminescence was also discussed.

  12. Parallel Synthesis of photoluminescent π-conjugated polymers by polymer reactions of an organotitanium polymer with a titanacyclopentadiene unit.

    PubMed

    Matsumura, Yoshimasa; Fukuda, Katsura; Inagi, Shinsuke; Tomita, Ikuyoshi

    2015-04-01

    A regioregular organometallic polymer with titanacyclopentadiene unit, obtained by the reaction of a 2,7-diethynylfluorene derivative and a low-valent titanium complex, is subjected to the reaction with three kinds of electrophiles (i.e., sulfur monochloride, hydrochloric acid, and dichlorophenylphosphine) to give π-conjugated polymers possessing both fluorene and building blocks originated from the transformation of the titanacycles in the main chain. For example, a phosphole-containing polymer whose number-average molecular weight is estimated as 5000 is obtained in 50% yield. The obtained thiophene, butadiene, and phosphole-containing polymers exhibit efficient photoluminescence (PL) with emission colors of blue, green, and yellow, respectively. For example, the phosphole-containing polymer exhibits yellow PL with an emission maximum (Emax ) of 533 nm and a quantum yield (Φ) of 0.37.

  13. Visible photoluminescence in polycrystalline terbium doped aluminum nitride (Tb:AlN) ceramics with high thermal conductivity

    SciTech Connect

    Wieg, A. T.; Kodera, Y.; Wang, Z.; Garay, J. E.; Imai, T.; Dames, C.

    2012-09-10

    Thermal management continues to be one of the major challenges in the development of high powered light sources such as solid state lasers. In particular, the relatively low thermal conductivity of standard photoluminescent (PL) materials limits the overall power output and/or duty cycle. We present a method based on current activated pressure assisted densification for the fabrication of high thermal conductivity PL materials: rare earth doped polycrystalline bulk aluminum nitride. Specifically, the ceramics are translucent and are doped with Tb{sup 3+}, allowing for emission in the visible. Remarkably, the ceramics have a room temperature thermal conductivity of 94 W/(m K) which is almost seven times higher than that of the state of the art host material, Nd-doped yttrium aluminum garnet. These light emitting properties coupled with very high thermal conductivity should enable the development of a wide variety of more powerful light sources.

  14. Sensitive Room Temperature Photoluminescence-Based Sensing of H2S with Novel CuO-ZnO Nanorods.

    PubMed

    Liu, Xiao; Du, Baosheng; Sun, Ye; Yu, Miao; Yin, Yongqi; Tang, Wei; Chen, Chong; Sun, Lei; Yang, Bin; Cao, Wenwu; Ashfold, Michael N R

    2016-06-29

    Novel CuO nanoparticle-capped ZnO nanorods have been produced using a pulsed laser deposition (PLD) method. These nanorods are shown to grow by a CuO-nanoparticle-assisted vapor-solid-solid (V-S-S) mechanism. The photoluminescence (PL) accompanying ultraviolet illumination of these capped nanorod samples shows large variations upon exposure to trace quantities of H2S gas. The present data suggest that both the Cu-doped ZnO stem and the CuO capping nanoparticle contribute to optical H2S sensing with these CuO-ZnO nanorods. This study represents the first demonstration of PL-based H2S gas sensing, at room temperature, with sub-ppm sensitivity. It also opens the way to producing CuO-ZnO nanorods by a V-S-S mechanism using gas-phase methods other than PLD.

  15. Plasmonic enhancements of photoluminescence in hybrid Si nanostructures with Au fabricated by fully top-down lithography

    PubMed Central

    2012-01-01

    The authors study plasmonic enhancements of photoluminescence (PL) in Si nanodisk (ND) arrays hybridized with nanostructures such as nanoplates of Au, where these hybrid nanostructures are fabricated by fully top-down lithography: neutral-beam etching using bio-nano-templates and high-resolution electron-beam lithography. The separation distance between the Si ND and Au nanostructure surfaces is precisely controlled by inserting a thin SiO2 layer with a thickness of 3 nm. We observe that PL intensities in the Si NDs are enhanced by factors up to 5 depending on the wavelength by integrating with the Au nanoplates. These enhancements also depend on the size and shape of the Au nanoplates. PMID:23158215

  16. Monitoring annealing via carbon dioxide laser heating of defect populations in fused silica surfaces using photoluminescence microscopy

    SciTech Connect

    Raman, R N; Matthews, M J; Adams, J J; Demos, S G

    2010-02-01

    Photoluminescence (PL) microscopy and spectroscopy under 266 nm and 355 nm laser excitation are explored as a means of monitoring defect populations in laser-modified sites on the surface of fused silica and their subsequent response to heating to different temperatures via exposure to a CO{sub 2} laser beam. Laser-induced temperature changes were estimated using an analytic solution to the heat flow equation and compared to changes in the PL emission intensity. The results indicate that the defect concentrations decrease significantly with increasing CO{sub 2} laser exposure and are nearly eliminated when the peak surface temperature exceeds the softening point of fused silica ({approx}1900K), suggesting that this method might be suitable for in situ monitoring of repair of defective sites in fused silica optical components.

  17. Color-tunable mixed photoluminescence emission from Alq3 organic layer in metal-Alq3-metal surface plasmon structure

    PubMed Central

    2014-01-01

    This work reports the color-tunable mixed photoluminescence (PL) emission from an Alq3 organic layer in an Au-Alq3-Au plasmonic structure through the combination of organic fluorescence emission and another form of emission that is enabled by the surface plasmons in the plasmonic structure. The emission wavelength of the latter depends on the Alq3 thickness and can be tuned within the Alq3 fluorescent spectra. Therefore, a two-color broadband, color-tunable mixed PL structure was obtained. Obvious changes in the Commission Internationale d’Eclairage (CIE) coordinates and the corresponding emission colors of Au-Alq3-Au samples clearly varied with the Alq3 thickness (90, 130, and 156 nm). PMID:25328506

  18. Effects of morphology on the structural and photoluminescence properties of co-precipitation derived GdVO4:Dy3+

    NASA Astrophysics Data System (ADS)

    Kumari, Puja; Manam, J.

    2016-10-01

    Herein, Dy3+ doped GdVO4 samples with various morphologies were prepared by the co-precipitation method at low temperature, and the effects of different morphologies on the structural and optical behaviors have been reported. The obtained samples were stabilized to the stable tetragonal structure. The IR and FESEM study were carried out to see the vibrational bonds position and surface morphology. At present PL, PLE, diffuse reflectance and decay curves have been discussed in detail. The morphology dependent photoluminescence studies were resulted to a suitable sample for the lighting and display applications.

  19. Photoluminescence spectroscopy and energy-level analysis of metal-organic-deposited Ga2O3:Cr3+ films

    NASA Astrophysics Data System (ADS)

    Tokida, Yoshinori; Adachi, Sadao

    2012-09-01

    The aims of this study are (i) to demonstrate the synthesis of Cr3+-activated β-Ga2O3 films by metal-organic deposition and (ii) to report the temperature-dependent photoluminescence (PL) properties of such films from 20 to 300 K. An activation energy of ˜0.9 eV for the Cr3+ ions in β-Ga2O3 is determined from a plot of PL intensity vs calcination temperature. The red-line emission doublet R1 and R2 at ˜1.8 eV and the broad emission band with a peak at ˜1.7 eV are ascribed to the Cr3+ ions in the β-Ga2O3 host. The energies of the excited states, i.e., 2E, 4T2, 2T2, 4T1, and 4T1, in Cr3+ are determined from the experimental PL and PL excitation spectra using a newly developed analysis model. The high-energy luminescence tail of the broad 4T2 → 4A2 emission band can be explained by the hot-carrier effect of the photoexcited electrons in the 4T2 state. The relative intensities of the R-line emission doublet can also be explained very well by the population and depopulation of the electron numbers in the E¯ (R1) and 2A¯ (R2) states. PL properties, such as the temperature-dependent PL intensity, peak energy, and spectral width, are analyzed in detail.

  20. Temperature dependence of photoluminescence spectra of bilayer two-dimensional electron gases in LaAlO{sub 3}/SrTiO{sub 3} superlattices: coexistence of Auger recombination and single-carrier trapping

    SciTech Connect

    Ma, H. J. Harsan Ariando; Venkatesan, T.; Wang, S. J.

    2015-06-15

    We report emerging photoluminescence (PL) of bilayer two-dimensional electron gases (2DEG) in LaAlO{sub 3}/SrTiO{sub 3} (LAO/STO) systems. A strong blue PL emerges in bilayer-2DEGs in LAO/STO/LAO/STO which doesn’t show in LAO/STO. PL band in bilayer-2DEGs includes both nearly temperature independent Auger recombination and temperature dependent free electron trapping while it crossovers from Auger recombination to single carrier trapping in LAO/STO. The PL signal of free electron trapping appears at high temperatures and it is much stronger than Auger recombination in the conducting channel in bilayer 2DEGs. This observation shows that high mobility carriers dominate the carrier dynamics in bilayer-2DEGs in LAO/STO superlattices.