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Sample records for afm photoluminescence pl

  1. Silica nanoparticles functionalized with polyamidoamine (PAMAM) dendrimers as platforms for photoluminescence (PL) sensing of copper and cyanide ions.

    PubMed

    Gerrans, Kateryna; Luhrs, Alicia; Feider, Clara; Margerum, Lawrence D

    2016-05-15

    Functionalized nanoparticles for photoluminescence (PL) applications are a promising technology for biomedical imaging and as sensors for small molecules. This work presents a new method to modify silica nanoparticles (SNP) using the bifunctional linker 1,1'-carbonyldiimidazole (CDI) with a series of polyamidoamine (PAMAM) dendrimer molecules followed by grafting of fluorescein isothiocyanate (FITC) or rhodamine B isothiocyanate (RITC) to create platforms for photoluminescence (PL) sensors. A dendrimer size and charge-variable response to only copper(II) ions confirmed the prediction of a selective turn-off sensor via proximity quenching. Both dye density and Cu(2+) quenching efficiency peaked with SNP-dendrimer generation 4 (64 terminal amines). In addition, changing the terminal dendrimer arms to carboxylic acid end groups increased the copper quenching suggesting that more metal ion binding sites were created in close proximity to the dyes. Of the small anions tested for a turn-off sensor, only cyanide ion fully restored the PL when reaching a 2:1 CN(-):Cu(2+) ratio, while EDTA was not as effective at the same ratio. Therefore, dendrimer size and surface charge on the nanoparticles controlled the dye loading and copper quenching efficiency, while creating multiple binding sites for cyanide over other metal binding anions. PMID:26962978

  2. Photomagnetism and photoluminescence (PL) of (Pb-Fe-e -) complex in lead magnesium niobate-lead titanate (PMN-PT) crystals containing β-PbO nanoclusters

    NASA Astrophysics Data System (ADS)

    Bairavarasu, Sundar R.; Edwards, Matthew E.; Sastry, Medury D.; Kochary, Faris; Kommidi, Praveena; Reddy, B. Rami; Lianos, Dimitrios; Aggarwal, Manmohan D.

    2008-12-01

    We present electron paramagnetic resonance (EPR)—evidence of photomagnetism under the conditions of in situ green laser illumination (photo-EPR) in lead magnesium niobate-lead titanate, Pb(Mg,Nb)O 3-PbTiO 3 (PMN-PT), containing nanoparticles/wires of orthorhombic β-PbO as identified by Raman spectroscopy. Photo-EPR studies of the sample containing β-PbO, brownish red in color, have shown intense line at g = 2.00, and its yield increased when produced in the presence of 7.5 kG external magnetic field suggesting the formation of magnetic polaron. This was identified as due to interaction between Fe 3+, photoinduced Pb 3+ and unpaired electron trapped at oxygen vacancies. The photoinduced growth and decay of magnetic polaron has shown a non-exponential behavior. Photoluminescence (PL) studies were conducted with excitation at 308 nm (XeCl laser) and also at 454.5, 488 and 514.5 nm using Ar + laser. The excitation with 308 nm gave broad PL centered at 500 and 710 nm the latter being quite prominent in β-PbO containing crystals, along with cooperative luminescence at 350 nm involving two emitting centers. The excitation with Ar + laser lines, close to the electronic absorption in samples containing β-PbO gave richer and sharp PL emission in red region from the constituents of the magnetic polaron and also intense anti-Stokes emission on excitation with 514.5 nm radiation. This appears to be due to phototransfer optically stimulated luminescence (PT-OSL) involving electron-hole recombination at photoinduced magnetic polaron site.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  5. Intrinsic Photoluminescence Emission from Subdomained Graphene Quantum Dots.

    PubMed

    Yoon, Hyewon; Chang, Yun Hee; Song, Sung Ho; Lee, Eui-Sup; Jin, Sung Hwan; Park, Chanae; Lee, Jinsup; Kim, Bo Hyun; Kang, Hee Jae; Kim, Yong-Hyun; Jeon, Seokwoo

    2016-07-01

    The photoluminescence (PL) origin of bright blue emission arising from intrinsic states in graphene quantum dots (GQDs) is investigated. The bright PL of intercalatively acquired GQDs is attributed to favorably formed subdomains composed of four to seven carbon hexagons. Random and harsh oxidation which hinders the energetically favorable formation of subdomains causes weak and redshifted PL. PMID:27153519

  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. Photoinduced spectral changes of photoluminescent gold nanoclusters.

    PubMed

    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. PMID:25517487

  8. Photoluminescence Study of Long Wavelength Superlattice Infrared Detectors

    NASA Technical Reports Server (NTRS)

    Hoglund, Linda; Khoshakhlagh, Arezou; Soibel, Alexander; Ting, David Z.; Hill, Cory J.; Keo, Sam; Gunapala, Sarath D.

    2011-01-01

    In this paper, the relation between the photoluminescence (PL) intensity and the PL peak wavelength was studied. A linear decrease of the PL intensity with increasing cut-off wavelength of long wavelength infrared CBIRDs was observed at 77 K and the trend remained unchanged in the temperature range 10 - 77 K. This relation between the PL intensity and the peak wavelength can be favorably used for comparison of the optical quality of samples with different PL peak wavelengths. A strong increase of the width of the PL spectrum in the studied temperature interval was observed, which was attributed to thermal broadening.

  9. Qplus AFM driven nanostencil.

    PubMed

    Grévin, B; Fakir, M; Hayton, J; Brun, M; Demadrille, R; Faure-Vincent, J

    2011-06-01

    We describe the development of a novel setup, in which large stencils with suspended silicon nitride membranes are combined with atomic force microscopy (AFM) regulation by using tuning forks. This system offers the possibility to perform separate AFM and nanostencil operations, as well as combined modes when using stencil chips with integrated tips. The flexibility and performances are demonstrated through a series of examples, including wide AFM scans in closed loop mode, probe positioning repeatability of a few tens of nanometer, simultaneous evaporation of large (several hundred of micron square) and nanoscopic metals and fullerene patterns in static, multistep, and dynamic modes. This approach paves the way for further developments, as it fully combines the advantages of conventional stenciling with the ones of an AFM driven shadow mask. PMID:21721701

  10. Photoluminescence method of testing double heterostructure wafers

    SciTech Connect

    Besomi, P.R.; Wilt, D.P.

    1984-04-10

    Under photoluminescence (PL) excitation, the lateral spreading of photo-excited carriers can suppress the photoluminescence signal from double heterostructure (DH) wafers containing a p-n junction. In any DH with a p-n junction in the active layer, PL is suppressed if the power of the excitation source does not exceed a threshold value. This effect can be advantageously used for a nondestructive optical determination of the top cladding layer sheet conductance as well as p-n junction misplacement, important parameters for injection lasers and LEDs.

  11. Photoluminescence, ellipsometric, optical and morphological studies of sprayed Co-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Gençyılmaz, O.; Atay, F.; Akyüz, I.

    2016-06-01

    In this study, undoped and cobalt (Co)-doped zinc oxide (ZnO) films were successfully produced by ultrasonic spray pyrolysis (USP) technique at low temperature (350°C). The optical and surface properties were investigated as a function of Co content. The optical parameters (thickness, refractive index and extinction coefficient) were determined using spectroscopic ellipsometry (SE) and it was seen that the refractive index and extinction coefficient values of Co-doped ZnO films decreased slightly depending on the increasing of Co doping. For investigation, the transmittance and photoluminescence (PL) spectra of the films, UV-Vis spectrophotometer and PL spectroscopy were used at room temperature. The transmittance spectra show that transmittance values decreased and Co+2 ions substitute Zn+2 ions of ZnO lattice. The optical band gap values decreased from 3.26 eV to 2.85 eV with the changing of Co content. The results of PL spectra exhibit the position of the different emission peaks unchanged but the intensity of peaks increased with increasing Co doping. Also, the surface properties of the films were obtained by atomic force microscopy (AFM) and these results indicated that the surface morphology and roughness values were prominently changed with Co doping.

  12. Photoluminescence from doped ZnS nanostructures

    NASA Astrophysics Data System (ADS)

    Karar, N.

    2007-05-01

    Photoluminescence (PL) properties of differently doped nanocrystalline ZnS encapsulated by ZnO (ZnS/ZnO) are reported. It is found that in all cases aluminium as an extra/additional dopant leads to PL enhancement. In comparison to reported blue emitting bulk ZnS:Ag, or green emitting bulk ZnS:Cu, our nanocrystalline samples show a different PL emission profile. This observation is attributed to nanogranule formation, different dopant levels and ZnO capping related energy level modifications.

  13. Substrate temperature dependent surface morphology and photoluminescence of germanium quantum dots grown by radio frequency magnetron sputtering.

    PubMed

    Samavati, Alireza; Othaman, Zulkafli; Ghoshal, Sib Krishna; Dousti, Mohammad Reza; Kadir, Mohammed Rafiq Abdul

    2012-01-01

    The visible luminescence from Ge nanoparticles and nanocrystallites has generated interest due to the feasibility of tuning band gap by controlling the sizes. Germanium (Ge) quantum dots (QDs) with average diameter ~16 to 8 nm are synthesized by radio frequency magnetron sputtering under different growth conditions. These QDs with narrow size distribution and high density, characterized using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) are obtained under the optimal growth conditions of 400 °C substrate temperature, 100 W radio frequency powers and 10 Sccm Argon flow. The possibility of surface passivation and configuration of these dots are confirmed by elemental energy dispersive X-ray (EDX) analysis. The room temperature strong visible photoluminescence (PL) from such QDs suggests their potential application in optoelectronics. The sample grown at 400 °C in particular, shows three PL peaks at around ~2.95 eV, 3.34 eV and 4.36 eV attributed to the interaction between Ge, GeO(x) manifesting the possibility of the formation of core-shell structures. A red shift of ~0.11 eV in the PL peak is observed with decreasing substrate temperature. We assert that our easy and economic method is suitable for the large-scale production of Ge QDs useful in optoelectronic devices. PMID:23202927

  14. 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.

  15. 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

  16. 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.

  17. Ge Nanocluster Enhanced Er Photoluminescence

    NASA Astrophysics Data System (ADS)

    Guzman, Julian; Chrzan, Daryl C.; Haller, Eugene E.

    2010-03-01

    We investigated the enhancement of the Er^3+ photoluminescence (PL) at 1540 nm by the incorporation of Ge nanoclusters into Er-doped silica using ion beams. We found that the Er^3+ PL enhancement is due to the presence of Ge and not to the radiation damage from the ion-implantation process. We determined that the Er^3+ PL depends on the Ge content, postgrowth annealing, and crystallinity of the Ge nanoclusters. Furthermore, we observed that the Er^3+ PL signal is maximized after annealing at 685 C for 1 h. This is the temperature at which Ge nanoclusters begin to crystallize. Transmission electron microscopy studies were conducted to determine the size distribution of the Ge nanoclusters. Moreover, extended X-ray absorption fine structure measurements performed at the Ge-K and Er-LIII edges revealed that there is negligible Ge-Er bonding. This suggests that Er is either fully oxidized or that it is not located in the Ge nanoclusters. Therefore, we believe that the energy transfer process from the Ge nanoclusters to the Er ions occurs through a non-optical resonant dipole transfer (F"orster ProcessfootnotetextT. F"orster, Discuss. Faraday Soc. 27, 7 (1959). similar to what has been proposed for the Si nanocrystal case.footnotetextM. Fujii, M. Yoshida, S. Hayashi, and K. Yamamoto, J. Appl. Phys. 84, 4525 (1998).

  18. Shape controlled synthesis of CaMoO{sub 4} thin films and their photoluminescence property

    SciTech Connect

    Marques, Ana Paula de Azevedo Longo, Valeria M.; Melo, Dulce M.A. de; Pizani, Paulo S.; Leite, Edson R.; Varela, Jose Arana; Longo, Elson

    2008-05-15

    CaMoO{sub 4} (CMO) disordered and ordered thin films were prepared by the complex polymerization method (CPM). The films were annealed at different temperatures and time in a conventional resistive furnace (RF) and in a microwave (MW) oven. The microstructure and surface morphology of the structure were monitored by atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HRSEM). Order and disorder were characterized by X-ray diffraction (XRD) and optical reflectance. A strong photoluminescence (PL) emission was observed in the disordered thin films and was attributed to complex cluster vacancies. The experimental results were compared with density functional and Hartree-Fock calculations. - Graphical abstract: CaMoO{sub 4} thin films were prepared by the complex polymerization method (CPM). The films were annealed at different temperatures and time in a conventional resistive furnace and in a microwave oven. A strong photoluminescence emission was observed in the disordered thin films and was attributed to complex cluster vacancies. The experimental results were confirmed by high level first principle calculations.

  19. 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.

  20. Photoluminescence by Interstellar Dust

    NASA Astrophysics Data System (ADS)

    Vijh, U. P.

    2005-12-01

    In this dissertation talk, I will 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 λ peak ˜ 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. I will also present first results from ongoing work: 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. Financial support for this study was provided through NSF Grant AST0307307 to The University of Toledo.

  1. 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

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    Nitrogen-doped graphene oxide (NGO) was synthesized by irradiation of graphene oxide (GO) in NH3 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.

  5. 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.

  6. Spatially resolved photoluminescence study of single ZnO tetrapods.

    PubMed

    Feng, L; Cheng, C; Lei, M; Wang, N; Loy, M M T

    2008-10-01

    ZnO tetrapods and nanowires were fabricated by a simple method of thermal evaporation of pure Zn powder in the air. These nanostructures, formed in different temperature regions of the same apparatus, displayed distinct photoluminescence (PL) characteristics. Spatially resolved PL measurements on legs of individual tetrapods show that the green luminescence (GL) decreases with decreasing leg diameter, and there was no detectable GL from nanowires grown simultaneously. These PL properties suggest that the green luminescence may not come from surface states, but rather from bulk defects. PMID:21832631

  7. 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.

  8. 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.

  9. Tunable photoluminescence of monolayer MoS₂ via chemical doping.

    PubMed

    Mouri, Shinichiro; Miyauchi, Yuhei; Matsuda, Kazunari

    2013-01-01

    We demonstrate the tunability of the photoluminescence (PL) properties of monolayer (1L)-MoS2 via chemical doping. The PL intensity of 1L-MoS2 was drastically enhanced by the adsorption of p-type dopants with high electron affinity but reduced by the adsorption of n-type dopants. This PL modulation results from switching between exciton PL and trion PL depending on carrier density in 1L-MoS2. Achievement of the extraction and injection of carriers in 1L-MoS2 by this solution-based chemical doping method enables convenient control of optical and electrical properties of atomically thin MoS2. PMID:24215567

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. PREFACE: Non-contact AFM Non-contact AFM

    NASA Astrophysics Data System (ADS)

    Giessibl, Franz J.; Morita, Seizo

    2012-02-01

    This special issue is focussed on high resolution non-contact atomic force microscopy (AFM). Non-contact atomic force microscopy was established approximately 15 years ago as a tool to image conducting and insulating surfaces with atomic resolution. Since 1998, an annual international conference has taken place, and although the proceedings of these conferences are a useful source of information, several key developments warrant devoting a special issue to this subject. In the theoretic field, the possibility of supplementing established techniques such as scanning tunneling microscopy (STM) and Kelvin probe microscopy with atomically resolved force micrsoscopy poses many challenges in the calculation of contrast and contrast reversal. The surface science of insulators, self-assembled monolayers and adsorbates on insulators is a fruitful field for the application of non-contact AFM: several articles in this issue are devoted to these subjects. Atomic imaging and manipulation have been pioneered using STM, but because AFM allows the measurement of forces, AFM has had a profound impact in this field as well. Three-dimensional force spectroscopy has allowed many important insights into surface science. In this issue a combined 3D tunneling and force microscopy is introduced. Non-contact AFM typically uses frequency modulation to measure force gradients and was initially used mainly in a vacuum. As can be seen in this issue, frequency modulation is now also used in ambient conditions, allowing better spatial and force resolution. We thank all of the contributors for their time and efforts in making this special issue possible. We are also very grateful to the staff of IOP Publishing for handling the administrative aspects and for steering the refereeing process. Non-contact AFM contents Relation between the chemical force and the tunnelling current in atomic point contacts: a simple model Pavel Jelínek, Martin Ondrácek and Fernando Flores Theoretical simulation of

  16. 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.

  17. Photoluminescence properties of silicon nanocrystals interacting with gold nanoparticles via exciton-plasmon coupling

    NASA Astrophysics Data System (ADS)

    Potrick, Karsten; Huisken, Friedrich

    2015-03-01

    The photoluminescence (PL) properties of silicon nanocrystals (Si NCs) deposited on gold nanostructures have been studied regarding PL intensity and lifetime. In contrast to most investigations, which attempt to optimize the overlap between the plasmon resonance and the Si NCs' PL band, we chose much smaller gold nanoparticles to achieve an improved exciton-plasmon coupling. PL enhancements of up to 20 were observed near the plasmon resonance. In the maximum of the PL band at 710 nm, we determined a PL enhancement of ˜4 while the average PL lifetime was found to increase from 45 to 66 μ s . The experimental observations were successfully explained with a model invoking bidirectional energy transfer between excitonic and plasmonic states, being operative in addition to the normal exciton recombination rate enhancement.

  18. 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.

  19. 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.

  20. 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.

  1. N2 Laser Induced Photoluminescence Emission in (ZnS: ZnO):Cu Phosphors

    NASA Astrophysics Data System (ADS)

    Muraleedharan, R.; Khokhar, M. S. K.; Namboodiri, V. P.; Girijavallabhan, C. P.

    Nitrogen laser induced photoluminescence (PL) emissions from (ZnS: ZnO):Cu powder phosphors have been carried out under varying conditions of sample preparation. The conditions for optimum efficiency of PL emission in (ZnS: ZnO):Cu phosphors and their spectral characteristics have been investigated. The emission peak in the PL spectra was found to shift towards longer wavelengths side as the concentrations of ZnO in (ZnS: ZnO) mixture was varied from 0% to 100%. The mechanism of PL emission in the above phosphor is explained on the basis of classical “Schon-Klassen” model.

  2. Polarization and time-resolved photoluminescence spectroscopy of excitons in MoSe2 monolayers

    NASA Astrophysics Data System (ADS)

    Wang, G.; Palleau, E.; Amand, T.; Tongay, S.; Marie, X.; Urbaszek, B.

    2015-03-01

    We investigate valley exciton dynamics in MoSe2 monolayers in polarization- and time-resolved photoluminescence (PL) spectroscopy at 4 K. Following circularly polarized laser excitation, we record a low circular polarization degree of the PL of typically ≤5%. This is about 10 times lower than the polarization induced under comparable conditions in MoS2 and WSe2 monolayers. The evolution of the exciton polarization as a function of excitation laser energy and power is monitored in PL excitation experiments. Fast PL emission times are recorded for both the neutral exciton of ≤3 ps and for the charged exciton (trion) of 12 ps.

  3. 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

  4. 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

  5. White Photoluminescence from Carbon-Incorporated Silica Fabricated from Rice Husk

    NASA Astrophysics Data System (ADS)

    Ishikawa, Yukari; Kawasaki, Shinji; Ishi, Yosuke; Sato, Koji; Matsumura, Akihiro

    2012-01-01

    White photoluminescence (PL) from thermally treated rice husk is demonstrated. The strongest PL is obtained after oxidation at 400 °C following carbonization at 600 °C. The PL intensity was strong enough to be detected by the naked eye in daylight under the irradiation of 370 nm light from a light-emitting-diode (LED)-type flashlight. Thermal treatment changes rice husk to silicon oxycarbide but the amorphous structure and cell-wall architecture of the plants are maintained. The origin of PL is speculated to be related to some centers or defects in strained silicon oxycarbide.

  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. TiO2 controlling photoluminescence of AWO4 (A =Ca,Sr,Ba) nanofilms

    NASA Astrophysics Data System (ADS)

    Jia, Runping; Zhang, Guoxin; Wu, Qingsheng; Ding, Yaping

    2006-07-01

    AWO4 (A =Ca,Sr,Ba) nanofilms are prepared by a self-inventive technique using collodion to disperse nanoparticles and form film, and their photoluminescence (PL) properties are controlled by a nano-TiO2 doping method. This cannot only reach the results of uniform film and PL enhancement, but also realize a PL increase/decrease shift effect. The PL behaviors of AWO4 nanofilms doped by TiO2 are in good agreement with Gaussion function relation. In addition, there is a positive correlation between the critical concentrations of TiO2 in AWO4-TiO2 nanofilm series and A's ionic potential.

  8. Photoluminescence structure, and composition of laterally anodized porous Si

    NASA Technical Reports Server (NTRS)

    Jung, K. H.; Shih, S.; Kwong, D. L.; George, T.; Lin, T. L.; Liu, H. Y.; Zavada, J.

    1992-01-01

    We have studied the photoluminescence (PL), structure, and composition of laterally anodized porous Si. Broad PL peaks were observed centered between about 620-720 nm with strong intensities measured from 500 to 860 nm. Macroscopic variations in PL intensities and peak positions are explained in terms of the structure and anodization process. Structural studies suggest that the PL appears to originate from a multilayered porous Si structure in which the top two layers are amorphous. X-ray diffraction spectra also suggest the presence of a significant amorphous phase. In addition to high concentrations of B and N, we have measured extremely high concentrations much greater than 10 exp 20 cu cm of H, C, O, and F. Our results indicate that laterally anodized porous Si does not fit the crystalline Si quantum wire model prevalent in the literature suggesting that some other structure is responsible for the observed luminescence.

  9. 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.

  10. Photoluminescence Studies in CuAlS2 Crystals

    NASA Astrophysics Data System (ADS)

    Shirakata, Sho; Aksenov, Igor; Sato, Katsuaki; Isomura, Shigehiro

    1992-08-01

    Photoluminescence (PL) measurements have been carried out at low temperature (77 and 10 K) on CuAlS2 crystals grown by the chemical vapor transport method. Seven sharp PL lines have been observed near the band edge. Based on the photoreflectance measurements, the PL line at 3.550 eV has been assigned to a free exciton emission. The lines at 3.540, 3.532, 3.500 and 3.475 eV are tentatively assigned to the bound excitons, and they are discussed in terms of the crystal composition and the annealing conditions. This study also refers to the PL lines and peaks at about 2.9 eV.

  11. 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. PMID:26744147

  12. 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.

  13. FT-PL analysis of CIGS/CdS/Zno interfaces

    NASA Astrophysics Data System (ADS)

    Webb, John D.; Keyes, Brian M.; Ramanathan, Kannan; Dippo, Patricia; Niles, David W.; Noufi, Rommel

    1997-02-01

    High-quality copper indium gallium diselenide (CIGS) films were subjected to a variety of surface treatments attendant to and including deposition of CdS and/or ZnO junctions or buffer layers. The resulting devices were analyzed at 87 K using Fourier transform photoluminescence (FT-PL) spectroscopy as part of a battery of analytical procedures, including surface analysis, ellipsometry, and I-V measurements, designed to elucidate the influences of the several interfaces on device performance. Our FT-PL system was upgraded with a miniature Joule-Thomson cryostat and a helium-neon laser excitation source to enable collection of highly-resolved, continuous PL spectra from 950-1750 nm. The PL intensity enhancements measured with the upgraded FT-PL system for devices fabricated using chemical bath deposition (CBD) of CdS, with or without a ZnO electrode, are much greater than for devices incorporating physical vapor deposited (PVD) CdS or ZnO/CIGS interfaces. Exposure of the CIGS films to components of the CBD solution alone, without deposition of CdS, also increases PL intensity, implying a reduction in the rate of non-radiative recombination in the films. Application of CBD CdS or a CBD background solution to the CIGS shifted its PL spectrum to shorter wavelengths, while application of PVD CdS or ZnO to the CIGS broadened its PL spectrum at longer wavelengths.

  14. Application of ZnO nanoparticles to enhance photoluminescence in porous silicon and its possible utilization for improving the short wavelength quantum efficiency of silicon solar cell

    NASA Astrophysics Data System (ADS)

    Verma, Daisy; Kharkwal, Aneeta; Singh, S. N.; Singh, P. K.; Sharma, S. N.; Mehdi, S. S.; Husain, M.

    2014-11-01

    We have formed photoluminescent porous silicon (PS) layers and over which a ZnO layer (hereafter called ZnOPS layers) is deposited. We studied the photoluminescent properties of individual layers as well as the composite layer under excitation with 405 nm wavelength. Using the data of PL a theoretical analysis of a solar cell having such a composite layer of a given photoluminescent conversion efficiency ηPL on the front surface has been done. The condition of a photoluminescent composite layer (ZnOPS) useful for enhancing the spectral response of n+-p-p+ structured silicon solar cell has been identified.

  15. 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.

  16. Hot Photoluminescence in γ-In2Se3 Nanorods

    PubMed Central

    2008-01-01

    The energy relaxation of electrons in γ-In2Se3nanorods was investigated by the excitation-dependent photoluminescence (PL). From the high-energy tail of PL, we determine the electron temperature (Te) of the hot electrons. TheTevariation can be explained by a model in which the longitudinal optical (LO)-phonon emission is the dominant energy relaxation process. The high-quality γ-In2Se3nanorods may be a promising material for the photovoltaic devices. PMID:21749734

  17. Hot Photoluminescence in γ-In2Se3 Nanorods

    NASA Astrophysics Data System (ADS)

    Yang, M. D.; Hu, C. H.; Shen, J. L.; Lan, S. M.; Huang, P. J.; Chi, G. C.; Chen, K. H.; Chen, L. C.; Lin, T. Y.

    2008-11-01

    The energy relaxation of electrons in γ-In2Se3 nanorods was investigated by the excitation-dependent photoluminescence (PL). From the high-energy tail of PL, we determine the electron temperature ( T e) of the hot electrons. The T e variation can be explained by a model in which the longitudinal optical (LO)-phonon emission is the dominant energy relaxation process. The high-quality γ-In2Se3 nanorods may be a promising material for the photovoltaic devices.

  18. Photoluminescence and spontaneous emission enhancement in metamaterial nanostructures

    NASA Astrophysics Data System (ADS)

    Singh, M. R.; Cox, J. D.; Brzozowski, M.

    2014-02-01

    We present a theory for the photoluminescence (PL) and spontaneous emission of semiconductor nanoparticles (quantum dots—QDS) doped in a metamaterial heterostructure. The heterostructure is formed by fabricating a split-ring resonator and metallic rod metamaterial on a dielectric substrate. QDs are doped near the interface in the heterostructure. Our results indicate that the PL and spontaneous emission of the QDs are enhanced in the presence of the metamaterial when the exciton and surface plasmon frequencies are resonant. These findings are consistent with recent experimental studies. The present study can be used to make new types of nanoscale optical devices for sensing, switching and imaging applications based on metamaterials.

  19. Tuning Photoluminescence Response by Electric Field in Electrically Soft Ferroelectrics.

    PubMed

    Khatua, Dipak Kumar; Kalaskar, Abhijeet; Ranjan, Rajeev

    2016-03-18

    We show that an electrically soft ferroelectric host can be used to tune the photoluminescence (PL) response of rare-earth emitter ions by external electric field. The proof of this concept is demonstrated by changing the PL response of the Eu^{3+} ion by electric field on a model system Eu-doped 0.94(Na_{1/2}Bi_{1/2}TiO_{3})-0.06(BaTiO_{3}). We also show that new channels of radiative transitions, forbidden otherwise, open up due to positional disorder in the system, which can as well be tuned by electric field. PMID:27035321

  20. Photoluminescence of a Te4+ center in zinc borate glass.

    PubMed

    Masai, Hirokazu; Yamada, Yasuhiro; Okumura, Shun; Kanemitsu, Yoshihiko; Yoko, Toshinobu

    2013-10-01

    Photoluminescent (PL) properties related to Te(4+) species in zinc borate glasses are examined. Broad emission was observed by the excitation of the PL excitation peak of Te(4+) present at the optical absorption edge. The emission intensity of Te(4+) in 5TeO(2)-50ZnO-45B(2)O(3) glass was thermally quenched in a temperature region over 100 K, suggesting that concentration quenching preferentially occurred. The lifetime of the emission was approximately 2.5 μs, which is characteristic of relaxation from the triplet excitation state of an ns(2)-type center. PMID:24081051

  1. 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.

  2. Preparation and photoluminescence properties of porous silicon

    NASA Astrophysics Data System (ADS)

    Chen, Zhiwei; Xu, Zhimou

    2009-08-01

    There are many preparation methods of porous silicon(PS), such as electrochemical etching(ECE), photochemical etching, chemical etching and so on. ECE, also known as anodic etching, is more common among these methods. A lot of holes are given priority to be etched on the surface of silicon. The top and vertical aspects of the holes are easily etched while horizontal aspects wall of the holes are quiet different, and then tree-like or sponge-like porous structure is formed. In this paper, we obtained porous structure on the surface of silicon using lithography and dry etching method. The diameter of the hole was 2μm or 6μm. The etching depth of the samples was about 70nm, 140nm and 260nm. Photoluminescence (PL) phenomenon was observed by using light of 270nm, 280nm, 330nm, 455nm and 460nm wavelength to excite the samples. The results showed that PL intensity was the best when excitation wavelength was 270nm or 280nm, compared with 330nm, 455nm and 460nm. From PL analysis of all samples, It exists three emission peaks about at 372nm, 425nm and 473nm. When the diameter of the PS was the same, it was found that PS with etching depth at 140nm was more efficient. It means that PL intensity of the was better than other samples when the etching depth was 140nm. Likewise, samples of which the diameter was 2μm has much better PL than that of the other samples.

  3. 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.

  4. Photoluminescence study of p-type CdGeAs2 ordered semiconductor crystals

    NASA Astrophysics Data System (ADS)

    McCrae, J. E.; Hengehold, R. L.; Yeo, Y. K.; Ohmer, M. C.; Schunemann, P. G.

    1997-01-01

    Results of a photoluminescence (PL) study as a function of excitation laser power, sample temperature, crystal orientation, and polarization are reported for the nonlinear optical material CdGeAs2. One broad weak PL peak near 0.38 eV, and another somewhat narrower and often far brighter PL peak near 0.55 eV were found at 4 K. The high energy PL peak shifts first towards lower, then higher, and back to lower energies again as the temperature increases from 2.2 to 295 K. This high energy peak is attributed to donor-acceptor pair dominant transitions at low temperatures, but it is attributed to band-to-band dominant transitions at higher temperatures. Strongly polarized PL was observed with the E field of the PL parallel to the material's c axis, and a polarization ratio as high as 6:1 was obtained.

  5. Practical photoluminescence and photoreflectance spectroscopic system for optical characterization of semiconductor devices

    NASA Astrophysics Data System (ADS)

    Ho, Ching-Hwa; Huang, Kuo-Wei; Lin, Yu-Shyan; Lin, Der-Yuh

    2005-05-01

    We present a practical experimental design for performing photoluminescence (PL) and photoreflectance (PR) measurements of semiconductors with only one PL spectroscopic system. The measurement setup is more cost efficient than typical PL-plus-PR systems. The design of the experimental setup of the PL-PR system is described in detail. Measurements of two actual device structures, a high-electron-mobility transistor (HEMT) and a double heterojunction-bipolar transistor (DHBT), are carried out by using this design. The experimental PL and PR spectra of the HEMT device, as well as polarized-photoreflectance (PPR) spectra of the DHBT structure, are analyzed in detailed and discussed. The experimental analyses demonstrate the well-behaved performance of this PL-PR design.

  6. 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.

  7. Spatially resolved photoluminescence spectroscopy of quantum dots

    NASA Astrophysics Data System (ADS)

    Dybiec, Maciej

    Recent advancements in nanotechnology create a need for a better understanding of the underlying physical processes that lead to the different behavior of nanoscale structures in comparison to bulk materials. The influence of the surrounding environment on the physical and optical properties of nanoscale objects embedded inside them is of particular interest. This research is focused on the optical properties of semiconductor quantum dots which are zero-dimensional nanostructures. There are many investigation techniques for measuring the local parameters and structural characteristics of Quantum Dot structures. They include X-ray diffraction, Transmission Electron Microscopy, Wavelength Dispersive Spectroscopy, etc. However, none of these is suitable for the study of large areas of quantum dots matrices and substrates. The existence of spatial inhomogeneity in the quantum dots allows for a deeper and better understanding of underlying physical processes responsible in particular for the observed changes in photoluminescence (PL) characteristics. Spectroscopic PL mapping can reveal areas of improved laser performance of InAs - InGaAs quantum dots structures. Establishing physical mechanisms responsible for two different types of spatial PL inhomogeneity in InAs/InGaAs quantum dots structures for laser applications was the first objective of this research. Most of the bio-applications of semiconductor quantum dots utilize their superior optical properties over organic fluorophores. Therefore, optimization of QD labeling performance with biomolecule attachment was another focus of this research. Semiconductor quantum dots suspended in liquids were investigated, especially the influence of surrounding molecules that may be attached or bio-conjugated to the quantum dots for specific use in biological reactions on the photoluminescence spectrum. Provision of underlying physical mechanisms of optical property instability of CdSe/ZnS quantum dots used for biological

  8. Compositional variation of photoluminescence from Mn doped MgAl2O4 spinel

    NASA Astrophysics Data System (ADS)

    Sakuma, Takashi; Minowa, Shunsuke; Katsumata, Toru; Komuro, Shuji; Aizawa, Hiroaki

    2014-11-01

    Spinel (MgAl2O4) crystals doped with 1.0% Mn have been grown by floating zone (FZ) technique with various Mg compositions, x = MgO/Al2O3, from 0.2 to 1.0. Compositional variations of photoluminescence are evaluated for a fluorescence thermometer application using crystals grown. Strong photoluminescence (PL) peak is observed at λ from 512 to 520 nm from the crystals grown from compositions, x, from 0.3 to 1.0. Peak wavelength of PL increases linearly from 512 to 520 nm with x. Weak PL peaking at λ = 750 nm is also observed from the specimens. Compositional variations of PL are considered to be due to the variation of crystal field surrounding the Mn2+ ions. The variation of crystal field strength agrees with the compositional variation of lattice constant.

  9. [The photoluminescence and absorption properties of Co/AAO nano-array composites].

    PubMed

    Li, Shou-Yi; Wang, Cheng-Wei; Li, Yan; Wang, Jian; Ma, Bao-Hong

    2008-03-01

    Ordered Co/AAO nano-array structures were fabricated by alternating current (AC) electrodeposition method within the cylindrical pores of anodic aluminum oxide (AAO) template prepared in oxalic acid electrolyte. The photoluminescence (PL) emission and photoabsorption of AAO templates and Co/AAO nano-array structures were investigated respectively. The results show that a marked photoluminescence band of AAO membranes occurs in the wavelength range of 350-550 nm and their PL peak position is at 395 nm. And with the increase in the deposition amount of Co nanoparticles, the PL intensity of Co/AAO nano-array structures decreases gradually, and their peak positions of the PL are invariable (395 nm). Meanwhile the absorption edges of Co/AAO show a larger redshift, and the largest shift from the near ultraviolet to the infrared exceeds 380 nm. The above phenomena caused by Co nano-particles in Co/AAO composite were analyzed. PMID:18536402

  10. Photoluminescence investigations of defects introduced during processing of mercuric iodide nuclear detectors

    NASA Astrophysics Data System (ADS)

    James, R. B.; Bao, X. J.; Schlesinger, T. E.; Cheng, A. Y.; Ortale, C.; van den Berg, L.

    1992-11-01

    Low-temperature photoluminescence (PL) spectroscopy was performed on a variety of HgI 2 samples to determine the effects of chemical etching with Kl and HNO 3 solutions and the modifications in the PL spectra due to the presence of carbon, chromium and parylene films. These investigations reveal that the processing steps used to manufacture HgI 2 nuclear detectors can lead to the incorporation of new defects into the near-surface region of the crystals. Moreover, correlations between the photoluminescence spectra and detector performance show that some of these defects are undesirable for producing high-quality devices.

  11. 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).

  12. Direct-bandgap GeSn grown on silicon with 2230 nm photoluminescence

    NASA Astrophysics Data System (ADS)

    Ghetmiri, Seyed Amir; Du, Wei; Margetis, Joe; Mosleh, Aboozar; Cousar, Larry; Conley, Benjamin R.; Domulevicz, Lucas; Nazzal, Amjad; Sun, Greg; Soref, Richard A.; Tolle, John; Li, Baohua; Naseem, Hameed A.; Yu, Shui-Qing

    2014-10-01

    Material and optical characterizations have been conducted for epitaxially grown Ge1-xSnx thin films on Si with Sn composition up to 10%. A direct bandgap Ge0.9Sn0.1 alloy has been identified by temperature-dependent photoluminescence (PL) study based on the single peak spectrum and the narrow line-width. Room temperature PL emission as long as 2230 nm has also been observed from the same sample.

  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. 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.

  15. 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

  16. Growth orientation dependent photoluminescence of GaAsN alloys

    NASA Astrophysics Data System (ADS)

    Han, Xiuxun; Tanaka, Tomohiro; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi; Sato, Shinichiro

    2012-01-01

    We report photoluminescence (PL) studies of both as-grown and electron-irradiated GaAsN epilayers on (311)A/B and (100) GaAs substrates. A long room-temperature (RT) PL lifetime, as well as an enhanced N incorporation, is observed in (311)B GaAsN epilayers as compared with (311)A and (100) samples. There is no direct correlation between the RT PL lifetime and the emission intensity from Ga vacancy complex detected at low temperature. The lifetime damage coefficient is relatively low for (311)B GaAsN. The irradiation-induced nonradiative recombination defects are suggested to be N- and/or As-related according to a geometrical analysis based on the tetrahedral coordination of GaAsN crystal.

  17. Phonon sidebands of photoluminescence in single wall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Yu, Guili; Liang, Qifeng; Jia, Yonglei; Dong, Jinming

    2010-01-01

    The multiphonon-assisted photoluminescence (PL) of the single wall carbon nanotubes (SWNTs) have been studied by solving the Schrödinger equation, showing a set of phonon sidebands, both the Stokes and anti-Stokes lines, which are induced by the longitudinal optical phonon and radial breathing mode phonon. All the calculated results are in a good agreement with the recent experimental PL spectra of the SWNTs [F. Plentz, H. B. Ribeiro, A. Jorio, M. S. Strano, and M. A. Pimenta, Phys. Rev. Lett. 95, 247401 (2005)] and J. Lefebvre and P. Finnie, Phys. Rev. Lett. 98, 167406 (2007)]. In addition, it is very interesting to find in the calculated PL several additional phonon sidebands with rather weak intensities, which are caused by the exciton's coupling with two kinds of phonons, and expected to be observed in future experiments.

  18. 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. PMID:26353616

  19. 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. PMID:26656180

  20. [Photoluminescence of nano-SiC annealed by pulse laser].

    PubMed

    Yu, Wei; He, Jie; Sun, Yun-tao; Han, Li; Fu, Guang-sheng

    2005-04-01

    Nanocrystalline silicon carbon (nc-SiC) from amorphous silicon carbon films was obtained through XeCl excimer laser annealing. The photoluminescence (PL) of the nc-SiC was analyzed at different annealing laser energy density. It was observed that PL presented a wide luminescence band from 300-600 nm in the nc-SiC films. The two main luminescence bands, situated at 398 and 470 nm respectively, are attributed to band to band and defect recombination in the 6H-SiC based on the structure changes of the nc-SiC films. The relative PL intensity of these two bands was determined by the surface state density in the nc-SiC films and their irradiative life PMID:16097671

  1. 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.

  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. Optical properties of GaAsBi/GaAs quantum wells: Photoreflectance, photoluminescence and time-resolved photoluminescence study

    NASA Astrophysics Data System (ADS)

    Kopaczek, J.; Linhart, W. M.; Baranowski, M.; Richards, R. D.; Bastiman, F.; David, J. P. R.; Kudrawiec, R.

    2015-09-01

    Photoreflectance (PR), photoluminescence (PL) and time-resolved PL were applied to study the optical properties, particularly the localized and delocalized states and carrier dynamics, in GaAs1-xBix/GaAs quantum wells. With increasing Bi concentration the ground state transition (i.e., the transition between the first heavy hole and the first electron subband) red shifts due to Bi-related reduction of the GaAs1-xBix energy gap. Additionally, the transition related to the excited states in the quantum wells is clearly observed for the sample with high Bi concentration of 5.6%, confirming these quantum wells are type I. The PL measurements show the S-shape behavior and indicate the strong localization effect below 150 K for all measured samples, while the PL emission above 150 K is related to delocalized states. The localized character of emission at low temperatures is confirmed by time-resolved PL studies. At 10 K the decay time has strong spectral dispersion (i.e. the decay time increases from ˜10 ns to ˜400 ns going from the high to low energy side of the PL peak). This dispersion disappears above 190 K. At room temperature the decay time is in the order of a few ns.

  4. Crystal growth and photoluminescence characteristics of Ca{sub 2}MgSi{sub 2}O{sub 7}:Eu{sup 3+} thin films grown by pulsed laser deposition

    SciTech Connect

    Yang, Hyun Kyoung; Moon, Byung Kee; Choi, Byung Chun; Jeong, Jung Hyun; Kim, Kwang Ho

    2012-10-15

    Ca{sub 2}MgSi{sub 2}O{sub 7}:Eu{sup 3+} films were deposited on Al{sub 2}O{sub 3} (0 0 0 1) substrates by pulsed laser deposition. The films were grown at various oxygen pressures ranging from 100 to 400 mTorr. The crystallinity and surface morphology of the films were examined by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD and AFM respectively showed that the Ca{sub 2}MgSi{sub 2}O{sub 7}:Eu{sup 3+} films had a zircon structure and consisted of homogeneous grains ranging from 100 to 400 nm depending on the deposition conditions. The radiation emitted was dominated by a red emission peak at 620 nm. The maximum PL intensity of the Ca{sub 2}MgSi{sub 2}O{sub 7}:Eu{sup 3+} films grown at 300 mTorr was increased by a factor of 1.3 compared to that of Ca{sub 2}MgSi{sub 2}O{sub 7}:Eu{sup 3+} films grown at 100 mTorr. The crystallinity, surface roughness and photoluminescence of the thin-film phosphors were strongly dependent on the deposition conditions, in particular, the oxygen partial pressure.

  5. Single ricin detection by AFM chemomechanical mapping

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This research reports a method of detecting ricin molecules immobilized on chemically modified gold (Au;111) surface by chemomechanically mapping the molecular interactions with a chemically modified Atomic Force Microscope (AFM) tip. AFM images resolved the different fold-up conformations of single...

  6. 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.

  7. Nonlinear photoluminescence properties of trions in hole-doped single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Akizuki, Naoto; Iwamura, Munechiyo; Mouri, Shinichiro; Miyauchi, Yuhei; Kawasaki, Tomohiro; Watanabe, Hiroshi; Suemoto, Tohru; Watanabe, Kouta; Asano, Kenichi; Matsuda, Kazunari

    2014-05-01

    We studied the excitation density dependence of photoluminescence (PL) spectra of excitons and trions (charged excitons) in hole-doped single-walled carbon nanotubes. We found that the PL intensity of trions exhibited a strong nonlinear saturation behavior as the excitation density increased, whereas that of excitons exhibited a weak sublinear behavior. The strong PL saturation of trions is attributed to depletion of doped holes that are captured by excitons in the formation processes. Moreover, the effective radiative lifetime of a trion was evaluated to be approximately 20 ns.

  8. Photoluminescence Study of Interdot Carrier Transfer on Strain-relaxed InAs Quantum Dots

    SciTech Connect

    Chiang, Chen-Hao; Chang, You-Cheng; Hsieh, Meng-Chien; Yang, Cheng-Hong; Wang, Jia-Feng; Chen, Jenn-Fang; Wu, Yue-Han; Chang, Li

    2011-12-23

    Photoluminescence (PL) properties of the strain relaxed InAs quantum dots (QDs) are studied as a function of temperature from 10 to 300 K. Two groups of QDs induced by strain relaxation are observed in the PL spectra. The PL peak position of the relaxed (non-relaxed) QDs locates at a higher (lower) energy. TEM image prove QDs are distributed into two groups and indicate the QDs relax the strain by diffusing indium to GaAs. In the 120-200 K temperature range, there are abnormal temperature behaviors attributed to the carrier transfer from the relaxed to non-relaxed QDs.

  9. Time-resolved photoluminescence properties of semiconductor quantum dot superlattices of different microcrystal shapes

    SciTech Connect

    Chae, Weon-Sik Choi, Eunjin; Ku Jung, Yun; Jung, Jin-Seung; Lee, Jin-Kyu

    2014-04-14

    We report time-resolved photoluminescence properties on semiconductor quantum dot (QD) superlattices (SLs) using PL lifetime imaging microscopy at a single particle level. PL lifetime imaging technique clearly reveals that different shaped QD SL microcrystals have different time-resolved PL characteristics. The faceted SL microcrystals consisted of well-organized QDs showed faster recombination rates than those of the spherical microparticles including randomly organized QDs, which can be explained by the different degree of energetic couplings among component QDs due to different packing fraction.

  10. Interference effects on room-temperature photoluminescence spectra of GaAs/Ge space solar cells

    SciTech Connect

    Timo, G.L.; Flores, C.

    1994-12-31

    This paper describes a new method, based on room-temperature photoluminescence (PL), for time-saving and non-destructive characterization of thin emitter GaAs/Ge solar cells used for space application. It has been shown that the interference phenomena produced between the PL directly escaping from the surface and the PL reflected on the GaAs/Ge interface can provide information on the doping level, thickness and uniformity of the GaAs structure deposited on Ge substrates. This method can be utilized for the quality control of mass-production of GaAs/Ge solar cells for space application.

  11. 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.

  12. The evolution of microstructure and photoluminescence of SiCN films with annealing temperature

    SciTech Connect

    Du Xiwen; Fu Yang; Sun Jing; Yao Pei

    2006-05-01

    Silicon carbonitride (SiCN) films were deposited by radio-frequency magnetron sputtering and then annealed at different temperatures from 1100 to 1300 deg. C in hydrogen atmosphere. The as-deposited films and films annealed at 1100 deg. C did not show photoluminescence (PL), whereas strong PL peaks appeared at 355 and 469 nm after annealing at 1200 and 1300 deg. C. X-ray diffraction, transmission electron microscope, and Fourier transform infrared spectrometer results show that the enhancement of PL properties is due to the change of microstructure and composition.

  13. Effects of surface oxide formation on germanium nanowire band-edge photoluminescence

    SciTech Connect

    Minaye Hashemi, Fatemeh Sadat; Laboratoire des Materiaux Semiconducteurs, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne ; Thombare, Shruti; Brongersma, Mark L.; Morral, Anna Fontcuberta i; McIntyre, Paul C.; Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305

    2013-06-24

    The effect of intentional surface oxide formation on band-edge photoluminescence (PL) of Ge nanowires was investigated. Thermal oxidation in molecular O{sub 2} was used to produce a surface oxide layer on assemblies of single crystal nanowires grown by the vapor-liquid-solid method. With increasing oxidation of the wires, the band-edge PL associated with the indirect gap transition becomes more intense. X-ray photoelectron spectroscopy confirms the formation of an increasingly GeO{sub 2}-like surface oxide under annealing conditions that enhance the indirect-gap PL, consistent with surface oxide passivation of nonradiative recombination centers initially present on the nanowire surface.

  14. 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.

  15. Effects of water molecules on photoluminescence from hierarchical peptide nanotubes and water probing capability.

    PubMed

    Wang, Minjie; Xiong, Shijie; Wu, Xinglong; Chu, Paul K

    2011-10-01

    Photoluminescence (PL) spectra reveal that deficiency of water molecules in the channel cores of bioinspired hierarchical diphenylalanine ( L -Phe- L -Phe, FF) peptide nanotubes (PNTs) not only modifies the bandgap of the subnanometer crystalline structure formed by the self-assembly process, but also induces a characteristic ultraviolet PL peak the position of which is linearly proportional to the number of water molecules in the PNTs. Addition or loss of water molecules gives rise to the UV PL redshift or blueshift. Density functional theory calculation also confirms that addition of water molecules to the PNTs causes splitting of the valence-band peak, which corresponds to the shift and splitting of the observed UV PL peak. Water molecules play an important role in the biological properties of FF PNTs and the results demonstrate that the PL spectra can be used to probe the number of water molecules bonded to the FF molecules. PMID:22049551

  16. 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.

  17. Photoluminescence of pyrochlore phase in SrBi2Ta2O9 thin films

    NASA Astrophysics Data System (ADS)

    Wang, Y. P.; Ning, H. F.; Zhou, L.; Shen, J. K.; Liu, Z. G.

    2003-07-01

    SrBi2Ta2O9 thin films were prepared by pulsed laser deposition at different substrate temperatures. Photoluminescence (PL) has been detected at room temperature from the pyrochlore phase in the SrBi2Ta2O9 film deposited at 850 °C. The PL shows five luminescence bands of 330, 365, 407, 490, and 600 nm. And the PL excitation shows six excitation bands of 278, 330, 365, 407, 490, and 600 nm. The one-to-one correspondence of PL and PL excitation spectra reveals a band-to-band excitation and a multienergy-gap structure in the pyrochlore phase in SrBi2Ta2O9 films.

  18. Structural order effect in visible photoluminescence properties of nanocrystalline Si :H thin films

    NASA Astrophysics Data System (ADS)

    Chen, H.; Shen, W. Z.; Wei, W. S.

    2006-03-01

    We report room-temperature visible photoluminescence (PL) properties of highly ordered hydrogenated nanocrystalline Si(nc-Si :H) with good electrical performance. The PL profiles can be well reproduced by the model of Islam and Kumar [J. Appl. Phys. 93, 1753 (2003)], incorporating the effects of quantum confinement and localized surface states, as well as a log-normal crystallite size distribution. Raman, PL, and electrical results consistently reveal that improvement of structural order within nc-Si :H is beneficial to enhance the PL efficiency. Owing to adequate order, strong visible PL and high electron mobility can coexist in nc-Si :H, which may provide possibilities in Si-based optoelectronics.

  19. 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

  20. 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. PMID:27152375

  1. Time-resolved photoluminescence study of m-plane GaN thin films

    NASA Astrophysics Data System (ADS)

    Pan, Ji-Hong; Jang, Der-Jun; Quadir, Shaham; Lo, Ikai

    2014-03-01

    The optical properties and the carrier relaxation of GaN thin films were studied by time-resolved photoluminescence apparatus. The m-plane GaN thin films were grown on GaN buffer layer and γ-LiAlO2 substrates by molecular beam epitaxy with variation of N/Ga ratio. We found that the PL associated with defect is prominent for large N/Ga ratio due to the increasing of stacking faults. The intensity of PL perpendicular to the GaN [0001] direction is more intensive than that of PL parallel to the perpendicular to the GaN [0001] direction. The PL decay times exhibit dependence on the direction of the PL polarizations.

  2. 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…

  3. Probing the molecular character of periodic mesoporous organosilicates via photoluminescence of Lewis acid-base adducts.

    PubMed

    Thiel, Indre; Fedorov, Alexey; Verel, Rene; Yakunin, Sergii; Kovalenko, Maksym V; Copéret, Christophe

    2016-05-18

    Photoluminescence decay was used as a structure-sensitive method to compare the distribution of emitting sites in periodic mesoporous organosilicates (PMOs) to their respective molecular analogs. The observed close similarity of PL decays confirms the molecular nature of PMOs and high homogeneity of emitting sites. PMID:27156706

  4. OPTICAL ABSORPTION AND PHOTOLUMINESCENCE IN PRISTINE AND PHOTOPOLYMERIZED C60 SOLID FILMS

    EPA Science Inventory

    The optical absorption (OA) and photoluminescence (PL) spectra of pristine, oxygen-free C60 films in the vicinity of the absorption edge across the highest-occupied-molecular-orbital to lowest-unoccupied-molecular-orbital (HOMO-LUMO) gap are studied to elucidate the nature of the...

  5. 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.

  6. Two types of photoluminescence blinking revealed by single quantum dot spectroelectrochemistry

    PubMed Central

    Galland, Christophe; Ghosh, Yagnaseni; Steinbrück, Andrea; Sykora, Milan; Hollingsworth, Jennifer A.; Klimov, Victor I.; Htoon, Han

    2012-01-01

    Photoluminescence (PL) intermittency (blinking), or random switching between states of high- (ON) and low (OFF) emissivities, is a universal property of molecular emitters exhibited by dyes1, polymers2, biological molecules3 and artificial nanostructures such as nanocrystal quantum dots, carbon nanotubes, and nanowires4,5,6. For the past fifteen years, colloidal nanocrystals have been used as a model system for studies of this phenomenon.5,6 The occurrence of OFF periods in nanocrystal emission has been commonly attributed to the presence of an additional charge7, which leads to PL quenching by nonradiative Auger recombination.8 However, the “charging” model was recently challenged in several reports.9,10 Here, to clarify the role of charging in PL intermittency, we perform time-resolved PL studies of individual nanocrystals while controlling electrochemically the degree of their charging. We find that two distinct mechanisms can lead to PL intermittency. We identify conventional blinking (A-type) due to charging/discharging of the nanocrystal core when lower PL intensities correlate with shorter PL lifetimes. Importantly, we observe a different blinking (B-type), when large changes in the PL intensity are not accompanied by significant changes in PL dynamics. We attribute this blinking behavior to charge fluctuations in the electron-accepting surface sites. When unoccupied, these sites intercept hot electrons before they relax into emitting core states. Both blinking mechanisms can be controlled electrochemically and under appropriate potential blinking can be completely suppressed. PMID:22071764

  7. 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.

  8. ezAFM: A low cost Atomic Force Microscope(AFM)

    NASA Astrophysics Data System (ADS)

    Celik, Umit; Celik, Kubra; Aslan, Husnu; Kehribar, Ihsan; Dede, Munir; Ozgur Ozer, H.; Oral, Ahmet

    2012-02-01

    A low cost AFM, ezAFM is developed for educational purposes as well as research. Optical beam deflection method is used to measure the deflection of cantilever. ezAFM scanner is built using voice coil motors (VCM) with ˜50x50x6 μm scan area. The microscope uses alignment free cantilevers, which minimizes setup times. FPGA based AFM feedback Control electronics is developed. FPGA technology allows us to drive all peripherals in parallel. ezAFM Controller is connected to PC by USB 2.0 interface as well as Wi-Fi. We have achieved <5nm lateral and ˜0.01nm vertical resolution. ezAFM can image single atomic steps in HOPG and mica. An optical microscope with <3 μm resolution is also integrated into the system. ezAFM supports different AFM operation modes such as dynamic mode, contact mode, lateral force microscopy. Advanced modes like magnetic force microscopy and electric force microscopy will be implemented later on. The new ezAFM system provides, short learning times for student labs, quick setup and easy to transport for portable applications with the best price/performance ratio. The cost of the system starts from 15,000, with system performance comparable with the traditional AFM systems.

  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. Effects of indium and tin overlayers on the photoluminescence spectrum of mercuric iodide

    NASA Astrophysics Data System (ADS)

    James, R. B.; Bao, X. J.; Schlesinger, T. E.; Ortale, C.; Cheng, A. Y.

    1990-03-01

    Mercuric iodide (HgI2 ) crystals with semitransparent metal overlayers of indium and tin were characterized using low-temperature photoluminescence (PL) spectroscopy. The PL spectra were found to differ for points beneath the thin metal overlayers and points that were masked off during each deposition. The photoluminescence data were compared with PL measurements taken on HgI2 photodetectors with indium-tin-oxide (ITO) entrance electrodes. The similarities of the spectra for the HgI2 samples with In, Sn, and ITO conducting overlayers indicate that the regions in the ITO-contacted photodetectors with relatively poor photoresponses are associated with the interaction of indium or tin with the mercuric iodide substrate.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  13. Synthesis of dithienosilole-based highly photoluminescent donor-acceptor type compounds.

    PubMed

    Ohshita, Joji; Tominaga, Yuta; Tanaka, Daiki; Ooyama, Yousuke; Mizumo, Tomonobu; Kobayashi, Norifumi; Higashimura, Hideyuki

    2013-03-14

    Highly photoluminescent acceptor-donor-acceptor (A-D-A) and donor-acceptor (D-A) type compounds with a dithienosilole unit as the donor and perfluorotolyl or dimesitylboryl group(s) as the acceptor were prepared by the reaction of lithiated dithienosilole derivatives with perfluorotoluene or fluorodimesitylborane, respectively. The resulting A-D-A and D-A type compounds showed red-shifted UV absorption and PL bands compared to those of simple dithienosiloles having no acceptor units, reported previously, and were highly photoluminescent in the solid state as well as in solution. Solvatochromic behaviour that would arise from the intramolecular donor-acceptor interaction were observed for the D-A type compounds with respect to the UV absorption and PL spectra. In addition, it was found that bis(dimesitylboryl)dithienosilole and (dimesitylboryl)(methylthio)dithienosilole responded to coexisting fluoride anions, leading to clear UV absorption and PL spectral changes in solutions. PMID:23295388

  14. Photoluminescence study of ZnS and ZnS:Pb nanoparticles

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  15. Preparation and photoluminescence properties of europium ions doped TiO2 nanocrystals.

    PubMed

    Liu, Hai; Yu, Lixin

    2013-07-01

    In this paper, pure and Eu3+ doped TiO2 nanocrystals (NCs) have been fabricated successfully by a two steps of sol-gel and hydrothermal methods. The microstructures, morphologies and photoluminescent properties of Eu(3+)-TiO2 were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and photoluminescence spectroscopy (PL). XRD and PL results show that the existent of rare earth can inhibit the transformation of TiO2 NCs from anatase to rutile phase and can improve the luminescence intensity of the prepared samples. The room-temperature PL emission of the as-grown samples is dominated by the 5D(0)-7F(j) transitions of Eu3+ ions. But the luminescence intensity drops dramatically when the annealing temperature reaches a relatively high degree because of the formation of the rutile phase of TiO2 NCs hosts. PMID:23901539

  16. Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials

    SciTech Connect

    Laurence, Ted A. Bude, Jeff D.; Shen, Nan; Steele, William A.; Ly, Sonny

    2014-02-28

    We previously reported a novel photoluminescence (PL) with a distribution of fast decay times in fused silica surface flaws that is correlated with damage propensity by high fluence lasers. The source of the PL was not attributable to any known silica point defect. Due to its broad spectral and temporal features, we here give this PL the name quasi-continuum PL (QC-PL) and describe the features of QC-PL in more detail. The primary features of QC-PL include broad excitation and emission spectra, a broad distribution of PL lifetimes from 20 ps to 5 ns, continuous shifts in PL lifetime distributions with respect to emission wavelength, and a propensity to photo-bleach and photo-brighten. We found similar PL characteristics in surface flaws of other optical materials, including CaF{sub 2}, DKDP, and quartz. Based on the commonality of the features in different optical materials and the proximity of QC-PL to surfaces, we suggest that these properties arise from interactions associated with high densities of defects, rather than a distribution over a large number of types of defects and is likely found in a wide variety of structures from nano-scale composites to bulk structures as well as in both broad and narrow band materials from dielectrics to semiconductors.

  17. Tailoring the photoluminescence characteristics of p-type GaSb: The role of surface chemical passivation

    NASA Astrophysics Data System (ADS)

    Wang, Bo; Wei, Zhipeng; Li, Mei; Liu, Guojun; Zou, Yonggang; Xing, Guozhong; Tan, Thiam Teck; Li, Sean; Chu, Xueying; Fang, Fang; Fang, Xuan; Li, Jinhua; Wang, Xiaohua; Ma, Xiaohui

    2013-01-01

    We report a systematic study on modulating optical properties in gallium antimonide (GaSb) with the sulfur surface passivation. Compared with the pristine sample, the intensity of the photoluminescence (PL) emission from the passivated GaSb was dramatically enhanced about 15 times at room temperature. The temperature-dependent surface states were further investigated via the low temperature PL spectroscopy. The bound-edge-related transition emission (BE4) at 795 meV and the residual acceptor associated emission located at 777 meV were identified clearly at 10 K. The observed passivation effects on the photoluminescence characteristics evolution of GaSb are discussed in detail.

  18. The dual roles of functional groups in the photoluminescence of graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, Shujun; Cole, Ivan S.; Zhao, Dongyuan; Li, Qin

    2016-03-01

    The photoluminescent properties of graphene nanoparticle (named graphene quantum dots) have attracted significant research attention in recent years owing to their profound application potential. However, the photoluminescence (PL) origin of this class of nanocarbons is still unclear. In this paper, combining direct experimental evidence enabled by a facile size-tunable oxygenated graphene quantum dots (GQDs) synthesis method and theoretical calculations, the roles of the aromatic core, functional groups and disordered structures (i.e. defects and sp3 carbon) in the PL of oxygenated GQDs are elucidated in detail. In particular, we found that the functional groups on GQDs play dual roles in the overall emission: (1) they enable π* --> n and σ* --> n transitions, resulting in a molecular type of PL, spectrally invariable with change of particle size or excitation energy; (2) similar to defects and sp3 carbon, functional groups also induce structural deformation to the aromatic core, leading to mid-gap states or, in other words, energy traps, causing π* --> mid-gap states --> π transitions. Therefore, functional groups contribute to both the blue edge and the red shoulder of GQDs' PL spectra. The new insights on the role of functional groups in PL of fluorescent nanocarbons will enable better designs of this new class of materials.The photoluminescent properties of graphene nanoparticle (named graphene quantum dots) have attracted significant research attention in recent years owing to their profound application potential. However, the photoluminescence (PL) origin of this class of nanocarbons is still unclear. In this paper, combining direct experimental evidence enabled by a facile size-tunable oxygenated graphene quantum dots (GQDs) synthesis method and theoretical calculations, the roles of the aromatic core, functional groups and disordered structures (i.e. defects and sp3 carbon) in the PL of oxygenated GQDs are elucidated in detail. In particular, we found

  19. Nano Mechanical Machining Using AFM Probe

    NASA Astrophysics Data System (ADS)

    Mostofa, Md. Golam

    Complex miniaturized components with high form accuracy will play key roles in the future development of many products, as they provide portability, disposability, lower material consumption in production, low power consumption during operation, lower sample requirements for testing, and higher heat transfer due to their very high surface-to-volume ratio. Given the high market demand for such micro and nano featured components, different manufacturing methods have been developed for their fabrication. Some of the common technologies in micro/nano fabrication are photolithography, electron beam lithography, X-ray lithography and other semiconductor processing techniques. Although these methods are capable of fabricating micro/nano structures with a resolution of less than a few nanometers, some of the shortcomings associated with these methods, such as high production costs for customized products, limited material choices, necessitate the development of other fabricating techniques. Micro/nano mechanical machining, such an atomic force microscope (AFM) probe based nano fabrication, has, therefore, been used to overcome some the major restrictions of the traditional processes. This technique removes material from the workpiece by engaging micro/nano size cutting tool (i.e. AFM probe) and is applicable on a wider range of materials compared to the photolithographic process. In spite of the unique benefits of nano mechanical machining, there are also some challenges with this technique, since the scale is reduced, such as size effects, burr formations, chip adhesions, fragility of tools and tool wear. Moreover, AFM based machining does not have any rotational movement, which makes fabrication of 3D features more difficult. Thus, vibration-assisted machining is introduced into AFM probe based nano mechanical machining to overcome the limitations associated with the conventional AFM probe based scratching method. Vibration-assisted machining reduced the cutting forces

  20. 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.

  1. 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.

  2. PL and FT-IR characterization of novel polymer thin films: PVCz mixed with perylene and fatty acids

    NASA Astrophysics Data System (ADS)

    Kusano, Hiroyuki; Kuruma, Ichiro; Kitagawa, Masahiko; Ichino, Kunio; Kobayashi, Hiroshi

    1997-04-01

    We have investigated the effect of addition of stearic acid in poly( N-vinylcarbazole) (PVCz) films doped with perylene. Samples were prepared by spin coating technique and characterized by photoluminescence (PL) and Fourier transform-infrared (FT-IR) absorption. It was elucidated that PL emission due to perylene at 450 nm and 480 nm was enhanced and the concentration quenching of the perylene emission was reduced by the addition of stearic acid. Orientation ordering of carbazole base plane and/or perylene ring plane was suggested from IR measurement.

  3. AFM CHARACTERIZATION OF RAMAN LASER INDUCED DAMAGE ON CDZNTECRYSTAL SURFACES

    SciTech Connect

    Teague, L.; Duff, M.

    2008-10-07

    High quality CdZnTe (or CZT) crystals have the potential for use in room temperature gamma-ray and X-ray spectrometers. Over the last decade, the methods for growing high quality CZT have improved the quality of the produced crystals however there are material features that can influence the performance of these materials as radiation detectors. The presence of structural heterogeneities within the crystals, such as twinning, pipes, grain boundaries (polycrystallinity), and secondary phases (SPs) can have an impact on the detector performance. There is considerable need for reliable and reproducible characterization methods for the measurement of crystal quality. With improvements in material characterization and synthesis, these crystals may become suitable for widespread use in gamma radiation detection. Characterization techniques currently utilized to test for quality and/or to predict performance of the crystal as a gamma-ray detector include infrared (IR) transmission imaging, synchrotron X-ray topography, photoluminescence spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy. In some cases, damage caused by characterization methods can have deleterious effects on the crystal performance. The availability of non-destructive analysis techniques is essential to validate a crystal's quality and its ability to be used for either qualitative or quantitative gamma-ray or X-ray detection. The work presented herein discusses the damage that occurs during characterization of the CZT surface by a laser during Raman spectroscopy, even at minimal laser powers. Previous Raman studies have shown that the localized annealing from tightly focused, low powered lasers results in areas of higher Te concentration on the CZT surface. This type of laser damage on the surface resulted in decreased detector performance which was most likely due to increased leakage current caused by areas of higher Te concentration. In this study

  4. Effects of Additives, Photodegradation, and Water-tree Degradation on the Photoluminescence in Polyethylene and Polypropylene

    NASA Astrophysics Data System (ADS)

    Ito, Toshihide; Fuse, Norikazu; Ohki, Yoshimichi

    Photoluminescence (PL) spectra induced by irradiation of ultraviolet photons are compared among low-density polyethylene (LDPE), crosslinked polyethylene (XLPE), and polypropylene (PP). Three PL bands appear around 4.2, 3.6, and 3.1 eV in LDPE and XLPE, while similar three PL bands are observed at similar energies in PP. The PL spectra and their decay profiles are independent of the presence of additives and are also independent of whether the samples were crosslinked or not. These results indicate that neither the additives nor the crosslinking has any significant effects on the respective three PLs in PE and PP. When the sample was pre-irradiated by the ultraviolet photons under different atmospheres (air, O2, and vacuum), all the PL intensities decrease with the progress of the pre-irradiation regardless of whether the sample is PE or PP. Therefore, all the PLs are considered to result from impurities. In all the pre-irradiated samples, a new PL band appears at 2.9 eV, of which intensity is stronger when the oxygen partial pressure during the pre-irradiation was lower. This PL is considered to be due to photo-induced conjugated double bonds. It has also been confirmed that water-tree degradation in LDPE or in XLPE does not contribute to PL.

  5. 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.

  6. 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.

  7. 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.

  8. Paramutation alters regulatory control of the maize pl locus.

    PubMed Central

    Hollick, J B; Patterson, G I; Asmundsson, I M; Chandler, V L

    2000-01-01

    The maize purple plant (pl) locus encodes a transcription factor required for anthocyanin pigment synthesis in vegetative and floral tissues. The strongly expressed Pl-Rhoades (Pl-Rh) allele is unstable, spontaneously changing to weaker expression states (Pl') at low frequencies and exclusively changing to Pl' in Pl'/Pl-Rh heterozygotes. The weakly expressed Pl' state is mitotically and meiotically stable, yet reversible. This type of allele-dependent, heritable alteration of gene control is called paramutation. Expression studies herein demonstrate that visible differences in anthocyanin pigment levels mirror pl RNA abundance and that pl paramutation is associated with reduced transcription of the pl gene. This transcriptional alteration is accompanied by acquisition of light-dependent regulation. Restriction endonuclease mapping indicates that these changes in pl gene regulation are not associated with detectable DNA alterations or with extensive changes in cytosine methylation patterns. Genetic tests show that Pl-Blotched (Pl-Bh), a structurally similar pl allele encoding an identical pl RNA and PL protein, does not participate in pl paramutation. This result suggests that if cis-acting sequences are required for pl paramutation they are distinct from the protein coding and immediately adjacent regions. A model is discussed in which pl paramutation results in heritable changes of chromatin structure that fundamentally alter regulatory interactions occurring during plant development. PMID:10747073

  9. 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

  10. Anomalous photoluminescence in InP1-xBix.

    PubMed

    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

  11. Hydration states of AFm cement phases

    SciTech Connect

    Baquerizo, Luis G.; Matschei, Thomas; Scrivener, Karen L.; Saeidpour, Mahsa; Wadsö, Lars

    2015-07-15

    The AFm phase, one of the main products formed during the hydration of Portland and calcium aluminate cement based systems, belongs to the layered double hydrate (LDH) family having positively charged layers and water plus charge-balancing anions in the interlayer. It is known that these phases present different hydration states (i.e. varying water content) depending on the relative humidity (RH), temperature and anion type, which might be linked to volume changes (swelling and shrinkage). Unfortunately the stability conditions of these phases are insufficiently reported. This paper presents novel experimental results on the different hydration states of the most important AFm phases: monocarboaluminate, hemicarboaluminate, strätlingite, hydroxy-AFm and monosulfoaluminate, and the thermodynamic properties associated with changes in their water content during absorption/desorption. This data opens the possibility to model the response of cementitious systems during drying and wetting and to engineer systems more resistant to harsh external conditions.

  12. AFM indentation study of breast cancer cells

    SciTech Connect

    Li, Q.S.; Lee, G.Y.H.; Ong, C.N.; Lim, C.T.

    2008-10-03

    Mechanical properties of individual living cells are known to be closely related to the health and function of the human body. Here, atomic force microscopy (AFM) indentation using a micro-sized spherical probe was carried out to characterize the elasticity of benign (MCF-10A) and cancerous (MCF-7) human breast epithelial cells. AFM imaging and confocal fluorescence imaging were also used to investigate their corresponding sub-membrane cytoskeletal structures. Malignant (MCF-7) breast cells were found to have an apparent Young's modulus significantly lower (1.4-1.8 times) than that of their non-malignant (MCF-10A) counterparts at physiological temperature (37 deg. C), and their apparent Young's modulus increase with loading rate. Both confocal and AFM images showed a significant difference in the organization of their sub-membrane actin structures which directly contribute to their difference in cell elasticity. This change may have facilitated easy migration and invasion of malignant cells during metastasis.

  13. Catalytic role of adsorbates in the photoluminescence emission of Si nanocrystals

    NASA Astrophysics Data System (ADS)

    Faraci, Giuseppe; Gibilisco, Santo; Pennisi, Agata R.; Franzó, Giorgia; La Rosa, Salvatore; Lozzi, Luca

    2008-12-01

    Silicon nanocrystals were synthesized and deposited on different substrates. In order to clarify the photoluminescence (PL) emission of these agglomerates, we studied the luminescence spectra of several samples as a function of the exposure to air, oxygen, nitrogen, and rare gases. Measurements at different pressures reveal a strong enhancement of the PL at atmospheric pressure, when the sample is in air. In contrast no significant PL is observed for clean Si quantum dot in rare-gas atmosphere and in air at low pressure. Different behavior is detected in oxygen and in nitrogen as a function of the pressure. These data point out a catalytic role of the surface adsorption adding significant information for clarifying the PL mechanism. A comparison of our results, including the decay-time spectra with data and models of literature, demonstrates the important role of the phonon interaction in the relaxation and decay processes.

  14. 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.

  15. Photoluminescence intensity enhancement in SWNT aqueous suspensions due to reducing agent doping: Influence of adsorbed biopolymer

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    The influence of biopolymer wrapped around nanotube on the enhancement of the semiconducting single-walled carbon nanotube (SWNT) photoluminescence (PL) in aqueous suspension which increases due to the reducing agent dithiothreitol (DTT) doping effect was revealed. The greatest enhancement of PL was observed for SWNTs covered with double- or single stranded DNA (above 170%) and DTT weak influence was revealed for SWNTs:polyC suspension (∼45%). The magnitude of the PL enhancement depends also on nanotube chirality and sample aging. The behavior of PL from SWNTs covered with various polymers is explained by the different biopolymers ordering on the nanotube surface. The ordered polymer conformation on the nanotube weakens the reducing agent doping effect. The method of reducing agent doping of nanotube:biopolymer aqueous suspension can serve as a sensitive luminescent probe of the biopolymer ordering on the carbon nanotube and can be used to increase the sensitivity of luminescent biosensors.

  16. Excitation Power Dependence Of Photoluminescence From GaAs Quantum Dot Prepared By Droplet Epitaxy Method

    NASA Astrophysics Data System (ADS)

    Choi, H. Y.; Kim, D. Y.; Cho, M. Y.; Kim, G. S.; Jeon, S. M.; Yim, K. G.; Kim, M. S.; Lee, D. Y.; Kim, J. S.; Kim, J. S.; Son, J. S.; Lee, J. I.; Leem, J. Y.

    2011-12-01

    GaAs quantum dot (QD) was grown by droplet epitaxy (DE) method and the excitation power dependence of photoluminescence (PL) were carried out. To investigate the effect of annealing temperature on QDs optical properties, the two step RTA process was carried out in a various temperature range from 800 to 1000 °C. As the thermal annealing temperature increases, the PL peak position is blue-shifted due to the change of the composition and size distribution of QDs, and the highest PL intensity is observed at the sample annealed at 900 °C. The integrated PL intensity (IPL) is plotted against the excitation density in a log-log scale and the slope was calculated.

  17. 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.

  18. Color-Tunable Resonant Photoluminescence and Cavity-Mediated Multistep Energy Transfer Cascade.

    PubMed

    Okada, Daichi; Nakamura, Takashi; Braam, Daniel; Dao, Thang Duy; Ishii, Satoshi; Nagao, Tadaaki; Lorke, Axel; Nabeshima, Tatsuya; Yamamoto, Yohei

    2016-07-26

    Color-tunable resonant photoluminescence (PL) was attained from polystyrene microspheres doped with a single polymorphic fluorescent dye, boron-dipyrrin (BODIPY) 1. The color of the resonant PL depends on the assembling morphology of 1 in the microspheres, which can be selectively controlled from green to red by the initial concentration of 1 in the preparation process of the microspheres. Studies on intersphere PL propagation with multicoupled microspheres, prepared by micromanipulation technique, revealed that multistep photon transfer takes place through the microspheres, accompanying energy transfer cascade with stepwise PL color change. The intersphere energy transfer cascade is direction selective, where energy donor-to-acceptor down conversion direction is only allowed. Such cavity-mediated long-distance and multistep energy transfer will be advantageous for polymer photonics device application. PMID:27348045

  19. Photoluminescence from quasi-dendritic ZnO nanostructures grown in anodic alumina nanochannels

    NASA Astrophysics Data System (ADS)

    Chen, Shih-Yung; Chen, Wei-Liang; Ko, Chung-Ting; Lai, Ming-Yu; Li, Feng-Chieh; Lee, Yu-Yang; Tsai, Kun-Tong; Chen, Miin-Jang; Chang, Yu-Ming; Wang, Yuh-Lin

    2015-11-01

    Atomic layer deposition (ALD) has been used to grow zinc oxide (ZnO) into a template of anodic aluminum oxide with quasi-dendritic nanochannels to form quasi-dendritic nanostructures. The characteristic photoluminescence (PL) emission from the inner region of the quasi-dendritic ZnO nanostructure peaks at 397 nm while that from its outer region at 424 nm. In between the two regions, the PL peak shows monotonic shift. In other words, the different layers of the single quasi-dendritic ZnO nanostructure emit PL with graded wavelengths spontaneously. The red shift in the PL peak positions is likely to be caused by the change in local stoichiometry between Zn and O, which are resulted from the limited supply of materials through the quasi-dendritic nanochannels during the ALD. The process to fabricate such quasi-dendritic ZnO nanostructures with spontaneously graded emission could help expand applications of ZnO-based devices.

  20. Contribution of Increased Extraction Efficiency to Increased Photo-Luminescence in Strained Polymer Films

    NASA Astrophysics Data System (ADS)

    Chen, Po-Jui; Yang, Arnold Chang-Mou; Hsu, Jui-Hung; White, Jonathon D.

    2011-03-01

    Potential applications of Luminescent Conjugated Polymers in thin film diodes, solar cells and flat panel displays have been limited by low efficiency. Craze formation in MEH-PPV/polystyrene thin films leads to a factor of 2 or 3 increase in collected photo-luminescence (PL) due to a combination of factors such as MEH-PPV chain conformation and increased extraction efficiency of PL. In order to determine the contribution of the latter effect, we used Monte Carlo based Ray Tracing to analyze the trajectory of photons generated in the thin film under different strain conditions. Our results indicate that increased PL extraction due to the existence of crazes contributes ~ 50 % of the observed increase in PL, the majority of this being due to light emitted near the craze edges.

  1. Contribution of Increased Extraction Efficiency to Increased Photo-Luminescence in Strained Polymer Films

    NASA Astrophysics Data System (ADS)

    Chen, Po-Jui; Chang-Mou Yang, Arnold; Hsu, Jui-Hung; White, Jonathon D.

    2012-02-01

    Potential applications of Luminescent Conjugated Polymers in thin film diodes, solar cells and flat panel displays have been limited by low efficiency. Craze formation in MEH-PPV/polystyrene thin film leads to a factor of 2 or 3 increase in collected photo-luminescence (PL) due to a combination of factors such as MEH-PPV chain conformation and increased extraction efficiency of PL. In order to determine the contribution of the latter effect, we used Monte Carlo based Ray Tracing to analyze the trajectory of photons generated in the thin film under different strain conditions. Our results indicate that increased PL extraction due to the existence of crazes contributes ˜15% of the observed increase in PL, the majority of this being due to light emitted near the craze edges.

  2. Defect-induced photoluminescence of strontium titanate and its modulation by electrostatic gating

    NASA Astrophysics Data System (ADS)

    Kumar, Dushyant; Budhani, R. C.

    2015-12-01

    The photoluminescence (PL) spectra of Ar+-ion irradiated single crystals of SrTiO3 (STO) excited by the 325 nm line of a He-Cd laser are compared with those of pristine crystals, epitaxial films, and amorphous layers of STO at several temperatures down to 20 K. The 550 eV Ar+-beam irradiation activates three distinctly visible PL peaks: blue (˜430 nm), green (˜550 nm), and infrared (˜820 nm) at room temperature, making the photoluminescence multicolored. The abrupt changes in PL properties below ≈100 K are discussed in relation with the antiferrodistortive structural phase transition in SrTiO3 from cubic to tetragonal symmetry, which makes it a direct bandgap semiconductor. The photoluminescence spectra are also tuned by an electrostatic gate field in a field-effect transistor geometry. At 20 K, we observed a maximum increase of ˜20 % in PL intensity under back gating of SrTiO3.

  3. 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

  4. Synthesis and Photoluminescence Properties of SnO2 Nanopowder

    NASA Astrophysics Data System (ADS)

    Arai, Takahiro; Adachi, Sadao

    2012-10-01

    SnO2 nanopowder was synthesized by calcining metastannic salt (SnO2·H2O) prepared by chemically etching metallic Sn in aqueous HNO3 solution. The calcined SnO2 nanopowder was investigated by X-ray diffraction (XRD) measurement and photoluminescence (PL) spectroscopy. The XRD and PL intensities increased with increasing calcining temperature, yielding an activation energy of ˜0.65 eV. The PL spectra of the calcined SnO2 nanopowder exhibited green (G) and red (R) emission bands with peaks at ˜2.5 and ˜2.0 eV, respectively, that were clearly dependent not only on the excitation light wavelength but also on the sample temperature. The temperature dependence of the PL intensity between 20 and 300 K was explained by the thermal quenching with activation energies of ˜15 meV (T=20-60 K) and ˜0.12-0.18 eV (T ≥100 K). The G and R emission states were found to originate from the Jahn-Teller effect of the 5s2 (Sn2+) ions in the SnO2 matrix and were similar to those generally observed in many ns2-doped alkali halides and SnCl2.

  5. Polarized Photoluminescence Study of CdGeAs_2.

    NASA Astrophysics Data System (ADS)

    McCrae, J. E.; Hengehold, R. L.; Yeo, Y. K.; Ohmer, M. C.; Schunemann, P. G.

    1996-03-01

    Cadmium Germanium Diarsenide (CdGeAs_2) is a chalcopyrite semiconductor with excellent nonlinear optical properties. It also has a very anisotropic thermal expansion coefficient which has made it almost impossible to obtain large crack-free oriented crystals of the material until the recent development of the seeded ultra-low gradient horizontal dynamic freeze technique. The low temperature photoluminescence (PL) spectrum contains two peaks; a broad, weak peak is found near 0.38 eV, and a somewhat narrower and often far brighter peak is found near 0.57 eV. The shift of the higher energy peak with excitation laser power indicates that it is due to donor-acceptor pair transitions. The variation of this peak with temperature suggests that band-to-band recombination also comes into play at higher temperatures. The PL signal persists up to at least room temperature. Additionally, the first polarization dependent PL study was made on oriented samples, and it has been found that the PL spectra are strongly polarized.

  6. The aggregation enhanced photoluminescence of gold nanorods in aqueous solutions.

    PubMed

    Cen, Yan; Huang, Xiao; Zhang, Ren; Chen, Ji-Yao

    2014-09-01

    The photoluminescence (PL) properties of single gold nanorod (AuNR) under one-photon excitation (OPE) have been reported recently. In this work, the PL of AuNRs in aqueous solutions were studied with OPE of 514 or 633 nm to characterize the emissions of transverse and longitudinal surface Plasmon resonance (TSPR and LSPR) bands, because the AuNRs aqueous solution was frequently used in bio-medical applications. We found that under 514 nm OPE the TSPR emissions of four groups of AuNRs with different aspect ratios in aqueous solutions were all strong dominating the PL emission with the quantum yield (QY) of 10(-4), which is at least three orders of magnitude higher than that of single AuNR. We further found that the aggregate was the basic form of AuNRs in aqueous solution and living cells, measured by the elastic light scattering and transmission electron microscopy measurements. The Plasmon coupling particularly the TSPR coupling between the neighbored AuNRs in aggregates enhanced the PL and increased the QY, because the conjugation of the rod side to side was a main aggregate mode. Under 633 nm OPE, only LSPR emissions of AuNRs aqueous solutions occurred with the QY level of 10(-5) which is very similar to that of singe AuNR, because of the negligible LSPR coupling. PMID:25096523

  7. 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

  8. Photoluminescence and upconversion on Ag/CdTe quantum dots

    NASA Astrophysics Data System (ADS)

    Ragab, A. E.; Gadallah, A.-S.; Mohamed, M. B.; Azzouz, I. M.

    2014-11-01

    Different sizes of aqueous CdTe QDs have been prepared by microwave via controlling the temperature and time of irradiation. To study the plasmonic effect on CdTe QDs, Silver NPs were prepared by using a chemical reduction method. Structure characterization of the nanocrystals (Ag NPs and CdTe QDs) was determined by transmission electron microscopy “TEM”. For optical characterization, the absorption and photolumincence (PL) spectra were measured. It has been found that there are two opposite behaviors (quenching and enhancement) in the fluorescence spectra based on the spectral coupling strength between Ag NPs and CdTe QDs. When there is strong overlapping, PL enhancement of CdTe QDs has been observed. On the other hand, when the overlapping is weak, the PL quenching was predominant at all Ag NPS concentrations. Input-output PL intensity dependence was also studied. Upconversion photoluminescence with low excitation intensity was observed in our CdTe QDs with a standard spectrofluorometer at excitation wavelength of 800 nm. Thermally assisted surface state mechanism has been proposed to be responsible for the upconverion process.

  9. 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

  10. Study of O2 sensitive photoluminescence of β-Ga2O3 nanostructures annealed in moist environments

    NASA Astrophysics Data System (ADS)

    Jangir, R.; Porwal, S.; Tiwari, Pragya; Rai, S. K.; Ganguli, Tapas

    2016-05-01

    In this study, effect of annealing in moist environment on the photoluminescence response to the oxygen (O2) is studied. β- Ga2O3 nanostructures were synthesized via vapor transport method on gold coated silicon substrate in N2 ambient. These β- Ga2O3 nanostructures were annealed in the different environment (water vapor and ammonia solution) and then room temperature PL measurements have been done at different oxygen partial pressures. PL results show that annealing modifies the surface of the nanostructures by creating permanent surface states which reduces the PL intensity response to the O2 because of competitive nonradiative paths. A possible mechanism for this behavior is also suggested.

  11. Experimental determination of band overlap in type II InAs/GaSb superlattice based on temperature dependent photoluminescence signal

    NASA Astrophysics Data System (ADS)

    Huang, Jianliang; Ma, Wenquan; Zhang, Yanhua; Cao, Yulian; Liu, Ke; Huang, Wenjun; Luo, Shuai; Ji, Haiming; Yang, Tao

    2015-12-01

    We have determined the band overlap in type II InAs/GaSb superlattice (SL) structure based on the temperature dependent photoluminescence (PL) results of a short wavelength SL sample. The band overlap value is treated as a temperature variable and is simulated by fitting the PL peak position using the 8K·P method. It is found that the band overlap monotonically decreases from 0.325 to 0.225 eV when temperature is increased from 12 to 90 K. The calculated e1-hh1 transition using the obtained band overlap data shows an agreement with the PL results of another SL sample.

  12. Conductance of AFM Deformed Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Maiti, Amitesh; Anatram, M. P.; Biegel, Bryan (Technical Monitor)

    2002-01-01

    This viewgraph presentation provides information on the electrical conductivity of carbon nanotubes upon deformation by atomic force microscopy (AFM). The density of states and conductance were computed using four orbital tight-binding method with various parameterizations. Different chiralities develop bandgap that varies with chirality.

  13. Contact nanomechanical measurements with the AFM

    NASA Astrophysics Data System (ADS)

    Geisse, Nicholas

    2013-03-01

    The atomic force microscope (AFM) has found broad use in the biological sciences largely due to its ability to make measurements on unfixed and unstained samples under liquid. In addition to imaging at multiple spatial scales ranging from micro- to nanometer, AFMs are commonly used as nanomechanical probes. This is pertinent for cell biology, as it has been demonstrated that the geometrical and mechanical properties of the extracellular microenvironment are important in such processes as cancer, cardiovascular disease, muscular dystrophy, and even the control of cell life and death. Indeed, the ability to control and quantify these external geometrical and mechanical parameters arises as a key issue in the field. Because AFM can quantitatively measure the mechanical properties of various biological samples, novel insights to cell function and to cell-substrate interactions are now possible. As the application of AFM to these types of problems is widened, it is important to understand the performance envelope of the technique and its associated data analyses. This talk will discuss the important issues that must be considered when mechanical models are applied to real-world data. Examples of the effect of different model assumptions on our understanding of the measured material properties will be shown. Furthermore, specific examples of the importance of mechanical stimuli and the micromechanical environment to the structure and function of biological materials will be presented.

  14. A Batch Fabricated SECM-AFM Probe

    NASA Astrophysics Data System (ADS)

    Dobson, P. S.; Macpherson, J. V.; Holder, M.; Weaver, J. M. R.

    2003-12-01

    A scheme for the fabrication of combined Scanning Electrochemical Microscopy — Atomic Force Microscopy (SECM-AFM) probes is presented for both silicon nitride and silicon cantilevers. The advantages over exsisting methods used for their production is explained. The process flow is described and initial results from electrodeposition of silver are presented.

  15. Quantum-confined Stark effect on photoluminescence and electroluminescence characteristics of InGaN-based light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Masui, Hisashi; Sonoda, Junichi; Pfaff, Nathan; Koslow, Ingrid; Nakamura, Shuji; Den Baars, Steven P.

    2008-08-01

    The quantum-confined Stark effect (QCSE) on InGaN-based light-emitting diodes (LEDs) was investigated as a part of the continuing study of exploring differences between photoluminescence (PL) and electroluminescence (EL) characteristics. The luminescence characteristics were related to electrical characteristics of green and amber LEDs by employing the electrical-bias-applied PL technique. By inspecting the band diagram, it has been found that the separation of quasi-Fermi levels, which strongly affects the QCSE, can be quantified and related to the luminescence. In order to compare PL and EL characteristics, attention was paid to the QCSE during the PL and EL measurements. Despite the control of the QCSE, differences were still confirmed between PL and EL characteristics, which have led us to the conclusion to that there are other unrevealed origins for the differences.

  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

    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

  19. 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.

  20. The dual roles of functional groups in the photoluminescence of graphene quantum dots.

    PubMed

    Wang, Shujun; Cole, Ivan S; Zhao, Dongyuan; Li, Qin

    2016-04-14

    The photoluminescent properties of graphene nanoparticle (named graphene quantum dots) have attracted significant research attention in recent years owing to their profound application potential. However, the photoluminescence (PL) origin of this class of nanocarbons is still unclear. In this paper, combining direct experimental evidence enabled by a facile size-tunable oxygenated graphene quantum dots (GQDs) synthesis method and theoretical calculations, the roles of the aromatic core, functional groups and disordered structures (i.e. defects and sp(3) carbon) in the PL of oxygenated GQDs are elucidated in detail. In particular, we found that the functional groups on GQDs play dual roles in the overall emission: (1) they enable π* → n and σ* → n transitions, resulting in a molecular type of PL, spectrally invariable with change of particle size or excitation energy; (2) similar to defects and sp(3) carbon, functional groups also induce structural deformation to the aromatic core, leading to mid-gap states or, in other words, energy traps, causing π* → mid-gap states → π transitions. Therefore, functional groups contribute to both the blue edge and the red shoulder of GQDs' PL spectra. The new insights on the role of functional groups in PL of fluorescent nanocarbons will enable better designs of this new class of materials. PMID:26731007

  1. Facile synthesis of novel photoluminescent ZnO micro- and nanopencils.

    PubMed

    Pol, Vilas G; Calderon-Moreno, Jose M; Thiyagarajan, P

    2008-12-01

    A single-step solvent-, catalyst-, and template-free synthesis process to prepare photoluminescent pencils of ZnO either in micro- or in nanosize diameters from a single precursor is demonstrated. The thermolysis of Zn's acetate dihydrate (ZAD) precursor in a closed stainless steel reactor at 700 degrees C under autogenic pressure (6.5 MPa), yielded carbon sphere-decorated ZnO micropencils (ZnO-M's). The ZnO-M's have novel room-temperature photoluminescence (PL) with well-defined emission peaks at the green, yellow, orange, and red regions of the visible spectra while suppressing the blue region. On the contrary, the thermolysis of ZAD in a closed stainless steel reactor at 700 degrees C with released pressure yielded uniformly carbon-coated ZnO nanopencils (ZN's). The coated carbon in ZN's quenches the complete UV-vis PL; however, after annealing ZN's at 600 degrees C/2 h in air, the UV PL is dominant, and the visible PL is suppressed. The carbon coating (partly or completely) on the one-dimensional (1D) ZnO surfaces plays an important role to modify PL properties. The insight into the reaction mechanism was gained through in situ mass spectrometry measurements. The as-prepared ZnO-M's and ZN's have been systematically characterized to determine their morphology, structure, and composition. PMID:18986186

  2. The effect of hydrogen/deuterium introduction on photoluminescence of 3C-SiC crystals

    SciTech Connect

    Lee, B.K.; Steckl, A.J.; Zavada, J.M.; Wilson, R.G.

    1998-12-31

    The effect of the incorporation and annealing of deuterium in 3C-SiC on its photoluminescence is reported. A 3C-SiC crystal has been implanted with 100 kev deuterium and subsequently annealed at temperatures between 1015 C and 1220 C for 1 to 5 minutes. SIMS depth profiles indicate hydrogen is strongly trapped by defects generated through ion bombardment, but a gradual damage repairing occurs during annealing. Photoluminescence was measured with 488 nm Ar laser excitation for sample temperatures from 89 K to 400 K. The PL peak wavelength of 540 nm at room temperature has shifted to 538 nm at 89 K. The peak PL intensity decreases with measurement temperature while its full width at half maximum (FWHM) exhibits an increasing trend. PL data were taken at five annealing stages. The post-implantation peak PL intensity and its integrated area increase initially with annealing temperature and time. After the final annealing at 1218 C for 2 minute, PL intensity and its integrated area exhibit a decrease in level.

  3. Photoluminescence of Energetic Particle-Irradiated InxGa1-xNAlloys

    SciTech Connect

    Li, S.X.; Jones, R.E.; Haller, E.E.; Yu, K.M.; Walukiewicz, W.; Ager III, J.W.; Liliental-Weber, Z.; Lu, Hai; Schaff, William J.

    2005-12-14

    A study of the photoluminescence (PL) characteristics of In{sub x}Ga{sub 1-x}N alloys in which the Fermi level is controlled by energetic particle irradiation is reported. In In-rich In{sub x}Ga{sub 1-x}N the intensity of the PL emission initially increases with irradiation dose before falling rapidly at high doses. This unusual trend is attributed to the location of the average energy of the dangling-bond type native defects (the Fermi level stabilization energy, or E{sub FS}), which lies about 0.9 eV above the conduction band edge of InN. As a result of this atypically high position of E{sub FS}, irradiation-induced defects formed at low doses are donors, and do not act as efficient recombination centers. Thus, low dose irradiation increases the electron concentration and leads to an increase of the photoluminescence intensity. However, at higher irradiation doses, the Fermi level approaches E{sub FS}, and the defects formed become increasingly effective as a non-radiative recombination centers and the PL quenches quickly. Our calculations of the PL intensity based on the effect of the electron concentration and the minority carrier lifetime, show good agreement with the experimental data. Finally, the blue shift of PL signal with increasing electron concentration is explained by the breakdown of momentum conservation due to the irradiation damage.

  4. Effect of Silica Nanoparticles on the Photoluminescence Properties of BCNO Phosphor

    NASA Astrophysics Data System (ADS)

    Nuryadin, Bebeh W.; Faryuni, Irfana Diah; Iskandar, Ferry; Abdullah, Mikrajuddin; Khairurrijal, Khairurrijal

    2011-12-01

    Effect of additional silica nanoparticles on the photoluminescence (PL) performance of boron carbon oxy-nitride (BCNO) phosphor was investigated. As a precursor, boric acid and urea were used as boron and nitrogen sources, respectively. The carbon sources was polyethylene glycol (PEG) with average molecule weight 20000 g/mol.. Precursor solutions were prepared by mixing these raw materials in pure water, followed by stirring to achieve homogeneous solutions. In this precursor, silica nanoparticles were added at various mass ratio from 0 to 7 %wt in the solution. The precursors were then heated at 750 °C for 60 min in a ceramic crucible under atmospheric pressure. The photoluminescence (PL) spectrum that characterized by spectrophotometer showed a single, distinct, and broad emission band varied from blue to near red color, depend on the PEG, boric acid and urea ratio in the precursor. The addition of silica nanoparticles caused the increasing of PL intensity as well as the shifting of peak wavelength of PL spectrum. The peak shifting of PL was affected by the concentration of silica nanoparticles that added into the precursor. We believe that the BCNO-silica composite phosphor becomes a promising material for the phosphor conversion-based white light-emitting diodes.

  5. Photoluminescence through in-gap states in phenylacetylene functionalized silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Angı, Arzu; Sinelnikov, Regina; Meldrum, Al; Veinot, Jonathan G. C.; Balberg, Isacc; Azulay, Doron; Millo, Oded; Rieger, Bernhard

    2016-04-01

    Optoelectronic properties of Si nanocrystals (SiNCs) were studied by combining scanning tunneling spectroscopy (STS) and optical measurements. The photoluminescence (PL) of phenylacetylene functionalized SiNCs red shifts relative to hexyl- and phenyl-capped counterparts, whereas the absorption spectra and the band gaps extracted from STS are similar for all surface groups. However, an in-gap state near the conduction band edge was detected by STS only for the phenylacetylene terminated SiNCs, which can account for the PL shift via relaxation across this state.Optoelectronic properties of Si nanocrystals (SiNCs) were studied by combining scanning tunneling spectroscopy (STS) and optical measurements. The photoluminescence (PL) of phenylacetylene functionalized SiNCs red shifts relative to hexyl- and phenyl-capped counterparts, whereas the absorption spectra and the band gaps extracted from STS are similar for all surface groups. However, an in-gap state near the conduction band edge was detected by STS only for the phenylacetylene terminated SiNCs, which can account for the PL shift via relaxation across this state. Electronic supplementary information (ESI) available: Detailed experimental procedures, additional HR-TEM images and PL lifetime data. See DOI: 10.1039/c6nr01435f

  6. 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

  7. Origin of photoluminescence in SrTiO{sub 3}: a combined experimental and theoretical study

    SciTech Connect

    Orhan, Emmanuelle . E-mail: emmanuelle.orhan@liec.ufscar.br; Pontes, Fenelon M.; Pinheiro, Carlos D.; Leite, Edson R.; Pizani, Paulo S.; Beltran, Armando; Andres, Juan; Varela, Jose A.; Longo, Elson

    2004-11-01

    A joint experimental and theoretical study has been carried out to rationalize the photoluminescence properties of SrTiO{sub 3} perovskite thin films synthesized through a soft chemical processing. Only the amorphous samples present photoluminescence at room temperature. From the theoretical side, first principles quantum mechanical techniques, based on density functional theory at B3LYP level, have been employed to study the electronic structure of a crystalline (ST-c) and an asymmetric (ST-a) model. Electronic properties are analyzed in the light of the experimental results and their relevance in relation to the PL behavior of ST is discussed.

  8. Magnetic and photoluminescence studies of electron irradiated Bi2Fe4O9 nanoparticles

    NASA Astrophysics Data System (ADS)

    Rao, Prashanth K. S.; Krishnan, Sheeja; Pattabi, Manjunatha; Sanjeev, Ganesh

    2016-03-01

    The effect of 8 MeV electron irradiation on the magnetic and photoluminescence properties of Bi2Fe4O9 has been investigated and reported in this paper. Magnetic parameters of unirradiated and irradiated Bi2Fe4O9 nanoparticles were investigated by Vibrating sample magnetometer (VSM). Modification in saturation magnetization, remanence magnetization and coercivity were observed after exposure of Bi2Fe4O9 nanoparticles to high energy electrons. A decrease in the intensity of photoluminescence (PL) spectra was observed in irradiated samples compared to the unirradiated samples.

  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. Radiation-stimulated photoluminescence in electron irradiated 4H-SiC

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The photoluminescence (PL) arising in low doped CVD grown n- and p-type 4H-SiC upon electron irradiation (0,9 MeV) has been studied. After each doze of irradiation spectrum of PL was measured. The PL spectrum was dominated by a band peaked at hv  ≈  2,45 eV, commonly observed upon irradiation of SiC. The experiments demonstrated that, for samples with both types of conduction, the PL intensity approaches a constant value with increasing irradiation dose. A model was suggested, describing the PL characteristics in terms of the radiative recombination via a donor-acceptor pair constituted by nitrogen and a structural defect formed in the course of irradiation. Also, the concentration of nitrogen atoms was measured by the SIMS method. The experimental data were used to calculate in terms of the suggested model the dependence of the PL intensity on the irradiation dose. A good agreement between the calculated and experimental dependences was observed. A conclusion is made that the PL is activated by donor—acceptor pairs constituted by a nitrogen atom and a structural defect.

  11. Strong photoluminescence enhancement of MoS(2) through defect engineering and oxygen bonding.

    PubMed

    Nan, Haiyan; Wang, Zilu; Wang, Wenhui; Liang, Zheng; Lu, Yan; Chen, Qian; He, Daowei; Tan, Pingheng; Miao, Feng; Wang, Xinran; Wang, Jinlan; Ni, Zhenhua

    2014-06-24

    We report on a strong photoluminescence (PL) enhancement of monolayer MoS2 through defect engineering and oxygen bonding. Micro-PL and Raman images clearly reveal that the PL enhancement occurs at cracks/defects formed during high-temperature annealing. The PL enhancement at crack/defect sites could be as high as thousands of times after considering the laser spot size. The main reasons of such huge PL enhancement include the following: (1) the oxygen chemical adsorption induced heavy p doping and the conversion from trion to exciton; (2) the suppression of nonradiative recombination of excitons at defect sites, which was verified by low-temperature PL measurements. First-principle calculations reveal a strong binding energy of ∼2.395 eV for an oxygen molecule adsorbed on a S vacancy of MoS2. The chemically adsorbed oxygen also provides a much more effective charge transfer (0.997 electrons per O2) compared to physically adsorbed oxygen on an ideal MoS2 surface. We also demonstrate that the defect engineering and oxygen bonding could be easily realized by mild oxygen plasma irradiation. X-ray photoelectron spectroscopy further confirms the formation of Mo-O bonding. Our results provide a new route for modulating the optical properties of two-dimensional semiconductors. The strong and stable PL from defects sites of MoS2 may have promising applications in optoelectronic devices. PMID:24836121

  12. 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.

  13. Room temperature photoluminescence at 4.5 {mu}m from InAsN

    SciTech Connect

    Zhuang, Q.; Godenir, A. M. R.; Krier, A.; Lai, K. T.; Haywood, S. K.

    2008-03-15

    Nitrogen incorporation in InAsN epilayers grown by radio-frequency plasma-assisted molecular beam epitaxy was investigated as a function of growth conditions. Reduced growth rate, growth temperature, and arsenic flux significantly enhance the nitrogen incorporation. Optimal growth conditions allowed us to obtain high quality InAsN with nitrogen composition of up to 2.5%. The epilayers exhibit intense 4 K photoluminescence (PL) with double-peak features, which were attributed to free carrier recombination and localized carrier recombination. Strong room temperature PL emission up to a wavelength of 4.5 {mu}m is obtained.

  14. Effects of electrolyte gating on photoluminescence spectra of large-area WSe2 monolayer films

    NASA Astrophysics Data System (ADS)

    Matsuki, Keiichiro; Pu, Jiang; Kozawa, Daichi; Matsuda, Kazunari; Li, Lain-Jong; Takenobu, Taishi

    2016-06-01

    We fabricated electric double-layer transistors comprising large-area WSe2 monolayers and investigated the effects of electrolyte gating on their photoluminescence (PL) spectra. Using the efficient gating effects of electric double layers, we succeeded in the application of a large electric field (∼107 V cm‑1) and the accumulation of high carrier density (>1013 cm‑2). As a result, we observed PL spectra based on both positively and negatively charged excitons and their gate-voltage-dependent redshifts, suggesting the effects of both an electric field and charge accumulation.

  15. Photoluminescent carbon dots synthesized by microwave treatment for selective image of cancer cells.

    PubMed

    Yang, Xudong; Yang, Xue; Li, Zhenyu; Li, Shouying; Han, Yexuan; Chen, Yang; Bu, Xinyuan; Su, Chunyan; Xu, Hong; Jiang, Yingnan; Lin, Quan

    2015-10-15

    In this work, a simple, low-cost and one-step microwave approach has been demonstrated for the synthesis of water-soluble carbon dots (C-dots). The average size of the resulting C-dots is about 4 nm. From the photoluminescence (PL) measurements, the C-dots exhibit excellent biocompatibility and intense PL with the high quantum yield (QY) at Ca. 25%. Significantly, the C-dots have excellent biocompatibility and the capacity to specifically target the cells overexpressing the folate receptor (FR). These exciting results indicate the as-prepared C-dots are promising biocompatible probe for cancer diagnosis and treatment. PMID:26074383

  16. Determination of the Exciton Binding Energy Using Photothermal and Photoluminescence Spectroscopy

    NASA Astrophysics Data System (ADS)

    Strzałkowski, K.; Zakrzewski, J.; Maliński, M.

    2013-04-01

    In this paper, experimental photoluminescence (PL) and piezoelectric photothermal (PPT) spectra of selected II-VI binary crystals are presented and analyzed. The quantitative analysis of the photothermal spectra was performed using a modified and extended Jackson-Amer model. The values of the bandgap energies of investigated semiconductors were computed from the PT amplitude and phase spectra. From the temperature dependence of the exciton emission so-called "excitonic energy gaps" have been determined. It follows from the theory that the exciton binding energy is the difference of these two values of energy gaps derived from PPT and PL spectroscopy.

  17. Transverse-microcavity modulation of photoluminescence from GaN nanowires

    NASA Astrophysics Data System (ADS)

    Long, J. P.; Flynn, R. A.; Vurgaftman, I.; Simpkins, B. S.; Mäkinen, A. J.; Mastro, M. A.; Pehrsson, P. E.

    2010-09-01

    Spatially resolved photoluminescence (PL) spectra from tapered GaN nanowires (NWs) with triangular cross section exhibit marked intensity modulations along the NW length. The modulation periodicity is attributed to previously unrecognized, leaky transverse standing-waves that occur when the PL wavelength matches path length criteria. These Fabry-Perot modes can affect optical measurements in transparent nanostructures even for dimensions less than ˜λ/2n, where λ is the free-space wavelength and n is the index of refraction.

  18. Improved infrared photoluminescence characteristics from circularly ordered self-assembled Ge islands

    PubMed Central

    2011-01-01

    The formation of circularly ordered Ge-islands on Si(001) has been achieved because of nonuniform strain field around the periphery of the holes patterned by focused ion beam in combination with a self-assembled growth using molecular beam epitaxy. The photoluminescence (PL) spectra obtained from patterned areas (i.e., ordered islands) show a significant signal enhancement, which sustained till 200 K, without any vertical stacking of islands. The origin of two activation energies in temperature-dependent PL spectra of the ordered islands has been explained in detail. PMID:21711943

  19. Effect of heat treatment on the structure of incorporated oxalate species and photoluminescent properties of porous alumina films formed in oxalic acid

    NASA Astrophysics Data System (ADS)

    Vrublevsky, I.; Jagminas, A.; Hemeltjen, S.; Goedel, W. A.

    2008-09-01

    The present work focuses on the use of IR spectroscopy and photoluminescence spectral measurements for studying the treatment temperature effect on the compositional and luminescent properties of oxalic acid alumina films. In line with the recent researches we have also found that heat treatment of porous alumina films formed in oxalic acid leads to considerable changes in their photoluminescence properties: upon annealing the intensity of photoluminescence (PL) increases reaching a maximum at the temperature of around 500 °C and then decreases. IR spectra of as-grown and heat-treated films have proved that PL emission in the anodic alumina films is related with the state of 'structural' oxalate species incorporated in the oxide lattice. These results allowed us to conclude that PL behavior of oxalic acid alumina films can be explained through the concept of variations in the bonding molecular orbitals of incorporated oxalate species including σ- and π-bonds.

  20. Photoluminescence of Sequential Infiltration Synthesized ZnO nanostructures

    NASA Astrophysics Data System (ADS)

    Ocola, Leonidas; Gosztola, David; Yanguas-Gil, Angel; Connolly, Aine

    We have investigated a variation of atomic layer deposition (ALD), called sequential infiltration synthesis (SiS), as an alternate method to incorporate ZnO and other oxides inside polymethylmethacrylate (PMMA) and other polymers. Energy dispersive spectroscopy (EDS) results show that we synthesize ZnO up to 300 nm inside a PMMA film. Photoluminescence data on a PMMA film shows that we achieve a factor of 400X increase in photoluminescence (PL) intensity when comparing a blank Si sample and a 270 nm thick PMMA film, where both were treated with the same 12 alternating cycles of H2O and diethyl zinc (DEZ). PMMA is a well-known ebeam resist. We can expose and develop patterns useful for photonics or sensing applications first, and then convert them afterwards into a hybrid polymer-oxide material. We show that patterning does indeed affect the photoluminescence signature of native ZnO. We demonstrate we can track the growth of the ZnO inside the PMMA polymer using both photoluminescence and Raman spectroscopy and determine the point in the process where ZnO is first photoluminescent and also at which point ZnO first exhibits long range order in the polymer. This work was supported by the Department of Energy under Contract No. DE-AC02-06CH11357. Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  1. Photoluminescence mechanism for blue-light-emitting porous silicon

    NASA Astrophysics Data System (ADS)

    Qin, G. G.; Liu, X. S.; Ma, S. Y.; Lin, J.; Yao, G. Q.; Lin, X. Y.; Lin, K. X.

    1997-05-01

    A comparative study of photoluminescence (PL) and photoluminescence excitation (PLE) spectra of porous silicon (PS) and Si oxide, both emitting blue light, is reported. The PLE spectrum of Si oxide monitored at 460 nm displays a three-peak structure with peak wavelengths around 265, 300, and 360 nm. The PLE intensity of the PS sample increases with decreasing excitation wavelength, and has three shoulders located at wavelengths near the three PLE peak wavelengths of Si oxide. When the PS sample is oxidized for half an hour at 1150 °C [the temperature at which nanometer Si particles (NSP's) inside PS disappear], blue-light PL intensity reduces greatly, and its PLE spectrum changes into a spectrum very similar to that of Si oxide. The experimental result strongly indicates that for the blue-light emission from PS there are two types of photoexcitation processes: photoexcitation occurs in NSP"s and in the Si oxide layers covering NSP's, and radiative recombination of electron-hole pairs is carried out in luminescence centers located on the interfaces between NSP"s and Si oxide and in those inside Si oxide layers.

  2. 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.

  3. 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.

  4. 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

  5. Detection of Pathogens Using AFM and SPR

    NASA Astrophysics Data System (ADS)

    Vaseashta, Ashok

    2005-03-01

    A priori detection of pathogens in food and water has become a subject of paramount importance. Several recent incidents have resulted in the government passing stringent regulations for tolerable amounts of contamination of food products. Identification and/or monitoring of bacterial contamination in food are critical. The conventional methods of pathogen detection require time-consuming steps to arrive disembark at meaningful measurement in a timely manner as the detection time exceeds the time in which perishable food recycles through the food chain distribution. The aim of this presentation is to outline surface plasmon resonance (SPR) and atomic force microscopy (AFM) as two methods for fast detect6ion of pathogens. Theoretical basis of SPR and experimental results of SPR and AFM on E. coli O157:H7 and prion are presented.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

  7. 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. PMID:25920456

  8. 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.

  9. 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.

  10. 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.

  11. 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+}.

  12. 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

  13. Characterizing Cell Mechanics with AFM and Microfluidics

    NASA Astrophysics Data System (ADS)

    Walter, N.; Micoulet, A.; Suresh, S.; Spatz, J. P.

    2007-03-01

    Cell mechanical properties and functionality are mainly determined by the cytoskeleton, besides the cell membrane, the nucleus and the cytosol, and depend on various parameters e.g. surface chemistry and rigidity, surface area and time available for cell spreading, nutrients and drugs provided in the culture medium. Human epithelial pancreatic and mammary cancer cells and their keratin intermediate filaments are the main focus of our work. We use Atomic Force Microscopy (AFM) to study cells adhering to substrates and Microfluidic Channels to probe cells in suspension, respectively. Local and global properties are extracted by varying AFM probe tip size and the available adhesion area for cells. Depth-sensing, instrumented indentation tests with AFM show a clear difference in contact stiffness for cells that are spread of controlled substrates and those that are loosely attached. Microfluidic Channels are utilized in parallel to evaluate cell deformation and ``flow resistance'', which are dependent on channel cross section, flow rate, cell nucleus size and the mechanical properties of cytoskeleton and membrane. The results from the study are used to provide some broad and quantitative assessments of the connections between cellular/subcellular mechanics and biochemical origins of disease states.

  14. 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

  15. Molybdenum disulfide quantum dots as a photoluminescence sensing platform for 2,4,6-trinitrophenol detection.

    PubMed

    Wang, Yong; Ni, Yongnian

    2014-08-01

    Transition metal chalcogenides, especially molybdenum disulfide (MoS2), have recently attracted wide attention from researchers as graphene-analogous materials. However, until now, little literature has reported the synthesis of photoluminescent MoS2 materials and their applications in analytical chemistry. We herein presented a facile bottom-up hydrothermal route for the synthesis of photoluminescent MoS2 quantum dots (QDs) by using sodium molybdate and cysteine as precursors. The prepared MoS2 QDs were characterized by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence spectroscopy, and UV-vis spectroscopy. The MoS2 QDs were then used as photoluminescent probes to construct a photoluminescence (PL) quenching sensor for detection of 2,4,6-trinitrophenol (TNP). The TNP sensor presented a wide linear range from 0.099 to 36.5 μM with a high detection limit of 95 nM. Furthermore, the sensor displayed a high sensitivity toward TNP over other structurally similar compounds like 2,4,6-trinitrotoluene, p-chlorophenol, phenol, and 2,6-di-tert-butyl-4-methylphenol. To understand the origin of the high sensitivity, we assessed the emission wavelength-dependent PL quenching behavior of MoS2 QDs by the above five compounds using Stem-Volmer equation in detail. The results showed that the novel approach we put forward can satisfactorily explain the interaction mechanisms between MoS2 QDs and the five compounds, and the high sensitivity for TNP very likely originated from a combination of the PL resonance energy transfer, electronic energy transfer, and electrostatic interactions between MoS2 QDs and TNP. Finally, the sensor was successfully applied for detection of TNP in water samples and test papers. PMID:25001878

  16. 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%.

  17. Photoluminescence of friction-induced polymer degradation products

    NASA Astrophysics Data System (ADS)

    Vettegren, V. I.; Savitskiĭ, A. V.; Scherbakov, I. P.

    2008-07-01

    We have studied the photoluminescence (PL) spectra of polyethylene (PE), polypropylene, and polyamide 6 excited using laser radiation with a photon energy (˜3.68 eV) within a spectral interval (3.65 3.75 eV) corresponding to the optical absorption due to C=O bonds. The PL spectra of the products of friction-induced degradation of these polymers display an intense peak in the region of about 2 2.5 eV. In order to elucidate the nature of this peak, the surface of PE film samples upon friction (rubbing) has been studied using IR spectroscopy in the attenuated total reflection (ATR) mode. The ATR spectra of these samples exhibit a sharp increase in the intensity of bands assigned to vibrations of the conjugated sequences of carbon-carbon bonds in the backbone of PE macromolecules. This result allows the PL peak at 2 2.5 eV to be assigned to the π* → π transition in the conjugated sequences of such bonds excited by means of the intramolecular energy transfer from C=O bonds.

  18. Photoluminescence of Erbium-Doped Potassium Tantalate Niobate Polycrystalline

    NASA Astrophysics Data System (ADS)

    Wen, Cheng‑Hung; Chu, Sheng‑Yuan; Shin, Yan‑Yu; Wen, Cheng‑Kuo

    2006-07-01

    In this study, we investigated the luminescence properties of erbium-doped potassium tantalite niobate (KTaxNb1-xO3 or KTN) ceramics, which were prepared by the conventional solid-state reaction synthesis method. In this work, we studied the relationships of the crystal structure, and Raman and photoluminescence (PL) spectra with the tantalum concentration, respectively. The experiments showed that the tantalum dopants modified the intensity of the green, red and near-infrared emission bands. The experiments also showed a blue shift for the 2 mol % erbium doped KTN samples with different tantalum compositions. Doping Ta not only led to the change in PL intensity but also in spectral shapes. The PL spectra showed the splitting peaks for the samples with low Ta compositions. Then these peaks combined and broadened as Ta concentration increase. When Ta was substituted for Nb completely, the luminescence intensity of the green emission band had an increase of approximately about one order of magnitude, which was because of the absence of the first-order phonon relaxation in the high-Ta-concentration samples.

  19. 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.

  20. Photoluminescence of He-implanted ZnO

    SciTech Connect

    Hamby, D. W.; Lucca, D. A.; Lee, J.-K.; Nastasi, Michael Anthony,

    2004-01-01

    A study of the effects of ion-implanted He{sup +} on the 4.2 K photoluminescence (PL) of ZnO is presented. This investigation is motivated by the need to further understand the effects of damage resulting from the implantation process on the PL of ZnO. For this study, 10 keV He{sup +} ions were implanted at a dose of 2.5 x 10{sup 13}/cm{sup 2} in the (0001) Zn-terminated surface. The implantation process is seen to reduce the overall luminescence efficiency, although the number and relative intensities of the bound-exciton peaks are observed to be similar to that of unimplanted ZnO. The 4.2 K PL of the implanted surface exhibits a broad orange/red peak near 1.86 eV nm and is attributed to damage introduced during the implantation process. This peak is identified as donor-acceptor pair (DAP) luminescence with a thermal activation energy of 11 meV. The 1.86 eV peak is not observed for H-implanted ZnO suggesting that H passivates the implantation-induced defects responsible for this luminescence.

  1. Photoluminescence of monovalent indium centres in phosphate glass

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  2. 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.

  3. 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.

  4. 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

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

    PubMed

    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 (E11(2*)) 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

  6. 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.

  7. 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+}.

  8. Visible Photoluminescence of Non-Stoichiometric Silicon Nitride Films: The Effect of Annealing Temperature and Atmosphere

    NASA Astrophysics Data System (ADS)

    Vlasukova, L. A.; Komarov, F. F.; Parkhomenko, I. N.; Milchanin, O. V.; Makhavikou, M. A.; Mudryi, A. V.; Żuk, J.; Kopychiński, P.; Togambayeva, A. K.

    2015-07-01

    The radiative properties of non-stoichiometric silicon nitride SiNx fi lms produced by plasma-enhanced chemical vapor deposition were studied. Intense room-temperature photoluminescence (PL) in the visible region was recorded after annealing for both Si-rich (x = 1.13) and N-rich (x = 1.5) silicon nitride fi lms. The position of the PL band maximum depended signifi cantly on the fi lm composition. The PL band maxima for Si-rich and N-rich SiNx fi lms were detected in the red (660 nm) and blue (450 nm) spectral regions, respectively. The effect of the annealing atmosphere on PL of the SiNx fi lms was studied. It was shown that the PL intensity depended not only on the annealing temperature but also on the annealing atmosphere. The observed features of the non-stoichiometric SiNx PL spectra were explained in terms of defect states in the SiNx band gap.

  9. 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

  10. Time-resolved photoluminescence characterization of oxygen-related defect centers in AlN

    NASA Astrophysics Data System (ADS)

    Genji, Kumihiro; Uchino, Takashi

    2016-07-01

    Time-resolved photoluminescence (PL) spectroscopy has been employed to investigate the emission characteristics of oxygen-related defects in AlN in the temperature region from 77 to 500 K. Two PL components with different decay constants are observed in the near-ultraviolet to visible regions. One is the PL component with decay time of <10 ns and its peak position shifts to longer wavelengths from ˜350 to ˜500 nm with increasing temperature up to 500 K. This PL component is attributed to the radiative relaxation of photoexcited electrons from the band-edge states to the ground state of the oxygen-related emission centers. In the time region from tens to hundreds of nanoseconds, the second PL component emerges in the wavelength region from 300 to 400 nm. The spectral shape and the decay profiles are hardly dependent on temperature. This temperature-independent PL component most likely results from the transfer of photoexcited electrons from the band-edge states to the localized excited state of the oxygen-related emission centers. These results provide a detailed insight into the radiative relaxation processes of the oxygen-related defect centers in AlN immediately after the photoexcitation process.

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

    NASA Astrophysics Data System (ADS)

    Sawada, Kenji; Adachi, Sadao

    2015-09-01

    Photo-induced luminescence intensity degradation in red-emitting Tb3Ga5O12:Eu3+ (TGG:Eu3+) phosphor is observed and studied using x-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation spectroscopy, and PL decay analysis. The red-emitting TGG:Eu3+ 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 λex = 355 and 266 nm suggest that the present degradation/recovery processes are caused by the electron traps formed in the TGG:Eu3+ phosphor. The Tb3+ emission in TGG shows the essentially same degradation characteristics as those observed in the TGG:Eu3+ phosphor. The present luminescence degradation/recovery phenomena of the trivalent ions (4f → 4f transitions) may universally occur in various oxide phosphors such as TGG (Tb3+ emission) and CaTiO3:Eu3+.

  12. Structure and photoluminescence properties of carbon nanotip-vertical graphene nanohybrids

    NASA Astrophysics Data System (ADS)

    Wang, B. B.; Zhu, K.; Ostrikov, K.; Shao, R. W.; Zheng, K.

    2016-01-01

    We report on the effective enhancement and tuning of photoluminescence (PL) by combining vertical graphene nanoflakes (VGs) and carbon nanotips (CNTPs). The VGs are grown on the vertical CNTPs by hot filament chemical vapor deposition in the methane environment, where the CNTPs are synthesized on silicon substrates by CH4-H2-N2 plasma-enhanced hot filament chemical vapor deposition. The results of field emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy indicate that the VGs can be grown on the CNTP and silicon substrate surfaces with the orientation perpendicular to the surfaces of CNTPs and silicon substrates. The PL properties of VG, CNTP, and CNTP-VG structures are studied using a 325 nm line of He-Cd laser as the excitation source. The PL results indicate that the PL of VGs is enhanced by the CNTPs due to the increasing density of PL emitters, while the PL properties of the nanohybrid system can be tuned. Furthermore, the potential applications of CNTP-VG structures in optoelectronic devices are analyzed. These results contribute to the design of functional graphene-based materials and the development of next-generation optoelectronic devices.

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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.

  18. Photoacoustic and Photoluminescence Characterization of Passivated and Unpassivated Mn-Doped ZnS Nanoparticles

    NASA Astrophysics Data System (ADS)

    Cruz, Almira Briones; Shen, Qing; Toyoda, Taro

    2005-06-01

    In this study, passivated and unpassivated nanocrystalline ZnS with varying Mn2+ concentrations (ZnS:Mn) were synthesized and their photoacoustic (PA) and photoluminescence (PL) characteristics were studied. The PA intensity peak for the nanocrystalline ZnS was found to be blue-shifted compared with that for the bulk material due to quantum confinement effects. The difference of the PA signals of doped ZnS and undoped ZnS yielded the Mn2+ optical absorption spectra. The intensity of the PA peak increased linearly with Mn concentration. The PL spectra showed a peak position at 2.08 eV corresponding to the d-d transition of Mn2+. For the unpassivated sample, a decrease in the PL intensities for higher Mn concentrations was observed. This could be attributed to concentration quenching. Addition of acrylic acid as a passivator led to an increase in PL intensity for all Mn concentrations and prevented the decrease in the PL intensity for higher Mn concentrations. These could be attributed to the surface passivation, which reduces the nonradiative recombination probabilities, thus increasing PL intensities.

  19. 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.

  20. 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

  1. Kinetics of PL quenching during single-walled carbon nanotube rebundling and diameter-dependent surfactant interactions.

    PubMed

    McDonald, Timothy J; Engtrakul, Chaiwat; Jones, Marcus; Rumbles, Garry; Heben, Michael J

    2006-12-21

    The kinetics of single-walled carbon nanotube rebundling have been investigated by photoluminescence (PL) spectroscopy. The rate of loss of PL intensity was measured for 12 different nanotubes in three common aqueous surfactants (sodium dodecyl sulfate, SDS; sodium dodecylbenzene sulfonate, SDBS; and sodium cholate, SC) as the surfactant suspensions were diluted to promote nanotube rebundling, quenching of semiconductor nanotube PL, and precipitation. The rate of PL decay was first-order in the concentration of isolated nanotubes, as expected if surfactant desorption is rate-limiting in the rebundling process. Temperature-dependent measurements permitted an Arrhenius analysis from which diameter-dependent activation energies were determined. SDS was found to have very strong diameter dependence for activation energy, with stronger binding to smaller-diameter nanotubes, whereas SDBS displayed a weaker diameter dependence. SC was found to bind strongly to certain nanotubes and weakly to the (10,2) nanotube. The PL emission red shifted with time after dilution as surfactant desorption proceeded. This effect is attributed to an increase in the micropolarity at the nanotube surface. PMID:17165980

  2. 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

  3. 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.

  4. 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.

  5. Photoluminescence based H2 and O2 gas sensing by ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Yadav, Kavita; Gahlaut, Shashank K.; Mehta, B. R.; Singh, J. P.

    2016-02-01

    Gas sensing properties of ZnO nanowires prepared via thermal chemical vapor deposition method were investigated by analyzing change in their photoluminescence (PL) spectra. The as-synthesized nanowires show two different PL peaks positioned at 380 nm and 520 nm. The 380 nm emission is ascribed to near band edge emission, and the green peak (520 nm) appears due to the oxygen vacancy defects. The intensity of the green PL signal enhances upon hydrogen gas exposure, whereas it gets quenched upon oxygen gas loading. The ZnO nanowires' sensing response values were observed as about 54% for H2 gas and 9% for O2 gas at room temperature for 50 sccm H2/O2 gas flow rate. The sensor response was also analyzed as a function of sample temperature ranging from 300 K to 400 K. A conclusion was derived from the observations that the H2/O2 gases affect the adsorbed oxygen species on the surface of ZnO nanowires. The adsorbed species result in the band bending and hence changes the depletion region which causes variation in PL signal. A photoluminescence based gas sensing technique has advantage over a conductometric technique due to its higher sensitivity and faster response time.

  6. 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

  7. Modifying the Photoluminescence of Monolayer MoS2 by Metal Deposition

    NASA Astrophysics Data System (ADS)

    Sun, Dezheng; You, Yumeng; Mak, Kin Fai; Zhang, Fan; Hone, James; Bartels, Ludwig; Heinz, Tony

    2013-03-01

    Monolayer MoS2 exhibits strong photoluminescence (PL) due to its direct band gap located at K point. Because of its monolayer thickness, light emission from MoS2 is known to be strongly influenced by interactions with surrounding media. In this study, we have investigated the effect on the photoluminescence of exfoliated monolayers of MoS2 induced by the deposition of gold atoms. The PL from the sample was recorded as a function of amount of gold deposited, up to an effective thickness of about 1 nm. Atomic force microscopy revealed that the gold forms isolated island structures on the surface. A progressive increase in quenching was seen with increasing gold coverage. Deposition of gold on suspended MoS2 samples led to quenching of the PL by more than a factor of 100. Given the low reactivity of gold, we attribute the PL quenching primarily to energy transfer of the photogenerated excitons to the metal clusters. The observed changes in the shape and intensity of emission spectra will be discussed in terms of this mechanism and possible effects of doping induced by the gold deposition.

  8. 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

  9. Red photoluminescence in praseodymium-doped titanate perovskite films epitaxially grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Takashima, Hiroshi; Ueda, Kazushige; Itoh, Mitsuru

    2006-12-01

    Intense red photoluminescence (PL) under ultraviolet (UV) excitation was observed in epitaxially grown Pr-doped Ca0.6Sr0.4TiO3 perovskite films. The films were grown on SrTiO3 (100) substrates by pulsed laser deposition, and their epitaxial growth was confirmed by x-ray diffraction and reflected high-energy electron diffraction. The observed sharp PL peak centered at 610nm was assigned to the transition of Pr3+ ions from the D21 state to the H43 state. The PL intensity was markedly enhanced by postannealing treatments at 1000°C, above the film-growth temperature of 600 or 800°C. Because the excitation and absorption spectra are similar to each other, it was suggested that the UV energy absorbed by the host lattice was transferred to the Pr ions, resulting in the red luminescence.

  10. 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.

  11. 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.

  12. Photoluminescence of nanosized Zn2SiO4:Mn depending upon preparation method

    NASA Astrophysics Data System (ADS)

    Petrovykh, K. A.; Kortov, V. S.; Rempel, A. A.

    2014-11-01

    Nanosized Zn2SiO4:Mn powders were prepared by two different methods: a high- energy ball-milling of microcrystalline powder (so-called "top-down") and a sol-gel method ("bottom-up"). It was shown that it is possible to obtain particles of 30±10 nm by means of the ball-milling. A particle size of the Zn2SiO4:Mn synthesized by the sol-gel method ranged from 20 to 110 nm. It was found all samples exhibit photoluminescence (PL) in the green spectral region with a maximum emission wavelength from 515 to 520 nm. A nanopowder obtained by the ball-milling showed a significant decrease of the PL intensity comparing with bulk material. The PL intensity of the samples prepared by sol-gel method is much higher than that of ball-milled Zn2SiO4:Mn.

  13. Imaging of the relative saturation current density and sheet resistance of laser doped regions via photoluminescence

    NASA Astrophysics Data System (ADS)

    Yang, Xinbo; Macdonald, D.; Fell, A.; Shalav, A.; Xu, Lujia; Walter, D.; Ratcliff, T.; Franklin, E.; Weber, K.; Elliman, R.

    2013-08-01

    We present an approach to characterize the relative saturation current density (Joe) and sheet resistance (RSH) of laser doped regions on silicon wafers based on rapid photoluminescence (PL) imaging. In the absence of surface passivation layers, the RSH of laser doped regions using a wide range of laser parameters is found to be inversely proportional to the PL intensity (IPL). We explain the underlying mechanism for this correlation, which reveals that, in principle, IPL is inversely proportional to Joe at any injection level. The validity of this relationship under a wide range of typical experimental conditions is confirmed by numerical simulations. This method allows the optimal laser parameters for achieving low RSH and Joe to be determined from a simple PL image.

  14. 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.

  15. Photoluminescence study of β-Ga2O3 nanostructures annealed in different environments

    NASA Astrophysics Data System (ADS)

    Jangir, R.; Porwal, S.; Tiwari, Pragya; Mondal, Puspen; Rai, S. K.; Ganguli, Tapas; Oak, S. M.; Deb, S. K.

    2012-08-01

    β-Ga2O3 nanostructures (nanowires, nanoribbons, and nanosheets) were synthesized via vapor transport method on gold coated silicon substrate in N2 ambient and these β-Ga2O3 nanostructures grown on silicon substrates were taken as the starting material to study the effect of annealing in the different environments (oxygen, water vapour, and ammonia solution) on the structural front and photoluminescence (PL) properties. The PL spectra of β-Ga2O3 nanostructures exhibit a UV-blue emission band whose intensity is strongly affected by the annealing in different environments. Annealing modifies the surface of the nanostructures by creating surface states which quench the PL by creating competitive nonradiative paths. This study also indicates the dominance of the formation of water induced surface states over ammonia induced surface states. The irreversible nature of these defects significantly affects the applicability of this system in moist high temperature environments.

  16. 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.

  17. 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.

  18. Three-dimensional optical memory using photoluminescence change in Sm-doped sodium borate glass

    SciTech Connect

    Lim, Jinhyong; Lee, Myeongkyu; Kim, Eunkyoung

    2005-05-09

    The feasibility of three-dimensional (3D) optical memory has been demonstrated by utilizing the photoluminescence (PL) spectrum change in a Sm-doped fluoride glass [K. Miura, J. Qiu, S. Fujiwara, S. Sakasuchi, and K. Hirao, Appl. Phys. Lett. 80 2263 (2002)]. We here report on a femtosecond laser-induced PL change in a Sm-doped sodium borate glass that is easier to synthesize and its potential application to 3D memory. Irradiation with a femtosecond pulsed laser (800 nm, 1 kHz, 100 fs) induced a PL peak near 682 nm, resulting from the photoreduction of the Sm ions. A multilayer pattern (bit size=1 {mu}m,layer separation=8 {mu}m) formed by femtosecond laser irradiation was read out by a reflection-type fluorescent confocal microscope, which detected the emission at 682 nm as a signal. High-contrast pattern images were obtained without crosstalk.

  19. 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

  20. Modulating Photoluminescence of Monolayer Molybdenum Disulfide by Metal-Insulator Phase Transition in Active Substrates.

    PubMed

    Hou, Jiwei; Wang, Xi; Fu, Deyi; Ko, Changhyun; Chen, Yabin; Sun, Yufei; Lee, Sangwook; Wang, Kevin X; Dong, Kaichen; Sun, Yinghui; Tongay, Sefaattin; Jiao, Liying; Yao, Jie; Liu, Kai; Wu, Junqiao

    2016-08-01

    The atomic thickness and flatness allow properties of 2D semiconductors to be modulated with influence from the substrate. Reversible modulation of these properties requires an "active," reconfigurable substrate, i.e., a substrate with switchable functionalities that interacts strongly with the 2D overlayer. In this work, the photoluminescence (PL) of monolayer molybdenum disulfide (MoS2 ) is modulated by interfacing it with a phase transition material, vanadium dioxide (VO2 ). The MoS2 PL intensity is enhanced by a factor of up to three when the underlying VO2 undergoes the thermally driven phase transition from the insulating to metallic phase. A nonvolatile, reversible way to rewrite the PL pattern is also demonstrated. The enhancement effect is attributed to constructive optical interference when the VO2 turns metallic. This modulation method requires no chemical or mechanical processes, potentially finding applications in new switches and sensors. PMID:27335137

  1. Effect of thermal treatment and ageing on IR transmission and visible photoluminescence of nanostructured aluminum oxyhydroxide

    NASA Astrophysics Data System (ADS)

    Karlash, A. Yu; Skryshevsky, V. A.; Khodan, A. N.; Kanaev, A. V.; Gayvoronsky, V. Ya

    2012-09-01

    IR transmission and visible photoluminescence (PL) were studied in raw nanoporous aluminum oxyhydroxide (NOA) and in samples after thermal treatment at different temperatures. Structural and chemical modifications of the NOA sample were related to the water content and adsorption/desorption process at the surface. The differences observed in the FTIR spectra in vacuum and after ageing of the samples can be explained by the effects of molecular water and OH- groups on the stability of the low-temperature phases of NOA. A considerable increase in PL intensity and spectrum expansion to longer wavelengths were observed in all NOA samples after water desorption. This was accompanied by strong changes in the PL decay kinetics. Quenching of the fast luminescent decay and low-energy transitions in aged samples were observed after ageing of the samples. Partial passivation of the NOA surface and defective sites under ambient conditions is discussed.

  2. Two beam photoluminescence of PbS quantum dots in polyvinyl alcohol

    NASA Astrophysics Data System (ADS)

    Babu Pendyala, Naresh; Koteswara Rao, K. S. R.

    2010-11-01

    We report the effect of dual beam excitation on the photoluminescence (PL) from PbS quantum dots in polyvinyl alcohol by using two excitation lasers, namely Ar + (514.5 nm) and He-Ne laser (670 nm). Both sources of excitation gave similar PL spectra around 1.67 eV (related to shallow traps) and 1.1 eV (related to deep traps). When both lasers were used at the same time, we found that the PL induced by each of the lasers was partly quenched by the illumination of the other laser. The proposed mechanism of this quenching effect involves traps that are populated by one specific laser excitation, being photo-ionized by the presence of the other laser. Temperature, laser intensity and modulation frequency dependent quenching efficiencies are presented in this paper. This reversible modulation has potential for optical switching and memory device applications.

  3. Enhanced photoluminescence of multilayer Ge quantum dots on Si(001) substrates by increased overgrowth temperature

    PubMed Central

    2012-01-01

    Four-bilayer Ge quantum dots (QDs) with Si spacers were grown on Si(001) substrates by ultrahigh vacuum chemical vapor deposition. In three samples, all Ge QDs were grown at 520 °C, while Si spacers were grown at various temperatures (520 °C, 550 °C, and 580 °C). Enhancement and redshift of room temperature photoluminescence (PL) were observed from the samples in which Si spacers were grown at a higher temperature. The enhancement of PL is explained by higher effective electrons capturing in the larger size Ge QDs. Quantum confinement of the Ge QDs is responsible for the redshift of PL spectra. The Ge QDs’ size and content were investigated by atomic force microscopy and Raman scattering measurements. PMID:22784702

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  5. BOREAS AFM-6 Surface Meteorological Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) collected surface meteorological data from 21 May to 20 Sep 1994 near the Southern Study Area-Old Jack Pine (SSA-OJP) tower site. The data are in tabular ASCII files. The surface meteorological data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  6. Mo-O bond doping and related-defect assisted enhancement of photoluminescence in monolayer MoS{sub 2}

    SciTech Connect

    Wei, Xiaoxu; Yu, Zhihao; Cheng, Ying; Yu, Linwei; Wang, Junzhuan Wang, Xinran; Shi, Yi; Hu, Fengrui; Wang, Xiaoyong; Xiao, Min

    2014-12-15

    In this work, we report a strong photoluminescence (PL) enhancement of monolayer MoS{sub 2} under different treatments. We find that by simple ambient annealing treatment in the range of 200 °C to 400 °C, the PL emission can be greatly enhanced by a factor up to two orders of magnitude. This enhancement can be attributed to two factors: first, the formation of Mo-O bonds during ambient exposure introduces an effective p-doping in the MoS{sub 2} layer; second, localized electrons formed around Mo-O bonds related defective sites where the electrons can be effectively localized with higher binding energy resulting in efficient radiative excitons recombination. Time resolved PL decay measurement showed that longer lifetime of the treated sample consistent with the higher quantum efficiency in PL. These results give more insights to understand the luminescence properties of the MoS{sub 2}.

  7. 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.

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

    DOE PAGESBeta

    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

  9. 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.

  10. 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.

  11. 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. PMID:26414396

  12. 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.

  13. 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.

  14. Investigation of Oxidation Profile in PMR-15 Polyimide using Atomic Microscope (AFM)

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Johnson, Lili L.; Eby, R. K.

    2002-01-01

    Nanoindentation measurements are made on thermosetting materials using cantiever deflection vs. piezoelectric scanner position behavior determined by AFM. The spring model is used to determine mechanical properties of materials. The generalized Sneddon's equation is utilized to calculate Young's moduli for thermosetting materials at ambient conditions. Our investigations show that the force-penetration depth curves during unloading in these materials can be described accurately by a power law relationship. The results show that the accuracy of the measurements can be controlled within 7%. The above method is used to study oxidation profiles in Pl\\1R-15 polyimide. The thermo-mechanical profiles ofPNIR-15 indicate that the elastic modulus at the surface portion of the specimen is different from that at the interior of the material. It is also shown that there are two zones within the oxidized portion of the samples. Results confirm that the surface layer and the core material have substantially different properties.

  15. [AFM fishing of proteins under impulse electric field].

    PubMed

    Ivanov, Yu D; Pleshakova, T O; Malsagova, K A; Kaysheva, A L; Kopylov, A T; Izotov, A A; Tatur, V Yu; Vesnin, S G; Ivanova, N D; Ziborov, V S; Archakov, A I

    2016-05-01

    A combination of (atomic force microscopy)-based fishing (AFM-fishing) and mass spectrometry allows to capture protein molecules from solutions, concentrate and visualize them on an atomically flat surface of the AFM chip and identify by subsequent mass spectrometric analysis. In order to increase the AFM-fishing efficiency we have applied pulsed voltage with the rise time of the front of about 1 ns to the AFM chip. The AFM-chip was made using a conductive material, highly oriented pyrolytic graphite (HOPG). The increased efficiency of AFM-fishing has been demonstrated using detection of cytochrome b5 protein. Selection of the stimulating pulse with a rise time of 1 ns, corresponding to the GHz frequency range, by the effect of intrinsic emission from water observed in this frequency range during water injection into the cell. PMID:27562998

  16. Influence of thiol capping on the photoluminescence properties of L-cysteine-, mercaptoethanol- and mercaptopropionic acid-capped ZnS nanoparticles.

    PubMed

    Tiwari, A; Dhoble, S J; Kher, R S

    2015-11-01

    Mercaptoethanol (ME), mercaptopropionic acid (MPA) and L-cysteine (L-Cys) having -SH functional groups were used as surface passivating agents for the wet chemical synthesis of ZnS nanoparticles. The effect of the thiol group on the optical and photoluminescence (PL) properties of ZnS nanoparticles was studied. L-Cysteine-capped ZnS nanoparticles showed the highest PL intensity among the studied capping agents, with a PL emission peak at 455 nm. The PL intensity was found to be dependent on the concentration of Zn(2+) and S(2-) precursors. The effect of buffer on the PL intensity of L-Cys-capped ZnS nanoparticles was also studied. UV/Vis spectra showed blue shifting of the absorption edge. PMID:25683960

  17. Longer than 1.9 μm photoluminescence emission from InAs quantum structure on GaAs (001) substrate

    SciTech Connect

    Liu, Ke; Ma, Wenquan Huang, Jianliang; Zhang, Yanhua; Cao, Yulian; Huang, Wenjun; Luo, Shuai; Yang, Tao

    2015-07-27

    We report on photoluminescence (PL) emission with long wavelength for quantum structure by the sub-monolayer (SML) growth technique on GaAs (001) substrate. It is found that the PL emission wavelength can be controlled by controlling the SML InAs deposition amount. At 12 K, the PL peak position of the grown samples changes from about 1.66 to 1.78 μm. At 120 K, the PL emission of a sample reaches 1.91 μm. The physical mechanism responsible for the measured long wavelength PL emission may be related to strong In segregation and intermixing effects occurred in the structure grown by SML growth technique.

  18. 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.

  19. BOREAS AFM-06 Mean Temperature Profile Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) tower from 21 May 1994 to 20 Sep 1994. The data set provides temperature profiles at 15 heights, containing the variables of virtual temperature, vertical velocity, the speed of sound, and w-bar. The data are stored in tabular ASCII files. The mean temperature profile data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  20. BOREAS AFM-6 Boundary Layer Height Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from National Oceanic and Atmospheric Adminsitration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) site. This data set provides boundary layer height information over the site. The data were collected from 21 May 1994 to 20 Sep 1994 and are stored in tabular ASCII files. The boundary layer height data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  1. BOREAS AFM-06 Mean Wind Profile Data

    NASA Technical Reports Server (NTRS)

    Wilczak, James; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Smith, David E. (Technical Monitor)

    2000-01-01

    The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Administration/Environment Technology Laboratory (NOAA/ETL) operated a 915-MHz wind/Radio Acoustic Sounding System (RASS) profiler system in the Southern Study Area (SSA) near the Old Jack Pine (OJP) tower from 21 May 1994 to 20 Sep 1994. The data set provides wind profiles at 38 heights, containing the variables of wind speed; wind direction; and the u-, v-, and w-components of the total wind. The data are stored in tabular ASCII files. The mean wind profile data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  2. Evidence for adduct formation at the semiconductor-solution interface. Photoluminescent properties of cadmium selenide in the presence of lanthanide. beta. -diketonate complexes

    SciTech Connect

    Murphy, C.J.; Ellis, A.B. )

    1990-04-05

    Photoluminescence (PL) measurements of etched, single-crystal n-CdSe demonstrate that the semiconductor surface engages in adduct formation with a family of lanthanide {beta}-diketonate complexes, Ln(fod){sub 3} (Ln = lanthanide; fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato anion), in isooctane ambient.

  3. Effect of vacuumization on the photoluminescence and photoresponse decay of the zinc oxide nanostructures grown by different methods

    NASA Astrophysics Data System (ADS)

    Kapustianyk, Volodymyr; Turko, Borys; Rudyk, Viktor; Rudyk, Yuriy; Rudko, Mykola; Panasiuk, Myron; Serkiz, Roman

    2016-06-01

    Influence of vacuumization on the photoluminescence (PL) spectra and photoresponse decay of ZnO nanostructures fabricated by different methods was investigated. The visible band of photoluminescence and ultraviolet (UV) photosensitivity of the samples grown from a vapor phase was associated with the intrinsic defects such as doubly charged zinc vacancies, and for the samples grown by hydrothermal method - with presence of the oxygen vacancies. The experimental results show that ZnO nanostructures grown from the vapor phase would be promising for producing of the low cost and effective UV detecting devices.

  4. Photoluminescence study of the effect of strain compensation on InAs/AlAsSb quantum dots

    NASA Astrophysics Data System (ADS)

    Zhao, Zhexin; Laghumavarapu, Ramesh B.; Simmonds, Paul J.; Ji, Haiming; Liang, Baolai; Huffaker, Diana L.

    2015-09-01

    We investigate stacked structures of InAs/AlAsSb/InP quantum dots using temperature- and power-dependent photoluminescence. The band gap of InAs/AlAsSb QDs is 0.73 eV at room temperature, which is close to the ideal case for intermediate band solar cells. As the number of quantum dot layers is increased, the photoluminescence undergoes a blue-shift due to the effects of accumulated compressive strain. This PL red shift can be counteracted using thin layers of AlAs to compensate the strain. We also derive thermal activation energies for this exotic quantum dot system.

  5. Chirality-Selective Photoluminescence Enhancement of ssDNA-Wrapped Single-Walled Carbon Nanotubes Modified with Gold Nanoparticles.

    PubMed

    Yang, Juan; Zhao, Qinghua; Lyu, Min; Zhang, Zhenyu; Wang, Xiao; Wang, Meng; Gao, Zhou; Li, Yan

    2016-06-01

    In this work, a convenient method to enhance the photoluminescence (PL) of single-walled carbon nanotubes (SWNTs) in aqueous solutions is provided. Dispersing by single-stranded DNA (ssDNA) and modifying with gold nanoparticles (AuNPs), about tenfold PL enhancement of the SWNTs is observed. More importantly, the selective PL enhancement is achieved for some particular chiralities of interest over all other chiralities, by using certain specific ssDNA sequences that are reported to recognize these particular chiralities. By forming AuNP-DNA-SWNT nanohybrids, ssDNA serves as superior molecular spacers that on one hand protect SWNT from direct contacting with AuNP and causing PL quench, and on the other hand attract the AuNP in close proximity to the SWNT to enhance its PL. This PL enhancement method can be utilized for the PL analysis of SWNTs in aqueous solutions, for biomedical imaging, and may serve as a prescreening method for the recognition and separation of single chirality SWNTs by ssDNA. PMID:27128378

  6. Improving stability of photoluminescence of ZnSe thin films grown by molecular beam epitaxy by incorporating Cl dopant

    NASA Astrophysics Data System (ADS)

    Wang, J. S.; Chen, W. J.; Yang, C. S.; Tsai, Y. H.; Wang, H. H.; Chen, R. H.; Shen, J. L.; Tsai, C. D.

    2011-01-01

    This investigation studies the effect of chlorine (Cl) dopant in ZnSe thin films that were grown by molecular beam epitaxy on their photoluminescence (PL) and the stability thereof. Free excitonic emission was observed at room-temperature in the Cl-doped sample. Photon irradiation with a wavelength of 404 nm and a power density of 9.1 W/cm2 has a much stronger effect on PL degradation than does thermal heating to a temperature of 150 °C. Additionally, this study shows that the generation of nonradiative centers by both photon irradiation and thermal heating can be greatly inhibited by incorporating Cl dopant.

  7. Influence of growth temperature on AlGaN multiquantum well point defect incorporation and photoluminescence efficiency

    NASA Astrophysics Data System (ADS)

    Armstrong, A.; Allerman, A. A.; Henry, T. A.; Crawford, M. H.

    2011-04-01

    The dependence of (Al)GaN/AlGaN multiquantum well (MQWs) optical efficiency and defect incorporation on the growth temperature (Tg) of the optically active region was investigated. Marked increase in MQW photoluminescence (PL) intensity was observed for increasing Tg. Correspondingly, increasing Tg also significantly reduced point defect incorporation under QW growth conditions, as determined by deep level optical spectroscopy. It is suggested that enhanced MQW PL with increasing Tg resulted from improved nonradiative lifetime through reduced nonradiative defect density in the MQW region.

  8. Enhanced Photoluminescence Property for Quantum Dot-Gold Nanoparticle Hybrid

    NASA Astrophysics Data System (ADS)

    Huang, Qianqian; Chen, Jing; Zhao, Jian; Pan, Jiangyong; Lei, Wei; Zhang, Zichen

    2015-10-01

    In this paper, we have synthesized ZnCdSeS quantum dots (QDs)-gold nanoparticle (Au NPs) hybrids in aqueous solution via bi-functional linker mercaptoacetic acid (MPA). The absorption peaks of ZnCdSeS QDs and Au are both located at 520 nm. It is investigated that PL intensity of QD-Au hybrid can be affected by the amounts of Au and pH value of hybrid solution. The located surface plasmon resonance (LSPR) effect of QD-Au NPs has been demonstrated by increased fluorescence intensity. The phenomenon of fluorescence enhancement can be maximized under the optimized pH value of 8.5. LSPR-enhanced photoluminescence property of QD-Au hybrid will be beneficial for the potential applications in the area of biological imaging and detection.

  9. Enhanced Photoluminescence Property for Quantum Dot-Gold Nanoparticle Hybrid.

    PubMed

    Huang, Qianqian; Chen, Jing; Zhao, Jian; Pan, Jiangyong; Lei, Wei; Zhang, Zichen

    2015-12-01

    In this paper, we have synthesized ZnCdSeS quantum dots (QDs)-gold nanoparticle (Au NPs) hybrids in aqueous solution via bi-functional linker mercaptoacetic acid (MPA). The absorption peaks of ZnCdSeS QDs and Au are both located at 520 nm. It is investigated that PL intensity of QD-Au hybrid can be affected by the amounts of Au and pH value of hybrid solution. The located surface plasmon resonance (LSPR) effect of QD-Au NPs has been demonstrated by increased fluorescence intensity. The phenomenon of fluorescence enhancement can be maximized under the optimized pH value of 8.5. LSPR-enhanced photoluminescence property of QD-Au hybrid will be beneficial for the potential applications in the area of biological imaging and detection. PMID:26471479

  10. Photoresponse from single upright-standing ZnO nanorods explored by photoconductive AFM

    PubMed Central

    Beinik, Igor; Kratzer, Markus; Wachauer, Astrid; Wang, Lin; Piryatinski, Yuri P; Brauer, Gerhard; Chen, Xin Yi; Hsu, Yuk Fan; Djurišić, Aleksandra B

    2013-01-01

    Summary Background: ZnO nanostructures are promising candidates for the development of novel electronic devices due to their unique electrical and optical properties. Here, photoconductive atomic force microscopy (PC-AFM) has been applied to investigate transient photoconductivity and photocurrent spectra of upright-standing ZnO nanorods (NRs). With a view to evaluate the electronic properties of the NRs and to get information on recombination kinetics, we have also performed time-resolved photoluminescence measurements macroscopically. Results: Persistent photoconductivity from single ZnO NRs was observed for about 1800 s and was studied with the help of photocurrent spectroscopy, which was recorded locally. The photocurrent spectra recorded from single ZnO NRs revealed that the minimum photon energy sufficient for photocurrent excitation is 3.1 eV. This value is at least 100 meV lower than the band-gap energy determined from the photoluminescence experiments. Conclusion: The obtained results suggest that the photoresponse in ZnO NRs under ambient conditions originates preferentially from photoexcitation of charge carriers localized at defect states and dominates over the oxygen photodesorption mechanism. Our findings are in agreement with previous theoretical predictions based on density functional theory calculations as well as with earlier experiments carried out at variable oxygen pressure. PMID:23616940

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. Synthesis and photoluminescence properties of Sm3+-doped YAl3(BO3)4 phosphor.

    PubMed

    Kumar, R Satheesh; Ponnusamya, V; Jose, M T

    2014-09-01

    A near ultraviolet excitable phosphor based on Sm3+-doped YAl3(BO3)4 has been synthesized by modified solid-state reaction at 1000°C. The phase purity and photoluminescence (PL) behavior of the phosphor are studied in detail using the powder X-ray diffraction technique and PL measurements. X-ray diffraction reveals that the phase purity of YAl3(BO3)4 critically depends upon the boric acid concentration. The phosphor has strong excitation at 406 nm in the near ultraviolet region (350–420 nm) and its emission peaks were monitored at 564, 599 and 643 nm. Further, detailed PL analysis demonstrates that the substitution of Sm3+ ions at sites of Y3+ and Al3+ ions enhances the PL efficiency of the phosphor appreciably. First, the PL efficiency of YAl3(BO3)4:Sm3+ was compared with commercial (Y,Gd)BO3:Eu3+ red phosphor. The Fourier transform infrared study provides essential information regarding the change in metal–oxygen bond vibrations of the phosphor. The morphology of the phosphor was investigated through scanning electron microscopy, which reveals that the phosphor possessed distorted spherical and rectangular shapes with average grain sizes in the range 0.5–1 μm. PMID:25337617

  16. 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.

  17. Bilayer hybrid nanoimprinting method for fabricating embedded silver nanostructure arrays with enhanced photoluminescence

    NASA Astrophysics Data System (ADS)

    Choi, Jun-Hyuk; Sung, Sang-Keun; Kim, Chul-Hyun; Jung, Yeon-Ho; Jung, Joo-Yun; Jeong, Jun-Ho; Lee, Eung-Sug

    2014-01-01

    A bilayer hybrid nanoimprinting (NI) method was developed for fabricating embedded metal nanopatterns with greater processability and improved reliability for enhanced photoluminescence (PL) in optoelectronic devices. Bilayer hybrid NI consists of the following: (a) spin-coating ultraviolet (UV) and thermally curable NI resists in sequence, (b) high-pressure thermal NI and UV exposure while maintaining the stamp in a pressed position, and (c) silver (Ag) deposition and lift-off using a thermal NI resist on the upper surface to create embedded Ag nanoarrays. Reference samples with no Ag nanopatterns and with protruding Ag dot-shaped nanopatterns were also fabricated for comparison. The transmittance and PL of all samples were measured. All samples containing Ag nanopatterns exhibited improved PL compared with reference samples with no Ag. For all pattern sizes, the samples with the embedded Ag nanoarrays exhibited the highest PL; the relative PL enhancements compared with samples with Ag dot-shaped nanoarrays were 32.2%, 36.1%, and 62.7% for pattern sizes of 150, 200, and 265 nm, respectively.

  18. High Contrast In vitro and In vivo Photoluminescence Bioimaging Using Near Infrared to Near Infrared Up-Conversion in Tm3+ and Yb3+ Doped Fluoride Nanophosphors

    PubMed Central

    Nyk, Marcin; Kumar, Rajiv; Ohulchanskyy, Tymish Y.; Bergey, Earl J.; Prasad, Paras N.

    2012-01-01

    A new approach for photoluminescence imaging in vitro and in vivo has been shown, utilizing near infrared to near infrared (NIR-to-NIR) up-conversion in nanophosphors. This NIR-to-NIR up-conversion process provides deeper light penetration into biological specimen and results in high contrast optical imaging due to absence of an autofluorescence background and decreased light scattering. Aqueous dispersible fluoride (NaYF4) nanocrystals (20–30 nm size) co-doped with the rare earth ions, Tm3+ and Yb3+, were synthesized and characterized by TEM, XRD and photoluminescence (PL) spectroscopy. In vitro cellular uptake was shown by the PL microscopy visualizing the characteristic emission of Tm3+ at ~ 800 nm excited with 975 nm. No apparent cytotoxicity was observed. Subsequent animal imaging studies were performed using Balb-c mice injected intravenously with up-converting nanophosphors, demonstrating the high contrast PL imaging in vivo. PMID:18928324

  19. 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

  20. 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.

  1. The role of N-Si-O bonding configurations in tunable photoluminescence of oxygenated amorphous silicon nitride films

    NASA Astrophysics Data System (ADS)

    Zhang, Pengzhan; Chen, Kunji; Lin, Zewen; Dong, Hengping; Li, Wei; Xu, Jun; Huang, Xinfan

    2015-06-01

    Last year, we have reported that the internal quantum efficiency of photoluminescence (PL) from amorphous silicon oxynitride (a-SiNxOy) 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-SiNx: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-SiNx) networks not only reduced the band tail structure disorder (Urbach tail width EU) but also created N-Si-O (Nx) defect states in the band gap. We have discovered the distinctive PL characteristics from a-SiNx:O films with various NH3/SiH4 ratios. The PL peak energy (EPL) is independent of the excitation energy (Eexc) and the PL intensity (IPL) is regardless of the optical band gap (Eopt) but is proportional to the Nx defects concentration, both of which are completely different from the PL characteristics by band tail states recombination mechanism, in which the EPL is proportional to Eexc (when Eexc ≤ Eopt) and the IPL is dependent on the relative position of Eexc and Eopt. 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-SiNx:O films.

  2. 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}.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. Particle deformation induced by AFM tapping under different setpoint voltages

    NASA Astrophysics Data System (ADS)

    Wu, Chung-Lin; Farkas, Natalia; Dagata, John A.; He, Bo-Ching; Fu, Wei-En

    2014-09-01

    The measured height of polystyrene nanoparticles varies with setpoint voltage during atomic force microscopy (AFM) tapping-mode imaging. Nanoparticle height was strongly influenced by the magnitude of the deformation caused by the AFM tapping forces, which was determined by the setpoint voltage. This influence quantity was studied by controlling the operational AFM setpoint voltage. A test sample consisting of well-dispersed 60-nm polystyrene and gold nanoparticles co-adsorbed on poly-l-lysine-coated mica was studied in this research. Gold nanoparticles have not only better mechanical property than polystyrene nanoparticles, but also obvious facets in AFM phase image. By using this sample of mixed nanoparticles, it allows us to confirm that the deformation resulted from the effect of setpoint voltage, not noise. In tapping mode, the deformation of polystyrene nanoparticles increased with decreasing setpoint voltage. Similar behavior was observed with both open loop and closed loop AFM instruments.

  8. 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".

  9. Temperature and polarization dependence of photoluminescence in monolayer tungsten diselenide

    NASA Astrophysics Data System (ADS)

    Huang, Jiani; Hoang, Thang; Mikkelsen, Maiken

    2015-03-01

    Two-dimensional transition metal dichalcogenides (TMDCs) have recently attracted considerable research interest, due to their wide direct band-gaps, strong spin-orbit couplings and inversion symmetry breaking when compared to graphene. These properties have rich physics and applications in electronics, optics and spintronics. Here, we experimentally study the evolution of photoluminescence (PL) from mechanically exfoliated monolayer tungsten diselenide (WSe2) from T = 10 K to room temperature. At T = 10 K , we observe a clear free exciton (X0) emission at 1.75 eV together with a charged trion emission at 1.72 eV, yielding a trion binding energy of 30 meV. Temperature dependent PL measurements show that both the free exciton and trion exist up to room temperature, as a result of the large exciton (~370 meV) and trion binding energies of WSe2, while other localized and defect-related emission peaks vanish above T = 65 K . Temperature dependent polarization of the exciton and trion emisisons reveal a combined effect of large exciton binding energy, anisotropic thermal expansion and exciton-phonon interaction. These findings may provide a new platform to explore the valley polarization and valley-spin coupling in monolayer TMDCs.

  10. 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

  11. Enhanced photoluminescence of porous silicon nanoparticles coated by bioresorbable polymers

    NASA Astrophysics Data System (ADS)

    Gongalsky, Maxim B.; Kharin, Alexander Yu; Osminkina, Liubov A.; Timoshenko, Victor Yu; Jeong, Jinyoung; Lee, Han; Chung, Bong Hyun

    2012-08-01

    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.

  12. Photoluminescence decay rate of silicon nanoparticles modified with gold nanoislands

    PubMed Central

    2014-01-01

    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. PACS 78. 67. Bf; 78.55.-m PMID:24708532

  13. Enhanced quantum yield of photoluminescent porous silicon prepared by supercritical drying

    NASA Astrophysics Data System (ADS)

    Joo, Jinmyoung; Defforge, Thomas; Loni, Armando; Kim, Dokyoung; Li, Z. Y.; Sailor, Michael J.; Gautier, Gael; Canham, Leigh T.

    2016-04-01

    The effect of supercritical drying (SCD) on the preparation of porous silicon (pSi) powders has been investigated in terms of photoluminescence (PL) efficiency. Since the pSi contains closely spaced and possibly interconnected Si nanocrystals (<5 nm), pore collapse and morphological changes within the nanocrystalline structure after common drying processes can affect PL efficiency. We report the highly beneficial effects of using SCD for preparation of photoluminescent pSi powders. Significantly higher surface areas and pore volumes have been realized by utilizing SCD (with CO2 solvent) instead of air-drying. Correspondingly, the pSi powders better retain the porous structure and the nano-sized silicon grains, thus minimizing the formation of non-radiative defects during liquid evaporation (air drying). The SCD process also minimizes capillary-stress induced contact of neighboring nanocrystals, resulting in lower exciton migration levels within the network. A significant enhancement of the PL quantum yield (>32% at room temperature) has been achieved, prompting the need for further detailed studies to establish the dominant causes of such an improvement.

  14. 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.

  15. Microrheology using a custom-made AFM

    NASA Astrophysics Data System (ADS)

    Kosgodagan Acharige, Sebastien; Benzaquen, Michael; Steinberger, Audrey

    In the past few years, a new method was developed to measure local properties of liquids (X. Xiong et al., Phys. Rev. E 80, 2009). This method consists of gluing a micron-sized glass fiber at the tip of an AFM cantilever and probing the liquid with it. In ENS Lyon, this method was perfected (C. Devailly et al., EPL, 106 5, 2014) with the help of an interferometer developped in the same laboratory (L. Bellon et al., Opt. Commun. 207 49, 2002 and P. Paolino et al., Rev. Sci. Instrum. 84, 2013), which background noise can reach 10-14 m /√{ Hz } . This method allows us to measure a wide range of viscosities (1 mPa . s to 500 mPa . s) of transparent and opaque fluids using a small sample volume ( 5 mL). In this presentation, I will briefly describe the interferometer developped in ENS Lyon, then explain precisely the microrheology measurements and then compare the experimental results to a model developped by M. Benzaquen. This work is supported financially by the ANR project NANOFLUIDYN (Grant Number ANR-13-BS10-0009).

  16. Manufacturing process of nanofluidics using afm probe

    NASA Astrophysics Data System (ADS)

    Karingula, Varun Kumar

    A new process for fabricating a nano fluidic device that can be used in medical application is developed and demonstrated. Nano channels are fabricated using a nano tip in indentation mode on AFM (Atomic Force Microscopy). The nano channels are integrated between the micro channels and act as a filter to separate biomolecules. Nano channels of 4 to7 m in length, 80nm in width, and at varying depths from 100nm to 850 nm allow the resulting device to separate selected groups of lysosomes and other viruses. Sharply developed vertical micro channels are produced from a deep reaction ion etching followed by deposition of different materials, such as gold and polymers, on the top surface, allowing the study of alternative ways of manufacturing a nanofluidic device. PDMS (Polydimethylsiloxane) bonding is performed to close the top surface of the device. An experimental setup is used to test and validate the device by pouring fluid through the channels. A detailed cost evaluation is conducted to compare the economical merits of the proposed process. It is shown that there is a 47:7% manufacturing time savings and a 60:6% manufacturing cost savings.

  17. BOREAS AFM-07 SRC Surface Meteorological Data

    NASA Technical Reports Server (NTRS)

    Osborne, Heather; Hall, Forrest G. (Editor); Newcomer, Jeffrey A. (Editor); Young, Kim; Wittrock, Virginia; Shewchuck, Stan; Smith, David E. (Technical Monitor)

    2000-01-01

    The Saskatchewan Research Council (SRC) collected surface meteorological and radiation data from December 1993 until December 1996. The data set comprises Suite A (meteorological and energy balance measurements) and Suite B (diffuse solar and longwave measurements) components. Suite A measurements were taken at each of ten sites, and Suite B measurements were made at five of the Suite A sites. The data cover an approximate area of 500 km (North-South) by 1000 km (East-West) (a large portion of northern Manitoba and northern Saskatchewan). The measurement network was designed to provide researchers with a sufficient record of near-surface meteorological and radiation measurements. The data are provided in tabular ASCII files, and were collected by Aircraft Flux and Meteorology (AFM)-7. The surface meteorological and radiation data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

  18. Segmental calibration for commercial AFM in vertical direction

    NASA Astrophysics Data System (ADS)

    Shi, Yushu; Gao, Sitian; Lu, Mingzhen; Li, Wei; Xu, Xuefang

    2013-01-01

    Atomic force microscopy (AFM) is most widely applied in scientific research and industrial production. AFM is a scanning probe imaging and measuring device, useful for physical and chemical studies. Depends on its basic structure, microscopic surface pattern can be measured and captured by mechanically scanning. Its vertical and horizon resolution can reach to 0.01nm and 0.1nm. Commonly the measurement values of commercial AFM are directly from scanning piezoelectric tube, so that it not a traceable value. In order to solve the problem of commercial AFM's traceability, step height standard references are applied to calibrate the piezoelectric ceramic housing in scanning tube. All of the serial of step height standard references, covering the commercial AFM vertical scale, are calibrated by Metrology AFM developed by National Institute of Metrology (NIM), China. Three interferometers have been assembled in its XYZ axis, therefore the measurement value can directly trace to laser wavelength. Because of nonlinear characteristic of PZT, the method of segmental calibration is proposed. The measurement scale can be divided into several subsections corresponding to the calibrated values of the series of step height standards references. By this method the accuracy of measurements can be ensured in each segment measurement scale and the calibration level of the whole instrument can be promoted. In order to get a standard step shape by commercial AFM, substrate removal method is applied to deal with the bow shape problem.

  19. 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.

  20. Temperature dependent photoluminescence from ZnO/MgZnO multiple quantum wells grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Misra, P.; Sharma, T. K.; Kukreja, L. M.

    2007-07-01

    We have studied temperature dependent photoluminescence (PL) from ZnO Multiple Quantum Wells (MQWs) of different well layer thicknesses in the range ˜1-4 nm grown on (0001) sapphire by a novel in-house developed buffer assisted pulsed laser deposition. At 10 K the PL peak shifted toward blue with decreasing well layer thickness and at constant well layer thickness the PL peak shifted towards red with increasing temperature. To the best of our knowledge we have observed for the first time an efficient room temperature (RT) PL emanating from such MQWs. The red shift of the PL peak with increasing temperature has been found to be due to the band gap shrinkage in accordance with the Varshni's empirical relation. The spectral linewidth was found to increase with increasing temperature due to the scattering of excitons with acoustic and optical phonons in different temperature regimes. Both at RT and at 10 K the PL peak shifted with respect to the well layer thickness in the range of ˜3.35-˜3.68 eV with decreasing thickness in agreement with the calculated values.

  1. 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

  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. Raman and AFM study of gamma irradiated plastic bottle sheets

    SciTech Connect

    Ali, Yasir; Kumar, Vijay; Dhaliwal, A. S.; Sonkawade, R. G.

    2013-02-05

    In this investigation, the effects of gamma irradiation on the structural properties of plastic bottle sheet are studied. The Plastic sheets were exposed with 1.25MeV {sup 60}Co gamma rays source at various dose levels within the range from 0-670 kGy. The induced modifications were followed by micro-Raman and atomic force microscopy (AFM). The Raman spectrum shows the decrease in Raman intensity and formation of unsaturated bonds with an increase in the gamma dose. AFM image displays rough surface morphology after irradiation. The detailed Raman analysis of plastic bottle sheets is presented here, and the results are correlated with the AFM observations.

  4. Dynamics of the nanoneedle probe in trolling mode AFM.

    PubMed

    Abdi, Ahmad; Pishkenari, Hossein Nejat; Keramati, Ramtin; Minary-Jolandan, Majid

    2015-05-22

    Atomic force microscopy (AFM), as an indispensable tool for nanoscale characterization, presents major drawbacks for operation in a liquid environment arising from the large hydrodynamic drag on the vibrating cantilever. The newly introduced 'Trolling mode' (TR-mode) AFM resolves this complication by using a specialized nanoneedle cantilever that keeps the cantilever outside of the liquid. Herein, a mechanical model with a lumped mass was developed to capture the dynamics of such a cantilever with a nanoneedle tip. This new developed model was applied to investigate the effects of the needle-liquid interface on the performance of the AFM, including the imaging capability in liquid. PMID:25915451

  5. AFM Studies of Conformational Changes in Proteins and Peptides

    NASA Astrophysics Data System (ADS)

    Ploscariu, Nicoleta; Sukthankar, Pinakin; Tomich, John; Szoszkiewicz, Robert

    2015-03-01

    Here, we present estimates of molecular stiffness and mechanical energy dissipation factors for some examples of proteins and peptides. The results are obtained from AFM force spectroscopy measurements. To determine molecular stiffness and mechanical energy dissipation factors we developed a model based on measuring several resonance frequencies of an AFM cantilever in contact with either single protein molecule or peptides adsorbed on arbitrary surface. We used compliant AFM cantilevers with a small aspect ratio - a ratio of length to width - in air and in liquid, including biologically relevant phosphate buffered saline medium. Department of Physics.

  6. Radiative recombination model of degenerate semiconductor and photoluminescence properties of 3C-SiC by P and N doping

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Fang, Xiao-Yong; Li, Ya-Qin; Yin, Ai-Cha; Jin, Hai-Bo; Yuan, Jie; Cao, Mao-Sheng

    2012-08-01

    Based on radiative recombination theory, we have established a recombination model that can be used to calculate photoluminescence (PL) intensity for degenerate semiconductors. Using this model and density functional theory, we calculated photoluminescence excitation (PLE) and PL spectra of intrinsic 3C-SiC, P-doped SiC and N-doped SiC. The violet or near ultraviolet PLE peaks were found to be observed in PLE spectra for Sin-1PCn and SinNCn-1 (n = 4, 8, 12, and 16). Compared to intrinsic 3C-SiC, doped 3C-SiC exhibits higher PL peaks which for P-doped SiC are in the indigo spectral region, near the 3C-SiC's peak, and for N-doped SiC appear in the green. The phenomena are studied through analyses of band structure, carrier concentration, and absorption. For doped 3C-SiC, the PL properties are mainly improved by the band-gap transformation from indirect to direct and the increase in carrier concentration near the Fermi level.

  7. Photoluminescence and structural studies on extended defect evolution during high-temperature processing of ion-implanted epitaxial silicon

    NASA Astrophysics Data System (ADS)

    Giri, P. K.; Coffa, S.; Raineri, V.; Privitera, V.; Galvagno, G.; La Ferla, A.; Rimini, E.

    2001-04-01

    Low-temperature photoluminescence (PL) spectroscopy, in conjunction with transmission electron microscopy (TEM) and optical microscopy (OM) have been carried out to investigate the origin of radiative recombination from various extended defects that evolve during high-temperature processing of ion-implanted epitaxial silicon. From PL studies on N2-annealed samples, we provide spectroscopic evidence of precipitation of the implanted impurities well below the solid-solubility limit. This result is being supported by observations from secondary ion mass spectrometry and spreading resistance profiling of the implanted ions. Cross sectional TEM analyses on these samples reveal <111>-oriented precipitates located in a region containing a high dislocation density. Postimplantation annealing in oxygen ambient results in the formation of dislocations and oxidation-induced stacking faults (OISF). A systematic analysis of PL spectra on different-implanted and preannealed samples, in conjunction with TEM and OM analyses, reveals that the conventionally observed dislocation-related D1 and D2 lines in the PL spectrum is not a characteristic of the OISF, but of the dislocations only. It is shown that the OISF acts as a nonradiative channel for luminescence in silicon. Various other sources of nonradiative channels in silicon are also presented and the efficacy of photoluminescence technique in the characterization of process-induced defects in silicon is discussed.

  8. Chemically-modulated photoluminescence of graphene oxide for selective detection of neurotransmitter by "turn-on" response.

    PubMed

    Jeon, Su-Ji; Kwak, Seon-Yeong; Yim, DaBin; Ju, Jong-Min; Kim, Jong-Ho

    2014-08-01

    Designing artificial nanomaterials capable of selectively detecting targets without the use of expensive and fragile antibodies is of great interest in the applications of nanomedicine. Here, we show that the photoluminescence (PL) of graphene oxide (GO) was chemically modulated for the selective detection of a neurotransmitter without the use of antibodies. GO was functionalized with nitrotriacetic acid (NTA) on which four different metal ions were chelated (M-NTA-GO), which led to its different PL responses to neurotransmitters. In particular, the Cu-NTA-GO hybrid was able to selectively detect norepinephrine at nanomolar concentrations in a simple manner via its "turn-on" PL. Moreover, it was successfully applied to the selective detection of norepinephrine secreted from living PC-12 cells. PMID:25036980

  9. 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.

  10. 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.

  11. 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.

  12. Quantitative characterization of modulation-doped strained quantum wells through line-shape analysis of room-temperature photoluminescence spectra

    NASA Astrophysics Data System (ADS)

    Brierley, Steven K.

    1993-08-01

    Room-temperature photoluminescence (PL) was presented as a nondestructive characterization method for modulation-doped strained quantum well epitaxial structures suited for pseudomorphic high electron mobility transistors (pHEMTs). Though the spectra showed broad peaks, in contrast to the sharp, well-defined peaks in low-temperature PL spectra, quantitative energy data was obtained through fitting a phenomenological line-shape model to the spectra. This model included the four transitions linking the first two electron subbands and the first two heavy-hole subbands, which can take credit for all of the peaks noted in pHEMT epitaxial configurations at realistic doping levels. The obtained results revealed that by using a simple line-shape model to the room-temperature PL spectrum of a pHEMT, a substantial amount of detailed structural and electronic data can be acquired regarding the quantum well.

  13. Investigation to the deep center related properties of low temperature grown InPBi with Hall and photoluminescence

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Pan, Wenwu; Wang, Kai; Wu, Xiaoyan; Yue, Li; Gong, Qian; Wang, Shumin

    2015-12-01

    InP1-xBix 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 InP1-xBix films Photoluminescence (PL) was investigated. N-type doping in the InP1-xBix 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.

  14. Studies of Adsorbate Effects on the Photoluminescence of Cadmium Sulfide and Cadmium Selenide.

    NASA Astrophysics Data System (ADS)

    Zhang, Zhongju

    1993-01-01

    Chapter One. The electronic properties of semiconductors and their surface and photoluminescence properties are introduced. A short introduction to chemisorption and the Langmuir adsorption isotherm model is presented. The properties of II-VI semiconductors are briefly reviewed. Chapter Two. Adsorption from CH_2 Cl_2 solution of a family of ring-substituted, 7,7,8,8-tetracyanoquinodimethane (TCNQ) derivatives onto the surface of etched, single-crystal n-CdSe quenches the band gap photoluminescence (PL) intensity of the semiconductor. PL quenching increases with the electron-withdrawing ability of the ring substituent. The C_{60} and C_ {70} fullerenes can also be adsorbed from toluene solution onto the surfaces of n-CdS and n-CdSe, causing quenching of the PL intensity. Quantitatively, the magnitude of the PL quenching can be fit to a dead -layer model, permitting an estimate of maximum expansions in dead-layer thickness caused by adsorption of TCNQ derivatives and C_{60} onto the n -CdSe surface to reach ~1400 A and ~300 A, respectively. The PL intensity changes are concentration-dependent and give good fits to the Langmuir adsorption isotherm model, yielding equilibrium binding constants on the order of ~10 ^5 to 10^6 M^{-1} for TCNQ derivatives and fullerenes, among the largest reported to date. With etched samples, the opposing Cd-rich (0001)and Se-rich (000 1) faces of individual CdSe samples are distinguishable through their interaction with TCNQ and C_ {60}, with adsorption onto the former face resulting in a substantially larger PL change but an experimentally indistinguishable equilibrium binding constant. Possible binding schemes that could account for these effects are presented. Chapter Three. The carrier concentration of CdS crystals can be increased by annealing the crystal in the vapor of Cd metal. The effect of the carrier concentration of CdS on its adsorption properties has been explored with p-toluidine and C_{60} adsorbates. The PL study has

  15. Synthesis, characterization and photoluminescence studies of undoped ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Chandrakar, Raju Kumar; Baghel, R. N.; Chandra, V. K.; Chandra, B. P.

    2015-08-01

    The present paper reports the synthesis, characterization and photoluminescence studies of undoped ZnS nanoparticles. The ZnS nanoparticles were prepared by chemical precipitation method and 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 (mercaptoethanol) used are 0 M, 0.01 M, 0.025 M, 0.040 M, and 0.060 M, the sizes of the nanoparticles are 2.86 nm, 2.69 nm, 2.40 nm, 1.90 nm and 1.80 nm, respectively. This means the size of nanoparticles decreases with increasing concentration of capping agent used. The PL spectra of ZnS nanoparticles were measured for different concentrations of merceptoethanol, in which the excitation wavelength was 289 nm for all the samples. One peak is obtained in the photoluminescence (PL) of ZnS, in which the peak shifts from 468 nm to 408 nm with decreasing size of the nanocrystals. The blue emission around the peak of PL intensity is very broad and originates from the radiative recombination involving defect states in the ZnS nanocrystals. The photoluminescence spectra of ZnS nanoparticles for different capping agent concentrations reveals that the emission becomes more intensive and shift towards blue side as the size of the nanoparticles is reduced. The optical absorption spectra of the nanoparticles obtained using UV-Vis spectrophotometer shows the blue-shift with decreasing particle size. The value of band gap energy has been found to be in range 4.60-5.18 eV, which is related to the quantization effect due to small the of the particles. The measurement of exciton luminescence can be used to determine the band gap of pure ZnS crystals.

  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. 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

  18. 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.

  19. Improved photoluminescence property of CTAB assisted polyaniline-AlZnO nanocomposite

    NASA Astrophysics Data System (ADS)

    Mitra, Mousumi; Kargupta, Kajari; Ganguly, Saibal; Banerjee, Dipali

    2015-06-01

    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.

  20. The synthesis of size-controlled 3C-SiC nanoflakes and their photoluminescent properties.

    PubMed

    Fan, Xiujun; Ye, Ruquan; Peng, Zhiwei; Wang, Juanjuan; Fan, Ailing; Guo, Xia

    2016-06-24

    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. PMID:27184338

  1. Strongly enhanced tunable photoluminescence in polymorphous silicon carbon thin films via excitation-transfer mechanism

    SciTech Connect

    Wang Junzhuan; Suendo, V.; Abramov, A.; Yu Linwei; Roca i Cabarrocas, Pere

    2010-11-29

    Here, we investigate the enhanced tunable photoluminescence (PL) of hydrogenated polymorphous silicon carbon (pm-Si{sub 1-x}C{sub x}:H) thin films fabricated in a plasma enhanced chemical vapor deposition system. The silicon nanocrystal (nc-Si) inclusions are formed during gas-phase nucleation and incorporated in the hydrogenated amorphous silicon carbon (a-SiC:H) matrix. The nc-Si provides high-quality recombination centers for the photogenerated carriers in the pm-Si{sub 1-x}C{sub x}:H material, while the a-SiC:H matrix plays a role of sensitizer. We elucidate and provide experimental evidence for this excitation-transfer mechanism. Strongly enhanced PL performance can be achieved by effective matrix passivation that favors a diffusion-driven carrier recombination in the nc-Si centers.

  2. Chemical doping modulation of nonlinear photoluminescence properties in monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Mouri, Shinichiro; Miyauchi, Yuhei; Matsuda, Kazunari

    2016-05-01

    We demonstrate a simple modulation technique of nonlinear optical properties in monolayer (1L) MoS2 via chemical doping. The strong nonlinear behavior of the exciton photoluminescence (PL) intensity is observed with increasing excitation power density for low-electron-density 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ)-doped 1L-MoS2, whereas the exciton PL intensity of as-prepared, heavily electron-doped 1L-MoS2 exhibits weak sublinear behavior. These results are attributable to an enhanced exciton–exciton annihilation rate for the excitons in F4TCNQ-doped 1L-MoS2 as the dominant decay pathway under strong optical excitation conditions.

  3. 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.

  4. 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).

  5. 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).

  6. Mg acceptor level in InN epilayers probed by photoluminescence

    NASA Astrophysics Data System (ADS)

    Khan, N.; Nepal, N.; Sedhain, A.; Lin, J. Y.; Jiang, H. X.

    2007-07-01

    Mg-doped InN epilayers were grown on sapphire substrates by metal organic chemical vapor deposition. Effects of Mg concentration on the photoluminescence (PL) emission properties have been investigated. An emission line at ˜0.76eV, which was absent in undoped InN epilayers and was about 60meV below the band-to-band emission peak at ˜0.82eV, was observed to be the dominant emission in Mg-doped InN epilayers. The PL spectral peak position and the temperature dependent emission intensity corroborated each other and suggested that the Mg acceptor level in InN is about 60meV above the valance band maximum.

  7. 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.

  8. Structural, photoluminescence and picosecond nonlinear optical effect of In-doped ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Yan, Xiao-Yan; Yao, Cheng-Bao; Li, Jin; Hu, Jun-Yan; Li, Qiang-Hua; Yang, Shou-Bin

    2016-05-01

    In-doped ZnO (IZO) nanowires were grown using the chemical vapour deposition method. The IZO nanowires have been characterized by scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and UV-Visible spectroscopy. The PL results demonstrated a larger band-gap for the IZO nanowires in comparison to the undoped ZnO. Two major emission peaks were observed for the IZO nanowires, one originated from the free exciton recombination (ultraviolet emission) and another possibly related to the deep-level emission (visible emission). Furthermore, the nonlinear optical characteristic of the nanowires was studied using picosecond Z-scan technique. The experimental results show that the two and three-photon absorption coefficient of samples were able to be observed. These studies make the promising potential applications of the samples in the development of multifunctional all-optical devices.

  9. 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.

  10. 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.

  11. 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.

  12. Near infrared photoluminescence observed in dilute GaSbBi alloys grown by liquid phase epitaxy

    NASA Astrophysics Data System (ADS)

    Das, S. K.; Das, T. D.; Dhar, S.; de la Mare, M.; Krier, A.

    2012-01-01

    We report the first observation of photoluminescence (PL) from the dilute bismide alloy GaSbBi. Epitaxial layers are grown by liquid phase epitaxy technique onto GaSb (1 0 0) substrates and PL is obtained in the near infrared spectral range ( λ ˜ 1.6 μm). Incorporation of 0.2, 0.3 and 0.4 at% Bi to the layer results in a decrease of band gap energy up to 40 meV as well as an increase of luminescence from the sample. Structural analysis confirms the successful incorporation of Bi consistent with an increase in lattice parameter. Raman spectroscopy measurements indicate vibrational modes due to GaBi as well as to free Bi atoms residing at interstitial spaces.

  13. Enhancement of field emission and photoluminescence properties of graphene-SnO2 composite nanostructures.

    PubMed

    Ding, Jijun; Yan, Xingbin; Li, Jun; Shen, Baoshou; Yang, Juan; Chen, Jiangtao; Xue, Qunji

    2011-11-01

    In this study, the SnO(2) nanostructures and graphene-SnO(2) (G-SnO(2)) composite nanostructures were prepared on n-Si (100) substrates by electrophoretic deposition and magnetron sputtering techniques. The field emission of SnO(2) nanostructures is improved largely by depositing graphene buffer layer, and the field emission of G-SnO(2) composite nanostructures can also further be improved by decreasing sputtering time of Sn nanoparticles to 5 min. The photoluminescence (PL) spectra of the SnO(2) nanostructures revealed multipeaks, which are consistent with previous reports except for a new peak at 422 nm. Intensity of six emission peaks increased after depositing graphene buffer layer. Our results indicated that graphene can also be used as buffer layer acting as interface modification to simultaneity improve the field emission and PL properties of SnO(2) nanostructures effectively. PMID:21967167

  14. 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.

  15. Correlation between photoluminescence and Fourier transform infrared spectra in tetra-ethyl-ortho-silicate thin films

    NASA Astrophysics Data System (ADS)

    Choi, Won Chel; Kim, Tae Geun; Kim, Jin-Sang

    2006-02-01

    We report strong visible photoluminescence (PL) from thermally treated tetra-ethyl-ortho-silicate (TEOS) thin films at room temperature. High-resolution transmission electron microscope (HRTEM) studies showed that the PL originated from nanocrystalline-Si (nc-Si). HRTEM images showed that as-grown TEOS thin films had quasi-static amorphous (QSA) SiO2 phases instead of the typical amorphous (TA) SiO2 phases, and that they divided into small pieces of nc-Si after thermal treatment. In addition, Fourier transform infrared (FTIR) investigations showed that the QSA-SiO2 phases were composed of three types of bonding modes (i.e., Si-O-Si bending, Si-O bending, and Si-O-Si stretching), which play important roles in the formation of the nc-Si at relatively lower annealing temperatures.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. [Effect of substrate temperature on structure and photoluminescence of ZnMgO films].

    PubMed

    Dong, Li-Na; Wang, Yu-Xin; Sun, Jing-Chang; Zheng, Ya-Ru; Zhang, Huan; Liang, Ming; Lin, Mao-Kui; Cui, Shuo

    2013-08-01

    ZnMgO films were deposited on quartz glass substrates by the ultrasonic spray pyrolysis at different substrate temperatures (450-550 degrees C). The structural, surface morphological and optical properties of the samples were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL) spectroscopy. The results demonstrate that the substrate temperature has important effect on structural and optical characteristics. All the films have hexagonal wurtzite polycrystalline structures and the c-axis preferential orientation has an optimum temperature of 530 degrees C. The sample prepared at this temperature owns uniform grain size, smooth surface morphology and better crystalline quality. The width of deep-level emission decreases and the near band edge (NBE) ultraviolet emission peak appears with the increase in temperature by the PL spectrum. When the temperature arrives to 530 degrees C, a distinct NBE emission peak can be observed at 374. 5 nm, while the deep level emission is almost undetectable. PMID:24159844

  1. Defect induced photoluminescence and ferromagnetic properties of bio-compatible SWCNT/Ni hybrid bundles.

    PubMed

    Gupta, Vinay; Gupta, Bipin Kumar; Kotnala, R K; Narayanan, T N; Grover, Vaneet; Shah, Jyoti; Agrawal, Vikash; Chand, Suresh; Shanker, Virendra

    2011-10-15

    Designing of bio-compatible nanomagnets with multiple functionalities receives immense scientific attention due to their potential applications in bio-labeling, medical diagnosis and treatment. Here we report the synthesis of Nickel (Ni) incorporated single-walled carbon nanotube (SWCNT) hybrid and bio-compatible bundles having interesting magnetic and photoluminescence (PL) properties. The SWCNT exhibits a high-crystallinity and it has an average diameter of ∼1.7 nm. Ni particles of 10-20 nm were incorporated within the SWCNT bundles. These hybrid bundles exhibit PL and it is attributed to the presence of delocalized π electrons and their recombination at the defective sites of SWCNT. Magnetic characterization revealed that the SWCNT/Ni hybrid bundle possesses a high (50 Oe) coercivity compared to bulk Ni and a long range ferromagnetic ordering at room temperature. MTT-assay has been conducted to study the cytotoxicity of these hybrid nanostructures. PMID:21802691

  2. Photoluminescence of CdTe Crystals Grown by Contactless PVT Method

    NASA Technical Reports Server (NTRS)

    Palosz, W.; Grasza, K.; Cui, Y.; Wright, G.; Roy, U. N.; Burger, A.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    High quality CdTe crystals with resistivities higher than 10(exp 8) Omega cm were grown by the 'contactless' PVT (physical vapor transport) technique. Group III elements In and Al, and the transition metal Sc 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. It was found that the emission peaks at 1.584 eV and 1.581 eV exist 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 dramatically with introduction of Sc.

  3. Photoluminescence of CdTe Crystals Grown by Physical Vapor Transport

    NASA Technical Reports Server (NTRS)

    Curreri, Peter A. (Technical Monitor); 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.

  4. 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.

  5. 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.

  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. 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

  8. 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.

  9. 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.

  10. 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

  11. Photoluminescence mechanism model for oxidized porous silicon and nanoscale-silicon-particle-embedded silicon oxide

    NASA Astrophysics Data System (ADS)

    Qin, G. G.; Li, Y. J.

    2003-08-01

    There is much debate about the photoluminescence (PL) mechanisms of the nanoscale Si/Si oxide systems containing oxidized porous silicon and a nanoscale-Si-particle (NSP)—embedded Si oxide deposited by chemical vapor deposition, sputtering, or Si-ion implanting into Si oxide. In this paper, we suggest that two competitive processes, namely, the quantum confinement (QC) process and the quantum confinement-luminescence center (QCLC) process, take place in the PL. The photoexcitation occurs in the NSPs for both of the processes, while the photoemission occurs either in the NSPs for the QC process or in the luminescence centers (LCs) in Si oxide adjacent to the NSPs for the QCLC process. The rates of the two processes are compared quantitatively. Which process plays the major role in PL is determined by the capture cross section, the luminescence efficiency, and the density of the LCs, and the sizes of the NSPs. For a nanoscale Si/Si oxide system with the LCs having certain capture cross-section and luminescence efficiency, the higher the LC density and the larger the sizes of NSPs, the more beneficial for the QCLC process to surpass the QC process, and vice versa. For certain LC parameters, there is a critical most probable size for the NSPs. When the most probable size of the NSPs is larger than the critical one, the QCLC process dominates the PL, and when the most probable size of the NSPs is smaller than the critical one, the QC process dominates the PL. When the most probable size of the NSPs is close to the critical one, both the QC and QCLC processes should be taken into account. We have used this model to discuss PL experimental results reported for some nanoscale Si/Si oxide systems.

  12. 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.

  13. 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.

  14. Photoluminescence, FTIR, and laser-Raman spectroscopic studies of PMN-PT containing iron

    NASA Astrophysics Data System (ADS)

    Bairavarasu, Sundar R.; Edwards, Matthew E.; Kukhtareva, Titania; Sastry, Medury D.; Lianos, Dimitrios; Kommidi, Praveena; Reddy, B. Rami; Janeisch, Holger M.; Aggarwal, Monmohan D.

    2007-09-01

    Lead magnesium niobate-lead titanate, Pb(Mg, Nb)O 3-PbTiO 3 is a piezoelectric, ferroelectric crystal at room temperature with large electromechanical coefficient. The crystals were grown by PbO-B IIO 3 flux method. Typically the crystals were colorless and transparent, but a small fraction of them were Brown/reddish colored and show interesting photoluminescence (PL) properties. The PL studies were conducted under XeCl (308nm) excitation and under Argon Ion (Ar +) laser excitation. The excitation with 308nm gave broad PL centered at 500nm and intense emission at 710nm. The emission at 710nm in colorless crystals is very weak. The excitation with Ar + laser coinciding with electronic absorption in brown samples gave rich and sharp PL particularly with 514.5 nm excitation. The PL with 514.5nm-Ar + laserexcitation, consisted of intense anti stokes emission in addition to intense red and near infrared emission, is a result of photo-transfer optically stimulated luminescence (PT-OSL). This involved electron-hole recombination at photoinduced magnetic polaron site. The PL emissions and the centers identified are the followings: 718nm emission due to magnetic polaron and 360nm emission due to cooperative emission from two polarons, Fe-R line at 660nm due to Fe 3+ coupled to a cation; 380nm and 399nm due to Pb 2+ clusters and Nb 5+ center; 630 and 860 nm due to 6p-->6s transition of Pb 3+ and 760nm due to isolated Fe 3+ ions. Raman spectrum of brown samples revealed the presence of nano particles/wires of orthorhombic β PbO. The FTIR spectrum gives evidence of significant amount of hydroxyl impurity.

  15. 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.

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

    DOE PAGESBeta

    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

  17. Photoassisted photoluminescence fine-tuning of gold nanodots through free radical-mediated ligand-assembly.

    PubMed

    Tseng, Yu-Ting; Cherng, Rochelle; Harroun, Scott G; Yuan, Zhiqin; Lin, Tai-Yuan; Wu, Chien-Wei; Chang, Huan-Tsung; Huang, Chih-Ching

    2016-05-14

    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. PMID:27118444

  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. 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.

  20. 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.

  1. Diameter Control and Photoluminescence of ZnO Nanorods from Trialkylamines

    DOE PAGESBeta

    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.

  2. 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

  3. Chemical vapor deposition synthesis and photoluminescence properties of ZnS hollow microspheres

    SciTech Connect

    Pi Zhengbang; Su Xiaolu; Yang Chao; Tian Xike Pei Fang; Zhang Suxin; Zhen Jianhua

    2008-08-04

    ZnS hollow microspheres were prepared via a facile template-free chemical vapor deposition (CVD) route using metallic zinc powders and sulphur sublimed as reactants. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometer (EDX). The results showed that the as-prepared ZnS hollow spheres had uniform size about 4-8 {mu}m in diameter. The growth mechanism of such interesting was discussed. The optical property of the products was also recorded by means of photoluminescence (PL) spectroscopy.

  4. Temperature- and field-dependent energy transfer in CdSe nanocrystal aggregates studied by magneto-photoluminescence spectroscopy.

    PubMed

    Blumling, Daniel E; Tokumoto, Takahisa; McGill, Stephen; Knappenberger, Kenneth L

    2012-08-21

    The influence of temperature and applied magnetic fields on photoluminescence (PL) emission and electronic energy transfer (ET) of both isolated and aggregated CdSe nanocrystals was investigated. Following 400-nm excitation, temperature-dependent, intensity-integrated and energy-resolved PL measurements were used to quantify the emission wavelength and amplitude of isolated CdSe nanocrystals. The results indicated an approximately three-fold increase in PL intensity upon decreasing the temperature from 300 K to 6 K; this was attributed to a reduction of charge carrier access to nanocrystal surface trap states and suppression of thermal loss channels. Temperature-dependent PL measurements of aggregated CdSe nanocrystals, which included both energy-donating and -accepting particles, were analyzed using a modified version of Förster theory. Temperature-dependent ET efficiency increased from 0.55 to 0.75 upon decreasing the sample temperature from 225 K to 6 K, and the ET data contained the same trend observed for the PL of isolated nanoclusters. The application of magnetic fields to increase nanocrystal ET efficiency was studied using magneto-photoluminescence measurements recorded at a sample temperature of 1.6 K. We demonstrated that the exciton fine structure population of the donor was varied using applied magnetic fields, which in turn dictated the PL yield and the resultant ET efficiency of the CdSe nanocrystal aggregate system. The experimental data indicated an ET efficiency enhancement of approximately 7%, which was limited by the random orientation of the spherical nanocrystals in the thin film. PMID:22767253

  5. Ability of Lactobacillus rhamnosus GAF01 to remove AFM1 in vitro and to counteract AFM1 immunotoxicity in vivo.

    PubMed

    Abbès, Samir; Salah-Abbès, Jalila Ben; Sharafi, Hakimeh; Jebali, Rania; Noghabi, Kambiz Akbari; Oueslati, Ridha

    2013-01-01

    Aflatoxin M1 (AFM1) has been detected in many parts of the world both in raw milk and many dairy products, causing great economic losses and human disease. Unfortunately, there are few studies dealing with AFM1 immunotoxicity/interactions with lactic acid bacteria for potential application as a natural preventive agent. The aim of this study was to isolate (from dairy products) food-grade probiotic bacteria able to degrade/bind AFM1 in vitro and evaluate whether the same organism(s) could impart a protective role against AFM1-induced immunotoxicity in exposed Balb/c mice. Bacteria (Lactobacillus plantarum MON03 and L. rhamnosus GAF01) were isolated from Tunisian artisanal butter and then tested for abilities to eliminate AFM1 from phosphate-buffered saline (PBS) and reconstituted milk (containing 0.05, 0.10, and 0.20 µg AFM1/ml) after 0, 6, and 24 h at 37°C. Results showed that the selected bacteria could 'remove' AFM1 both in PBS and skimmed milk. The binding abilities of AFM1 by L. plantarum MON03 and L. rhamnosus GAF01 strains (at 10(8) CFU/ml) in PBS and reconstituted milk ranged, respectively, from 16.1-78.6% and 15.3-95.1%; overall, L. rhamnosus showed a better potential for removal than L. plantarum. 'Removal' appeared to be by simple binding; the bacteria/AFM1 complex was stable and only a very small proportion of mycotoxin was released back into the solution. L. rhamnosus GAF01 had the highest binding capacity and was selected for use in the in vivo study. Those results indicated that use of the organism prevented AFM1-induced effects on total white and red blood cells, and lymphocyte subtypes, after 15 days of host treatment. These studies clearly indicated that L. rhamnosus GAF01 was able to bind AFM1 in vitro and-by mechanisms that might also be related to a binding effect-counteract AFM1-induced immunotoxicity. Moreover, by itself, this bacterium was not toxic and could potentially be used as an additive in dairy products and in biotechnology for

  6. 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

  7. Efficient long wavelength interband photoluminescence from HgCdTe epitaxial films at wavelengths up to 26 μm

    SciTech Connect

    Morozov, S. V.; Rumyantsev, V. V. Antonov, A. V.; Gavrilenko, V. I.; Maremyanin, K. V.; Kudryavtsev, K. E.; Krasilnikova, L. V.; Mikhailov, N. N.; Dvoretskii, S. A.

    2014-02-17

    Photoluminescence (PL) and photoconductivity (PC) studies of Hg{sub 1−x}Cd{sub x}Te (0.19 ≤ x ≤ 0.23) epitaxial films are presented. Interband PL is observed at wavelengths from 26 to 6 μm and in the temperature range 18 K–200 K. The PL line full width at half maximum is about 6 meV (4kT) at 18 K and approaches its theoretical limit of 1.8kT at higher temperatures. Carrier recombination process is also investigated by time resolved studies of PL and PC at pulsed excitation. Radiative transitions are shown to be the dominating mechanism of carrier recombination at high excitation levels.

  8. Time resolved photoluminescence spectroscopy of narrow gap Hg1-xCdxTe/CdyHg1-yTe quantum well heterostructures

    NASA Astrophysics Data System (ADS)

    Morozov, S. V.; Rumyantsev, V. V.; Antonov, A. V.; Kadykov, A. M.; Maremyanin, K. V.; Kudryavtsev, K. E.; Mikhailov, N. N.; Dvoretskii, S. A.; Gavrilenko, V. I.

    2014-07-01

    Photoluminescence (PL) spectra and kinetics of narrow gap Hg1-xCdxTe/CdyHg1-yTe quantum well (QW) heterostructures grown by molecular beam epitaxy technique are studied. Interband PL spectra are observed from 18 K up to the room temperature. Time resolved studies reveal an additional PL line with slow kinetics (7 μs at 18 K) related to deep defect states in barrier layers. These states act as traps counteracting carrier injection into QWs. The decay time of PL signal from QW layers is about 5 μs showing that gain can be achieved at wavelengths 10-20 μm by placing such QWs in HgCdTe structures with waveguides.

  9. 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.

  10. 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.

  11. Defect study of Cu2ZnSn(SxSe1-x)4 thin film absorbers using photoluminescence and modulated surface photovoltage spectroscopy

    NASA Astrophysics Data System (ADS)

    Lin, Xianzhong; Ennaoui, Ahmed; Levcenko, Sergiu; Dittrich, Thomas; Kavalakkatt, Jaison; Kretzschmar, Steffen; Unold, Thomas; Lux-Steiner, Martha Ch.

    2015-01-01

    Defect states in Cu2ZnSn(SxSe1-x)4 thin films with x = 0.28, 0.36, and 1 were studied by combining photoluminescence (PL) and modulated surface photovoltage (SPV) spectroscopy. A single broad band emission in the PL spectra was observed and can be related to quasi-donor-acceptor pair transitions. The analysis of the temperature dependent quenching of the PL band (x = 0.28, 0.36, and 1) and SPV (x = 0.28) signals resulted in activation energies below 150 meV for PL and about 90 and 300 meV for SPV. Possible intrinsic point defects that might be associated with these observed activation energies are discussed.

  12. 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.

  13. Atomic force microscopy combined with optical tweezers (AFM/OT)

    NASA Astrophysics Data System (ADS)

    Pierini, F.; Zembrzycki, K.; Nakielski, P.; Pawłowska, S.; Kowalewski, T. A.

    2016-02-01

    The role of mechanical properties is essential to understand molecular, biological materials, and nanostructures dynamics and interaction processes. Atomic force microscopy (AFM) is the most commonly used method of direct force evaluation, but due to its technical limitations this single probe technique is unable to detect forces with femtonewton resolution. In this paper we present the development of a combined atomic force microscopy and optical tweezers (AFM/OT) instrument. The focused laser beam, on which optical tweezers are based, provides us with the ability to manipulate small dielectric objects and to use it as a high spatial and temporal resolution displacement and force sensor in the same AFM scanning zone. We demonstrate the possibility to develop a combined instrument with high potential in nanomechanics, molecules manipulation and biological studies. AFM/OT equipment is described and characterized by studying the ability to trap dielectric objects and quantifying the detectable and applicable forces. Finally, optical tweezers calibration methods and instrument applications are given.

  14. Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures.

    PubMed

    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

  15. Photoluminescence and SIMS studies of hydrogen passivation of Mg-doped p-type gallium nitride

    SciTech Connect

    Li, Y.; Lu, Y.; Hwang, C.Y.; Schurman, M.; Mayo, W.; Shen, H.; Wraback, M.; Salagaj, T.; Stall, R.A.

    1996-11-01

    The effects of hydrogen passivation in MOCVD grown Mg doped p-type GaN were studied using low temperature (5K) photoluminescence (PL) and secondary-ion-mass spectroscopy (SIMS). GaN films with different Mg doping level were annealed at 700 C in N{sub 2} ambient with different annealing times. The SIMS results indicate that the hydrogen concentration increases with increasing Mg doping level in the as-grown Mg:GaN film. After 20 minutes of annealing, most of the hydrogen escapes form the film. The 3.455 eV PL peak before annealing and the 3.446 eV peak after annealing found in the mg doped samples were attributed to the exciton bound to the Mg-H complex and to the Mg acceptor, respectively. The shift of the bound exciton peak to higher energy (3.465 eV) in the lightly doped sample is due to an effective n-type compensation associated with an annealing-induced increase in the nitrogen vacancies. In heavily doped Mg:GaN, the decreases in the integrated PL intensity after 700 C annealing may be associated with the hydrogen depassivation of nonradiative recombination centers in the film. The increase of PL intensity in the lightly doped sample after annealing is attributed to the reduction of defects by the annealing process.

  16. Dynamics of GaN band edge photoluminescence at near-room-temperature regime

    NASA Astrophysics Data System (ADS)

    Chen, Xiang-Bai; Huso, Jesse; Morrison, John L.; Bergman, Leah

    2006-02-01

    In this paper we present an approach based on the known radiative recombination rate model to study the dynamics and characteristics of photoluminescence (PL) transitions at room-temperature (RT) regime of GaN thin film. The model states that the dependence of the PL intensity on the laser excitation intensity is IPL~Ilaserα in which the value of the exponent α reveals whether the PL is due to an exciton or band gap recombination mechanism. We elaborated on the model and studied the temperature behavior of the exponent α in the range of 180-400 K in order to explore the recombination type for that range. It was found that at the temperature range just below RT ~180-270 K the exponent is a slowly increasing function of temperature and has an average value of ~1.2, implying a free-exciton recombination mechanism. At ~280 K the value of the exponent was found to exhibit a step-function-like behavior with a sharp increase from 1.2 to 1.7. At the temperature range just above RT ~300-400 K the exponent was found again to be a slowly increasing function of temperature with an average value of ~1.7, implying that at that temperature range the PL involves mainly band gap transitions. From the temperature behavior of the exponent, the activation energy of the free exciton was inferred to be ~24 meV.

  17. 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

  18. Synthesis and photoluminescence spectroscopy of BaGeF6:Mn4+ red phosphor

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Daisuke; Adachi, Sadao

    2015-04-01

    We synthesized Mn4+-activated BaGeF6 red phosphor by the chemical reaction method from HF, H2SiF6, BaF2, KMnO4, and GeO2 powder. The structural and optical properties of BaGeF6:Mn4+ were investigated using X-ray diffraction analysis, secondary electron microscopy observation, electron spin resonance measurement, photoluminescence (PL), PL excitation (PLE) and Raman scattering spectroscopies, and luminescence decay time measurement. Temperature dependence of the PL intensity was measured from T = 20 to 500 K and analyzed by taking into consideration the Bose-Einstein phonon occupation number. The PLE spectra measured at T = 20 and 300 K and luminescence decay time at T = 20-460 K were also analyzed based on the Franck-Condon and conventional thermal quenching models, respectively. Comprehensive discussion was given on the Mn4+-related PL properties and Raman scattering behaviors in a family of the barium hexafluorometallate phosphors.

  19. Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures

    NASA Astrophysics Data System (ADS)

    Chen, Yulu; Wu, Qiong; Ma, Yingjie; Liu, Tao; Fan, Yongliang; Yang, Xinju; Zhong, Zhenyang; Xu, Fei; Lu, Jianping; Jiang, Zuimin

    2015-12-01

    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.

  20. 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.

  1. Temperature-dependent photoluminescence imaging of GaAs/AlGaAs heterostructure quantum well tubes

    NASA Astrophysics Data System (ADS)

    Shi, Teng; Jackson, Howard; Smith, Leigh; Yarrison-Rice, Jan; Jiang, Nian; Tan, Hoe; Gao, Qiang; Jagadish, Chennupati

    2014-03-01

    Two sets of GaAs/AlGaAs core-multi shell nanowire quantum well tubes (QWTs) grown by MOCVD, with QW widths of 2nm and 6nm are dispersed onto a 4mm diameter hemispherical solid immersion lens. We obtain high spatial resolution photoluminescence (PL) images of single nanowires (NWs) from 10 K up to 120 K. High spectral resolution PL spectra reveal several narrow emission lines on high energy side of the 2nm QWT at low temperatures. In the 6nm QW, such narrow emission lines are not observed. Spatially-resolved PL images show that these localized states are randomly distributed along the NW long axis. Temperature-dependent PL imaging indicates that the quantum dot emissions disappear at temperatures above 50K. The recombination lifetime for electrons and holes in the QWT for the 2nm and 6nm QWTs are 500ps and 800 ps, respectively. We observe the recombination lifetime increases slightly with increasing temperature. We acknowledge the NSF through DMR-1105362, 1105121 and ECCS-1100489, and the Australian Research Council.

  2. Comparison of Photoluminescence Imaging on Starting Multi-Crystalline Silicon Wafers to Finished Cell Performance: Preprint

    SciTech Connect

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

    2012-06-01

    Photoluminescence (PL) imaging techniques can be applied to multicrystalline silicon wafers throughout the manufacturing process. Both band-to-band PL and defect-band emissions, which are longer-wavelength emissions from sub-bandgap transitions, are used to characterize wafer quality and defect content on starting multicrystalline silicon wafers and neighboring wafers processed at each step through completion of finished cells. Both PL imaging techniques spatially highlight defect regions that represent dislocations and defect clusters. The relative intensities of these imaged defect regions change with processing. Band-to-band PL on wafers in the later steps of processing shows good correlation to cell quality and performance. The defect band images show regions that change relative intensity through processing, and better correlation to cell efficiency and reverse-bias breakdown is more evident at the starting wafer stage as opposed to later process steps. We show that thermal processing in the 200 degrees - 400 degrees C range causes impurities to diffuse to different defect regions, changing their relative defect band emissions.

  3. Temperature dependence of Er3+ ionoluminescence and photoluminescence in Gd2O3:Bi nanopowder

    NASA Astrophysics Data System (ADS)

    Boruc, Zuzanna; Gawlik, Grzegorz; Fetliński, Bartosz; Kaczkan, Marcin; Malinowski, Michał

    2014-06-01

    Ionoluminescence (IL) and photoluminescence (PL) of trivalent erbium ions (Er3+) in Gd2O3 nanopowder host activated with Bi3+ ions has been studied in order to establish the link between changes in luminescent spectra and temperature of the sample material. IL measurements have been performed with H2+ 100 keV ion beam bombarding the target material for a few seconds, while PL spectra have been collected for temperatures ranging from 20 °C to 700 °C. The PL data was used as a reference in determining the temperature corresponding to IL spectra. The collected data enabled the definition of empirical formula based on the Boltzmann distribution, which allows the temperature to be determined with a maximum sensitivity of 9.7 × 10-3 °C-1. The analysis of the Er3+ energy level structure in terms of tendency of the system to stay in thermal equilibrium, explained different behaviors of the line intensities. This work led to the conclusion that temperature changes during ion excitation can be easily defined with separately collected PL spectra. The final result, which is empirical formula describing dependence of fluorescence intensity ratio on temperature, raises the idea of an application of method in temperature control, during processes like ion implantation and some nuclear applications.

  4. 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.

  5. Adjustable YAG : Ce3+ photoluminescence from photonic crystal microcavity

    NASA Astrophysics Data System (ADS)

    Li, Yigang; Almeida, Rui M.

    2013-04-01

    Four different photonic bandgap (PBG) structures embedding a YAG : Ce3+ layer inside two three-period Bragg mirrors were prepared by sol-gel processing, forming Fabry-Perot microcavities whose defect peaks moved from red to green. Under irradiation of blue Ar+ laser light, the typical broad YAG : Ce3+ photoluminescence (PL) emission band was highly narrowed in these four samples, with the new position of the modified PL peaks corresponding to the resonance wavelength of each microcavity sample, while the simultaneous colour changes could be easily observed by the human eye. The adjustable range demonstrated here was wide enough to generate white light with colour temperatures from warm white (˜2700 K) to daylight white (˜5600 K), by mixing the modified PL with light from any usual blue LED excitation source. This result provides a novel technique to solve the red-deficiency problem in the white LED industry: instead of relying on the development of new phosphors, the well-known PL of YAG : Ce3+ can be conveniently adjusted by 1D PBG structures.

  6. Photoluminescence and lasing properties of MAPbBr3 single crystals grown from solution

    NASA Astrophysics Data System (ADS)

    Aryal, Sandip; Lafalce, Evan; Zhang, Chuang; Zhai, Yaxin; Vardeny, Z. Valy

    Recent studies of solution-grown single crystals of inorganic-organic hybrid lead-trihalide perovskites have suggested that surface traps may play a significant role in their photophysics. We study electron-hole recombination in single crystal MAPbBr3 through such trap states using cw photoluminescence (PL) and ps transient photoinduced absorption (PA) spectroscopies. By varying the depth of the collecting optics we examined the contributions from surface and bulk radiative recombination. We found a surface dominated PL band at the band-edge that is similar to that observed from polycrystalline thin films, as well as a weaker red-shifted emission band that originates from the bulk crystal. The two PL bands are distinguished in their temperature, excitation intensity and polarization dependencies, as well as their ps dynamics. Additionally, amplified spontaneous emission and crystal-related cavity lasing modes were observed in the same spectral range as the PL band assigned to the surface recombination. This work was funded by AFOSR through MURI Grant RA 9550-14-1-0037.

  7. 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

  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. PMID:22372372

  9. Temperature-dependent photoluminescence studies of GdTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Verma, Amit; Raghavan, Santosh; Protasenko, Vladimir; Stemmer, Susanne; Jena, Debdeep

    2013-03-01

    GdTiO3 (GTO), a Mott-insulator, has acquired increased prominence in last few years since the discovery of a 2-dimensional electron gas (2DEG) at its heterojunction with the band-insulator SrTiO3. These 2DEGs have very large electron densities (~3x1014 cm-2) amounting to half electron per unit cell. To realize many possible applications of this large 2DEG, an understanding of the GTO bandstructure is needed. With this goal in mind, in this work we present photoluminescence (PL) studies of GTO thin films (10nm and 20nm) grown by molecular beam epitaxy (MBE) on (001) LSAT substrates. When pumped with a 325 nm He-Cd laser, we observe a red PL (~683 nm at 300K) from both GTO thin films at RT. Upon lowering the temperature from 300K to 80K, the PL peak blue shifts by ~0.14eV. Interestingly, the reported activation energy of the resistivity of MBE-grown GTO thin films is also ~0.14eV (Moetakef et al., J. Crystal Growth 355, 166 (2012)). We connect the observed temperature-dependent PL data with the expected electronic bandstructure and electrical resistivity, and explain the sharp transition in the peak that occurs between 120K-200K from ~636nm to ~683nm. Office of Naval Research through grant number (N00014-12-1-0976).

  10. 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.

  11. Heterogeneous core/shell fluoride nanocrystals with enhanced upconversion photoluminescence for in vivo bioimaging

    NASA Astrophysics Data System (ADS)

    Hao, Shuwei; Yang, Liming; Qiu, Hailong; Fan, Rongwei; Yang, Chunhui; Chen, Guanying

    2015-06-01

    We report on heterogeneous core/shell CaF2:Yb3+/Ho3+@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:Yb3+/Ho3+ 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.We report on heterogeneous core/shell CaF2:Yb3+/Ho3+@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:Yb3+/Ho3+ 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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02287h

  12. Nanoscale structural features determined by AFM for single virus particles.

    PubMed

    Chen, Shu-wen W; Odorico, Michael; Meillan, Matthieu; Vellutini, Luc; Teulon, Jean-Marie; Parot, Pierre; Bennetau, Bernard; Pellequer, Jean-Luc

    2013-11-21

    In this work, we propose "single-image analysis", as opposed to multi-image averaging, for extracting valuable information from AFM images of single bio-particles. This approach allows us to study molecular systems imaged by AFM under general circumstances without restrictions on their structural forms. As feature exhibition is a resolution correlation, we have performed AFM imaging on surfaces of tobacco mosaic virus (TMV) to demonstrate variations of structural patterns with probing resolution. Two AFM images were acquired with the same tip at different probing resolutions in terms of pixel width, i.e., 1.95 and 0.49 nm per pixel. For assessment, we have constructed an in silico topograph based on the three-dimensional crystal structure of TMV as a reference. The prominent artifacts observed in the AFM-determined shape of TMV were attributed to tip convolutions. The width of TMV rod was systematically overestimated by ~10 nm at both probing resolutions of AFM. Nevertheless, the effects of tip convolution were less severe in vertical orientation so that the estimated height of TMV by AFM imaging was in close agreement with the in silico X-ray topograph. Using dedicated image processing algorithms, we found that at low resolution (i.e., 1.95 nm per pixel), the extracted surface features of TMV can be interpreted as a partial or full helical repeat (three complete turns with ~7.0 nm in length), while individual protein subunits (~2.5 nm) were perceivable only at high resolution. The present study shows that the scales of revealed structural features in AFM images are subject to both probing resolution and processing algorithms for image analysis. PMID:24056758

  13. The Conductance of Nanotubes Deformed by the AFM Tip

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Maiti, Amitesh; Anantram, M. P.

    2003-01-01

    The conductance drop under AFM-tip deformation can be explained by stretching of the tube length. NT sensors can be built utilizing uniform stretching. Single sp3 bond cross section cannot block electrons, because another conducting path may exist. AFM tip which forms sp3 bonds with the tube will decrease conductance. In the "table experiment" a conductance drop of 2 orders of magnitude happened only after some bonds were broken.

  14. Characterization of the interaction between AFM tips and surface nanobubbles.

    PubMed

    Walczyk, Wiktoria; Schönherr, Holger

    2014-06-24

    While the presence of gaseous enclosures observed at various solid-water interfaces, the so-called "surface nanobubles", has been confirmed by many groups in recent years, their formation, properties, and stability have not been convincingly and exhaustively explained. Here we report on an atomic force microscopy (AFM) study of argon nanobubbles on highly oriented pyrolitic graphite (HOPG) in water to elucidate the properties of nanobubble surfaces and the mechanism of AFM tip-nanobubble interaction. In particular, the deformation of the nanobubble-water interface by the AFM tip and the question whether the AFM tip penetrates the nanobubble during scanning were addressed by this combined intermittent contact (tapping) mode and force volume AFM study. We found that the stiffness of nanobubbles was smaller than the cantilever spring constant and comparable with the surface tension of water. The interaction with the AFM tip resulted in severe quasi-linear deformation of the bubbles; however, in the case of tip-bubble attraction, the interface deformed toward the tip. We tested two models of tip-bubble interaction, namely, the capillary force and the dynamic interaction model, and found, depending on the tip properties, good agreement with experimental data. The results showed that the tip-bubble interaction strength and the magnitude of the bubble deformation depend strongly on tip and bubble geometry and on tip and substrate material, and are very sensitive to the presence of contaminations that alter the interfacial tension. In particular, nanobubbles interacted differently with hydrophilic and hydrophobic AFM tips, which resulted in qualitatively and quantitatively different force curves measured on the bubbles in the experiments. To minimize bubble deformation and obtain reliable AFM results, nanobubbles must be measured with a sharp hydrophilic tip and with a cantilever having a very low spring constant in a contamination-free system. PMID:24856074

  15. Effect of annealing on the structural and UV photoluminescence properties of Sb-doped SnO2 films deposited on Al2O3 (0001) substrates by RF magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Feng, Xianjin; Luo, Yi; Luan, Caina

    2014-11-01

    The antimony-doped tin oxide (SnO2∶Sb) films have been deposited on the Al2O3 (0001) substrates by RF magnetron sputtering. The influence of annealing on the structural and photoluminescence (PL) properties of the SnO2∶Sb films was investigated. The prepared samples were polycrystalline films having a rutile structure of pure SnO2 and a preferred orientation along the (110) direction, with an improvement in the film crystallinity observed after annealing. An ultraviolet PL peak near 334 nm was observed at room temperature both before and after annealing. The corresponding PL mechanism was discussed in detail.

  16. Modeling the Interaction between AFM Tips and Pinned Surface Nanobubbles.

    PubMed

    Guo, Zhenjiang; Liu, Yawei; Xiao, Qianxiang; Schönherr, Holger; Zhang, Xianren

    2016-01-26

    Although the morphology of surface nanobubbles has been studied widely with different AFM modes, AFM images may not reflect the real shapes of the nanobubbles due to AFM tip-nanobubble interactions. In addition, the interplay between surface nanobubble deformation and induced capillary force has not been well understood in this context. In our work we used constraint lattice density functional theory to investigate the interaction between AFM tips and pinned surface nanobubbles systematically, especially concentrating on the effects of tip hydrophilicity and shape. For a hydrophilic tip contacting a nanobubble, its hydrophilic nature facilitates its departure from the bubble surface, displaying a weak and intermediate-range attraction. However, when the tip squeezes the nanobubble during the approach process, the nanobubble shows an elastic effect that prevents the tip from penetrating the bubble, leading to a strong nanobubble deformation and repulsive interactions. On the contrary, a hydrophobic tip can easily pierce the vapor-liquid interface of the nanobubble during the approach process, leading to the disappearance of the repulsive force. In the retraction process, however, the adhesion between the tip and the nanobubble leads to a much stronger lengthening effect on nanobubble deformation and a strong long-range attractive force. The trends of force evolution from our simulations agree qualitatively well with recent experimental AFM observations. This favorable agreement demonstrates that our model catches the main intergradient of tip-nanobubble interactions for pinned surface nanobubbles and may therefore provide important insight into how to design minimally invasive AFM experiments. PMID:26751634

  17. 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.

  18. Photoluminescence of Conjugated Star Polymers

    NASA Astrophysics Data System (ADS)

    Ferguson, J. B.; Prigodin, N. V.; Epstein, A. J.; Wang, F.

    2000-10-01

    Higher dimensionality "star" polymers provide new properties beyond those found in their linear analogs. They have been used to improving electronic properties for nonlinear optics through exciton transfer and molecular antenna structures for example (M. Kawa, J. M. J. Frechet, Chem. Mater. 10, 286 (1998).). We report on photoluminescence properties of star polymers with a hyperbranched core (both hyperbranched phenlyene and hyperbranched triphenylamine) and polyhexylthiophene arms. The arm is a conjugated oligomer of polythiophene that has been investigated extensively for metallic like conductivity when doped as well as utilized in field effect transistors in its undoped form (A. Tsumara, H. Koezuka, T. Ando, Appl. Phys. Lett. 49, 1210 (1986).). The cores are respectively, a nonconjugated polymer in the case of hyperbranched phenlyene and a conjugated polymer in the case of hyperbranched triphenylamine. The photoluminesce spectrum (λ_max at 575 nm) is identical for both star polymers with the two electronically different hyperbranched cores and for linear polythiophene alone. We conclude the wave functions of the core and arms do not strongly interact to form states different from their individual states and excitons formed on the hyperbranched cores migrate to the lower bandgap polythiophene before recombining.

  19. 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.

  20. 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

  1. 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

  2. Improving the Photoluminescence Properties of Perovskite CH3NH3PbBr3-xClx Films by Modulating Organic Cation and Chlorine Concentrations.

    PubMed

    Yan, Jun; Zhang, Bing; Chen, Yunlin; Zhang, Ao; Ke, Xiaohan

    2016-05-25

    The photoluminescence (PL) properties of inorganic-organic perovskites can be drastically changed by tuning the halogen composition, especially the Cl content. However, our research demonstrated that in addition to the influence of Cl concentration, the PL emission intensity of CH3NH3PbBr3 strongly depends on the content of CH3NH3Br in the coating solution. The effects of CH3NH3Br and Cl concentrations on the PL properties of CH3NH3PbBr3-xClx were investigated. We found that a strong PL emission intensity of CH3NH3PbBr3 can be obtained from solutions with a high CH3NH3Br concentration. The PL emission intensities of CH3NH3PbBr3-xClx films were enhanced by adjusting the molar ratio of PbBr to PbCl2 only in a highly concentrated CH3NH3Br environment. Moreover, it was found that an optimum CH3NH3Br/PbBr2/PbCl2 ratio in the precursor solutions can be used to obtain the strongest PL emission intensity of CH3NH3PbBr3-xClx films. Further studies revealed that both CH3NH3Br and Cl concentrations significantly influence the CH3NH3PbBr3-xClx films evolution, which affects their PL properties. PMID:27163386

  3. Observation of heavy- and light-hole split direct bandgap photoluminescence from tensile-strained GeSn (0.03% Sn)

    NASA Astrophysics Data System (ADS)

    Harris, Thomas R.; Yeo, Yung Kee; Ryu, Mee-Yi; Beeler, Richard T.; Kouvetakis, John

    2014-09-01

    Temperature- (T-) and laser power-dependent photoluminescence (PL) measurements have been made for the tensile-strained, undoped GeSn (0.03% Sn) film grown on Si substrate. The PL results show not only clear strain-split direct bandgap transitions to the light-hole (LH) and heavy-hole (HH) bands at energies of 0.827 and 0.851 eV at 10 K, respectively, but also clearly show both strong direct and indirect bandgap related PL emissions at almost all temperatures, which are rarely observed. This split of PL emissions can be directly observed only at low T and moderate laser power, and the two PL peaks merge into one broad PL peak at room temperature, which is mainly due to the HH PL emission rather than LH transition. The evolution of T-dependent PL results also clearly show the competitive nature between the direct and indirect bandgap related PL transitions as T changes. The PL analysis also indicates that the energy gap reduction in Γ valley could be larger, whereas the bandgap reduction in L valley could be smaller than the theory predicted. As a result, the separation energy between Γ and L valleys (˜86 meV at 300 K) is smaller than theory predicted (125 meV) for this Ge-like sample, which is mainly due to the tensile strain. This finding strongly suggests that the indirect-to-direct bandgap transition of Ge1-ySny could be achieved at much lower Sn concentration than originally anticipated if one utilizes the tensile strain properly. Thus, Ge1-ySny alloys could be attractive materials for the fabrication of direct bandgap Si-based light emitting devices.

  4. 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.

  5. AFM investigation of Martian soil simulants on micromachined Si substrates.

    PubMed

    Vijendran, S; Sykulska, H; Pike, W T

    2007-09-01

    The micro and nanostructures of Martian soil simulants with particles in the micrometre-size range have been studied using a combination of optical and atomic force microscopy (AFM) in preparation for the 2007 NASA Phoenix Mars Lander mission. The operation of an atomic force microscope on samples of micrometre-sized soil particles is a poorly investigated area where the unwanted interaction between the scanning tip and loose particles results in poor image quality and tip contamination by the sample. In order to mitigate these effects, etched silicon substrates with a variety of features have been used to facilitate the sorting and gripping of particles. From these experiments, a number of patterns were identified that were particularly good at isolating and immobilizing particles for AFM imaging. This data was used to guide the design of micromachined substrates for the Phoenix AFM. Both individual particles as well as aggregates were successfully imaged, and information on sizes, shapes and surface morphologies were obtained. This study highlights both the strengths and weaknesses of AFM for the potential in situ investigation of Martian soil and dust. Also presented are more general findings of the limiting operational constraints that exist when attempting the AFM of high aspect ratio particles with current technology. The performance of the final designs of the substrates incorporated on Phoenix will be described in a later paper. PMID:17760618

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

    PubMed

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

    2015-01-01

    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. The effect of RH on O2 sensing is also presented. Dye:EC films are sensitive to the RH, as shown by the change of the dye's PL decay time with RH at a given O2 concentration. Surprisingly, this RH sensitivity vanishes by adding PEG to EC, including by washing PEG off. In contrast, doping EC with TiO2 nanoparticles maintains the RH effect with the advantage of significant PL enhancement. This

  7. Highly Efficient Nondoped Green Organic Light-Emitting Diodes with Combination of High Photoluminescence and High Exciton Utilization.

    PubMed

    Wang, Chu; Li, Xianglong; Pan, Yuyu; Zhang, Shitong; Yao, Liang; Bai, Qing; Li, Weijun; Lu, Ping; Yang, Bing; Su, Shijian; Ma, Yuguang

    2016-02-10

    Photoluminescence (PL) efficiency and exciton utilization efficiency are two key parameters to harvest high-efficiency electroluminescence (EL) in organic light-emitting diodes (OLEDs). But it is not easy to simultaneously combine these two characteristics (high PL efficiency and high exciton utilization) into a fluorescent material. In this work, an efficient combination was achieved through two concepts of hybridized local and charge-transfer (CT) state (HLCT) and "hot exciton", in which the former is responsible for high PL efficiency while the latter contributes to high exciton utilization. On the basis of a tiny chemical modification in TPA-BZP, a green-light donor-acceptor molecule, we designed and synthesized CzP-BZP with this efficeient combination of high PL efficiency of η(PL) = 75% in the solid state and maximal exciton utilization efficiency up to 48% (especially, the internal quantum efficiency of η(IQE) = 35% substantially exceed 25% of spin statistics limit) in OLED. The nondoped OLED of CzP-BZP exhibited an excellent performance: a green emission with a CIE coordinate of (0.34, 0.60), a maximum current efficiency of 23.99 cd A(-1), and a maximum external quantum efficiency (EQE, η(EQE)) of 6.95%. This combined HLCT state and "hot exciton" strategy should be a practical way to design next-generation, low-cost, high-efficiency fluorescent OLED materials. PMID:26785427

  8. 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.

  9. Charge generation in PbS quantum dot solar cells characterized by temperature-dependent steady-state photoluminescence.

    PubMed

    Gao, Jianbo; Zhang, Jianbing; van de Lagemaat, Jao; Johnson, Justin C; Beard, Matthew C

    2014-12-23

    Charge-carrier generation and transport within PbS quantum dot (QD) solar cells is investigated by measuring the temperature-dependent steady-state photoluminescence (PL) concurrently during in situ current-voltage characterization. We first compare the temperature-dependent PL quenching for PbS QD films where the PbS QDs retain their original oleate ligand to that of PbS QDs treated with 1,2-ethanedithiol (EDT), producing a conductive QD layer, either on top of glass or on a ZnO nanocrystal film. We then measure and analyze the temperature-dependent PL in a completed QD-PV architecture with the structure Al/MoO3/EDT-PbS/ZnO/ITO/glass, collecting the PL and the current simultaneously. We find that at low temperatures excitons diffuse to the ZnO interface, where PL is quenched via interfacial charge transfer. At high temperatures, excitons dissociate in the bulk of the PbS QD film via phonon-assisted tunneling to nearby QDs, and that dissociation is in competition with the intrinsic radiative and nonradiative rates of the individual QDs. The activation energy for exciton dissociation in the QD-PV devices is found to be ∼40 meV, which is considerably lower than that of the electrodeless samples, and suggests unique interactions between injected and photogenerated carriers in devices. PMID:25485555

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. Charging C60 islands with the AFM tip.

    PubMed

    Hoff, Brice; Henry, Claude R; Barth, Clemens

    2016-01-01

    We show that electrons can be transferred on demand from an AFM tip into single bulk-like C60 islands, which are supported on the insulating NaCl(001) surface. We exemplify this by controlled charge-manipulation experiments conducted in ultrahigh vacuum by noncontact AFM (nc-AFM), electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM). KPFM shows a homogeneous contrast at the islands, which is a signature for an equal distribution of the electrons in the T1u band. The charge dissipates during half a day due to an interaction of the charged C60 islands with defects in the near surface region of NaCl. Our results open the perspective in photo-voltaics to study charge attachment, stability and charge exchange with the environment of any C60 bulk-like system. PMID:26617348

  16. Liquid contact resonance AFM: analytical models, experiments, and limitations

    NASA Astrophysics Data System (ADS)

    Parlak, Zehra; Tu, Qing; Zauscher, Stefan

    2014-11-01

    Contact resonance AFM (CR-AFM) is a scanning probe microscopy technique that utilizes the contact resonances of the AFM cantilever for concurrent imaging of topography and surface stiffness. The technique has not been used in liquid until recently due to analytical and experimental difficulties, associated with viscous damping of cantilever vibrations and fluid loading effects. To address these difficulties, (i) an analytical approach for contact resonances in liquid is developed, and (ii) direct excitation of the contact resonances is demonstrated by actuating the cantilever directly in a magnetic field. By implementing the analytical approach and the direct actuation through magnetic particles, quantitative stiffness imaging on surfaces with a wide range of stiffness can be achieved in liquid with soft cantilevers and low contact forces.

  17. Imaging resolution of AFM with probes modified with FIB.

    PubMed

    Skibinski, J; Rebis, J; Wejrzanowski, T; Rozniatowski, K; Pressard, K; Kurzydlowski, K J

    2014-11-01

    This study concerns imaging of the structure of materials using AFM tapping (TM) and phase imaging (PI) mode, using probes modified with focused ion beam (FIB). Three kinds of modifications were applied - thinning of the cantilever, sharpening of the tip and combination of these two modifications. Probes shaped in that way were used for AFM investigations with Bruker AFM Nanoscope 8. As a testing material, titanium roughness standard supplied by Bruker was used. The results show that performed modifications influence the oscillation of the probes. In particular thinning of the cantilever enables one to acquire higher self-resonant frequencies, which can be advantageous for improving the quality of imaging in PI mode. It was found that sharpening the tip improves imaging resolution in tapping mode, which is consistent with existing knowledge, but lowered the quality of high frequency topography images. In this paper the Finite Element Method (FEM) was used to explain the results obtained experimentally. PMID:25080273

  18. AFM of biological complexes: what can we learn?

    PubMed Central

    Gaczynska, Maria; Osmulski, Pawel A.

    2009-01-01

    The term “biological complexes” broadly encompasses particles as diverse as multisubunit enzymes, viral capsids, transport cages, molecular nets, ribosomes, nucleosomes, biological membrane components and amyloids. The complexes represent a broad range of stability and composition. Atomic force microscopy offers a wealth of structural and functional data about such assemblies. For this review, we choose to comment on the significance of AFM to study various aspects of biology of selected nonmembrane protein assemblies. Such particles are large enough to reveal many structural details under the AFM probe. Importantly, the specific advantages of the method allow for gathering dynamic information about their formation, stability or allosteric structural changes critical for their function. Some of them have already found their way to nanomedical or nanotechnological applications. Here we present examples of studies where the AFM provided pioneering information about the biology of complexes, and examples of studies where the simplicity of the method is used toward the development of potential diagnostic applications. PMID:19802337

  19. Improvement in metrology on new 3D-AFM platform

    NASA Astrophysics Data System (ADS)

    Schmitz, Ingo; Osborn, Marc; Hand, Sean; Chen, Qi

    2008-10-01

    According to the 2007 edition of the ITRS roadmap, the requirement for CD uniformity of isolated lines on a binary or attenuated phase shift mask is 2.1nm (3σ) in 2008 and requires improvement to1.3 nm (3σ) in 2010. In order to meet the increasing demand for CD uniformity on photo masks, improved CD metrology is required. A next generation AFM, InSightTM 3DAFM, has been developed to meet these increased requirements for advanced photo mask metrology. The new system achieves 2X improvement in CD and depth precision on advanced photo masks features over the previous generation 3D-AFM. This paper provides measurement data including depth, CD, and sidewall angle metrology. In addition the unique capabilities of damage-free defect inspection and Nanoimprint characterization by 3D AFM are presented.

  20. Mounting of Escherichia coli spheroplasts for AFM imaging.

    SciTech Connect

    Sullivan, Claretta J; Morrell-Falvey, Jennifer L; Allison, David P; Doktycz, Mitchel John

    2005-11-01

    The cytoplasmic membrane of Escherichia coli (E. coli) is the location of numerous, chemically specific transporters and recognition elements. Investigation of this membrane in vivo by atomic force microscopy (AFM) requires removal of the cell wall and stable immobilization of the spheroplast. AFM images demonstrate that spheroplasts can be secured with warm gelatin applied to the mica substrate just before the addition of a spheroplast suspension. The resulting preparation can be repeatedly imaged by AFM over the course of several hours. Confocal fluorescence imaging confirms the association of the spheroplasts with the gelatin layer. Gelatin molecules are known to reorder into a network after heating. Entrapment within this gelatin network is believed to be responsible for the immobilization of spheroplasts on mica.

  1. Surface Morphological Studies on Nerve Cells by AFM

    NASA Astrophysics Data System (ADS)

    Durkaya, Goksel; Zhong, Lei; Rehder, Vincent; Dietz, Nikolaus

    2009-03-01

    Surface morphological properties of fixed and living nerve cells removed from the buccal ganglion of Helisoma trivolvis have been studied by using Atomic Force Microscopy (AFM). Identified, individual neurons were removed from the buccal ganglion of Helisoma trivolvis and plated into poly-L-lysine coated glass cover-slips. The growth of the nerve cells was stopped and fixed with 0.1% Glutaraldehyde and 4% Formaldehyde solution after extension of growth cones at the tip of the axons. Topography and softness of growth cone filopodia and overlying lamellopodium (veil) were probed by AFM. Information obtained from AFM's amplitude and phase channels have been used for determination of softness of the region probed. The results of structural studies on the cells are linked to their mechanical properties and internal molecular density distribution.

  2. 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.

  3. 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.

  4. 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

  5. Charging C60 islands with the AFM tip

    NASA Astrophysics Data System (ADS)

    Hoff, Brice; Henry, Claude R.; Barth, Clemens

    2015-12-01

    We show that electrons can be transferred on demand from an AFM tip into single bulk-like C60 islands, which are supported on the insulating NaCl(001) surface. We exemplify this by controlled charge-manipulation experiments conducted in ultrahigh vacuum by noncontact AFM (nc-AFM), electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM). KPFM shows a homogeneous contrast at the islands, which is a signature for an equal distribution of the electrons in the T1u band. The charge dissipates during half a day due to an interaction of the charged C60 islands with defects in the near surface region of NaCl. Our results open the perspective in photo-voltaics to study charge attachment, stability and charge exchange with the environment of any C60 bulk-like system.We show that electrons can be transferred on demand from an AFM tip into single bulk-like C60 islands, which are supported on the insulating NaCl(001) surface. We exemplify this by controlled charge-manipulation experiments conducted in ultrahigh vacuum by noncontact AFM (nc-AFM), electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM). KPFM shows a homogeneous contrast at the islands, which is a signature for an equal distribution of the electrons in the T1u band. The charge dissipates during half a day due to an interaction of the charged C60 islands with defects in the near surface region of NaCl. Our results open the perspective in photo-voltaics to study charge attachment, stability and charge exchange with the environment of any C60 bulk-like system. Electronic supplementary information (ESI) available. See DOI: 10.1039/C5NR04541J

  6. Investigations on optoelectronic transition mechanisms of silicon nanoporous pillar array by using surface photovoltage spectroscopy and photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Hu, Zhen-Gang; Tian, Yong-Tao; Li, Xin-Jian

    2014-03-01

    We report the electronic transition mechanisms for hydrothermally prepared silicon nanoporous pillar array (Si-NPA), investigated by surface photovoltage (SPV) spectroscopy and photoluminescence (PL) spectroscopy. By comparing the SPV spectra of single crystal silicon (sc-Si) with that of Si-NPA, the silicon nano-crystallites (nc-Si)/SiOx nanostructure in the Si-NPA could produce SPV in the wavelength range of 300-580 nm. And 580 nm (˜2.14 eV) was considered as the absorption edge of the nc-Si/SiOx nanostructure. After the sample was annealed and oxidized in air at different temperatures, both the SPV in the wavelength range of 300-580 nm and the PL emission band around 690 nm from the nc-Si/SiOx nanostructure weakened and disappeared as the annealing temperature increased from 100 to 500 °C. But both the red-infrared PL band (>710 nm) and the violet-blue PL band were enhanced by increasing the annealing temperature. After 2 years of natural oxidation in air, the SPV features for sc-Si disappeared completely, and the SPV characteristics of the nc-Si/SiOx nanostructure could be clearly observed. After analysis, the Si-O structure related localized states at the nc-Si/SiOx interface dominated the electronic transitions during the red PL emission and the SPV for the nc-Si/SiOx nanostructure in Si-NPA, the red-infrared PL was due to the Si=O structure related electronic transitions, and the violet-blue PL emission could attribute to the oxygen-related defect related recombination of the photo induced carriers.

  7. 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

  8. Pressure dependence of the photoluminescence from γ-In2Se3 thin films prepared using MOCVD with a single-source precursor

    NASA Astrophysics Data System (ADS)

    Choi, In Hwan; Park, Hyeon Jeong

    2014-05-01

    Single γ-phase In2Se3 films were prepared by using metal-organic chemical-vapor deposition(MOCVD) with a single-source precursor [(Me)2In( μ-SeMe)]2. The basic physical properties of the grown films were examined by using X-ray diffraction, Raman spectroscopy, and photoluminescence spectroscopy at room temperature. The pressure dependence of the photoluminescence spectrum of the In2Se3 films was measured at room temperature. At 1 atm, 2 PL peaks were observed, one at 1.88 eV due to a bound exciton transition and the other at 1.50 eV due to a bound-to-free transition. While the pressure coefficients, at pressures below 1.4 GPa were nearly zero, the pressure coefficients of both PL peaks at pressures above 1.4 GPa were -25 meV/GPa.

  9. 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

  10. BOREAS AFM-04 Twin Otter Aircraft Flux Data

    NASA Technical Reports Server (NTRS)

    MacPherson, J. Ian; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Desjardins, Raymond L.; Smith, David E. (Technical Monitor)

    2000-01-01

    The BOREAS AFM-5 team collected and processed data from the numerous radiosonde flights during the project. The goals of the AFM-05 team were to provide large-scale definition of the atmosphere by supplementing the existing AES aerological network, both temporally and spatially. This data set includes basic upper-air parameters collected from the network of upper-air stations during the 1993, 1994, and 1996 field campaigns over the entire study region. The data are contained in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884) or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  11. GPIM AF-M315E Propulsion System

    NASA Technical Reports Server (NTRS)

    Spores, Ronald A.; Masse, Robert; Kimbrel, Scott; McLean, Chris

    2014-01-01

    The NASA Space Technology mission Directorate's (STMD) Green Propellant Infusion Mission (GPIM) Technology Demonstration Mission (TDM) will demonstrate an operational AF-M315E green propellant propulsion system. Aerojet-Rocketdyne is responsible for the development of the propulsion system payload. This paper statuses the propulsion system module development, including thruster design and system design; Initial test results for the 1N engineering model thruster are presented. The culmination of this program will be high-performance, green AF-M315E propulsion system technology at TRL 7+, with components demonstrated to TRL 9, ready for direct infusion to a wide range of applications for the space user community.

  12. Applicability of Langmuir equation to oxygen pressure dependent photoluminescence from β-Ga2O3 nanostructures

    NASA Astrophysics Data System (ADS)

    Jangir, R.; Ganguli, Tapas; Porwal, S.; Tiwari, Pragya; Rai, S. K.; Bhaumik, Indranil; Kukreja, L. M.; Gupta, P. K.; Deb, S. K.

    2013-08-01

    β-Ga2O3 nanostructures were synthesized via vapor transport method on gold coated Silicon substrate in N2 ambient. The as synthesized products were investigated by grazing incident X-ray diffraction, scanning electron microscopy and photoluminescence (PL) spectroscopy. It is shown that the intensity of photoluminescence from the ensemble of β-Ga2O3 nanostructures in oxygen gas ambience is correlated with the oxygen pressure through the Langmuir equation. This correlation is found to be reversible and reproducible. This phenomenon, which was not observed in the bulk β-Ga2O3 single crystal, is attributed to the oxygen related shallow trap surface states of the nanostructures with energies at about 4.2 eV above the valance band. Based on the changes in the PL intensity with the oxygen pressures, a possible mechanism for the observed photoluminescence is suggested. The present results provide a route for room-temperature response of oxygen in the gallium oxide nanostructures.

  13. Quantitative modeling of the role of surface traps in CdSe/CdS/ZnS nanocrystal photoluminescence decay dynamics.

    PubMed

    Jones, Marcus; Lo, Shun S; Scholes, Gregory D

    2009-03-01

    Charge carrier trapping is an important phenomenon in nanocrystal (NC) decay dynamics because it reduces photoluminescence (PL) quantum efficiencies and obscures efforts to understand the interaction of NC excitons with their surroundings. Particularly crucial to our understanding of excitation dynamics in, e.g., multiNC assemblies, would be a way of differentiating between processes involving trap states and those that do not. Direct optical measurement of NC trap state processes is not usually possible because they have negligible transition dipole moments; however, they are known to indirectly affect exciton photoluminescence. Here, we develop a framework, based on Marcus electron transfer theory, to determine NC trap state dynamics from time-resolved NC exciton PL measurements. Our results demonstrate the sensitivity of PL to interfacial dynamics, indicating that the technique can be used as an indirect but effective probe of trap distribution changes. We anticipate that this study represents a step toward understanding how excitons in nanocrystals interact with their surroundings: a quality that must be optimized for their efficient application in photovoltaics, photodetectors, or chemical sensors. PMID:19218443

  14. 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

  15. Temperature-dependent photoluminescence of cadmium-free Cu-Zn-In-S quantum dot thin films as temperature probes.

    PubMed

    Wang, Lan; Kang, Xiaojiao; Huang, Lijian; Pan, Daocheng

    2015-12-21

    We reported temperature-dependent photoluminescence (PL) studies on Cu-Zn-In-S quantum dot (QD) thin films. In this paper, cadmium-free and luminescent Cu-Zn-In-S quantum dot thin films were in situ formed by thermal decomposition of molecular-based precursors in the open air, without need of the complicated quantum dot synthesis. Molecular-based precursor solutions were prepared by dissolving Cu2O, ZnO, and In(OH)3 in the ethanol solution of butylamine and carbon disulfide. The effects of sintering temperature, sintering time, and the concentration of capping agents on the photoluminescence properties of Cu-Zn-In-S QD thin films have been systematically investigated. It was found that alkali metal ions play an important role in enhancing the PL quantum yield of quantum dot thin films. The as-prepared QD thin films show composition-tunable emission in the range of 535 nm to 677 nm, and the absolute PL quantum yields can reach as high as 22.1%. All of the as-deposited QD thin films show a single-exponential decay to temperature, indicating that these cadmium-free QD thin films have high potential as temperature probes. PMID:26567537

  16. A novel ascorbic acid sensor based on the Fe3+/Fe2+ modulated photoluminescence of CdTe quantum dots@SiO2 nanobeads

    NASA Astrophysics Data System (ADS)

    Ma, Qiang; Li, Yang; Lin, Zi-Han; Tang, Guangchao; Su, Xing-Guang

    2013-09-01

    In this paper, CdTe quantum dot (QD)@silica nanobeads were used as modulated photoluminescence (PL) sensors for the sensing of ascorbic acid in aqueous solution for the first time. The sensor was developed based on the different quenching effects of Fe2+ and Fe3+ on the PL intensity of the CdTe QD@ silica nanobeads. Firstly, the PL intensity of the CdTe QDs was quenched in the presence of Fe3+. Although both Fe2+ and Fe3+ could quench the PL intensity of the CdTe QDs, the quenching efficiency were quite different for Fe2+ and Fe3+. The PL intensity of the CdTe QD@silica nanobeads can be quenched by about 15% after the addition of Fe3+ (60 μmol L-1), while the PL intensity of the CdTe QD@silica nanobeads can be quenched about 49% after the addition of Fe2+ (60 μmol L-1). Therefore, the PL intensity of the CdTe QD@silica nanobeads decreased significantly when Fe3+ was reduced to Fe2+ by ascorbic acid. To confirm the strategy of PL modulation in this sensing system, trace H2O2 was introduced to oxidize Fe2+ to Fe3+. As a result, the PL intensity of the CdTe QD@silica nanobeads was partly recovered. The proposed sensor could be used for ascorbic acid sensing in the concentration range of 3.33-400 μmol L-1, with a detection limit (3σ) of 1.25 μmol L-1 The feasibility of the proposed sensor for ascorbic acid determination in tablet samples was also studied, and satisfactory results were obtained.In this paper, CdTe quantum dot (QD)@silica nanobeads were used as modulated photoluminescence (PL) sensors for the sensing of ascorbic acid in aqueous solution for the first time. The sensor was developed based on the different quenching effects of Fe2+ and Fe3+ on the PL intensity of the CdTe QD@ silica nanobeads. Firstly, the PL intensity of the CdTe QDs was quenched in the presence of Fe3+. Although both Fe2+ and Fe3+ could quench the PL intensity of the CdTe QDs, the quenching efficiency were quite different for Fe2+ and Fe3+. The PL intensity of the CdTe QD

  17. 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.

  18. 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.

  19. 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.

  20. 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+}.

  1. Metal crack propagation monitoring by photoluminescence enhancement of quantum dots.

    PubMed

    Zhao, Ziming; Luan, Weiling; Yin, Shaofeng; Brandner, Juergen J

    2015-07-20

    A visualization method for monitoring minor metal crack propagation is presented in this paper. Through CdS@ZnS core-shell quantum dots (QDs) enhanced emission of photoluminescence (PL), this crack detection method provides a visualization signal in real time and through a noncontact fashion. The crack of the CdS@ZnS core-shell QDs-epoxy resin kept a synchronous propagation with the metal crack. Detection of the tip growth in the film layers demonstrated that the actual crack propagation on the metal surface could be deduced from the tips in the film layers. The fluorescence peak tended to increase along the crack from the initial opening to the tip. Crack width as small as 10 μm can be detected with a precision of 0.1 μm and the minimum crack tip width of the QDs-epoxy resin was measured as 0.72 μm. PMID:26367834

  2. 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

  3. 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.

  4. AFM CHARACTERIZATION OF LASER INDUCED DAMAGE ON CDZNTE CRYSTAL SURFACES

    SciTech Connect

    Hawkins, S; Lucile Teague, L; Martine Duff, M; Eliel Villa-Aleman, E

    2008-06-10

    Semi-conducting CdZnTe (or CZT) crystals can be used in a variety of detector-type applications. CZT shows great promise for use as a gamma radiation spectrometer. However, its performance is adversely affected by point defects, structural and compositional heterogeneities within the crystals, such as twinning, pipes, grain boundaries (polycrystallinity), secondary phases and in some cases, damage caused by external forces. One example is damage that occurs during characterization of the surface by a laser during Raman spectroscopy. Even minimal laser power can cause Te enriched areas on the surface to appear. The Raman spectra resulting from measurements at moderate intensity laser power show large increases in peak intensity that is attributed to Te. Atomic Force Microscopy (AFM) was used to characterize the extent of damage to the CZT crystal surface following exposure to the Raman laser. AFM data reveal localized surface damage in the areas exposed to the Raman laser beam. The degree of surface damage to the crystal is dependent on the laser power, with the most observable damage occurring at high laser power. Moreover, intensity increases in the Te peaks of the Raman spectra are observed even at low laser power with little to no visible damage observed by AFM. AFM results also suggest that exposure to the same amount of laser power yields different amounts of surface damage depending on whether the exposed surface is the Te terminating face or the Cd terminating face of CZT.

  5. 3D Color Digital Elevation Map of AFM Sample

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This color image is a three dimensional (3D) view of a digital elevation map of a sample collected by NASA's Phoenix Mars Lander's Atomic Force Microscope (AFM).

    The image shows four round pits, only 5 microns in depth, that were micromachined into the silicon substrate, which is the background plane shown in red. This image has been processed to reflect the levelness of the substrate.

    A Martian particle only one micrometer, or one millionth of a meter, across is held in the upper left pit.

    The rounded particle shown at the highest magnification ever seen from another world is a particle of the dust that cloaks Mars. Such dust particles color the Martian sky pink, feed storms that regularly envelop the planet and produce Mars' distinctive red soil.

    The particle was part of a sample informally called 'Sorceress' delivered to the AFM on the 38th Martian day, or sol, of the mission (July 2, 2008). The AFM is part of Phoenix's microscopic station called MECA, or the Microscopy, Electrochemistry, and Conductivity Analyzer.

    The AFM was developed by a Swiss-led consortium, with Imperial College London producing the silicon substrate that holds sampled particles.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  6. Structural investigations on native collagen type I fibrils using AFM

    SciTech Connect

    Strasser, Stefan; Zink, Albert; Janko, Marek; Heckl, Wolfgang M.; Thalhammer, Stefan . E-mail: stefan.thalhammer@gsf.de

    2007-03-02

    This study was carried out to determine the elastic properties of single collagen type I fibrils with the use of atomic force microscopy (AFM). Native collagen fibrils were formed by self-assembly in vitro characterized with the AFM. To confirm the inner assembly of the collagen fibrils, the AFM was used as a microdissection tool. Native collagen type I fibrils were dissected and the inner core uncovered. To determine the elastic properties of collagen fibrils the tip of the AFM was used as a nanoindentor by recording force-displacement curves. Measurements were done on the outer shell and in the core of the fibril. The structural investigations revealed the banding of the shell also in the core of native collagen fibrils. Nanoindentation experiments showed the same Young's modulus on the shell as well as in the core of the investigated native collagen fibrils. In addition, the measurements indicate a higher adhesion in the core of the collagen fibrils compared to the shell.

  7. Introduction to Atomic Force Microscopy (AFM) in Biology.

    PubMed

    Kreplak, Laurent

    2016-01-01

    The atomic force microscope (AFM) has the unique capability of imaging biological samples with molecular resolution in buffer solution over a wide range of time scales from milliseconds to hours. In addition to providing topographical images of surfaces with nanometer- to angstrom-scale resolution, forces between single molecules and mechanical properties of biological samples can be investigated from the nano-scale to the micro-scale. Importantly, the measurements are made in buffer solutions, allowing biological samples to "stay alive" within a physiological-like environment while temporal changes in structure are measured-e.g., before and after addition of chemical reagents. These qualities distinguish AFM from conventional imaging techniques of comparable resolution, e.g., electron microscopy (EM). This unit provides an introduction to AFM on biological systems and describes specific examples of AFM on proteins, cells, and tissues. The physical principles of the technique and methodological aspects of its practical use and applications are also described. © 2016 by John Wiley & Sons, Inc. PMID:27479503

  8. Hydrodynamic effects in fast AFM single-molecule force measurements.

    PubMed

    Janovjak, Harald; Struckmeier, Jens; Müller, Daniel J

    2005-02-01

    Atomic force microscopy (AFM) allows the critical forces that unfold single proteins and rupture individual receptor-ligand bonds to be measured. To derive the shape of the energy landscape, the dynamic strength of the system is probed at different force loading rates. This is usually achieved by varying the pulling speed between a few nm/s and a few microm/s, although for a more complete investigation of the kinetic properties higher speeds are desirable. Above 10 microm/s, the hydrodynamic drag force acting on the AFM cantilever reaches the same order of magnitude as the molecular forces. This has limited the maximum pulling speed in AFM single-molecule force spectroscopy experiments. Here, we present an approach for considering these hydrodynamic effects, thereby allowing a correct evaluation of AFM force measurements recorded over an extended range of pulling speeds (and thus loading rates). To support and illustrate our theoretical considerations, we experimentally evaluated the mechanical unfolding of a multi-domain protein recorded at 30 microm/s pulling speed. PMID:15257425

  9. AFM Structural Characterization of Drinking Water Biofilm under Physiological Conditions

    EPA Science Inventory

    Due to the complexity of mixed culture drinking water biofilm, direct visual observation under in situ conditions has been challenging. In this study, atomic force microscopy (AFM) revealed the three dimensional morphology and arrangement of drinking water relevant biofilm in air...

  10. Conductive supports for combined AFM SECM on biological membranes

    NASA Astrophysics Data System (ADS)

    Frederix, Patrick L. T. M.; Bosshart, Patrick D.; Akiyama, Terunobu; Chami, Mohamed; Gullo, Maurizio R.; Blackstock, Jason J.; Dooleweerdt, Karin; de Rooij, Nico F.; Staufer, Urs; Engel, Andreas

    2008-09-01

    Four different conductive supports are analysed regarding their suitability for combined atomic force and scanning electrochemical microscopy (AFM-SECM) on biological membranes. Highly oriented pyrolytic graphite (HOPG), MoS2, template stripped gold, and template stripped platinum are compared as supports for high resolution imaging of reconstituted membrane proteins or native membranes, and as electrodes for transferring electrons from or to a redox molecule. We demonstrate that high resolution topographs of the bacterial outer membrane protein F can be recorded by contact mode AFM on all four supports. Electrochemical feedback experiments with conductive cantilevers that feature nanometre-scale electrodes showed fast re-oxidation of the redox couple Ru(NH3)63+/2+ with the two metal supports after prolonged immersion in electrolyte. In contrast, the re-oxidation rates decayed quickly to unpractical levels with HOPG or MoS2 under physiological conditions. On HOPG we observed heterogeneity in the re-oxidation rate of the redox molecules with higher feedback currents at step edges. The latter results demonstrate the capability of conductive cantilevers with small electrodes to measure minor variations in an SECM signal and to relate them to nanometre-scale features in a simultaneously recorded AFM topography. Rapid decay of re-oxidation rate and surface heterogeneity make HOPG or MoS2 less attractive for combined AFM-SECM experiments on biological membranes than template stripped gold or platinum supports.

  11. Origin of visible and near-infrared photoluminescence from chemically etched Si nanowires decorated with arbitrarily shaped Si nanocrystals.

    PubMed

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

    2014-01-31

    Arrays of vertically aligned single crystalline Si nanowires (NWs) decorated with arbitrarily shaped Si nanocrystals (NCs) have been fabricated by a silver assisted wet chemical etching method. Scanning electron microscopy and transmission electron microscopy are performed to measure the dimensions of the Si NWs as well as the Si NCs. A strong broad band and tunable visible (2.2 eV) to near-infrared (1.5 eV) photoluminescence (PL) is observed from these Si NWs at room temperature (RT). Our studies reveal that the Si NCs are primarily responsible for the 1.5-2.2 eV emission depending on the cross-sectional area of the Si NCs, while the large diameter Si/SiOx NWs yield distinct NIR PL consisting of peaks at 1.07, 1.10 and 1.12 eV. The latter NIR peaks are attributed to TO/LO phonon assisted radiative recombination of free carriers condensed in the electron-hole plasma in etched Si NWs observed at RT for the first time. Since the shape of the Si NCs is arbitrary, an analytical model is proposed to correlate the measured PL peak position with the cross-sectional area (A) of the Si NCs, and the bandgap (E(g)) of nanostructured Si varies as E(g) = E(g) (bulk) + 3.58 A(-0.52). Low temperature PL studies reveal the contribution of non-radiative defects in the evolution of PL spectra at different temperatures. The enhancement of PL intensity and red-shift of the PL peak at low temperatures are explained based on the interplay of radiative and non-radiative recombinations at the Si NCs and Si/SiO(x) interface. Time resolved PL studies reveal bi-exponential decay with size correlated lifetimes in the range of a few microseconds. Our results help to resolve a long standing debate on the origin of visible-NIR PL from Si NWs and allow quantitative analysis of PL from arbitrarily shaped Si NCs. PMID:24394591

  12. Facile synthesis and photoluminescence characteristics of blue-emitting nitrogen-doped graphene quantum dots.

    PubMed

    Gu, Jian; Zhang, Xiaoping; Pang, Aimin; Yang, Jun

    2016-04-22

    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. PMID:26964866

  13. 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.

  14. Exciton photoluminescence in strained and unstrained ZnSe under hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Tuchman, Judah A.; Kim, Sangsig; Sui, Zhifeng; Herman, Irving P.

    1992-11-01

    Near-band-gap photoluminescence (PL) from exciton recombination in bulk crystalline ZnSe and in strained and strain-relaxed ZnSe epilayers grown on GaAs substrates is examined for pressures up to 80 kbar at 9 K in a diamond-anvil cell. The small sublinear dependence of PL energy with pressure for bulk ZnSe is attributed to the pressure dependence of the bulk modulus. In the strained ZnSe film, the change in biaxial strain with pressure is seen by the changing separation of the heavy- and light-hole exciton peaks. The heavy-hole exciton energy goes from being 12.5 meV below that of the light hole (1 bar), to the same energy as the light hole (~29 kbar), to relatively higher enegy (>29 kbar) as pressure is increased, which shows that the strain in the ZnSe film has been tuned from being compressive to tensile. In contrast, PL suggests that strain-relaxed films slip when pressure is applied. The hydrostatic deformation potential for near-band-gap transitions in ZnSe is a=-4.37 eV, while ||a|| is unexpectedly larger for transitions associated with deep levels. There is evidence that the tetragonal deformation potential b is a function of either volume deformation or strain.

  15. Photoluminescence of GaN Film Exposed to Chlorine-Containing Plasma

    NASA Astrophysics Data System (ADS)

    Ogawa, Daisuke; Banno, Yoshitsugu; Nakano, Yoshitaka; Nakamura, Keiji

    2015-09-01

    Gallium nitride (GaN) has been an attractive semiconductor material for the application to not only light emitting diodes, but also high power devices. The advantage of the material is that it can be fabricated to maximize the number density of devices a single wafer. In our current technology, we mainly utilize low-temperature plasma for dry etching. In fact, GaN generally requires chlorine-containing plasma for chemical etching. However, the use of plasma has a drawback that can induce unwanted changes on the fabricating devices in some conditions. This is called as plasma-induced damage (PID). We have so far monitored the development of PIDs with photoluminescence (PL) emitted from the GaN surface during argon plasma process. In this time, we exposed a GaN film to chlorine-containing plasma and monitored the PID development. Our PL measurements show that the chlorine-containing plasma almost gave no change in PL property of GaN, while argon plasma gave drastic changes. This is because the speed of etching by chlorine species was faster than the speed of damage creations by plasma. In this presentation, we will show further results of this experiment along with some analyses for the purpose of industrial application.

  16. Superbroadband near-IR photoluminescence from Pr3+-doped fluorotellurite glasses.

    PubMed

    Zhou, Bo; Tao, Lili; Tsang, Yuen H; Jin, Wei; Pun, Edwin Yue-Bun

    2012-02-13

    Praseodymium(Pr3+)-doped fluorotellurite glasses were synthesized and broadband photoluminescence (PL) covering a wavelength range from 1.30 to 1.67 μm was observed under both 488 and 590 nm wavelength excitations. The broadband PL emission is mainly due to the radiative transition from the manifolds Pr3+: 1D2 to 1G4. The PL line-shape, band width, and lifetime were modified by the Pr3+ dopant concentration, and a quantum efficiency as high as 73.7% was achieved with Pr3+ dopant in a low concentration of 0.05 mol%. The good spectroscopic properties were also predicted by the Judd-Ofelt analysis, which indicates a stronger asymmetry and covalent bonding between the Pr3+ sites and the matrix lifgand field. The large stimulated emission cross-section, long measured lifetime, and broad emission bandwidth confirm the potential of the Pr3+-singly doped fluorotellurite glass as broadband luminescence sources for the broadband near-infrared optical amplifications and tunable lasers. PMID:22418137

  17. Study of stoichiometry in mercuric iodide by low-temperature photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Bao, Xue J.; James, Ralph B.; Hung, C.-Y.; Schlesinger, Tuviah E.; Cheng, A. Y.; Ortale, Carol; van den Berg, Lodewijk

    1993-02-01

    Low temperature (4.2 K) photoluminescence spectroscopy (PL) measurements were performed on mercuric iodide (HgI(subscript 2)) crystals that were surface-doped with either iodine or mercury. Two methods of treatment were used to achieve the surface doping. The first is the direct immersion of HgI(subscript 2) samples into potassium iodide (KI) aqueous solution saturated with iodine or immersion into elemental mercury liquid. The second is the storage of HgI(subscript 2) crystals under either iodine or mercury vapor. Certain features in the PL spectra were correlated with the stoichiometry of the HgI(subscript 2/ crystals modified by the surface doping. It was also found that if HgI(subscript 2) was exposed to air, an iodine deficient surface layer would form within a one-day period due to the preferential loss of iodine. Finally, the behavior of a broad emission band in the PL spectra and its implication in the fabrication of high quality HgI(subscript 2) nuclear detector is discussed.

  18. Effect of Water Adsorption on the Photoluminescence of Silicon Quantum Dots.

    PubMed

    Yang, Jinrong; Fang, Haiping; Gao, Yi

    2016-05-19

    The optical properties of silicon quantum dots (Si QDs) are strongly influenced by circumjacent surface-adsorbed molecules, which would highly affect their applications; however, water, as the ubiquitous environment, has not received enough attention yet. We employed the time-dependent density functional calculations to investigate the water effect of photoluminescence (PL) spectra for Si QDs. In contrast with the absorption spectra, PL spectra exhibit distinct characteristics. For Si32H38, PL presents the single maximum in the dry and humid environment, while the emission spectrum displays a dual-band fluorescence spectroscopy in the low-humidity environment. This phenomenon is also observed in the larger Si QDs. The distinct character in spectroscopy is dominated by the stretching of the Si-Si bond, which could be explained by the self-trapped exciton model. Our results shed light on the Si-water interaction that is important for the development of optical devices based on Si-coated surfaces. PMID:27117881

  19. 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.

  20. 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.

  1. 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.

  2. Photoluminescence Studies of ZnSe Starting Materials and Vapor Grown Bulk Crystals

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Feth, S.; Wang, Ling Jun; Lehoczky, S. L.

    2001-01-01

    Low-temperature photoluminescence (PL) spectra were measured on ZnSe starting materials provided by various vendors and on bulk crystals grown from these starting materials by physical vapor transport (PVT) to study the effects of purification and contamination during PVT process. The impurity levels in one set of starting material/grown crystal were also measured by glow discharge mass spectroscopy (GDMS). The purification effect of pre-growth heat treatments and the PVT process is evidenced from the GDMS results which showed orders of magnitude reduction in the Li and Na concentration and a factor of 3 reduction in the O content after growth. The PL spectra showed that the strong emissions associated with Li (or Na) in one of the starting materials disappeared after growth. The GDMS results also showed increases in the At and Si contents by orders of magnitude after growth. To evaluate the contamination of the crystal during the high temperature growth process, three growth runs were processed using similar growth parameters but different furnace environments. The PL spectra suggest that the At contamination originated from the fused silica ampoule and that the Inconel cartridge might have been the cause of the broad Cu green and Cu red bands observed in one of the grown crystals.

  3. Photoluminescence Studies of ZnSe Starting Materials and Vapor Grown Bulk Crystals

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Feth, Shari; Wang, Ling Jun; Lehoczky, Sandor L.

    1999-01-01

    Low-temperature photoluminescence (PL) spectra and glow discharge mass spectroscopy (GDMS) were measured on ZnSe starting materials provided by various vendors and on bulk crystals grown from these starting materials by physical vapor transport (PVT) to study the effects of purification and contamination during crystal growth process. The purification effect of pre-growth heat treatments and the PVT process is evidenced from the GDMS results which showed orders of magnitude reduction in the Li and Na concentration and a factor of 3 reduction in the 0 content after growth. The PL spectra showed that the strong emissions associated with Li (or Na) in one of the starting materials disappeared after growth. To evaluate the contamination of the crystal during the high temperature growth process three growth runs were processed using similar growth parameters but with different furnace environments. The GDMS results showed orders of magnitude increase in the Al and Si contents after growth. The PL spectra suggest that the Al contamination was originated from the fused silica ampoule and the Inconel cartridge might have been the cause for the broad Cu green and Cu red bands observed in one of the grown crystal.

  4. Influence of Eu doping on the microstructure and photoluminescence of CdS nanocrystals

    NASA Astrophysics Data System (ADS)

    Zhang, Kexin; Yu, Yaxin; Sun, Shuqing

    2012-07-01

    The CdS:Eu nanocrystals with a strong white emission have been synthesized by solvothemal method using ethylene glycol as solvents. From X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analysis it was observed that the average diameter of the CdS:Eu nanocrystals is about 5 nm. The traces of groups adsorbed on CdS:Eu nanocrystals were confirmed via FT-IR spectra. UV-visible spectroscopy study was carried out to determine the band gap of the nanocrystals and the absorbance peaks showed blue shift with respect to the bulk CdS. From photoluminescence (PL) studies at λex = 398 nm, the PL emission intensity of CdS:Eu nanocrystals enhanced by doping Eu3+ ions. In addition, the synthesis parameters including the concentration of doped Eu3+ ions, the reaction time, and the reaction temperature have influence on the optical properties of CdS:Eu nanocrystals. The charge compensation agent is a decisive factor for PL emission intensity of CdS:Eu nanocrystals. Furthermore, the storage time and condition on the fluorescence of CdS:Eu nanocrystals were also investigated.

  5. Photoreflectance and photoluminescence study of localization effects in GaAsBi alloys

    NASA Astrophysics Data System (ADS)

    Fitouri, H.; Essouda, Y.; Zaied, I.; Rebey, A.; El Jani, B.

    2015-04-01

    Photoreflectance (PR) and photoluminescence (PL) spectra of GaAs1-xBix alloys grown by metalorganic vapor phase epitaxy, for x up to 4.8%, were measured at temperatures ranging from 12 to 300 K. The PR signal shifts due to the temperature change decreases with increasing Bi content of GaAsBi alloys. For temperature below 100 K, a dominant peak in PL spectra of GaAsBi was observed. This peak is attributed to carrier localization resulting from Bi-related localized states in GaAsBi. A decrease in PR signal has been also found when the temperature was lowered. This behavior is attributed to a weakening of modulation efficiency, which is induced by carrier localization that has been evidenced in low temperature PL. The localized state emission partly contributes to the decrease in the band gap energy shift. In addition, at high temperatures the small PR signal shift is due to the reduction in the temperature dependence of the band gap energy. The analysis of the band gap energy evolution with temperature using the Bose-Einstein statistical expression shows that the average phonon energy is much larger than that expected from the linear interpolation between GaAs and GaBi. This fact is related to the interaction between electrons and phonons localized at Bi atoms playing an important role in the reduction of the temperature dependence of the band gap energy of GaAsBi alloys.

  6. 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. PMID:27255897

  7. 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

  8. 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

  9. 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.

  10. Enhancement of Charge Transfer and Quenching of Photoluminescence of Capped CdS Quantum Dots

    PubMed Central

    Mehata, Mohan Singh

    2015-01-01

    Quantum dots (Q-dots) of cadmium sulfide (CdS) with three different capping ligands, 1-butanethiol (BT), 2-mercaptoethanol (ME) and benzyl mercaptan (BM) have been investigated. An external electric field of variable strength of 0.2–1.0 MV cm−1 was applied to the sample of capped CdS Q-dots doped in a poly(methyl methacrylate) (PMMA) films. Field-induced changes in optical absorption of capped CdS Q-dots were observed in terms of purely the second-derivative of the absorption spectrum (the Stark shift), indicating an enhancement in electric dipole moment following transition to the first exciton state. The enhancement depends on the shape and size of the Q-dots prepared using different capping ligands. Field induced-change in photoluminescence (PL) reveals similar changes, an enhancement in charge-transfer (CT) character in exciton state. PL of capped CdS Q-dots is significantly quenched in presence of external electric field. The strong field-induced quenching occurs as a result of the increased charge separation resulting exciton dissociation. Thus, understanding the CT character and field-induced PL quenching of CdS Q-dots is important for photovoltaic, LEDs and biological applications. PMID:26166553

  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. 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

  13. 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.

  14. Shock-induced phase transition on Y2O3:Eu3+ studied by photoluminescence

    NASA Astrophysics Data System (ADS)

    Kishimura, Hiroaki; Hamada, Sho; Aruga, Atsushi; Matsumoto, Hitoshi

    2015-06-01

    A series of shock-recovery experiments on Y2O3:Eu3+ powder was carried out by the impact of a flyer plate accelerated by a single-stage powder-propellant gun. 5.038-g of samples were pressed into copper capsules at 63% of the theoretical maximum density (TMD) of the powder. The recovered samples were characterized by X-ray diffraction (XRD) analysis, Raman spectroscopy, and photoluminescence (PL) spectroscopy. The XRD, Raman, and PL results of samples shocked at pressures of 13 GPa indicated that a phase transition from a cubic phase (C-type) to a monoclinic phase (B-type) occurred. The recovered samples shocked at 21 and 25 GPa consisted of Y2O3:Eu3+ with the C-type and the B-type. Although the sample shocked at pressures of 35 GPa was consisted of the C-type and the B-type, proportion of the B-type derived from the XRD peaks decreased and no PL peaks from the B-type were observed. For recovered samples shocked at pressures of 48 GPa and above, no signatures of the B-type were obtained. These results indicated that the shock-induced phase transition were the partial completion of the phase transition.

  15. Anomalous temperature dependence of charged exciton photoluminescence polarization in monolayer WS2

    NASA Astrophysics Data System (ADS)

    Hanbicki, A. T.; Kioseoglou, G.; Currie, M.; Hellberg, C. S.; Friedman, A. L.; McCreary, K. M.; Jonker, B. T.

    2015-03-01

    Monolayer WS2 is a direct-gap transition metal dichalcogenide semiconductor. Its low-dimensional hexagonal structure leads to two inequivalent K-points in the Brillioun zone. The valley index and spin are intrinsically coupled with spin-dependent selection rules that enable populating and interrogating each valley using circularly polarized light. Here, we probe the degree of circular polarization of the emitted photoluminescence (PL) as function of the photo-excitation energy and temperature to elucidate spin-dependent inter- and intra-valley relaxation mechanisms. Monolayer WS2 flakes have PL emission from the free and charged exciton near 2.0 eV. We reproducibly isolate these excitons via appropriate sample preparation. With excitation using positive helicity light, we analyze the PL for positive and negative helicities to determine polarization. Unlike MoS2, we measure significant polarization from the charged exciton for high excitation energies, even at room temperature. There is also an enhancement of polarization of the charged exciton at intermediate temperatures. We discuss the polarization behavior in terms of phonon assisted intervalley scattering processes. This work was supported by internal programs at NRL and the NRL Nanoscience Institute.

  16. Two Color DNA Barcode Detection in Photoluminescence Suppressed Silicon Nitride Nanopores

    PubMed Central

    2015-01-01

    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

  17. 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

  18. 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.

  19. 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

  20. Suppression of UV photoluminescence in sandwich-structured Si/C composite films

    NASA Astrophysics Data System (ADS)

    Zhu, Y.; Yuan, C. L.; Liu, R.; Ong, P. P.

    2002-10-01

    Thin films of composite silicon/carbon (Si/C) were prepared by pulsed-laser ablation alternately on C and Si materials on a rotary target, followed by vacuum deposition of the ablated materials on an ultra-clean glass substrate. The film structure consisted of alternate nanolayers of Si nanocrystals and amorphous C, with a fairly sharp demarcation boundary between adjacent layers forming well-defined sandwich structures. At room temperature, this composite nanolayered structure was found to yield much lower photoluminescent (PL) emission in the ultra violet region (300 390 nm) in comparison with that obtained for pure Si or for Si/Al2O3 thin films (see Zhu Y., Wang H. and Ong P. P. J. Phys. D, 33 (2000) 1965, and Zhu Y. and Ong P. P. J. Phys. Condens. Matter, 13 (2001) L1). The suppression mechanism of the UV PL emission appeared to occur in the interfacial surfaces between adjacent crystalline Si and amorphous C layers. It provides a possible way to selectively filter out the usually undesirable UV component of the PL emission from the silicon nanoparticles.

  1. Photoluminescence from the Wigner Crystal.

    NASA Astrophysics Data System (ADS)

    Kodiyalam, S.; Fertig, H. A.; Das Sarma, S.

    1997-03-01

    We calculate within the harmonic approximation and first order time dependent perturbation theory the line shape of the photoluminescence spectrum corresponding to the recombination of an electron from a 2-d Wigner crystal with a hole bound to an acceptor atom. The recombination process is modeled as a sudden perturbation of the Hamiltonian for the x-y degrees of freedom of the electrons. Using the theoretical results of Dodonov and Manko, (Proc. Lebedev Phys. Inst., 183), 263 (1987) we are able to include in the perturbation, in addition to changes in the equilibrium positions of electrons, changes in the curvatures of the harmonically approximated potential. The computed line shapes are similar to that seen in a recent experiment by Kukushkin (I.V. Kukushkin, V.I. Falko, R.J. Haug, K. von Klitzing, K. Eberl and K. Totemayer, Phys. Rev. Lett. 72), 3594 (1994) et al - they have a faster rising as compared to the falling edge. However, for recombination processes beginning with the perfect Wigner lattice the spectral width is only ~ frac1 3 of that observed in experiment^3 whereas inclusion of disorder due to already recombined electrons results in the width being greater than in the experiment^3 by a factor of ~ 3. We speculate on the possible mechanisms that may lead to better agreement with experiment.

  2. Photoluminescence from the Wigner Crystal.

    NASA Astrophysics Data System (ADS)

    Kodiyalam, S.; Price, R.; Fertig, H. A.; Das Sarma, S.

    1996-03-01

    Motivated by recent experiments on radiative recombination of two-dimensional electrons in acceptor δ-doped GaAs/AlGaAs heterojunctions (I.V. Kukushkin, V.I. Falko, R.J. Haug, K. von Klitzing, K. Eberl and K. Totemayer, Phys. Rev. Lett. 72), 3594 (1994) as well as the success of a harmonic solid model (P. Johansson and J.M. Kinaret, Phys. Rev. Lett. 71), 1435 (1993) in describing tunneling between two-dimensional electron systems, we calculate within the harmonic approximation and sudden perturbation theory the photoluminescence spectrum from the recombination process. The potential for both the perturbed and unperturbed hamiltonians is computed using a recent algorithm for molecular dynamics which is expected to result in the classical ground state. (V.A. Schweigert and F.M. Peeters, Phys. Rev. B 51), 7700 (1995) Using the theoretical results of Dodonov and Manko (Proc. Lebedev Phys. Inst., 183), 263 (1987), we are able to include in the perturbation, in addition to changes in the equilibrium positions of electrons, changes in curvatures of the potential. Supported by NSF and the U.S. ONR

  3. Radiation damage to Kokchetav UHPM diamonds in zircon: Variations in Raman, photoluminescence, and cathodoluminescence spectra

    NASA Astrophysics Data System (ADS)

    Shimizu, Rentaro; Ogasawara, Yoshihide

    2014-10-01

    We conducted detailed in-situ Raman, photoluminescence (PL) and cathodoluminescence (CL) studies on microdiamonds in a tourmaline-rich quartzofeldspathic rock from the Kokchetav Massif, Kazakhstan. The microdiamonds occur as inclusions in the cores of K-tourmaline and in zoned zircons with varying U contents. The results of 2D Raman mapping of zircon showed that the U-rich parts were more metamictized than the U-poor parts. All the diamonds showed a strong Raman band at approximately 1332 cm- 1, however, the features of the Raman bands were distinctly different depending on the host minerals. On the one hand, diamonds in tourmaline had a sharp Raman band that is similar to that of kimberlite diamonds [full width at half maximum (FWHM): 2-3 cm- 1]. On the other hand, diamonds in zircon had a broad and downshifted band compared to those in tourmaline. In particular, diamonds in U-rich cores of zircons (up to 0.15 wt.% UO2) showed broader and more downshifted Raman bands (FWHMs and peak positions varied up to 9.3 cm- 1 and 1328 cm- 1, respectively), with additional small bands at approximately 1490 cm- 1 and 1630 cm- 1. A negative correlation was observed between the peak position and the FWHM of the principal Raman band of microdiamonds. Furthermore, the PL and CL spectra showed systematic variations. Diamonds in zircons with low to moderate U-concentrations had very strong PL and CL compared to diamonds in U-rich zircons and in tourmalines. Several characteristic peaks appeared in the PL and CL spectra, indicating the presence of irradiation and/or nitrogen-related point defects in the diamonds. PL and CL of microdiamonds in high-U zircon were weak, but still showed irradiation-related peaks. The relationship between the occurrence of microdiamonds (i.e., corresponding to the estimated total α-dose since crystallization) and the Raman, PL, and CL spectral characteristics of microdiamonds strongly suggests that radiation damage predominantly caused by

  4. 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.

  5. Novel Polymer Linkers for Single Molecule AFM Force Spectroscopy

    PubMed Central

    Tong, Zenghan; Mikheikin, Andrey; Krasnoslobodtsev, Alexey; Lv, Zhengjian; Lyubchenko, Yuri L.

    2013-01-01

    Flexible polymer linkers play an important role in various imaging and probing techniques that require surface immobilization, including atomic force microscopy (AFM). In AFM force spectroscopy, polymer linkers are necessary for the covalent attachment of molecules of interest to the AFM tip and the surface. The polymer linkers tether the molecules and provide their proper orientation in probing experiments. Additionally, the linkers separate specific interactions from nonspecific short-range adhesion and serve as a reference point for the quantitative analysis of single molecule probing events. In this report, we present our results on the synthesis and testing of a novel polymer linker and the identification of a number of potential applications for its use in AFM force spectroscopy experiments. The synthesis of the linker is based on the well-developed phosphoramidate (PA) chemistry that allows the routine synthesis of linkers with predetermined lengths and PA composition. These linkers are homogeneous in length and can be terminated with various functional groups. PA linkers with different functional groups were synthesized and tested in experimental systems utilizing different immobilization chemistries. We probed interactions between complementary DNA oligonucleotides; DNA and protein complexes formed by the site-specific binding protein SfiI; and interactions between amyloid peptide (Aβ42). The results of the AFM force spectroscopy experiments validated the feasibility of the proposed approach for the linker design and synthesis. Furthermore, the properties of the tether (length, functional groups) can be adjusted to meet the specific requirements for different force spectroscopy experiments and system characteristics, suggesting that it could be used for a large number of various applications. PMID:23624104

  6. MOS-based nanocapacitor using C-AFM

    NASA Astrophysics Data System (ADS)

    Hill, Daniel; Sadewasser, Sascha; Aymerich, Xavier

    2003-04-01

    This report details the attempts made to realise nanocapacitors for nanoscale MOS based integrated circuits by AFM anodic oxidation, and therefore isolation, of nano-sized squares of poly-silicon, titanium and aluminium on Si/SiO2. Conductive AFM (C-AFM) was used to perform topographical and electrical characterisation. The experiments were performed with contact mode C-AFM, in ambient air, using Pt-Ir, Co-Cr and Ti coated (20nm) n-type silicon cantilevers. Each sample consisted of a 3-5nm thick conductor deposited on 6nm of SiO2, which was thermally grown on Phosphorus doped (1019 cm-3) n-type Si(100) substrates. Standard cleaning and passivation processes were used. Poly-silicon was immediately found to be too rough to oxidise. Initial current-voltage measurements inside of the titanium-oxide squares suggest initial isolation followed by degradation through Fowler-Nordheim tunnelling. Measurement inconsistencies seen suggest charge storage on the surface or tip with the barrier height of the native titanium oxide thought to be responsible. Al has a thicker natural oxide. To overcome this we designed a series of structures consisting of a Ti finger on SiO2, that is connected to a Ti bond pad, allowing direct probing by a semiconductor parameter analyser. AFM anodic oxidation was performed upon these Ti fingers to reduce their in-plane dimensions towards the nanoscale. To confirm the existence of a nanocapacitor topographical and electrical measurements were then done on and around them.

  7. 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

  8. 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.

  9. Interference effects in photoluminescence spectra of Cu2ZnSnS4 and Cu(In,Ga)Se2 thin films

    NASA Astrophysics Data System (ADS)

    Larsen, J. K.; Li, S.-Y.; Scragg, J. J. S.; Ren, Y.; Hägglund, C.; Heinemann, M. D.; Kretzschmar, S.; Unold, T.; Platzer-Björkman, C.

    2015-07-01

    Photoluminescence (PL) is commonly used for investigations of Cu2ZnSnS(e)4 [CZTS(e)] and Cu(In,Ga)Se2 (CIGS) thin film solar cells. The influence of interference effects on these measurements is, however, largely overlooked in the community. Here, it is demonstrated that PL spectra of typical CZTS absorbers on Mo/glass substrates can be heavily distorted by interference effects. One reason for the pronounced interference in CZTS is the low reabsorption of the PL emission that typically occurs below the band gap. A similar situation occurs in band gap graded CIGS where the PL emission originates predominantly from the band gap minimum located at the notch region. Based on an optical model for interference effects of PL emitted from a thin film, several approaches to reduce the fringing are identified and tested experimentally. These approaches include the use of measured reflectance data, a calculated interference function, use of high angles of incidence during PL measurements as well as the measurement of polarized light near the Brewster angle.

  10. Genetic factors required to maintain repression of a paramutagenic maize pl1 allele.

    PubMed Central

    Hollick, J B; Chandler, V L

    2001-01-01

    A genetic screen identified two novel gene functions required to maintain mitotically and meiotically heritable gene silencing associated with paramutation of the maize purple plant 1 (pl1) locus. Paramutation at pl1 leads to heritable alterations of pl1 gene regulation; the Pl-Rhoades (Pl-Rh) allele, which typically confers strong pigmentation to juvenile and adult plant structures, changes to a lower expression state termed Pl'-mahogany (Pl'). Paramutation spontaneously occurs at low frequencies in Pl-Rh homozygotes but always occurs when Pl-Rh is heterozygous with Pl'. We identified four mutations that caused increased Pl' pigment levels. Allelism tests revealed that three mutations identified two new maize loci, required to maintain repression 1 (rmr1) and rmr2 and that the other mutation represents a new allele of the previously described mediator of paramutation 1 (mop1) locus. RNA levels from Pl' are elevated in rmr mutants and genetic tests demonstrate that Pl' can heritably change back to Pl-Rh in rmr mutant individuals at variable frequencies. Pigment levels controlled by two pl1 alleles that do not participate in paramutation are unaffected in rmr mutants. These results suggest that RMR functions are intimately involved in maintaining the repressed expression state of paramutant Pl' alleles. Despite strong effects on Pl' repression, rmr mutant plants have no gross developmental abnormalities even after several generations of inbreeding, implying that RMR1 and RMR2 functions are not generally required for developmental homeostasis. PMID:11139517

  11. Allelic Interactions Heritably Alter the Activity of a Metastable Maize Pl Allele

    PubMed Central

    Hollick, J. B.; Patterson, G. I.; Coe-Jr., E. H.; Cone, K. C.; Chandler, V. L.

    1995-01-01

    The maize pl locus encodes a transcriptional activator of anthocyanin biosynthetic genes. The Pl-Rhoades (Pl-Rh) allele confers robust purple anthocyanin pigment in several tissues. Spontaneous derivatives of Pl-Rh, termed Pl'-mahogany (Pl'-mah), arise that confer reduced pigment and are meiotically heritable. These derivatives influence other Pl-Rh alleles such that only Pl'-mah alleles are transmitted from a Pl-Rh/Pl'-mah heterozygote. Genetic crosses establish that chromosomal segregation distortion does not explain this exclusive transmission and suggest that Pl-Rh invariably changes to Pl'-mah when exposed to Pl'-mah. Such behavior is a hallmark of paramutation. Cosegregation experiments demonstrate that this paramutagenic activity is genetically linked to the pl locus. By visually quantifying pl action through successive crosses, we find that phenotypic expression is inversely related to paramutagenic strength. In addition, the paramutagenic state is metastable; reversion to a nonparamutagenic Pl-Rh state can occur. The behavior of Pl-Rh is unique, yet it shares characteristics with paramutation at two other maize loci, b and r. Previous analysis of b and r paramutation revealed extensive differences and led to suggestions of distinct molecular mechanisms. Consideration of the common features of all three systems reinvigorates the interpretation that the mechanistic processes of these three allelic interactions are similar. PMID:8647404

  12. Comparison of long-term outcome between anti-Jo1- and anti-PL7/PL12 positive patients with antisynthetase syndrome.

    PubMed

    Marie, I; Josse, S; Decaux, O; Dominique, S; Diot, E; Landron, C; Roblot, P; Jouneau, S; Hatron, P Y; Tiev, K P; Vittecoq, O; Noel, D; Mouthon, L; Menard, J-F; Jouen, F

    2012-08-01

    The aims of the present study were to: compare the characteristics between antisynthetase syndrome (ASS) patients with anti-Jo1 antibody and those with anti-PL7/PL12 antibody. The medical records of 95 consecutive patients with ASS were reviewed. Seventy-five of these patients had anti-Jo1 antibody; the other patients had anti-PL7 (n=15) or anti-PL12 (n=5) antibody. At ASS diagnosis, the prevalence of myalgia (p=0.007) and muscle weakness (p=0.02) was significantly lower in the group of anti-PL7/PL12-positive patients than in those with anti-Jo1 antibody; median value of CK (p=0.00003) was also lower in anti-PL7/PL12 patients. Anti-Jo1 positive patients developed more rarely myositis resolution (21.3% vs. 46.2%); in addition, the overall recurrence rate of myositis was higher in anti-Jo1 positive patients than in patients with anti-PL7/PL12 antibody (65.9% vs. 19.4%). Anti-Jo1-positive patients, compared with those with anti-PL7/PL12 antibody, more often experienced: joint involvement (63.3%vs. 40%) and cancer (13.3% vs. 5%). By contrast, anti-PL7/PL12 positive patients, compared with those with anti-Jo1 antibody, more commonly exhibited: ILD (90% vs. 68%); in anti-PL7/PL12 positive patients, ILD was more often symptomatic at diagnosis, and led more rarely to resolution of lung manifestations (5.6% vs. 29.4%). Finally, the group of anti-PL7/PL12 positive patients more commonly experienced gastrointestinal manifestations related to ASS (p=0.02). Taken together, although anti-Jo1 positive patients with ASS share some features with those with anti-PL7/PL12 antibody, they exhibit many differences regarding clinical phenotype and long-term outcome. Our study underscores that the presence of anti-Jo1 antibody results in more severe myositis, joint impairment and increased risk of cancer. On the other hand, the presence of anti-PL7/PL12 antibody is markedly associated with: early and severe ILD, and gastrointestinal complications. Thus, our study interestingly indicates

  13. 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

  14. Enhancement of photoluminescence from n-type tensile-strained GeSn wires on an insulator fabricated by lateral liquid-phase epitaxy

    NASA Astrophysics Data System (ADS)

    Shimura, Takayoshi; Matsue, Masahiro; Tominaga, Kohei; Kajimura, Keiko; Amamoto, Takashi; Hosoi, Takuji; Watanabe, Heiji

    2015-11-01

    We investigated the optical properties of undoped and n-type GeSn wires fabricated by a lateral liquid-phase epitaxial method. The Sn concentration was approximately 0.5% in the region from the seed to near the wire end. Moreover, the Sn concentration increased to 6% at the wire end, whereas Si diffusion from the seed was enhanced and extended to 200 μm from the seed. Tensile strain gradually decreased from 0.5% close the seed to 0.25% at the wire end. The photoluminescence (PL) peak was red-shifted by Sn incorporation into the Ge wires, and a PL peak at 0.66 eV was observed from the wire end. Upon n-type doping, the PL intensity of the GeSn layers was significantly enhanced to approximately 10 times higher than that of the undoped GeSn wires.

  15. The 1.54-{mu}m photoluminescence from an (Er, Ge) co-doped SiO{sub 2} film deposited on Si by rf magnetron sputtering

    SciTech Connect

    Heng, C.L.; Finstad, T.G.; Storaas, P.; Li, Y.J.; Gunnaes, A.E.; Nilsen, O.

    2004-11-08

    In this work, we report on quite strong 1.54-{mu}m photoluminescence (PL) from an (Er, Ge) co-doped SiO{sub 2} film deposited by rf magnetron sputtering. The PL intensity reaches a maximum value after the film is annealed at 700 deg. C for 30 min in N{sub 2}. High-resolution transmission electron microscopy observation, together with energy dispersive x-ray spectroscopy analysis, indicates that amorphous Ge-rich nanoclusters precipitate in the film after 700 deg. C annealing. X-ray diffraction shows the presence of Ge nanocrystals after 900 deg. C annealing, and increasing Ge nanocrystal size with increasing annealing temperature up to 1100 deg. C. The results suggest that the amorphous Ge-rich nanoclusters are more effective than Ge nanocrystals in exciting the Er{sup 3+} PL.

  16. 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

  17. STM and AFM; Which is Better for Surface Structural Analysis? Non- contact AFM Studies on Ge/Si(105) Surface

    NASA Astrophysics Data System (ADS)

    Hasegawa, Yukio

    2006-03-01

    Scanning tunneling microscopy (STM) has been utilized to determine surface atomic structure with its highly resolved images. Probing surface electronic states near the Fermi energy (EF), STM images, however, do not necessarily represent the atomic structure of surfaces. It has been believed that atomic force microscopy (AFM) provides us surface topographic images without being disturbed by the electronic states. In order to prove the surpassing performance, we performed noncontact (nc) AFM on the Ge/Si(105) surface [1], which is a facet plane of the ?hut? clusters formed on Ge-deposited Si(001) surface. It is found that STM images taken on the surface, either filled- or empty-state images, do not show all surface atoms because of the electronic effect; some surface atoms have dangling bond states below EF and other surface atoms have states above EF. [2]. In a nc-AFM image, on the other hand, all surface atoms having a dangling bond are observed [3], directly representing an atomic structure of the surface. Electronic information can also be obtained in AFM by using a Kelvin-probe method. From atomically resolved potential profile we obtained, charge transfer among the dangling bond states is directly demonstrated. These results clearly demonstrate that highly-resolved nc-AFM with a Kelvin-probe method is an ideal tool for analysis of atomic structures and electronic properties of surfaces. This work was done in collaboration with T. Eguchi, K. Akiyama, T. An, and M. Ono, ISSP, Univ. Tokyo and JST, Y. Fujikawa and T. Sakurai, IMR. Tohoku Univ. T. Hashimoto, AIST, Y. Morikawa, ISIR, Osaka Univ. K. Terakura, Hokkaido Univ., and M.G. Lagally, University of Wisconsin-Madison. [1] T. Eguchi et al., Phys. Rev. Lett. 93, 266102 (2004). [2] Y. Fujikawa et al., Phys. Rev. Lett. 88, 176101 (2002). [3] T. Eguchi and Y. Hasegawa, Phys. Rev. Lett. 89, 256105 (2002)

  18. 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

  19. 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.

  20. 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.