Science.gov

Sample records for ga co-doping effect

  1. Enhanced stability of Eu in GaN nanoparticles: Effects of Si co-doping

    SciTech Connect

    Kaur, Prabhsharan; Sekhon, S. S.; Zavada, J. M.; Kumar, Vijay

    2015-06-14

    Ab initio calculations on Eu doped (GaN){sub n} (n = 12, 13, and 32) nanoparticles show that Eu doping in nanoparticles is favorable compared with bulk GaN as a large fraction of atoms lie on the surface where strain can be released compared with bulk where often Eu doping is associated with a N vacancy. Co-doping of Si further facilitates Eu doping as strain from an oversized Eu atom and an undersized Si atom is compensated. These results along with low symmetry sites in nanoparticles make them attractive for developing strongly luminescent nanomaterials. The atomic and electronic structures are discussed using generalized gradient approximation (GGA) for the exchange-correlation energy as well as GGA + U formalism. In all cases of Eu (Eu + Si) doping, the magnetic moments are localized on the Eu site with a large value of 6μ{sub B} (7μ{sub B}). Our results suggest that co-doping can be a very useful way to achieve rare-earth doping in different hosts for optoelectronic materials.

  2. Enhanced stability of Eu in GaN nanoparticles: Effects of Si co-doping

    NASA Astrophysics Data System (ADS)

    Kaur, Prabhsharan; Sekhon, S. S.; Zavada, J. M.; Kumar, Vijay

    2015-06-01

    Ab initio calculations on Eu doped (GaN)n (n = 12, 13, and 32) nanoparticles show that Eu doping in nanoparticles is favorable compared with bulk GaN as a large fraction of atoms lie on the surface where strain can be released compared with bulk where often Eu doping is associated with a N vacancy. Co-doping of Si further facilitates Eu doping as strain from an oversized Eu atom and an undersized Si atom is compensated. These results along with low symmetry sites in nanoparticles make them attractive for developing strongly luminescent nanomaterials. The atomic and electronic structures are discussed using generalized gradient approximation (GGA) for the exchange-correlation energy as well as GGA + U formalism. In all cases of Eu (Eu + Si) doping, the magnetic moments are localized on the Eu site with a large value of 6μB (7μB). Our results suggest that co-doping can be a very useful way to achieve rare-earth doping in different hosts for optoelectronic materials.

  3. Effect of Mg2+ ions co-doping on timing performance and radiation tolerance of Cerium doped Gd3Al2Ga3O12 crystals

    NASA Astrophysics Data System (ADS)

    Lucchini, M. T.; Babin, V.; Bohacek, P.; Gundacker, S.; Kamada, K.; Nikl, M.; Petrosyan, A.; Yoshikawa, A.; Auffray, E.

    2016-04-01

    Inorganic scintillators with high density and high light yield are of major interest for applications in medical imaging and high energy physics detectors. In this work, the optical and scintillation properties of Mg co-doped Ce:Gd3Al2Ga3O12 crystals, grown using Czochralski technique, have been investigated and compared with Ce:Gd3Al2Ga3O12 ones prepared with identical technology. Improvements in the timing performance of the Mg co-doped samples with respect to Ce:Gd3Al2Ga3O12 ones have been measured, namely a substantial shortening of the rise time and scintillation decay components and lower afterglow were achieved. In particular, a significantly better coincidence time resolution of 233 ps FWHM, being a fundamental parameter for TOF-PET devices, has been observed in Mg co-doped crystals. The samples have also shown a good radiation tolerance under high doses of γ-rays, making them suitable candidates for applications in harsh radiation environments, such as detectors at future collider experiments.

  4. Colossal Dielectric Behavior of Ga+Nb Co-Doped Rutile TiO2.

    PubMed

    Dong, Wen; Hu, Wanbiao; Berlie, Adam; Lau, Kenny; Chen, Hua; Withers, Ray L; Liu, Yun

    2015-11-18

    Stimulated by the excellent colossal permittivity (CP) behavior achieved in In+Nb co-doped rutile TiO2, in this work we investigate the CP behavior of Ga and Nb co-doped rutile TiO2, i.e., (Ga(0.5)Nb(0.5))(x)Ti(1-x)O2, where Ga(3+) is from the same group as In(3+) but with a much smaller ionic radius. Colossal permittivity of up to 10(4)-10(5) with an acceptably low dielectric loss (tan δ = 0.05-0.1) over broad frequency/temperature ranges is obtained at x = 0.5% after systematic synthesis optimizations. Systematic structural, defect, and dielectric characterizations suggest that multiple polarization mechanisms exist in this system: defect dipoles at low temperature (∼10-40 K), polaronlike electron hopping/transport at higher temperatures, and a surface barrier layer capacitor effect. Together these mechanisms contribute to the overall dielectric properties, especially apparent observed CP. We believe that this work provides comprehensive guidance for the design of new CP materials. PMID:26512874

  5. Ceria co-doping: synergistic or average effect?

    PubMed

    Burbano, Mario; Nadin, Sian; Marrocchelli, Dario; Salanne, Mathieu; Watson, Graeme W

    2014-05-14

    Ceria (CeO2) co-doping has been suggested as a means to achieve ionic conductivities that are significantly higher than those in singly doped systems. Rekindled interest in this topic over the last decade has given rise to claims of much improved performance. The present study makes use of computer simulations to investigate the bulk ionic conductivity of rare earth (RE) doped ceria, where RE = Sc, Gd, Sm, Nd and La. The results from the singly doped systems are compared to those from ceria co-doped with Nd/Sm and Sc/La. The pattern that emerges from the conductivity data is consistent with the dominance of local lattice strains from individual defects, rather than the synergistic co-doping effect reported recently, and as a result, no enhancement in the conductivity of co-doped samples is observed. PMID:24658460

  6. Sol-gel derived Al-Ga co-doped transparent conducting oxide ZnO thin films

    NASA Astrophysics Data System (ADS)

    Serrao, Felcy Jyothi; Sandeep, K. M.; Bhat, Shreesha; Dharmaprakash, S. M.

    2016-05-01

    Transparent conducting ZnO doped with Al, Ga and co-doped Al and Ga (1:1) (AGZO) thin films were grown on glass substrates by cost effective sol-gel spin coating method. The XRD results showed that all the films are polycrystalline in nature and highly textured along the (002) plane. Enhanced grain size was observed in the case of AGZO thin films. The transmittance of all the films was more than 83% in the visible region of light. The electrical properties such as carrier concentration and mobility values are increased in case of AGZO compared to that of Al and Ga doped ZnO thin films. The minimum resistivity of 2.54 × 10-3 Ω cm was observed in AGZO thin film. The co-doped AGZO thin films exhibited minimum resistivity and high optical transmittance, indicate that co-doped ZnO thin films could be used in transparent electronics mainly in display applications.

  7. Control of selforganized magnetic nanocrystals aggregation in (Ga,Fe)N by co-doping with shallow donors and acceptors

    NASA Astrophysics Data System (ADS)

    Bonanni, A.; Navarro-Quezada, A.; Li, T.; Kiecana, M.; Sawicki, M.; Dietl, T.

    2008-03-01

    A number of possible room temperature functionalities has recently been proposed for magnetically doped semiconductors, in which spinodal decomposition leads to the self-organized formation of coherent ferromagnetic nanodots or nanocolumns [1]. It has also been suggested that the decomposition can be controlled in a wide range by growth conditions and co-doping [2]. We have extended our previous structural and magnetic studies of (Ga,Fe)N [3] by examining the effects of Si and Mg co-doping. As before, we have found the magnetic response to consist of a paramagnetic signal from substitutional Fe and of a ferromagnetic component due to Fe1-xN nanocrystals. Our results demonstrate that the co-doping reduces the fractional concentration of Fe contributing to the nanocrystals. This shows that tuning of the Fermi energy by changing the charge state of the transition metal ions affects their aggregation, as proposed recently [2].1. H.Katayama-Yosida et al., phys.stat. sol. (a) 204, 15 (2007); T.Dietl, arXiv:0711.0343. 2. S.Kuroda et al., Nature Mat. 6, 440 (2007). 3. A.Bonanni et al., Phys. Rev. B 75, 125210 (2007).

  8. Isoelectronic co-doping

    DOEpatents

    Mascarenhas, Angelo

    2004-11-09

    Isoelectronic co-doping of semiconductor compounds and alloys with deep acceptors and deep donors is used to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, N and Bi, to customize solar cells, thermal voltaic cells, light emitting diodes, photodetectors, and lasers on GaP, InP, GaAs, Ge, and Si substrates. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  9. Co-doping effects of Gd and Ag on YBCO films derived by metalorganic deposition

    NASA Astrophysics Data System (ADS)

    Sun, Meijuan; Liu, Zhiyong; Bai, Chuanyi; Guo, Yanqun; Lu, Yuming; Fan, Feng; Cai, Chuanbing

    2015-12-01

    Y1-xGdxBa2Cu3O7-δ-Ag (x = 0, 0.25, 0.5, 0.75, 1) thin films were prepared on oxide buffered Hastelloy substrates by low fluorine metalorganic depostion (MOD) process. The effects of co-doping of Ag and Gd on the microstructures and superconducting properties of YBCO thin films are investigated with respect to improvement on texture and superconducting performance in case of optimized doping content. It is found that optimum addition of Ag and Gd may lead to better c-axis orientation, superior surface microstructure and finally give rise to much improvement of superconducting performance.

  10. The contact and photoconductivity characteristics between Co doped amorphous carbon and GaAs: n-type low-resistivity and semi-insulated high-resistivity GaAs

    NASA Astrophysics Data System (ADS)

    Zhai, Zhangyin; Yu, Hualing; Zuo, Fen; Guo, Chunlian; Chen, Guibin; Zhang, Fengming; Wu, Xiaoshan; Gao, Ju

    2016-06-01

    The Co doped amorphous carbon films (a-C:Co), deposited by pulsed laser deposition, show p-n and ohmic contact characteristics with n-type low resistivity GaAs (L-GaAs) and semi-insulated high-resistivity GaAs (S-GaAs). The photosensitivity enhances for a-C:Co/L-GaAs, while inverse decreases for a-C:Co/S-GaAs heterojunction, respectively. Furthermore, the enhanced photosensitivity for the a-C:Co/L-GaAs/Ag heterojunction also shows deposition temperature dependence behavior, and the optimum deposition temperature is around 500 °C.

  11. Vibrationally induced center reconfiguration in co-doped GaN:Eu, Mg epitaxial layers: Local hydrogen migration vs. activation of non-radiative channels

    SciTech Connect

    Mitchell, B.; Dierolf, V.; Lee, D.; Lee, D.; Fujiwara, Y.

    2013-12-09

    Europium doped gallium nitride (GaN:Eu) is a promising candidate as a material for red light emitting diodes. When Mg was co-doped into GaN:Eu, additional incorporation environments were discovered that show high excitation efficiency at room temperature and have been attributed to the coupling of Mg-H complexes to the majority Eu site. Electron beam irradiation, indirect and resonant (direct) laser excitation were found to modify these complexes, indicating that vibrational energy alone can trigger the migration of the H while the presence of additional charges and excess energy controls the type of reconfiguration and the activation of non-radiative decay channels.

  12. Effects of acceptor-donor complexes on electronic structure properties in co-doped TiO2: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Cai, L. L.; Yuan, X. B.; Hu, G. C.; Ren, J. F.

    2016-07-01

    We theoretically investigate the doping effects induced by impurity complexes on the electronic structures of anatase TiO2 based on the density functional theory. Mono-doping and co-doping effects are discussed separately. The results show that the impurity doping can make the band-edges shift. The induced defect levels in the band gaps by impurity doping reduce the band gap predominantly. The compensated acceptor-donor pairs in the co-doped TiO2 will improve the photoelectrochemical activity. From the calculations, it is also found that (S+Zr)-co-doped TiO2 has the ideal band gap and band edge, at the same time, the binding energy is higher than other systems, so (S+Zr)-co-doping in TiO2 is more promise in photoelectrochemical experiments.

  13. Electrode effects in dielectric spectroscopy measurements on (Nb +In) co-doped TiO2

    NASA Astrophysics Data System (ADS)

    Crandles, David; Yee, Susan; Savinov, Maxim; Nuzhnyy, Dimitri; Petzelt, Jan; Kamba, Stanislav; Prokes, Jan

    Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and ac conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four contact van der Pauw dc conductivity measurements and bulk conductivity values extracted from two contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature. Nserc, Czech Science Foundation (Project 15-08389S).

  14. Magneto-optical spectrum and the effective excitonic Zeeman splitting energies of Mn and Co-doped CdSe nanowires

    SciTech Connect

    Xiong, Wen; Chen, Wensuo

    2013-12-21

    The electronic structure of Mn and Co-doped CdSe nanowires are calculated based on the six-band k·p effective-mass theory. Through the calculation, it is found that the splitting energies of the degenerate hole states in Mn-doped CdSe nanowires are larger than that in Co-doped CdSe nanowires when the concentration of these two kinds of magnetic ions is the same. In order to analysis the magneto-optical spectrum of Mn and Co-doped CdSe nanowires, the four lowest electron states and the four highest hole states are sorted when the magnetic field is applied, and the 10 lowest optical transitions between the conduction subbands and the valence subbands at the Γ point in Mn and Co-doped CdSe nanowires are shown in the paper, it is found that the order of the optical transitions at the Γ point almost do not change although two different kinds of magnetic ions are doped in CdSe nanowires. Finally, the effective excitonic Zeeman splitting energies at the Γ point are found to increase almost linearly with the increase of the concentration of the magnetic ions and the magnetic field; meanwhile, the giant positive effective excitonic g factors in Mn and Co-doped CdSe nanowires are predicted based on our theoretical calculation.

  15. Effect of Co doping on the structural and dielectric properties of ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Ram, Mast; Bala, Kanchan; Sharma, Hakikat; Negi, N. S.

    2016-05-01

    This paper reports on the synthesis of Co doped Zn1-xCoxO (x= 0.0, 0.01, 0.02, 0.03 and 0.05) nanoparticles by solution combustion method using urea as a fuel. The Structural and dielectric properties of the samples were studied. Crystallite sizes were obtained from X-ray diffraction (XRD) patterns whose values decreased with increase in Co concentration. The XRD study reveals that Co2+ ions substitute the Zn2+ ion without changing the wurtzite structure of pristine ZnO up to Co concentrations of 5%. The dielectric constants, dielectric loss (tanδ) and ac conductivity (σac) were studied as the function of frequency and composition, which have been explained by Maxwell-Wagner type interfacial polarization and discussed Koops phenomenological theory.

  16. Effects of Co doping on electronic structure and electric/magnetic properties of La0.1Bi0.9FeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Wang, ShouYu; Feng, Yu; Liu, WeiFang; Yu, DaShu; Li, DeJun

    2013-10-01

    In this work, we report the influence of Co-doping on the electronic band structure, dielectric and magnetic properties of La0.1Bi0.9Fe1- x Co x O3 ceramics. X-ray photoelectron spectroscopy investigation shows that Co dopant can shift the valence band spectrum and core-level lines of constituent elements towards higher bind energy regions simultaneously increase the concentration of oxygen vacancies in ceramics. The effects of dopant are discussed with focus given to the Co-doping induced enhancement of electrical conductivity and resistive switching phenomena.

  17. Effect of Co Doping on the Structural, Optical and Magnetic Properties of ZnO Nanoparticles

    SciTech Connect

    Hays, Jason; Reddy, K. M.; Graces, N. Y.; Engelhard, Mark H.; Shutthanandan, V.; Luo, M.; Xu, Changqing; Giles, N. C.; Wang, Chong M.; Thevuthasan, Suntharampillai; Punnoose, Alex

    2007-07-04

    We report the results of a detailed investigation of sol-gel synthesized nanoscale Zn1-xCoxO powders processed at 350 °C with 0 @ x @ 0.12 to understand how the structural, morphological, optical and magnetic properties of ZnO are modified by Co doping, in addition to searching for the theoretically predicated ferromagnetism. With x increasing to 0.03, both lattice parameters a and c of the hexagonal ZnO decreased suggesting substitutional doping of Co at the tetrahedral Zn2+ sites. For x > 0.03, these trends reversed and the lattice showed a gradual expansion as x approached 0.12, probably due to additional interstitial incorporation of Co. Raman spectroscopy measurements showed a rapid change in the ZnO peak positions for x > 0.03 suggesting significant disorder and changes in the ZnO structure, in support of additional interstitial Co doping possibility. Combined x-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy, photoluminescence spectroscopy and diffuse reflectance spectroscopy showed clear evidence for tetrahedrally coordinated high spin Co2+ ions occupying the lattice sites of ZnO host system, which became saturated for x > 0.03. Magnetic measurements showed a paramagnetic behavior in Zn1-xCoxO with increasing antiferromagnetic interactions as x increased to 0.10. Surprisingly, a weak ferromagnetic behavior was observed for the sample with x = 0.12 with a characteristic hysteresis loop showing a coercivity Hc ~ 350 Oe, 25% remanence Mr, a low saturation magnetization Ms ~ 0.04 emu/g and with a Curie temperature Tc ~ 540 K. The XPS data collected from Zn1-xCoxO samples showed a gradual increase in the oxygen concentration, changing the oxygen deficient undoped ZnO to an excess oxygen state for x = 0.12. This indicates that such high Co concentrations and appropriate oxygen stoichiometry may be needed to achieve adequate ferromagnetic exchange coupling between the incorporated Co2+ ions.

  18. Large power factor and anomalous Hall effect and their correlation with observed linear magneto resistance in Co-doped Bi2Se3 3D topological insulator

    NASA Astrophysics Data System (ADS)

    Singh, Rahul; Shukla, K. K.; Kumar, A.; Okram, G. S.; Singh, D.; Ganeshan, V.; Lakhani, Archana; Ghosh, A. K.; Chatterjee, Sandip

    2016-09-01

    Magnetoresistance (MR), thermo power, magnetization and Hall effect measurements have been performed on Co-doped Bi2Se3 topological insulators. The undoped sample shows that the maximum MR as a destructive interference due to a π-Berry phase leads to a decrease of MR. As the Co is doped, the linearity in MR is increased. The observed MR of Bi2Se3 can be explained with the classical model. The low temperature MR behavior of Co doped samples cannot be explained with the same model, but can be explained with the quantum linear MR model. Magnetization behavior indicates the establishment of ferromagnetic ordering with Co doping. Hall effect data also supports the establishment of ferromagnetic ordering in Co-doped Bi2Se3 samples by showing the anomalous Hall effect. Furthermore, when spectral weight suppression is insignificant, Bi2Se3 behaves as a dilute magnetic semiconductor. Moreover, the maximum power factor is observed when time reversal symmetry (TRS) is maintained. As the TRS is broken the power factor value is decreased, which indicates that with the rise of Dirac cone above the Fermi level the anomalous Hall effect and linearity in MR increase and the power factor decreases.

  19. Large power factor and anomalous Hall effect and their correlation with observed linear magneto resistance in Co-doped Bi2Se3 3D topological insulator.

    PubMed

    Singh, Rahul; Shukla, K K; Kumar, A; Okram, G S; Singh, D; Ganeshan, V; Lakhani, Archana; Ghosh, A K; Chatterjee, Sandip

    2016-09-21

    Magnetoresistance (MR), thermo power, magnetization and Hall effect measurements have been performed on Co-doped Bi2Se3 topological insulators. The undoped sample shows that the maximum MR as a destructive interference due to a π-Berry phase leads to a decrease of MR. As the Co is doped, the linearity in MR is increased. The observed MR of Bi2Se3 can be explained with the classical model. The low temperature MR behavior of Co doped samples cannot be explained with the same model, but can be explained with the quantum linear MR model. Magnetization behavior indicates the establishment of ferromagnetic ordering with Co doping. Hall effect data also supports the establishment of ferromagnetic ordering in Co-doped Bi2Se3 samples by showing the anomalous Hall effect. Furthermore, when spectral weight suppression is insignificant, Bi2Se3 behaves as a dilute magnetic semiconductor. Moreover, the maximum power factor is observed when time reversal symmetry (TRS) is maintained. As the TRS is broken the power factor value is decreased, which indicates that with the rise of Dirac cone above the Fermi level the anomalous Hall effect and linearity in MR increase and the power factor decreases. PMID:27419361

  20. The combined effect of alumina and silica co-doping on the ageing resistance of 3Y-TZP bioceramics.

    PubMed

    Samodurova, Anastasia; Kocjan, Andraž; Swain, Michael V; Kosmač, Tomaž

    2015-01-01

    The combined effect of alumina and silica co-doping on the ageing resistance of 3Y-TZP bioceramics was investigated. In order to differentiate between the distinct contributions of two dopants to the overall resistance to low-temperature degradation (LTD), specimens were prepared by infiltration of silica sol into pre-sintered 3Y-TZP pellets, produced from commercially available powders, which were alumina-free or contained 0.05 and 0.25 wt.%. After sintering, specimens were exposed to accelerated ageing in distilled water at 134°C for 6-48 h. X-ray diffraction was applied to quantify the tetragonal-to-monoclinic (t-m) phase transformation associated with the LTD, while a focused ion beam-scanning electron microscopy technique was employed to study the microstructural features in the transformed layer. The results showed that the minor alumina and/or silica additions did not drastically change the densities, grain sizes or mechanical properties of 3Y-TZP, but they did significantly reduce LTD. The addition of either alumina or silica has the potential to influence both the nucleation and the propagation of moisture-induced transformation, but in different ways and to different extents. The co-doped ceramics exhibited predominantly transgranular fracture, reflecting strong grain boundaries (limiting microcracking of the transformed layer), for alumina doping, and rounded grains with a glassy phase at multiple grain junctions (reducing internal stresses) for silica-doped material. These two additives evidently have different dominant mechanisms associated with the deceleration of LTD of 3Y-TZP, but their combination increases resistance to ageing, importantly, without reducing the fracture toughness of this popular biomaterial. PMID:25234155

  1. First-principles study of n-type tin/fluorine co-doped beta-gallium oxides

    NASA Astrophysics Data System (ADS)

    Yinnü, Zhao; Jinliang, Yan

    2015-08-01

    Defect formation energies, electronic structures and optical properties of Sn-doped β-Ga2O3, F-doped β-Ga2O3, and Sn/F co-doped β-Ga2O3 were calculated using the first-principles. The calculated results of the pure and Sn-doped β-Ga2O3 using the local-density approximation (LDA) method show that the lattice parameters and electronic structures are in agreement with previous data. The defect formation energies demonstrate that the doped systems are relatively easy to form under O-rich conditions. Sn-doping, F-doping and Sn/F co-doping make β-Ga2O3 become an n-type semiconductor. Sn/F co-doping β-Ga2O3 has the smallest effective electron mass and the biggest relative electron number, which is expected to possess good conductivity. Sn/F co-doping β-Ga2O3 displays an intense absorption in visible light. Project supported by the National Natural Science Foundation of China (No. 10974077), and the Innovation Project of Shandong Graduate Education, China (No. SDYY13093).

  2. Effect of WO 3 on the spectroscopic properties in Er 3+/Yb 3+ co-doped bismuth-borate glasses

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Zhou, Yaxun; Dai, Shixun; Xu, Tiefeng; Nie, Qiuhua

    2007-11-01

    The spectroscopic properties of Er 3+/Yb 3+ co-doped Bi 2O 3-B 2O 3-WO 3 (BBW) glasses were analyzed and discussed. The effect of WO 3 content on the absorption spectra, the Judd-Ofelt parameters Ω t ( t=2, 4, 6), emission spectra and the lifetime of the 4I 13/2 level and the quantum efficiency of Er 3+: 4I 13/2→ 4I 15/2 transition were also investigated. With the substitution of WO 3 for B 2O 3, the measured lifetime of the 4I 13/2 level and the quantum efficiency of Er 3+: 4I 13/2→ 4I 15/2 transition increase from 0.98 to 1.31 ms and from 38.2% to 49.2%, respectively. The effective width of emission band and the emission cross-section both decrease slightly. And the emission spectra is analyzed via the different curve ( σe- σa) of BBW glasses, the influence of OH - is also discussed.

  3. The effect of K-na co-doping on the formation and particle size of Bi-2212 phase

    NASA Astrophysics Data System (ADS)

    Kır, M. Ebru; Özkurt, Berdan; Aytekin, M. Ersin

    2016-06-01

    Superconducting K-Na co-doped Bi2Sr2KxCa1Cu1.75Na0.25Oy (x=0, 0.05, 0.1 and 0.25) ceramics are prepared by a solid-state reaction method. It is clearly determined from XRD data that the characteristic peaks of Bi-2212 phase are observed in all samples. The resistivity measurements show that Tc (onset) values is gradually increasing as K content is increased. It is also found that K-Na co-doping influence the grain sizes for Bi-2212 phase significantly. The critical current densities as a function of magnetic field have been calculated from M-H hysteresis loops of samples according to Bean's critical model, indicating that K-Na co-doping cause higher Jc values than the pure ones.

  4. Effects of rare-earth co-doping on the local structure of rare-earth phosphate glasses using high and low energy X-ray diffraction.

    PubMed

    Cramer, Alisha J; Cole, Jacqueline M; FitzGerald, Vicky; Honkimaki, Veijo; Roberts, Mark A; Brennan, Tessa; Martin, Richard A; Saunders, George A; Newport, Robert J

    2013-06-14

    Rare-earth co-doping in inorganic materials has a long-held tradition of facilitating highly desirable optoelectronic properties for their application to the laser industry. This study concentrates specifically on rare-earth phosphate glasses, (R2O3)x(R'2O3)y(P2O5)(1-(x+y)), where (R, R') denotes (Ce, Er) or (La, Nd) co-doping and the total rare-earth composition corresponds to a range between metaphosphate, RP3O9, and ultraphosphate, RP5O14. Thereupon, the effects of rare-earth co-doping on the local structure are assessed at the atomic level. Pair-distribution function analysis of high-energy X-ray diffraction data (Q(max) = 28 Å(-1)) is employed to make this assessment. Results reveal a stark structural invariance to rare-earth co-doping which bears testament to the open-framework and rigid nature of these glasses. A range of desirable attributes of these glasses unfold from this finding; in particular, a structural simplicity that will enable facile molecular engineering of rare-earth phosphate glasses with 'dial-up' lasing properties. When considered together with other factors, this finding also demonstrates additional prospects for these co-doped rare-earth phosphate glasses in nuclear waste storage applications. This study also reveals, for the first time, the ability to distinguish between P-O and P[double bond, length as m-dash]O bonding in these rare-earth phosphate glasses from X-ray diffraction data in a fully quantitative manner. Complementary analysis of high-energy X-ray diffraction data on single rare-earth phosphate glasses of similar rare-earth composition to the co-doped materials is also presented in this context. In a technical sense, all high-energy X-ray diffraction data on these glasses are compared with analogous low-energy diffraction data; their salient differences reveal distinct advantages of high-energy X-ray diffraction data for the study of amorphous materials. PMID:23518599

  5. Effect of calcination temperature on the structure and visible-light photocatalytic activities of (N, S and C) co-doped TiO2 nano-materials

    NASA Astrophysics Data System (ADS)

    Lei, X. F.; Xue, X. X.; Yang, H.; Chen, C.; Li, X.; Niu, M. C.; Gao, X. Y.; Yang, Y. T.

    2015-03-01

    The (N, S and C) co-doped TiO2 samples (NSC-TiO2) were synthesized by the sol-gel method combining with the high energy ball milling method calcined at the different temperature (400-700 °C), employing butyl titanate as the titanium source and thiourea as the doping agent. The structures of NSC-TiO2 samples were characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), X-ray photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetry and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), scanning electron microscopy (SEM) and nitrogen adsorption-desorption isotherms. The photocatalytic activities were checked through the photocatalytic reduction of Cr(VI) as a model compound under visible light irradiation. The results showed that the (N, S and C) co-doping and the calcination temperature played important role on the microstructure and photocatalytic activity of the samples. According to XPS spectra, sulfur was mainly attributed to the Tisbnd Osbnd S bond; nitrogen was ascribed to the Tisbnd Osbnd N and Tisbnd N bonds; carbon was assigned to the Tisbnd Osbnd C bond in the NSC-TiO2 samples. (N, S and C) co-doped TiO2 samples calcinated at 500 °C exhibits higher photocatalytic activity than that of the other samples under visible light irradiation, which can be attributed to the synergic effect of its enhancing crystallization of anatase and (N, S and C) co-doping.

  6. A clear effect of charge compensation through Na+ co-doping on the luminescence spectra and decay kinetics of Nd3+-doped CaAl4O7

    NASA Astrophysics Data System (ADS)

    Puchalska, M.; Watras, A.

    2016-06-01

    We present a detailed analysis of luminescence behavior of singly Nd3+ doped and Nd3+, Na+ co-doped calcium aluminates powders: Ca1-xNdxAl4O7 and Ca1-2xNdxNaxAl4O7 (x=0.001-0.1). Relatively intense Nd3+ luminescence in IR region corresponding to typical 4F3/2→4IJ (J=9/2-13/2) transitions with maximum located at about 1079 nm was obtained in all samples on direct excitation into f-f levels. The effect of dopant concentration and charge compensation by co-doping with Na+ ions on morphology and optical properties were studied. The results show that both, the Nd3+ concentration and the alkali metal co-doping affected the optical properties but had no influence on the powders morphology. The studies of luminescence spectra (298 and 77 K) in a function of dopant concentration showed an increasing distortion of the local symmetry of Nd3+with raising activator content due to certain defects created in the crystal lattice. On the other hand Na+ addition led to significant narrowing of absorption and luminescence bands and also a reduction of the number of their components, showing smaller disturbance of Nd3+ ions local symmetries. Consequently, charge compensated by Na+ co-doping materials showed significantly enhanced Nd3+ luminescence. The decrease of emission intensity and luminescence lifetimes with increase of activator concentration was attributed mainly to phonon-assisted cross-relaxation processes between Nd3+ ions. Analysis with Inokuti-Hirayama model indicated dipole-dipole mechanism of ion-ion interaction. Na+ addition led to much smaller concentration quenching due to smaller clustering of dopant ions in CaAl4O7 lattice.

  7. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics

    PubMed Central

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-01-01

    The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I–V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I–V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I–V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I–V behavior of (Nb + In) co-doped TiO2 ceramics. PMID:25656713

  8. Effect of annealing atmosphere on photoluminescence and gas sensing of solution-combustion-synthesized Al, Pd co-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Li, Yan; Liu, Min; Lv, Tan; Wang, Qiong; Zou, Yun-ling; Lian, Xiao-xue; Liu, Hong-peng

    2015-11-01

    Al, Pd co-doped ZnO nanoparticles (NPs) synthesized using a solution combustion method and subsequent annealing process under various atmospheres, including air, nitrogen, and hydrogen, were characterized using x-ray diffraction, energy-dispersive x-ray spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The gas-sensing properties of the sensors based on the NPs were also examined. The results indicated that the Al, Pd co-doped ZnO NPs, with an average crystallite size of 10 nm, exhibited enhanced gas-sensing performance compared with that of pure ZnO and Al-doped ZnO. The response of the Al, Pd co-doped ZnO NPs annealed in N2 to ethanol (49.22) was nearly 5.7 times higher than that to acetone (8.61) and approximately 20 - 27 times higher than that to benzene (2.38), carbon monoxide (2.23), and methane (1.78), which demonstrates their excellent selectivity to ethanol versus other gases. This high ethanol response can be attributed to the combined effects of the small size, Schottky barrier, lattice defects, and catalysis. [Figure not available: see fulltext.

  9. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-02-01

    The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I-V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I-V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I-V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I-V behavior of (Nb + In) co-doped TiO2 ceramics.

  10. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics.

    PubMed

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-01-01

    The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I-V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I-V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I-V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I-V behavior of (Nb + In) co-doped TiO2 ceramics. PMID:25656713

  11. Electrode effects in dielectric spectroscopy measurements on (Nb+In) co-doped TiO2

    NASA Astrophysics Data System (ADS)

    Crandles, D. A.; Yee, S. M. M.; Savinov, M.; Nuzhnyy, D.; Petzelt, J.; Kamba, S.; Prokeš, J.

    2016-04-01

    Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and alternating current (ac) conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness, and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four-contact van der Pauw direct current conductivity measurements and bulk conductivity values extracted from two-contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature.

  12. Study of synergistic effect of Sc and C co-doping on the enhancement of visible light photo-catalytic activity of TiO2

    NASA Astrophysics Data System (ADS)

    Nasir, Muhammad; Lei, Juying; Iqbal, Waheed; Zhang, Jinlong

    2016-02-01

    Scandium and carbon co-doped TiO2 catalyst was prepared through a simple sol-gel synthesis method by using scandium nitrate as scandium dopant precursor, glucose as carbon precursor and tetrabutyl orthotitanate as titanium precursor and calcined them at 450 °C for 3 h. The characterizations of the prepared samples were accomplished through X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence spectroscopy (PL), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET). The X-ray diffraction results of the samples showed the decrease in the crystal size of the sample with the subsequent increase in the specific surface area as shown by Brunauer-Emmett-Teller. The UV-visible diffuse reflectance spectroscopy displayed the blue shift in the absorption together with the photoluminescence spectroscopy revealed the decrease in the recombination of electrons and holes by the addition of the scandium and then after the certain optimum value, the further increase of the scandium further increased the recombination of electrons and holes. The photo-catalytic activity of the samples was investigated with the help of photo-catalytic degradation of Acid orange 7 under visible light irradiation. The degradation of Acid orange 7 was highly increased for the Sc and C co-doped samples compared to the single C doped sample. And the sample 0.2 Sc/C-TiO2 had the maximum increase. The enhanced photo-catalytic performance was due the decrease of the crystal size, increase of the surface area, increase in the surface hydroxyl groups, and increase of the lifetime of the electrons and holes because of the synergistic effect of the Sc and C co-doping in TiO2.

  13. Effect of co-doping Tm{sup 3+} ions on the emission properties of Dy{sup 3+} ions in tellurite glasses

    SciTech Connect

    Sasikala, T.; Rama Moorthy, L.; Mohan Babu, A.; Srinivasa Rao, T.

    2013-07-15

    The present work reports the absorption, photoluminescence and decay properties of singly doped Dy{sup 3+} and co-doped Dy{sup 3+}/Tm{sup 3+} ions in TeO{sub 2}+ZnO+K{sub 2}O+CaO (TZKC) glasses prepared by the melt quenching technique. The glassy nature of the host glass has been confirmed by X-ray diffraction analysis and the primary vibrational modes were determined from the Raman spectrum. Judd–Ofelt (JO) analysis has been used to calculate the radiative transition rates, branching ratios and radiative lifetime of the emitting {sup 4}F{sub 9/2} state. The effect of co-doping of different concentrations of Tm{sup 3+} ions on the emission properties of Dy{sup 3+} ions has been investigated. The decay profiles of the {sup 4}F{sub 9/2} level were fitted to double exponential as well as Inokuti–Hirayama (IH) model to determine the energy transfer rates between Dy{sup 3+} and Tm{sup 3+} ions. The energy transfer rates found to increase with the increase of Tm{sup 3+} ions concentration. The chromaticity coordinates and color purity of the emitted light for all glasses were determined. - Graphical abstract: The graphical abstract shows the emission spectra of Dy{sup 3+}, Tm{sup 3+} and Dy{sup 3+}/Tm{sup 3+} co-doped TZKC glasses recorded by exciting at 355 nm wavelength. - Highlights: • Zinc tellurite glasses doped with Dy{sup 3+}, Tm{sup 3+} and Dy{sup 3+}/Tm{sup 3+} ions were prepared. • XRD, DTA and Raman spectral measurements were recorded to know the nature of host. • Energy transfer occurs from Dy{sup 3+} ions to Tm{sup 3+} ions. • The color purity of the emitted light was determined.

  14. Thermal conductivity of bulk GaN—Effects of oxygen, magnesium doping, and strain field compensation

    SciTech Connect

    Simon, Roland B.; Anaya, Julian; Kuball, Martin

    2014-11-17

    The effect of oxygen doping (n-type) and oxygen (O)-magnesium (Mg) co-doping (semi-insulating) on the thermal conductivity of ammonothermal bulk GaN was studied via 3-omega measurements and a modified Callaway model. Oxygen doping was shown to significantly reduce thermal conductivity, whereas O-Mg co-doped GaN exhibited a thermal conductivity close to that of undoped GaN. The latter was attributed to a decreased phonon scattering rate due the compensation of impurity-generated strain fields as a result of dopant-complex formation. The results have great implications for GaN electronic and optoelectronic device applications on bulk GaN substrates.

  15. γ irradiation induced effects on bismuth active centres and related photoluminescence properties of Bi/Er co-doped optical fibres.

    PubMed

    Sporea, D; Mihai, L; Neguţ, D; Luo, Yanhua; Yan, Binbin; Ding, Mingjie; Wei, Shuen; Peng, Gang-Ding

    2016-01-01

    We investigate the effects of γ irradiation on bismuth active centres (BACs) and related photoluminescence properties of bismuth/erbium co-doped silica fibre (BEDF), [Si] ~28, [Ge] ~1.60, [Al] ~0.10, [Er] ~ <0.10 and [Bi] ~0.10 atom%, fabricated by in-situ solution doping and Modified Chemical Vapor Deposition (MCVD). The samples were irradiated at 1 kGy, 5 kGy, 15 kGy, 30 kGy and 50 kGy doses, and dose rate of 5.5 kGy/h, at room temperature. The optical properties of BEDF samples are tested before and after γ irradiation. We found that high dose γ irradiation could significantly influence the formation and composition of BACs and their photoluminescence performance, as important changes in absorption and emission properties associated with the 830 nm pump produces the direct evidence of γ irradiation effects on BAC-Si. We notice that the saturable to unsaturable absorption ratio at pump wavelength could be increased with high dose γ irradiation, indicating that emission and pump efficiency could be increased by γ irradiation. Our experimental results also reveal good radiation survivability of the BEDF under low and moderate γ irradiation. Our investigation suggests the existence of irradiation related processing available for tailoring the photoluminescence properties and performance of bismuth doped/co-doped fibres. PMID:27440386

  16. γ irradiation induced effects on bismuth active centres and related photoluminescence properties of Bi/Er co-doped optical fibres

    NASA Astrophysics Data System (ADS)

    Sporea, D.; Mihai, L.; Neguţ, D.; Luo, Yanhua; Yan, Binbin; Ding, Mingjie; Wei, Shuen; Peng, Gang-Ding

    2016-07-01

    We investigate the effects of γ irradiation on bismuth active centres (BACs) and related photoluminescence properties of bismuth/erbium co-doped silica fibre (BEDF), [Si] ~28, [Ge] ~1.60, [Al] ~0.10, [Er] ~ <0.10 and [Bi] ~0.10 atom%, fabricated by in-situ solution doping and Modified Chemical Vapor Deposition (MCVD). The samples were irradiated at 1 kGy, 5 kGy, 15 kGy, 30 kGy and 50 kGy doses, and dose rate of 5.5 kGy/h, at room temperature. The optical properties of BEDF samples are tested before and after γ irradiation. We found that high dose γ irradiation could significantly influence the formation and composition of BACs and their photoluminescence performance, as important changes in absorption and emission properties associated with the 830 nm pump produces the direct evidence of γ irradiation effects on BAC-Si. We notice that the saturable to unsaturable absorption ratio at pump wavelength could be increased with high dose γ irradiation, indicating that emission and pump efficiency could be increased by γ irradiation. Our experimental results also reveal good radiation survivability of the BEDF under low and moderate γ irradiation. Our investigation suggests the existence of irradiation related processing available for tailoring the photoluminescence properties and performance of bismuth doped/co-doped fibres.

  17. Pump saturation effect of the Er3+/Yb3+ co-doped Y2Ti2O7 phosphors containing nanocrystals

    NASA Astrophysics Data System (ADS)

    Song, Feng; Wang, Fengxiao; Zhang, Jun; Chen, Gui-Yang; Feng, Ming

    2014-03-01

    Er3+ and Yb3+ co-doped Y2Ti2O7 phosphors containing nanocrystals were prepared by sol-gel method and annealed at 800 °C for 1 h in air. The X-ray diffraction (XRD) and transmission electron microscope (TEM) images showed that the mean size of nano-crystals is about 40-50nm, which corresponds well with the calculated results by Scherrer equation. Photoluminescence spectra and its upconversion properties were investigated. The anomalous slopes of the fitted line in the log-log plots for upconversion emissions and the pump-saturation effect of near infrared (NIR) emission were observed in the nanocrystalline samples. The reasons for the highly efficient upconversion luminescence and pump-saturation effect of NIR emission were discussed by a theoretical model of practical Er3+/Yb3+ co-doped system based on the rate equations. This work is supported by International Cooperation Program sponsored by Ministry of Science and Technology (MOST) of People's Republic of China.

  18. γ irradiation induced effects on bismuth active centres and related photoluminescence properties of Bi/Er co-doped optical fibres

    PubMed Central

    Sporea, D.; Mihai, L.; Neguţ, D.; Luo, Yanhua; Yan, Binbin; Ding, Mingjie; Wei, Shuen; Peng, Gang-Ding

    2016-01-01

    We investigate the effects of γ irradiation on bismuth active centres (BACs) and related photoluminescence properties of bismuth/erbium co-doped silica fibre (BEDF), [Si] ~28, [Ge] ~1.60, [Al] ~0.10, [Er] ~ <0.10 and [Bi] ~0.10 atom%, fabricated by in-situ solution doping and Modified Chemical Vapor Deposition (MCVD). The samples were irradiated at 1 kGy, 5 kGy, 15 kGy, 30 kGy and 50 kGy doses, and dose rate of 5.5 kGy/h, at room temperature. The optical properties of BEDF samples are tested before and after γ irradiation. We found that high dose γ irradiation could significantly influence the formation and composition of BACs and their photoluminescence performance, as important changes in absorption and emission properties associated with the 830 nm pump produces the direct evidence of γ irradiation effects on BAC-Si. We notice that the saturable to unsaturable absorption ratio at pump wavelength could be increased with high dose γ irradiation, indicating that emission and pump efficiency could be increased by γ irradiation. Our experimental results also reveal good radiation survivability of the BEDF under low and moderate γ irradiation. Our investigation suggests the existence of irradiation related processing available for tailoring the photoluminescence properties and performance of bismuth doped/co-doped fibres. PMID:27440386

  19. Effect of thermal treatment on room-temperature ferromagnetism in Co-doped ZnO powders

    NASA Astrophysics Data System (ADS)

    Zhou, Xueyun; Ge, Shihui; Yao, Dongsheng; Zuo, Yalu; Xiao, Yuhua

    2008-09-01

    The Co-doped ZnO powders were synthesized by sol-gel method, and treated at different temperatures (673-873 K) in the presence or absence of NH 3 atmosphere for 0.5 and 2 h, respectively. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) show that better crystal structure can cause larger ferromagnetism and the second phase (Co 3O 4) is the reason for saturation magnetization decrease of the sample sintered at higher temperature in air. XPS and nuclear magnetic resonance (NMR) prove the existence of Co 2+ ions in the Zn 0.9Co 0.1O and the absence of Co clusters, indicating intrinsic ferromagnetism of the samples treated in air. However, strong ferromagnetism of the samples annealed in NH 3 is ascribed to cobalt nitride formed during annealing.

  20. Effect of Er3+ and Yb3+ co-doping on the performance of a ZnO-based DSSC

    NASA Astrophysics Data System (ADS)

    Tsege, Ermias Libnedengel; Vu, Hong Ha Thi; Atabaev, Timur Sh.; Kim, Hyung-Kook; Hwang, Yoon-Hwae

    2016-06-01

    Zinc-oxide (ZnO) nanoparticles (NPs) co-doped with different concentrations of rare-earth ions of erbium and ytterbium, (ZnO: Er3+, Yb3+) were synthesized for applications to ZnO-based dye sensitized solar cells (DSSC). The composite NPs used for the photoelectrode (PE) were synthesized using a simple co-precipitation technique. X-ray diffraction and scanning electron microscopy measurements on the prepared samples revealed a single phase wurzite ZnO powder with approximate sizes in the range from 15 to 20 nm. Photoluminescence (PL) measurements confirmed that the synthesized composite NPs had a good up-conversion (UPC) property. The prepared powders were directly used to make PEs for DSSCs. The photovoltaic efficiency of the DSSCs was enhanced compared to that of pure ZnO-based DSSCs. Particularly, the PE made up of ZnO: Er3+, Yb3+ NPs with 4 wt% of Er3+ and Yb3+ generates a short-circuit current density ( J sc ) of 4.794 mA·cm -2 and an open circuit voltage ( V oc ) of 0.602 V with an efficiency ( η) of 1.58%. The result indicates a 48.4% J sc improvement compared to a pure ZnO PE-based DSSC. The photocurrent improvement is due to an increase in the light-harvesting capacity of the PEs attained through the UPC property of ZnO: Er3+, Yb3+ NPs. As confirmed by PL and electrochemical impedance spectra (EIS), the use of ZnO: Er3+,Yb3+ NPs as PEs for DSSCs enhances charge concentration and transport as a result of n-type doping. However, all ZnO: Er3+, Yb3+ NP based PEs exhibited a lower V oc as a result of a down shift in the Fermi energy, which affects the overall efficiency of the cell.

  1. Effect of Co doping on structural, optical, magnetic and dielectric properties of Bi{sub 2}Fe{sub 4}O{sub 9}

    SciTech Connect

    Mohapatra, S. R.; Sahu, B.; Singh, A. K.; Kaushik, S. D.

    2015-06-24

    Polycrystalline Bi{sub 2}Fe{sub 4}O{sub 9} and 2% Co doped Bi{sub 2}Fe{sub 4}O{sub 9} were prepared by solid state reaction route. X-ray diffraction (XRD) result reveals that there is no change in the crystal structure due to Co doping and the compound has orthorhombic structure. UV-visible spectroscopy confirms the decrease in band gap due Co doping. Zero field cooled magnetization measurement at 100 Oe magnetic field shows substantial decrease in the magnetic transition temperature. Room temperature frequency dependent dielectric permittivity at 1V DC bias shows ∼10% increase in Co doped sample with respect to pure Bi{sub 2}Fe{sub 4}O{sub 9}.

  2. Effect of substrate temperature on transparent conducting Al and F co-doped ZnO thin films prepared by rf magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Wang, Fang-Hsing; Chang, Chiao-Lu

    2016-05-01

    ZnO is a wide bandgap semiconductor that has many potential applications such as solar cells, thin film transistors, light emitting diodes, and gas/biological sensors. In this study, a composite ceramic ZnO target containing 1 wt% Al2O3 and 1.5 wt% ZnF2 was prepared and used to deposit transparent conducting Al and F co-doped zinc oxide (AFZO) thin films on glass substrates by radio frequency magnetron sputtering. The effect of substrate temperatures ranging from room temperature (RT) to 200 °C on structural, morphological, electrical, chemical, and optical properties of the deposited thin films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Hall effect measurement, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and UV-vis spectrophotometer. The XRD results showed that all the AFZO thin films had a (0 0 2) diffraction peak, indicating a typical wurtzite structure with a preferential orientation of the c-axis perpendicular to the substrate. The FE-SEM and AFM analyses indicated that the crystallinity and grain size of the films were enhanced while the surface roughness decreased as the substrate temperature increased. Results of Hall effect measurement showed that Al and F co-doping decreased the resistivity more effectively than single-doping (either Al or F doping) in ZnO thin films. The resistivity of the AFZO thin films decreased from 5.48 × 10-4 to 2.88 × 10-4 Ω-cm as the substrate temperature increased from RT to 200 °C due to the increased carrier concentration and Hall mobility. The optical transmittances of all the AFZO thin films were over 92% in the wavelength range of 400-800 nm regardless of substrate temperature. The blue-shift of absorption edge accompanied the rise of the optical band gap, which conformed to the Burstein-Moss effect. The developed AFZO thin films are suitable as transparent conducting electrodes for various optoelectronic

  3. Effects of Ho3+ and Yb3+ doping concentrations and Li+ co-doping on the luminescence of GdVO4 powders

    NASA Astrophysics Data System (ADS)

    Gavrilović, Tamara V.; Jovanović, Dragana J.; Trandafilović, Lidija V.; Dramićanin, Miroslav D.

    2015-07-01

    We present the structural and luminescent properties of Ho3+/Yb3+-doped GdVO4 and Li+-co-doped GdVO4:Ho3+/Yb3+ powder phosphors. The materials were prepared by high-temperature solid state method with different concentrations (between 0.5 and 2 mol%) of dopant Ho3+ emitting ions and different concentrations (between 5 and 20 mol%) of sensitizer Yb3+ ions. The dopant ions provided the material with intense luminescence emission; green emissions (centered at 542 nm from 5F4,5S2 → 5I8 electronic transition of Ho3+ ions) resulted upon ultraviolet excitation, and red (centered at 659 nm from 5F5 → 5I8 electronic transition of Ho3+ ions) upon near-infrared excitation. The co-doped materials were obtained under identical experimental conditions by adding Li+ ions (5, 7.5, 10, and 15 mol%). The powders co-doped with 7.5 mol% Li+ ions showed a downconversion emission intensity more than twice as high as the samples without Li+ co-doping. In upconversion, an equal intensification of emission was achieved with co-doping with 10 mol% Li+. The influences of Ho3+/Yb3+ concentration ratio and Li+ co-doping level on emission color and emission branching was investigated and analyzed for both downconversion and upconversion emission. Increasing Yb3+ concentration was found to increase the share of dominant emission (green) in downconversion, but decreased the share of dominant emission (red) in upconversion.

  4. Infrared to visible upconversion in Ho³+/Yb³+ co-doped Y₂ O₃ phosphor: effect of laser input power and external temperature.

    PubMed

    Rai, Monika; Mishra, K; Singh, S K; Verma, R K; Rai, S B

    2012-11-01

    In the present paper, Ho(3+) doped and Ho(3+)/Yb(3+) co-doped Y(2)O(3) phosphors have been synthesized using solution combustion technique and characterized for its structure and upconversion (UC) fluorescence as a function of Yb(3+) concentration. Effect of a variation in laser input power and external temperature on the UC emission intensity has been studied to explore the UC mechanism and temperature dependent behavior of the phosphor, respectively. On excitation with near infrared (NIR) light (976 nm), the phosphor emits strong green emission along with relatively weak emission bands in red and blue regions at 553, 670 and 497 nm due to (5)S(2)→(5)I(8), (5)F(5)→(5)I(8) and (5)F(3)→(5)I(8), respectively. The emission shows a decrease in intensity with an increase in external temperature, however contrary to the normal behavior of Ho(3+), no significant change in the FIR (fluorescence intensity ratio) of (5)F(4)→(5)I(8) and (5)S(2)→(5)I(8) transitions is noted in the present host. This peculiar behavior of the sample with external temperature has been explained by temperature dependent lifetime study of the thermally coupled levels. PMID:22902580

  5. Sn/Be Sequentially co-doped Hematite Photoanodes for Enhanced Photoelectrochemical Water Oxidation: Effect of Be2+ as co-dopant

    PubMed Central

    Annamalai, Alagappan; Lee, Hyun Hwi; Choi, Sun Hee; Lee, Su Yong; Gracia-Espino, Eduardo; Subramanian, Arunprabaharan; Park, Jaedeuk; Kong, Ki-jeong; Jang, Jum Suk

    2016-01-01

    For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn4+ and Be2+ dopants into hematite (α–Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm2) compared to pristine α–Fe2O3 (0.7 mA/cm2), and Sn4+ mono-doped α-Fe2O3 photoanodes (1.0 mA/cm2). From first-principles calculations, we found that Sn4+ doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn4+-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be2+ was co-doped with Sn4+-doped α–Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure. PMID:27005757

  6. Sn/Be Sequentially co-doped Hematite Photoanodes for Enhanced Photoelectrochemical Water Oxidation: Effect of Be(2+) as co-dopant.

    PubMed

    Annamalai, Alagappan; Lee, Hyun Hwi; Choi, Sun Hee; Lee, Su Yong; Gracia-Espino, Eduardo; Subramanian, Arunprabaharan; Park, Jaedeuk; Kong, Ki-Jeong; Jang, Jum Suk

    2016-01-01

    For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn(4+) and Be(2+) dopants into hematite (α-Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm(2)) compared to pristine α-Fe2O3 (0.7 mA/cm(2)), and Sn(4+) mono-doped α-Fe2O3 photoanodes (1.0 mA/cm(2)). From first-principles calculations, we found that Sn(4+) doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn(4+)-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be(2+) was co-doped with Sn(4+)-doped α-Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure. PMID:27005757

  7. Sn/Be Sequentially co-doped Hematite Photoanodes for Enhanced Photoelectrochemical Water Oxidation: Effect of Be2+ as co-dopant

    NASA Astrophysics Data System (ADS)

    Annamalai, Alagappan; Lee, Hyun Hwi; Choi, Sun Hee; Lee, Su Yong; Gracia-Espino, Eduardo; Subramanian, Arunprabaharan; Park, Jaedeuk; Kong, Ki-Jeong; Jang, Jum Suk

    2016-03-01

    For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn4+ and Be2+ dopants into hematite (α–Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm2) compared to pristine α–Fe2O3 (0.7 mA/cm2), and Sn4+ mono-doped α-Fe2O3 photoanodes (1.0 mA/cm2). From first-principles calculations, we found that Sn4+ doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn4+-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be2+ was co-doped with Sn4+-doped α–Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure.

  8. Samarium and Nitrogen Co-Doped Bi2 WO6 Photocatalysts: Synergistic Effect of Sm(3+) /Sm(2+) Redox Centers and N-Doped Level for Enhancing Visible-Light Photocatalytic Activity.

    PubMed

    Wang, Fangzhi; Li, Wenjun; Gu, Shaonan; Li, Hongda; Wu, Xue; Liu, Xintong

    2016-08-26

    Samarium and nitrogen co-doped Bi2 WO6 nanosheets were successfully synthesized by using a hydrothermal method. The crystal structures, morphology, elemental compositions, and optical properties of the prepared samples were investigated. The incorporation of samarium and nitrogen ions into Bi2 WO6 was proved by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. UV/Vis diffuse reflectance spectroscopy indicated that the samarium and nitrogen co-doped Bi2 WO6 possessed strong visible-light absorption. Remarkably, the samarium and nitrogen co-doped Bi2 WO6 exhibited higher photocatalytic activity than single-doped and pure Bi2 WO6 under visible-light irradiation. Radical trapping experiments indicated that holes (h(+) ) and superoxide radicals ((.) O2 (-) ) were the main active species. The results of photoluminescence spectroscopy and photocurrent measurements demonstrated that the recombination rate of the photogenerated electrons and holes pairs was greatly depressed. The enhanced activity was attributed to the synergistic effect of the in-built Sm(3+) /Sm(2+) redox pair centers and the N-doped level. The mechanism of the excellent photocatalytic activity of Sm-N-Bi2 WO6 is also discussed. PMID:27464522

  9. Boron, bismuth co-doping of gallium arsenide and other compounds for photonic and heterojunction bipolar transistor devices

    SciTech Connect

    Mascarenhas, Angelo

    2015-07-07

    Isoelectronic co-doping of semiconductor compounds and alloys with acceptors and deep donors is sued to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. For example, Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, B and Bi, to customize solar cells, and other semiconductor devices. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  10. The effect of sulfur and zirconium co-doping on the oxidation of NiCrAl

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1988-01-01

    The adhesion behavior of Al2O3 scales formed on NiCrAl+Zr alloys was examined as a function of both sulfur and zirconium doping levels. In general, very high levels of zirconium were required to counteract the detrimental effects of sulfur. A sulfur-zirconium adherence map was constructed, as determined from the oxidation and spalling behavior in 1100 C cyclic tests. For low sulfur alloys (less than 500 ppma), the amount of zirconium required for adherence at any given sulfur level can be described by Zr greater than 600 S(0.2) (in ppma). These results underscore the importance of sulfur to adhesion mechanisms and suggest that sulfur gettering is a first order effect of reactive element additions to MCrAl alloys.

  11. The effect of sulfur and zirconium Co-doping on the oxidation of NiCrAl

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1987-01-01

    The adhesion behavior of Al2O3 scales formed on NiCrAl+Zr alloys was examined as a function of both sulfur and zirconium doping levels. In general, very high levels of zirconium were required to counteract the detrimental effects of sulfur. A sulfur-zirconium adherence map was constructed, as determined from the oxidation and spalling behavior in 1100 C cyclic tests. For low sulfur alloys, the amount of zirconium required for adherence at any given sulfur level can be described by Zr greater than 600 S sup 0.2 (in ppma). These results underscore the importance of sulfur to adhesion mechanisms and suggests that sulfur gettering is a first order effect of reactive element additions to MCrAl alloys.

  12. Effect of co-doped SnO{sub 2} nanoparticles on photoluminescence of cu-doped potassium lithium borate glass

    SciTech Connect

    Namma, Haydar Aboud; Wagiran, H.; Hussin, R.; Ariwahjoedi, B.

    2012-09-26

    The SnO{sub 2} co-doped lithium potassium borate glasses doped with 0.05, 0.10, 0.25 and 0.50 mol% of Cu were synthesized by the melt quenching technique. The SnO{sub 2} co-dope was added to the compounds in the amounts of 0.05, 0.10, and 0.20 mol%. The photoluminescent spectrum for different concentrations of copper was studied. It was observed that the intensity of blue emission (450, 490 nm) varies with concentration mol%. In addition, with different concentration of SnO{sub 2} to 0.10 mol% Cu, the influence of the luminescence has been observed to enhance intensity and shifted to blue and red (490, 535 nm) emissions.

  13. Effect of local structural distortion on magnetic and dielectric properties in BiFeO3 with Ba, Ti co-doping

    NASA Astrophysics Data System (ADS)

    Cheng, G. F.; Ruan, Y. J.; Liu, W.; Wu, X. S.

    2015-07-01

    The structural, magnetic, and dielectric properties of Bi1-xBaxFe1-xTixO3 (x≤0.25) ceramics are studied systematically. The symmetry of the unit cell for BiFeO3 co-doping with Ba and Ti remains the space group of R3c. The addition of Ba and Ti increases the unit cell volume without changing the unit cell symmetry. The remnant magnetization decreases monotonically with increasing the doping content, which may originate from contraction in Fe-O-Fe bond and FeO6 octahedron. Charge compensation occurs in BiFeO3 with Ba and Ti co-doping, which may suppress the charge defects and decrease the magnetism. The substitution of Fe with smaller radial Ti ion supplies larger vibration space in FeO6 octahedron, which may enhance the dielectric constant and decrease the dielectric loss significantly.

  14. Effect of Co doping, capping agent and optical-structural studies of ZnO:Co2+ nanoparticles

    NASA Astrophysics Data System (ADS)

    Taheri Otaqsara, S. M.

    2011-08-01

    Co2+ doped ZnO nanoparticles (NPs) using PEG as a capping agent were prepared by colloidal wet-chemical method. The structure, morphology and characteristics of as-prepared samples were investigated. X-ray diffraction patterns studies revealed wurtzite crystal phase. STM-TEM micrographs show a spherical shape and nearly well distribution with an average particle size of ~15-20 nm. UV-VIS spectra show the presence of exciton peak at 349 nm which can be effectively tuned versus cobalt doping and PEG concentration. PL studies were done under the excitation of 347 nm, which exhibited a UV (~386 nm) and visible (blue-orange) emission peak because of free-exciton recombination and oxygen vacancy.

  15. Effect of co-doped metal caions on the properties of Y2O3:Eu3+ phosphors synthesized by gel-combustion method

    NASA Astrophysics Data System (ADS)

    Hui, Shi; Xi-Yan, Zhang; Wei-Li, Dong; Xiao-Yun, Mi; Neng-Li, Wang; Yan, Li; Hong-Wei, Liu

    2016-04-01

    Y2O3:Eu3+ phosphors co-doped with different metal cations (Li+, Na+, K+, Mg2+, Ca2+) are prepared by the gel-combustion method with Y2O3, Eu2O3, and R(NO3) x (R = Li, Na, K, Mg, Ca) serving as raw materials and glycine as fuel, calcined at 1000 °C for 2 h. The synthesized Y2O3:Eu3+ phosphors doped with different metal cations and doping ratios are characterized by x-ray diffractometry (XRD), fluorescence and phosphorescent spectrophotometer. The co-doping metal cations are advantageous to the development of Y2O3:Eu3+ lattice. All the samples can emit red light peaked at 611 nm under 254-nm excited. The luminescence intensities of co-doping samples are increased because the cations increase the electron transition probability of Eu3+ from 5D0 level to 7F level. The fluorescence lifetime of Eu3+ (5D0 → 7F2) is increased by doping metal cations.

  16. Al-Mg co-doping effect on optical and magnetic properties of ZnO nanopowders

    NASA Astrophysics Data System (ADS)

    Si, Xiaodong; Liu, Yongsheng; Wu, Xinfang; Lei, Wei; Lin, Jia; Gao, Tian; Zheng, Li

    2015-07-01

    Zn0.97 - xMgxAl0.03O (x = 0 , 0.01 , 0.03 and 0.05) nanoparticles were prepared by hydrothermal growth, and their optical and magnetic properties were systematically studied by the X-ray diffraction (XRD), the UV-visible spectrophotometer, the infrared spectrometer and the physical properties measurement system (PPMS). These results showed that all the nanopowders had hexagonal wurtzite structures. With increasing the content of Mg, the strength of the (110) intensity peak increased. When Mg atoms were not incorporated into the Zn0.97Al0.03O lattice, the infrared light transmittance was higher than that of other groups of samples. In the UV range, the absorption decreased with the increase of the concentration of Mg. Mg doping weakened the magnetic property of the nanoparticles at room temperature. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves were separated with the decrease of temperature due to the pinning effect between the ferromagnetic domain and antiferromagnetic domain.

  17. Co-doping of Ag into Mn:ZnSe Quantum Dots: Giving Optical Filtering effect with Improved Monochromaticity

    PubMed Central

    Hu, Zhiyang; Xu, Shuhong; Xu, Xiaojing; Wang, Zhaochong; Wang, Zhuyuan; Wang, Chunlei; Cui, Yiping

    2015-01-01

    In optics, when polychromatic light is filtered by an optical filter, the monochromaticity of the light can be improved. In this work, we reported that Ag dopant atoms could be used as an optical filter for nanosized Mn:ZnSe quantum dots (QDs). If no Ag doping, aqueous Mn:ZnSe QDs have low monochromaticity due to coexisting of strong ZnSe band gap emission, ZnSe trap emission, and Mn dopant emission. After doping of Ag into QDs, ZnSe band gap and ZnSe trap emissions can be filtered, leaving only Mn dopant emission with improved monochromaticity. The mechanism for the optical filtering effect of Ag was investigated. The results indicate that the doping of Ag will introduce a new faster deactivation process from ZnSe conduction band to Ag energy level, leading to less electrons deactived via ZnSe band gap emission and ZnSe trap emission. As a result, only Mn dopant emission is left. PMID:26446850

  18. Co doped ZnO nanowires as visible light photocatalysts

    NASA Astrophysics Data System (ADS)

    Šutka, Andris; Käämbre, Tanel; Pärna, Rainer; Juhnevica, Inna; Maiorov, Mihael; Joost, Urmas; Kisand, Vambola

    2016-06-01

    High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV-visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10-3 min-1 in case of nanoparticles and 4.2·10-3 min-1 in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn0.95Co0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.

  19. Photodegradation of ibuprofen by TiO2 co-doping with urea and functionalized CNT irradiated with visible light - Effect of doping content and pH.

    PubMed

    Yuan, Ching; Hung, Chung-Hsuang; Li, Huei-Wen; Chang, Wei-Hsian

    2016-07-01

    Ibuprofen (IBP) is one kind of non-steroidal anti-inflammatory drugs (NSAIDs), which are classified as Pharmaceuticals and Personal Care Products (PPCPs). IBP possesses bioactive property and the substantial use of IBP results in a harmful impact on bioreceptors even in small concentrations. Accordingly, the treatment of these wastewaters is important before discharging them into the ecosystem. The photodegradation of IBP with TiO2 co-doped with functionalized CNTs (CNT-COOH and CNT-COCl) and urea, named as N-doping CNT/TiO2, irradiated with visible light of 410 nm was investigated in this study. The titanium tetrachloride was used as the precursor of Ti. The N-doping CNT-COCl/TiO2 photocatalysts exhibited a better crystalline structure and smaller crystal size than the N-doping CNT-COOH/TiO2 photocatalyst. It might largely ascribe to strong binding between acyl chloride functional group and TiO2. About 85.0%-86.0% of IBP was degraded with N-doping CNT/TiO2 within 120 min at natural condition, which obeyed the pseudo first order reaction and the rate constant was 4.45 × 10(-3)-1.22 × 10(-2) min(-1) and 5.03 × 10(-3)-1.47 × 10(-2) min(-1) for N-doping CNT-COOH/TiO2 and N-doping CNT-COCl/TiO2, respectively. The best IBP degradation of 87.9%-89.0% was found at pH 5, which indicated superoxide radicals (O2(-)) played a key role. The optimal pH was majorly dominated by the nature of IBP and N-doping CNT/TiO2. A successful synergy effect of TiO2 and dopants was exhibited and this mainly attributed to the strong binding strength by functional group of acyl chloride (COCl) and carboxylic acid (COOH). In summary, IBP could be effectively photodegraded by the fabricated N-doping CNT/TiO2 photocatalysts. PMID:27145421

  20. Analysis of thermal and structural properties of germanate glasses co-doped with Yb3+/Tb3+ ions

    NASA Astrophysics Data System (ADS)

    Zmojda, J.; Kochanowicz, M.; Miluski, P.; Dorosz, D.; Jelen, P.; Sitarz, M.

    2014-10-01

    In the work the new glass compositions in the GeO2-GaO-BaO system have been prepared and thermal, structural properties of in germanate glasses co-doped with Yb3+/Tb3+ions were studied. Glasses were obtained by conventional high-temperature melt-quenching technique. The study of the crystallization kinetics processes of glasses co-doped with 0.7Yb2O3:0.7Tb2O3 was performed with DSC measurements. The activation energies have been calculated using Freedman analysis and verified with the Flynn-Wall-Ozawa method. In this order, the DSC curves have been registered with different heating rates, between 5 and 15 degrees/min. The structure of fabricated glasses has been studied by infrared and Raman spectroscopes. The effect of heat treatment on the structural properties was determined. In all glass samples the dominated infrared absorbance band at 800 cm-1 corresponds to asymmetric stretching motions of GeO4 tetrahedra containing bridging (Ge-O(Ge)) and non-bridging (Ge-O-) oxygens. Additionally, the influence of heat treatment on the luminescent properties was evaluated. Strong luminescence at 489, 543, 586 and 621 nm corresponding to 5D4 → 7FJ (J = 6, 5, 4, 3) transitions was measured. The highest upconversion emission intensity was obtained in the germanate glass co-doped with 0.7Yb2O3/0.7Tb2O3.

  1. Effect of Ag/Al co-doping method on optically p-type ZnO nanowires synthesized by hot-walled pulsed laser deposition

    PubMed Central

    2012-01-01

    Silver and aluminum-co-doped zinc oxide (SAZO) nanowires (NWs) of 1, 3, and 5 at.% were grown on sapphire substrates. Low-temperature photoluminescence (PL) was studied experimentally to investigate the p-type behavior observed by the exciton bound to a neutral acceptor (A0X). The A0X was not observed in the 1 at.% SAZO NWs by low-temperature PL because 1 at.% SAZO NWs do not have a Ag-O chemical bonding as confirmed by XPS measurement. The activation energies (Ea) of the A0X were calculated to be about 18.14 and 19.77 meV for 3 and 5 at.% SAZO NWs, respectively, which are lower than the activation energy of single Ag-doped NW which is about 25 meV. These results indicate that Ag/Al co-doping method is a good candidate to make optically p-type ZnO NWs. PMID:22647319

  2. Effect of (Fe, Co) co-doping on the structural, electrical and magnetic properties of ZnO nanocrystals prepared by solution combustion method

    NASA Astrophysics Data System (ADS)

    Ram, Mast; Negi, N. S.

    2016-01-01

    The structural, electrical and magnetic properties of Zn1-xCo0.05FexO (where, x=0, 1, 2, 3 and 5 mol%) nanoparticles prepared by solution combustion method are reported. The X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive analysis of X-rays (EDX) have been used for structural and compositional analysis. The X-ray diffraction pattern showed the existence of hexagonal wurtzite structure of parent ZnO with co-doping. The microstructural studies reveal the dense nanostructured morphology of these samples. The DC electrical conductivity measurements have been carried out in the temperature range of 300-450 K. The DC electrical conductivity decreases with the increasing Fe concentration. The magnetic studies reveal room temperature ferromagnetisation in doped ZnO nanoparticles. The magnetic properties of ZnO nanoparticles improve with increasing Fe dopant concentration.

  3. Electrical and optical properties of Co-doped and undoped MoS2

    NASA Astrophysics Data System (ADS)

    Ko, Tsung-Shine; Huang, Cheng-Ching; Lin, Der-Yuh; Ruan, Yan-Jia; Huang, Ying Sheng

    2016-04-01

    Co-doped and undoped layered MoS2 crystals were grown by the chemical vapor transport method using iodine as the transport agent. Both reflectance and piezoreflectance measurements reveal two exciton transitions of the direct band edge around 1.86 and 2.06 eV for undoped MoS2 and 1.84 and 2.03 eV for Co-doped MoS2. Hall effect measurements show that the Co-doped MoS2 sample has a lower carrier concentration and mobility than the undoped sample. These differences between undoped and Co-doped MoS2 were attributed to the effect of cobalt atoms causing a small lattice distortion, lattice imperfections and/or impurity states that form trap states between the conduction band and valence band. Furthermore, photoconductivity (PC) and persistent PC results show that Co-doped MoS2 has a longer time constant and better responsivity than undoped MoS2. This work discusses the advantages of Co-doped MoS2 for photodetector applications.

  4. Formation and Characteristics of Anatase-Type Titania Solid Solution Nanoparticles Doped with Nb5+ M (M = Ga3+, Al3+, Sc3+)

    NASA Astrophysics Data System (ADS)

    Hirano, Masanori; Ito, Takaharu

    2011-10-01

    Anatase-type titania solid solutions co-doped with Nb5+ and cation M (M = Ga3+, Al3+, Sc3+) with composition Ti1-2XNbXMXO2 were directly formed as nanoparticles from precursor solutions of TiOSO4, NbCl5, and metal salts (Ga(SO4)3, Al(NO3)3, and Sc(NO3)3) under mild hydrothermal conditions at 180 °C for 5 h using the hydrolysis of urea. The effect of co-doped cation M on the formation and properties of anatase-type titania solid solutions was investigated. The region of anatse-type solid solution depended on the co-doped cation M. The composition range of anatase-type titania solid solution in the case of M = Sc3+ was much wider than that in the case of M = Ga3+ and Al3+. The increase in the amount of co-doped cation M = Ga3+, Al3+ enhanced the crystallite growth of anatase solid solutions under the hydrothermal conditions. The solid solutions co-doped with M = Al3+ showed the most improved photocatalytic activity in the three cations. The anatase-to-rutile phase transformation of solid solutions was promoted at lower temperature via the presence of co-doped cation M = Ga3+.

  5. Synthesis and spectroscopic characterization of YPO{sub 4} activated with Tb{sup 3+} and effect of Bi{sup 3+} co-doping on the luminescence properties

    SciTech Connect

    Angiuli, Fabio; Cavalli, Enrico; Belletti, Alessandro

    2012-08-15

    Single crystals of YPO{sub 4}:Tb{sup 3+}(1%) have been grown from Pb{sub 2}P{sub 2}O{sub 7} flux and their emission dynamics have been characterized by steady state and time resolved optical spectroscopy. The investigation has then been extended to green emitting phosphors with composition Y{sub 0.95-x}Tb{sub 0.05}Bi{sub x}PO{sub 4} (x=0, 0.0025, 0.005, 0.01, 0.025), synthesized by the Pechini sol-gel method and by solid state reaction. The former procedure has yielded higher quality materials in terms of size and morphology of the particles and of emission performance. The effect of the Bi{sup 3+} co-doping on the emission properties has been related to the Bi{sup 3+}{yields}Tb{sup 3+} energy transfer process as well as to the influence of the bismuth ions on the optical properties of the host lattice. - Graphical abstract: The intensity of the 370 nm excited luminescence increases with the Bi{sup 3+} content. A possible mechanism accounting for this behavior is proposed and discussed. Highlights: Black-Right-Pointing-Pointer Green emitting YPO{sub 4}:Tb{sup 3+} phosphors were synthesized by different methods. Black-Right-Pointing-Pointer The emission dynamics have been investigated under different experimental conditions. Black-Right-Pointing-Pointer The co-doping with Bi{sup 3+} ions increases the emission performance of the phosphors.

  6. Co-doped spinels: promising materials for solid state lasers

    NASA Astrophysics Data System (ADS)

    Kuleshov, Nickolai V.; Mikhailov, Victor P.; Scherbitsky, V. G.

    1994-07-01

    Optical absorption, luminescence, saturation of absorption and lifetime measurements have been carried out on Co-doped MgAl2O4 and ZnGa2O4. The crystal field parameters are estimated for the tetrahedral Co2+ ion. Three luminescence bands observed in the visible and near infrared are assigned to transitions from the 4T1(4P) level to the lower levels 4A2(4F), 4T2(4F), and 4T1(4F), respectively. Strong luminescence quenching due to nonradiative decay processes is observed MgAl2O4:Co. Saturation of Co2+ absorption at 540 nm is measured and the absorption cross section is estimated to be 2.1 + 0.2 X 10-19 cm2 in MgAl2O4.

  7. Characterization of co-doped (In, N): ZnO by indigenous thermopower measurement system

    NASA Astrophysics Data System (ADS)

    Kedia, Sanjay Kumar; Singh, Anil; Chaudhary, Sujeet

    2016-05-01

    The thermopower measurement of (In, N) co-doped ZnO thin films have been carried out using indigenous high and low temperature thermopower measurement system. The compact thermopower measurement system has been designed, developed, tested in house. The sensitivity and accuracy of indigenous thermopower system have been investigated by measuring thermopower of standard samples like Cu, Ni, Sb etc. It has been also investigated by the comparison of carrier concentration using Hall Effect and Thermopower measurement of these (In, N) co-doped ZnO thin films. The constant temperature gradient between hot and cold junction has been maintained by using the temperature controller. The room temperature and low temperature Seebeck coefficient measurements were performed on these co-doped ZnO samples. A series of experiments have been performed to detect the p-type conductivity in co-doped ZnO thin films, particularly at low temperature. The negative Seebeck coefficient observed down to 40 K established the n-type behavior in these co-doped samples.

  8. Band gap tuning and room temperature ferromagnetism in Co doped Zinc stannate nanostructures

    NASA Astrophysics Data System (ADS)

    Sumithra, S.; Victor Jaya, N.

    2016-07-01

    The effect of Co doping on structural, optical and magnetic behavior of pure and Co doped Zinc stannate (ZTO) nanostructures was investigated. Pure and Co (1%, 3% & 5%) doped Zn2SnO4 compounds were prepared through simple precipitation route. Formation of cubic inverse spinel structure and metal oxide vibrations of the samples were investigated using XRD and FTIR. Co doping influences the crystallite size producing micro strain in ZTO lattice. Poly dispersed rod like shape of the particles was examined by FESEM. Elemental composition of prepared samples was identified by EDAX analysis. Optical Absorption spectra shows significant red shift on increasing the dopant concentration which indicates the reduction in optical band gap. Visible luminescence observed from photoluminescence studies confirms the presence of oxygen vacancies and trap sites in the lattice. Magnetization analysis reveals the enhanced ferromagnetic behavior in all Co doped ZTO samples. The amplified ferromagnetic ordering in Co doped ZTO compounds has been explained in terms of defects serving as free spin polarized prophetic carriers.

  9. Suppression of boron-oxygen defects in Czochralski silicon by carbon co-doping

    SciTech Connect

    Wu, Yichao; Yu, Xuegong He, Hang; Chen, Peng; Yang, Deren

    2015-03-09

    We have investigated the influence of carbon co-doping on the formation of boron-oxygen defects in Czochralski silicon. It is found that carbon can effectively suppress the formation of boron-oxygen defects. Based on our experiments and first-principle theoretical calculations, it is believed that this effect is attributed to the formation of more energetically favorable carbon-oxygen complexes. Moreover, the diffusion of oxygen dimers in carbon co-doped silicon also becomes more difficult. All these phenomena should be associated with the tensile stress field induced by carbon doping in silicon.

  10. Magnetic and ferroelectric properties of Zn and Mn co-doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Keshari Das, Sangram; Kumar Roul, Binod

    2015-06-01

    This paper reports an approach to obtaining multiferroic properties in co-doped (Zn:Mn) BaTiO3 near room temperature. Interestingly, an unusual magnetic hysteresis loop is observed in the co-doped compositions in which the central portion of the loop is squeezed. However, in the composition Ba0.9Zn0.1Ti0.9Mn0.1O3, a broad magnetic hysteresis loop is observed. Such a magnetic effect is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. The observation of the above type of magnetic properties is likely to be due to the presence of exchange interactions between Mn ions. A lossy-type of ferroelectric hysteresis loop is also observed in co-doped ceramic compositions near room temperature. Author S. K. Das supported financially by CSIR, New Delhi (Grant No. 09/750 (0005)/2009-EMR-I).

  11. Nitrogen and Phosphorous Co-Doped Graphene Monolith for Supercapacitors.

    PubMed

    Wen, Yangyang; Rufford, Thomas E; Hulicova-Jurcakova, Denisa; Wang, Lianzhou

    2016-03-01

    The co-doping of heteroatoms has been regarded as a promising approach to improve the energy-storage performance of graphene-based materials because of the synergetic effect of the heteroatom dopants. In this work, a single precursor melamine phosphate was used for the first time to synthesise nitrogen/phosphorus co-doped graphene (N/P-G) monoliths by a facile hydrothermal method. The nitrogen contents of 4.27-6.58 at% and phosphorus levels of 1.03-3.00 at% could be controlled by tuning the mass ratio of melamine phosphate to graphene oxide in the precursors. The N/P-G monoliths exhibited excellent electrochemical performances as electrodes for supercapacitors with a high specific capacitance of 183 F g(-1) at a current density of 0.05 A g(-1), good rate performance and excellent cycling performance. Additionally, the N/P-G electrode was stable at 1.6 V in 1 m H2 SO4 aqueous electrolyte and delivered a high energy density of 11.33 Wh kg(-1) at 1.6 V. PMID:26834002

  12. Nitrogen-fluorine co-doped titania inverse opals for enhanced solar light driven photocatalysis.

    PubMed

    Rahul, T K; Sandhyarani, N

    2015-11-21

    Three dimensionally ordered nitrogen-fluorine (N-F) co-doped TiO2 inverse opals (IOs) were fabricated by templating with polystyrene (PS) colloidal photonic crystals (CPCs) by infiltration. During preparation, the TiO2 precursor was treated with a mixture of nitric acid and trifluoroacetic acid to facilitate N-F co-doping into the TiO2 lattice. Enhanced solar light absorption was observed in the samples as a consequence of the red shift in the electronic band gap of TiO2 due to N-F co-doping. The photonic band gap (PBG) of these TiO2 IO films was tuned by varying the sphere size of the PS CPC templates. The as-prepared N-F co-doped TiO2 IO films were used as photocatalysts for the degradation of Rhodamine B (RhB) dye under solar light irradiation. A significant enhancement in the photocatalytic activity was observed in N-F co-doped TiO2 IO films prepared using PS spheres of 215 nm as a template, with the red edge of the PBG closer to the electronic band gap (EBG) of TiO2. 100% of the dye molecules were degraded within 2 minutes under direct solar irradiation, which is one of the fastest reaction times ever reported for RhB degradation in the presence of TiO2 photocatalysts. The N-F co-doped TiO2 IO film prepared using PS of 460 nm with its PBG centered at 695 nm also showed good photocatalytic activity. It was found that the IO films displayed improved photocatalytic activity in comparison to ordinary nanocrystalline (nc)-TiO2 films. The enhancement could be attributed to the bandgap scattering effect and the slow photon effect, leading to a significant improvement in solar light harvesting. PMID:26487369

  13. Nitrogen-fluorine co-doped titania inverse opals for enhanced solar light driven photocatalysis

    NASA Astrophysics Data System (ADS)

    Rahul, T. K.; Sandhyarani, N.

    2015-10-01

    Three dimensionally ordered nitrogen-fluorine (N-F) co-doped TiO2 inverse opals (IOs) were fabricated by templating with polystyrene (PS) colloidal photonic crystals (CPCs) by infiltration. During preparation, the TiO2 precursor was treated with a mixture of nitric acid and trifluoroacetic acid to facilitate N-F co-doping into the TiO2 lattice. Enhanced solar light absorption was observed in the samples as a consequence of the red shift in the electronic band gap of TiO2 due to N-F co-doping. The photonic band gap (PBG) of these TiO2 IO films was tuned by varying the sphere size of the PS CPC templates. The as-prepared N-F co-doped TiO2 IO films were used as photocatalysts for the degradation of Rhodamine B (RhB) dye under solar light irradiation. A significant enhancement in the photocatalytic activity was observed in N-F co-doped TiO2 IO films prepared using PS spheres of 215 nm as a template, with the red edge of the PBG closer to the electronic band gap (EBG) of TiO2. 100% of the dye molecules were degraded within 2 minutes under direct solar irradiation, which is one of the fastest reaction times ever reported for RhB degradation in the presence of TiO2 photocatalysts. The N-F co-doped TiO2 IO film prepared using PS of 460 nm with its PBG centered at 695 nm also showed good photocatalytic activity. It was found that the IO films displayed improved photocatalytic activity in comparison to ordinary nanocrystalline (nc)-TiO2 films. The enhancement could be attributed to the bandgap scattering effect and the slow photon effect, leading to a significant improvement in solar light harvesting.

  14. An effective method to detect the Curie transition of Er3+/  Yb3+ co-doped BaTiO3 ceramics by up-conversion photoluminescence intensity ratio

    NASA Astrophysics Data System (ADS)

    Zuo, Qianghui; Luo, Laihui; Li, Weiping; Wang, Feifei

    2016-07-01

    In this work, BaTi1‑x‑y O3:xEr/yYb (BTO:xEr/yYb, x  =  0, y  =  0 x  =  0.005, y  =  0.005 x  =  0.01, y  =  0.005 x  =  0.01, y  =  0.01 x  =  0.015, y  =  0.01) ceramics were prepared using a conventional solid-reaction method to investigate the relation between the Curie transition and up-conversion photoluminescence (UC PL) properties. We did not find that the green or red UC PL absolute intensity of Er3+ ions had any direct correlation with the Curie phase transition. However, the variation of the ratio I g/I r of green and red UC emission intensities with temperature has similar behavior as that of dielectric constant. An evident peak of I g/I r ratio was also obtained at T C in all the BTO:xEr/yYb ceramics with different Er3+/Yb3+ co-doping contents. The present study demonstrates that UC PL intensity ratio, rather than the absolute PL intensity, is an effective optical non-contact method to detect the Curie phase transition of ferroelectrics.

  15. Study of new states in visible light active W, N co-doped TiO{sub 2} photo catalyst

    SciTech Connect

    Sajjad, Ahmed Khan Leghari; Shamaila, Sajjad; Zhang, Jinlong

    2012-11-15

    Highlights: ► Visible light efficient W, N co-doped TiO{sub 2} photo catalysts are prepared by sol–gel. ► Oxygen vacancies are detected in the form of new linkages as N-Ti-O, N-W-O, Ti-O-N and W-O-N. ► W, N co-doped titania has new energy states which narrows the band gap effectively. ► Oxygen vacancies are proved to be the cause for high photo catalytic activity. ► W and N co-doping plays the major role to make the composite thermally stable. -- Abstract: The visible light efficient W, N co-doped TiO{sub 2} photo catalysts are prepared by sol–gel method. New linkages of N, W and O are formed as N-Ti-O, N-W-O, Ti-O-N and W-O-N. Electron paramagnetic resonance illustrates the presence of oxygen vacancies in W, N co-doped TiO{sub 2} acting as trapping agencies for electrons to produce active species. X-ray photoelectron spectroscopy confirms the presence of new energy states. New linkages and oxygen vacancies are proved to be the main cause for the improved photo catalytic performances. W, N co-doped TiO{sub 2} has new energy states which narrow the band gap effectively. W, N co-doped TiO{sub 2} is thermally stable and retains its anatase phase up to 900 °C. 4.5% W, N co-doped TiO{sub 2} showed superior activity for the degradation of Rhodamine B and 2,4-dichlorophenol as compared to pure titania, Degussa P-25, traditional N-doped TiO{sub 2} and pure WO{sub 3}.

  16. Role of Gd3+ ion on downshifting and upconversion emission properties of Pr3+, Yb3+ co-doped YNbO4 phosphor and sensitization effect of Bi3+ ion

    NASA Astrophysics Data System (ADS)

    Dwivedi, A.; Mishra, Kavita; Rai, S. B.

    2016-07-01

    Dual-mode luminescence (downshifting-DS and upconversion-UC) properties of Pr3+/Yb3+ co-doped Y1-xGdxNbO4 (x = 0.0, 0.5, and 1.0) phosphors synthesized by solid state reaction technique have been explored with and without Gd3+ ion. The structural characterizations (XRD, SEM, and FTIR) confirm the pure phase of YNbO4 phosphor. Further, with the Gd3+ ion co-doping, the YNbO4 phosphors having a random shape and the large particle size are found to be transformed into nearly spherical shape particles with the reduced particle size. The optical band gaps (Eg) of Y1-xGdxNbO4 (x = 0.00, 0.25, 0.50, and 1.00) calculated from UV-Vis-NIR measurements are ˜3.69, 4.00, 4.38, and 4.44 eV, respectively. Moreover, YNbO4 phosphor is a promising blue emitting material, whereas Y1-x-y-zPryYbzGdxNbO4 phosphor gives intense green, blue, and red emissions via dual-mode optical processes. The broad blue emission arises due to (NbO4)3- group of the host with λex = 264 nm, whereas Pr3+ doped YNbO4 phosphor gives dominant red and blue emissions along with comparatively weak green emission on excitation with λex = 300 nm and 491 nm. The concentration dependent variation in emission intensity at 491 nm (3P0→3H4 transition) and 612 nm (1D2→3H4 transition); at 612 nm (1D2→3H4 transition) and 658 nm (3P0→3F2 transition) of Pr3+ ion in YNbO4 phosphor with λex = 300 nm and 491 nm excitations, respectively, has been thoroughly explored and explained by the cross-relaxation process through different channels. The sensitization effect of Bi3+ ion co-doping on DS properties of the phosphor has also been studied. The observed DS results have been optimized by varying the concentration of Pr3+ and Bi3+ ions, and the results are explained by the well-known simple band structure model. The study of Gd3+ co-doping reveals noticeable differences in DS characteristics of Y1-xPrxNbO4 phosphors: the overall decrement and increment (except for 612 nm emission) in intensity of DS emission on

  17. PL and EL characteristics in Bi- and rare earth-co-doped (La1-XGaX)2O3 phosphor thin films prepared by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Miyata, Toshihiro; Nishi, Yuki; Minami, Tadatsugu

    2011-12-01

    Multicolor photoluminescence (PL) and electroluminescence (EL) were observed from newly developed Bi- and rare earth (RE)-co-doped (La1-XGaX)2O3 ((La1-XGaX)2O3:Bi,RE) phosphor thin films. (La1-XGaX)2O3:Bi,RE phosphor thin films were prepared by varying the Ga content (Ga/(La+Ga) atomic ratio) or the co-doped RE content (RE/(RE+La+Ga) atomic ratio) under co-doping Bi at a constant content (Bi/(Bi+La+Ga) atomic ratio) of 3 at.% using a combinatorial r.f. magnetron sputtering deposition method. High PL intensity was obtained in postannealed (La0.9Ga0.1)2O3:Bi,RE phosphor thin films prepared with a Ga content around 10 at.%; TFEL devices fabricated using the phosphor thin films exhibited high luminance. The obtained luminance intensities in EL and PL in the phosphor thin films prepared with various contents of co-doped RE, such as Dy, Er, Eu, Tb and Tm changed considerably as the kind and content of RE were varied. Color changes from blue and blue-green to various colors in PL and EL emissions, respectively, were obtained in postannealed (La0.9Ga0.1)2O3:Bi,RE phosphor thin films, i.e., films prepared by co-doping Bi at a constant content with various REs at varying levels of content. All the observed emission peaks in PL and EL from (La0.9Ga0.1)2O3:Bi,RE phosphor thin films were assigned to either the broad emission originating from the transition in Bi3+ or the visible emission peaks originating from the transition in the co-doped trivalent RE ion.

  18. Sulfur and Nitrogen Co-Doped Graphene for Metal-Free Catalytic Oxidation Reactions.

    PubMed

    Duan, Xiaoguang; O'Donnell, Kane; Sun, Hongqi; Wang, Yuxian; Wang, Shaobin

    2015-07-01

    Sulfur and nitrogen co-doped reduced graphene oxide (rGO) is synthesized by a facile method and demonstrated remarkably enhanced activities in metal-free activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol. Based on first-order kinetic model, S-N co-doped rGO (SNG) presents an apparent reaction rate constant of 0.043 ± 0.002 min(-1) , which is 86.6, 22.8, 19.7, and 4.5-fold as high as that over graphene oxide (GO), rGO, S-doped rGO (S-rGO), and N-doped rGO (N-rGO), respectively. A variety of characterization techniques and density functional theory calculations are employed to investigate the synergistic effect of sulfur and nitrogen co-doping. Co-doping of rGO at an optimal sulfur loading can effectively break the inertness of carbon systems, activate the sp(2) -hybridized carbon lattice and facilitate the electron transfer from covalent graphene sheets for PMS activation. Moreover, both electron paramagnetic resonance (EPR) spectroscopy and classical quenching tests are employed to investigate the generation and evolution of reactive radicals on the SNG sample for phenol catalytic oxidation. This study presents a novel metal-free catalyst for green remediation of organic pollutants in water. PMID:25786381

  19. Magnetic structure and interaction in (Sb, Co) co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Samanta, K.; Sardar, M.; Singh, S. P.; Katiyar, R. S.

    2014-10-01

    The magnetic behaviour of (Co, Sb) co-doped ZnO thin films grown by pulsed laser deposition is investigated. The irreversibility (ZFC-FC bifurcation) in low field (H = 100 Oe) magnetization and small hysteresis below 300 K are similar in samples with or without Sb co-doping. Both the phenomena originate from the presence of blocked supermoments in the samples. Incorporation of Sb only increases the saturation magnetization and coercivity. The quantitative increase in moment due to Sb co-doping suggests a transfer of electrons from Co ions to Sb-related acceptor complexes. This is supported by a decrease in the number of electronic transitions from Co d electrons to the conduction band seen in optical transmission spectroscopy when Sb is added. The high field susceptibility data show the existence of supermoments with antiferromagnetic interaction between them. We find that the value of the effective antiferromagnetic molecular field constant decreases with increasing Co concentration, revealing that the supermoments are bound magnetic polarons around intrinsic donors, rather than coming from Co precipitates. True ferromagnetism (overlapping polarons) can emerge either with larger intrinsic donors, or with acceptors with shallower levels, than those created by Sb co-doping. Our results suggest that Sb-related acceptor states may be unstable towards accepting electrons from deep d levels of Co ions.

  20. Co-doped mesoporous titania photocatalysts prepared from a peroxo-titanium complex solution

    SciTech Connect

    El Saliby, Ibrahim; Erdei, Laszlo; McDonagh, Andrew; Kim, Jong-Beom; Kim, Jong-Ho; Shon, Ho Kyong

    2014-01-01

    Graphical abstract: - Highlights: • Peroxotitanium complex for the synthesis of doped photocatalysts. • Fabrication of N doped and N/Ag co-doped photocatalysts. • Characterization of photocatalysts by SEM, XRD, BET, DRS and XPS. • Bench scale photocatalysis under simulated solar light using crystal violet pollutant. - Abstract: In this study, nitrogen doped and nitrogen/silver co-doped TiO{sub 2} photocatalsysts were fabricated using a sol–gel method at room temperature. The obtained gels were neutralized, washed with pure water, and calcined at 400 °C for 4 h. The photocatalysts were characterized by scanning and transmission electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and BET specific surface area. The results showed that spherical particles with anatase structure were produced after annealing at 400 °C. N 1s (400 eV) and Ag 3d (367.3 eV) states indicated that nitrogen doping and silver co-doping were in the form of NO bonds and AgO, respectively. The photocatalytic activity of photocatalysts was investigated using a batch reactor system exposed to artificial solar irradiation. Both nitrogen and silver/nitrogen co-doped materials were effective in the photocatalytic degradation of hexamethyl pararosaniline chloride.

  1. Microstructure and dielectric properties of (Nb + In) co-doped rutile TiO2 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Jinglei; Li, Fei; Zhuang, Yongyong; Jin, Li; Wang, Linghang; Wei, Xiaoyong; Xu, Zhuo; Zhang, Shujun

    2014-08-01

    The (Nb + In) co-doped TiO2 ceramics recently attracted considerable attention due to their colossal dielectric permittivity (CP) (˜100,000) and low dielectric loss (˜0.05). In this research, the 0.5 mol. % In-only, 0.5 mol. % Nb-only, and 0.5-7 mol. % (Nb + In) co-doped TiO2 ceramics were synthesized by standard conventional solid-state reaction method. Microstructure studies showed that all samples were in pure rutile phase. The Nb and In ions were homogeneously distributed in the grain and grain boundary. Impedance spectroscopy and I-V behavior analysis demonstrated that the ceramics may compose of semiconducting grains and insulating grain boundaries. The high conductivity of grain was associated with the reduction of Ti4+ ions to Ti3+ ions, while the migration of oxygen vacancy may account for the conductivity of grain boundary. The effects of annealing treatment and bias filed on electrical properties were investigated for co-doped TiO2 ceramics, where the electric behaviors of samples were found to be susceptible to the annealing treatment and bias field. The internal-barrier-layer-capacitance mechanism was used to explain the CP phenomenon, the effect of annealing treatment and nonlinear I-V behavior for co-doped rutile TiO2 ceramics. Compared with CaCu3Ti4O12 ceramics, the high activation energy of co-doped rutile TiO2 (3.05 eV for grain boundary) was thought to be responsible for the low dielectric loss.

  2. Proton and Gamma Radiation Effects in Undoped, Single-doped and co-doped YLiF4 and LuLiF4

    NASA Technical Reports Server (NTRS)

    Lee, Hyung; Bai, Yingxin; Yu, Kirong; Singh, U.

    2009-01-01

    Proton and gamma radiation effects in various YLiF4 and LuLiF4 crystals have been investigated. The radiation induced color centers compared with six different kinds of crystal samples in ranges up to 200 krads and 200 MeV. The radiation induced absorption coefficients are strongly dependent on polarization and concentration of rare-earth ions.

  3. Intense upconversion luminescence and effect of local environment for Tm3+/Yb3+ co-doped novel TeO2-BiCl3 glass system.

    PubMed

    Wang, Guonian; Dai, Shixun; Zhang, Junjie; Wen, Lei; Yang, Jianhu; Jiang, Zhonghong

    2006-05-15

    We present the results of a study that uses theoretical and experimental methods to investigate the characteristics of the upconversion luminescence of Tm3+/Yb3+ codoped TeO2-BiCl3 glass system as a function of the BiCl3 fraction. These glasses are potentially important in the design of upconversion fiber lasers. Effect of local environment around Tm3+ on upconversion fluorescence intensity was analyzed by theoretical calculations. The structure and spectroscopic properties were investigated in the experiments by measuring the Raman spectra, IR transmission spectra, and absorption and fluorescence intensities at room temperature. The results indicate that blue luminescence quantum efficiency increases with increasing BiCl3 content from 10 to 60 mol%, which were interpreted by the increase of asymmetry of glass structure, decrease of phonon energy and removing of OH- groups. PMID:16378753

  4. Enhanced open circuit voltage in photovoltaic effect of polycrystalline La and Ni co-doped BiFeO3 film

    NASA Astrophysics Data System (ADS)

    Peng, Zeng-Wei; Wang, Ying-Long; Liu, Bao-Ting

    2015-08-01

    Photovoltaic (PV) effect of polycrystalline Bi0.975La0.025Fe0.975Ni0.025O3 (BLFNO) film grown on Pt(111)/Ti/SiO2/Si(001) substrate using sol-gel method has been investigated. The BLFNO film possesses good ferroelectric property and large twice-remanent polarization. It is found that PV response exhibited a strong dependence on the potential of top indium tin oxide (ITO) and bottom Pt electrode. The open circuit voltage is -0.67 V when the potential of ITO electrode is higher than that of Pt electrode and 0.45 V when the potential of ITO electrode is lower than that of Pt electrode. This can be interpreted by the variation of barrier heights at both ITO/BLFNO and BLFNO/Pt interfaces.

  5. A comparative investigation on structure and multiferroic properties of bismuth ferrite thin films by multielement co-doping

    SciTech Connect

    Dong, Guohua; Tan, Guoqiang Luo, Yangyang; Liu, Wenlong; Xia, Ao; Ren, Huijun

    2014-12-15

    Highlights: • Multielement (Tb, Cr and Mn) co-doped BiFeO{sub 3} films were fabricated by CSD method. • Multielement co-doping induces a structural transition. • It is found effective to stabilize the valence of Fe ions at +3 by the strategy. • The co-doping at A/B-sites gives rise to the superior multiferroic properties. - Abstract: (Tb, Cr and Mn) multielement co-doped BiFeO{sub 3} (BTFCMO) thin films were prepared by the chemical solution deposition method on fluorine doped tin oxide (FTO) substrates. X-ray diffraction, Rietveld refinement and Raman analyses revealed that a phase transition from rhombohedral to triclinic structure occurs in the multielement co-doped BiFeO{sub 3} films. It is found that the doping is conducive to stabilizing the valence of Fe ions and reducing leakage current. In addition, the highly enhanced ferroelectric properties with a huge remanent polarization (2P{sub r}) of 239.6 μC/cm{sup 2} and a low coercive field (2E{sub c}) of 615.6 kV/cm are ascribed to the well film texture, the structure transition and the reduced leakage current by the co-doping. Moreover, the structure transition is the dominant factor resulting in the significant enhancement observed in magnetization (M{sub s} ∼ 10.5 emu/cm{sup 3}), owing to the collapse of the space-modulated spin structure. In this contribution, these results demonstrate that the multielement co-doping is in favor of the enhanced multiferroic properties of the BFO films for possible multifunctional applications.

  6. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction.

    PubMed

    Peera, S Gouse; Arunchander, A; Sahu, A K

    2016-08-14

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity

  7. Influence of praseodymium and nitrogen co-doping on the photocatalytic activity of TiO{sub 2}

    SciTech Connect

    Wu, Jing; Liu, Qingju; Gao, Pan; Zhu, Zhongqi

    2011-11-15

    Highlights: {yields} The praseodymium and nitrogen co-doped TiO{sub 2} (Pr-N-TiO{sub 2}) powders were prepared and characterized. {yields} The effects on the photocatalytic activity were studied. {yields} The results exhibit that the spectrum absorption region of the co-doped sample is red-shifted to visible light and the recombination of the photo-generated pairs is inhibited. {yields} The photocatalytic activity is greatly improved. -- Abstract: TiO{sub 2} nanoparticles co-doped with different doping concentration of Pr and N were prepared by sol-gel method combined with microwave chemical method. The samples were characterized by XRD, FT-IR, UV-vis, TEM, XPS, PL, and the photocatalytic activity were investigated by photocatalytic degradation of methylene blue (MB). The results indicate that Pr and N ions incorporate into the lattice of TiO{sub 2}, co-doping restrains the increase of grain size, broadens the absorption region to visible light, and inhibits the recombination of the photo-generated electrons and holes. Moreover, the photocatalytic activity of Pr-N-TiO{sub 2} is remarkable improved due to the synergistic effect of the co-doped ions. The degradation rate of MB in 6 h is 92.81%, which is much higher than that of Degussa P25 (45.01%).

  8. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Peera, S. Gouse; Arunchander, A.; Sahu, A. K.

    2016-07-01

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ~110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and

  9. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Peera, S. Gouse; Arunchander, A.; Sahu, A. K.

    2016-07-01

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ~110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and

  10. Fabrication and photoelectric properties of Er3+ and Yb3+ co-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Feng, Wei; Wang, Xiangfu; Meng, Lan; Yan, Xiaohong

    2016-01-01

    In this paper, the Er3+ and Yb3+ co-doped ZnO films deposited by a novel thermal decomposition method under different annealing temperature process have been reported. The effects of annealing temperature on the morphology and properties of the films are systematically studied. The resulting spectra demonstrate that the Er3+ and Yb3+ co-doped ZnO films possessed the property of up-conversion, converting IR light into visible light that can be absorbed by amorphous silicon solar cell. After all, inner photoelectric effect of the Er3+ and Yb3+ co-doped ZnO films in the amorphous as a light scattering layer are also found with an infrared 980 nm laser as excitation source.

  11. W/Mo co-doped BiVO4 for photocatalytic treatment of polymer-containing wastewater in oilfield

    NASA Astrophysics Data System (ADS)

    Zhou, Ying; Li, Wei; Wan, Wenchao; Zhang, Ruiyang; Lin, Yuanhua

    2015-06-01

    Polymer flooding is an effective way to enhance oil recovery (EOR). However, the treatment of the oily wastewater becomes an urgent issue. Photocatalysis is a promising approach for this purpose. In this report, W/Mo co-doped BiVO4 particles are synthesized by hydrothermal method. W/Mo co-doping could promote an effective separation of photogenerated carriers reflecting from the 6 times higher photocurrent density compared to pure BiVO4. The photodegradation of partially hydrolyzed polyacrylamide (HPAM) over 0.5 at.% W and 1.5 at.% Mo co-doped BiVO4 is 43% under UV-vis light irradiation for 3 h, which is much higher than that of pure BiVO4 (18%).

  12. Local structure investigation of (Co, Cu) co-doped ZnO nanocrystals and its correlation with magnetic properties

    NASA Astrophysics Data System (ADS)

    Tiwari, N.; Doke, S.; Lohar, A.; Mahamuni, Shailaja; Kamal, C.; Chakrabarti, Aparna; Choudhary, R. J.; Mondal, P.; Jha, S. N.; Bhattacharyya, D.

    2016-03-01

    Pure, Co doped and (Co, Cu) co-doped ZnO nanocrystals have been prepared by wet chemical route at room temperature to investigate the effect of Cu doping in Co doped ZnO nanocrystals . The nanocrystals have initially been characterized by X-ray diffraction, FTIR, Raman, optical absorption and EPR spectroscopy and the results were corroborated with DFT based electronic structure calculations. Magnetic properties of the samples have been investigated by studying their magnetic hysteresis behavior and temperature dependence of susceptibilities. Finally the local structure at the host and dopant sites of the nanocrystals have been investigated by Zn, Co and Cu K edges EXAFS measurements with synchrotron radiation to explain their experimentally observed magnetic properties.

  13. Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: Optical and electrochemical properties

    NASA Astrophysics Data System (ADS)

    Romeiro, Fernanda C.; Marinho, Juliane Z.; Lemos, Samantha C. S.; de Moura, Ana P.; Freire, Poliana G.; da Silva, Luis F.; Longo, Elson; Munoz, Rodrigo A. A.; Lima, Renata C.

    2015-10-01

    We report for the first time a rapid preparation of Zn1-2xCoxNixO nanoparticles via a versatile and environmentally friendly route, microwave-assisted hydrothermal (MAH) method. The Co, Ni co-doped ZnO nanoparticles present an effect on photoluminescence and electrochemical properties, exhibiting excellent electrocatalytic performance compared to undoped ZnO sample. Photoluminescence spectroscopy measurements indicated the reduction of the green-orange-red visible emission region after adding Co and Ni ions, revealing the formation of alternative pathways for the generated recombination. The presence of these metallic ions into ZnO creates different defects, contributing to a local structural disorder, as revealed by Raman spectra. Electrochemical experiments revealed that the electrocatalytic oxidation of dopamine on ZnO attached to multi-walled carbon nanotubes improved significantly in the Co, Ni co-doped ZnO samples when compared to pure ZnO.

  14. Structural, optical and magnetic properties of ultrafine mono dispersed Co doped maghemite nanoparticles

    NASA Astrophysics Data System (ADS)

    Gaur, Umesh Kumar; Priyadarshi, Himanshu; Kumar, Anil; Varma, G. D.

    2015-06-01

    Ultrafine Co doped γ- Fe2O3 nanoparticles have been synthesized by co-precipitation method and studied the effect of doping on structural, optical and magnetic properties. The XRD results confirm that synthesized material is γ- Fe2O3 nanoparticles, and the particle sizes are 10 and 3.6 nm for 5 and 10 % Co doped samples, respectively. FESEM, TEM and optical characterization reveal decrease in particle size and increase in band gap with increased doping level. Room temperature M-H plots indicate the increase in magnetization (63.7 emu/g for 10 % doped sample) with increasing doping. A small shift towards positive axis is observed in the M-H plots of doped sample. In this paper the correlation between the structural characteristics and observed optical and magnetic properties has been described and discussed.

  15. Synthesis of N, F and S co-doped graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Kundu, Sumana; Yadav, Ram Manohar; Narayanan, T. N.; Shelke, Manjusha V.; Vajtai, Robert; Ajayan, P. M.; Pillai, Vijayamohanan K.

    2015-07-01

    Graphene quantum dots (GQDs) are a promising category of materials with remarkable size dependent properties like tunable bandgap and photoluminescence along with the possibility of effective chemical functionalization. Doping of GQDs with heteroatoms is an interesting way of regulating their properties. Herein, we report a facile and scalable one-step synthesis of luminescent GQDs, substitutionally co-doped with N, F and S, of ~2 nm average size by a microwave treatment of multi-walled carbon nanotubes in a customized ionic liquid medium. The use of an ionic liquid coupled with the use of a microwave technique enables not only an ultrafast process for the synthesis of co-doped GQDs, but also provides excellent photoluminescence quantum yield (70%), perhaps due to the interaction of defect clusters and dopants.Graphene quantum dots (GQDs) are a promising category of materials with remarkable size dependent properties like tunable bandgap and photoluminescence along with the possibility of effective chemical functionalization. Doping of GQDs with heteroatoms is an interesting way of regulating their properties. Herein, we report a facile and scalable one-step synthesis of luminescent GQDs, substitutionally co-doped with N, F and S, of ~2 nm average size by a microwave treatment of multi-walled carbon nanotubes in a customized ionic liquid medium. The use of an ionic liquid coupled with the use of a microwave technique enables not only an ultrafast process for the synthesis of co-doped GQDs, but also provides excellent photoluminescence quantum yield (70%), perhaps due to the interaction of defect clusters and dopants. Electronic supplementary information (ESI) available: PLQY calculation, MWCNT synthetic details, TGA analysis and tabular format of GQD synthesis processes. See DOI: 10.1039/c5nr02427g

  16. Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: Optical and electrochemical properties

    SciTech Connect

    Romeiro, Fernanda C.; Marinho, Juliane Z.; Lemos, Samantha C.S.; Moura, Ana P. de; Freire, Poliana G.; Silva, Luis F. da; Longo, Elson; Munoz, Rodrigo A.A.; Lima, Renata C.

    2015-10-15

    We report for the first time a rapid preparation of Zn{sub 1−2x}Co{sub x}Ni{sub x}O nanoparticles via a versatile and environmentally friendly route, microwave-assisted hydrothermal (MAH) method. The Co, Ni co-doped ZnO nanoparticles present an effect on photoluminescence and electrochemical properties, exhibiting excellent electrocatalytic performance compared to undoped ZnO sample. Photoluminescence spectroscopy measurements indicated the reduction of the green–orange–red visible emission region after adding Co and Ni ions, revealing the formation of alternative pathways for the generated recombination. The presence of these metallic ions into ZnO creates different defects, contributing to a local structural disorder, as revealed by Raman spectra. Electrochemical experiments revealed that the electrocatalytic oxidation of dopamine on ZnO attached to multi-walled carbon nanotubes improved significantly in the Co, Ni co-doped ZnO samples when compared to pure ZnO. - Graphical abstract: Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: optical and electrochemical properties. Co, Ni co-doped ZnO hexagonal nanoparticles with optical and electrocatalytic properties were successfully prepared for the first time using a microwave hydrothermal method at mild conditions. - Highlights: • Co{sup 2+} and Ni{sup 2+} into ZnO lattice obtained a mild and environmentally friendly process. • The heating method strongly influences in the growth and shape of the particles. • Short-range defects generated by the ions insertion affects the photoluminescence. • Doped ZnO nanoparticles improve the electrocatalytic properties of pure oxide.

  17. Preparation and photocatalytic activity of nonmetal Co-doped titanium dioxide photocatalyst

    NASA Astrophysics Data System (ADS)

    Sun, Xiaogang; Xing, Jun; Qiu, Jingping

    2016-06-01

    A series of boron and sulfur co-doped titanium dioxide (TiO2) photocatalysts were prepared by a sol-gel method using boric acid, thiourea and tetrabutyl titanate [Ti(OC4H9)4] as precursors. The photoabsorbance of as-prepared photocatalysts was measured by UV-Vis diffuse reflectance spectroscopy (DRS), and its microstructure was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 adsorption-desorption measurements. The prepared photocatalysts consisted of the anatase phase mainly in the form of spherical particles. The photocatalytic performance was studied by photodegradation of methyl blue (MB) in water under UV and visible light irradiation. The calcination temperature and the codoping content influenced the photoactivity. The synergistic effect of boron and sulfur co-doping played an important role in improving the photocatalytic activity. In addition, the possibility of cyclic usage of codoped TiO2 was also confirmed, the photocatalytic activity of TiO2 remained above 91% of that of the fresh sample after being used four times. It was shown that the co-doped TiO2 could be activated by visible light and could thus be potentially applied for the treatment of water contaminated by organic pollutants.

  18. Growth of Co-doped (Ba,Sr)TiO 3 single crystals and their characterization

    NASA Astrophysics Data System (ADS)

    Madeswaran, S.; Giridharan, N. V.; Jayavel, R.; Subramanian, C.

    2002-04-01

    Single crystals of Co-doped B 1- xSr xTiO 3 (Co:BST) have been grown by high-temperature solution growth technique. The dopant has significant effect on the growth parameters and considerably reduced the twin formation in the grown crystal. Bulk single crystals of dimensions 5×5×4 mm 3 have been grown with optimized growth parameters. Layer growth and vein-like structure patterns, indicative of 2D nucleation mechanism, have been observed on the grown crystals. The presence of dopant in the grown crystals was confirmed by EDX analysis. For lower doping concentration (0.1 mol%), the crystal possesses tetragonal structure and changes to cubic for higher dopant level (1 and 5 mol%) Co doping in BST increases the dielectric constant values and decreases the Curie temperature ( Tc). The spontaneous polarization ( Ps) value for 0.1 mol% of Co-doped BST crystal is measured to be 22 μc/cm 2 and the value decreases with increasing Co concentration.

  19. Spectroscopic properties of bismuth-germanate glasses co-doped with erbium and holmium ions

    NASA Astrophysics Data System (ADS)

    Ragin, Tomasz; Kochanowicz, Marcin; Żmojda, Jacek; Dorosz, Dominik

    2014-05-01

    In the article an analysis of thermal and spectroscopic properties of heavy metal oxide glasses from the Bi2O3-Ga2O3- Na2O-Ge2O3 system doped with rare earth elements were presented. It has been focused on the elaboration of the glass composition in terms of low phonon energy, high transparency in the range of infrared region and high thermal stability (ΔT=160 °C) required in optical fiber technology. Fabricated glasses co-doped with Er3+/Ho3+ions under 980 nm laser diode excitation exhibit emission at 1.55 μm (Er3+: 4I 13/2 → 4I15/2) and 2.0 μm (Ho3+: 4I7 → 5I8). The emission at 2.0 μm results from the Er3+ → Ho3+energy transfer. Taking into account great thermal stability and good optical properties such as high transparency (up to 80%) or high refractive index (2.23), the fabricated bismuth-germanate glass co-doped with Er3+/Ho3+ is promising material for construction of active optical fibers operating in the range of mid-infrared.

  20. ND laser with co-doped ion(s) pumped by visible laser diodes

    NASA Astrophysics Data System (ADS)

    Scheps, Richard

    1993-04-01

    The 1.06 microns Nd transition in a co-doped Cr,Nd:Gd3Sc2Ga3O12 (Cr,Nd:GSGG) gain element is obtained by diode pumping Cr(3+) at 670 run and produces efficient, low threshold laser operation. Although co-doped Cr,Nd:GSGG was developed for more efficient flashlamp pumping, it has the desirable property of having an extraordinarily broad absorption to allow for efficient diode pumping relative to the ND:YAG laser. The consequent broad bandwidth tolerance of the Cr,Nd:GSGG for the diode pumping radiation allows diode pumping of the 1.06 microns transition without regard to the wavelength of the visible diodes which has the potential for reducing the cost of the semiconductor pump and also demonstrates the extended versatility of these diodes which previously had been restricted to pump the Cr(3+) tunable vibronic lasers. CW and long pulse diode pumping provided pump power levels as high as 300 mW CW and 1 W pulsed. The lowest threshold power was measured at 938 micron W and the highest output power was obtained at 43 mW CW and 173 mW pulsed. The best slope efficiency obtained was 42.1%, 78% of the theoretical maximum. Loss measurements indicate a value of 0.4%/cm.

  1. Er{sup 3+}/Yb{sup 3+}co-doped bismuth molybdate nanosheets upconversion photocatalyst with enhanced photocatalytic activity

    SciTech Connect

    Adhikari, Rajesh; Gyawali, Gobinda; Cho, Sung Hun; Narro-García, R.; Sekino, Tohru; Lee, Soo Wohn

    2014-01-15

    In this paper, we report the microwave hydrothermal synthesis of Er{sup 3+}/Yb{sup 3+} co-doped Bi{sub 2}MoO{sub 6} upconversion photocatalyst. Crystal structure, morphology, elemental composition, optical properties and BET surface area were analyzed in detail. Infrared to visible upconversion luminescence at 532 nm and 546 nm of the co-doped samples was investigated under excitation at 980 nm. The results revealed that the co-doping of Er{sup 3+}/Yb{sup 3+} into Bi{sub 2}MoO{sub 6} exhibited enhanced photocatalytic activity for the decomposition of rhodamine B under simulated solar light irradiation. Enhanced photocatalytic activity can be attributed to the energy transfer between Er{sup 3+}/Yb{sup 3+} and Bi{sub 2}MoO{sub 6} via infrared to visible upconversion from Er{sup 3+}/Yb{sup 3+} ion and higher surface area of the Bi{sub 2}MoO{sub 6} nanosheets. Therefore, this synthetic approach may exhibit a better alternative to fabricate upconversion photocatalyst for integral solar light absorption. - Graphical abstract: Schematic illustration of the upconversion photocatalysis. Display Omitted - Highlights: • Er{sup 3+}/Yb{sup 3+} co-doped Bi{sub 2}MoO{sub 6} upconversion photocatalyst is successfully synthesized. • We obtained the nanosheets having high surface area. • Upconversion of IR to visible light was confirmed. • Upconversion phenomena can be utilized for effective photocatalysis.

  2. Magnetic and optical properties of Co-doped and Mn-doped ZnO nanocrystalline particles

    NASA Astrophysics Data System (ADS)

    Alsmadi, Abdel; Salameh, B.; Shatnawi, M.; Alnawashi, G.; Bsoul, I.

    We carried out a systematic study on the effect of Co doping and Mn doping on the structural, magnetic and optical properties of ZnO nanocrystalline particles, using x-ray diffraction, x-ray photoelectron spectroscopy (XPS), Quantum Design PPMS-9 magnetometry, and Ultra Violet-Visible spectroscopy. The Zn1- x CoxO and Zn1- x MnxO nanoparticles with 0 <= x <= 0 . 1 were successfully prepared by the formal solid-state reaction method. The XPS results and the XRD analysis with full structural Rietveld refinement reveal that both structures have hexagonal wurtzite structure. For all Co-doped ZnO nanoparticles under investigation, the field dependence of the magnetization curves exhibits ferromagnetic behavior with relatively small coercive fields at room temperature. In addition, we found a signature for antiferromagnetic ordering between the Co ions. For the Mn-doped ZnO nanoparticles, we observed ferromagnetic behavior only below 50 K. We also observed a strong correlation between the magnetic and optical behavior of the Co-doped ZnO nanoparticles. Optical diffuse reflectance and absorption spectra exhibit a red shift at room temperature in the absorption band edge with increasing Co-doping. The red shift is attributed to the sp-d exchange interaction between free charge carriers in ZnO band and the localized magnetic moments.

  3. Structural transformation and multiferroic properties of Ba-Mn co-doped BiFeO3

    NASA Astrophysics Data System (ADS)

    Rout, Jyoshna; Choudhary, R. N. P.

    2016-01-01

    Pure BiFeO3 and Bi1-xBaxFe1-xMnxO3 (x = 0.10, 0.20) fine ceramics were synthesized using mechano-synthesis route. The influence of co-doping (Ba-Mn) on structural and multiferroic properties of BiFeO3 has been studied in different experimental conditions. X-ray diffraction patterns, Rietveld structural refinement of XRD patterns and Fourier transform infrared (FTIR) spectra reveal the structural transition from rhombohedral (R3c) to the biphasic structure (R3c + P4mm) on co-doping. The co-doping improves surface morphology and also reduces the particle size. The room temperature M-H loops of all samples showed antiferromagnetic/weak ferromagnetic behavior. Magnetoelectric coupling coefficient determination is carried out to reveal extent of intimate interaction between electric and magnetic dipoles interaction in the samples. Room temperature occurrence of ferromagnetism, ferroelectricity and magnetoelectric effect supports the observation of multiferroism and magnetoelectric coupling in BiFeO3. Thus, co-doping at Bi- and Fe-sites of BiFeO3 can improve multiferroic properties of BiFeO3 for various applications.

  4. Transparent and conductive Al/F and In co-doped ZnO thin films deposited by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Hadri, A.; Taibi, M.; El hat, A.; Mzerd, A.

    2016-02-01

    In doped ZnO (IZO), In-Al co-doped ZnO (IAZO) and In-F co-doped ZnO (IFZO) were deposited on glass substrates at 350 °C by spray pyrolysis technique. The structural, optical and electrical properties of as-deposited thin films were investigated and compared. A polycrystalline and (002) oriented wurtzite crystal structure was confirmed by X-ray patterns for all films; and the full width at half -maximum (FWHM) of (002) diffraction peak increased after co-doping. The investigation of the optical properties was performed using Uv-vis spectroscopy. The average transmittances of all the films were between 70 and 85%. Hall Effect measurements showed that the electrical conductivity of co-doped films increased as compared with IZO thin film. The highest conductivity of about 16.39 Ω-1 cm-1 was obtained for as-deposited IFZO thin film. In addition, the thin films were annealed at 350 °C for two hour under Ar atmosphere and their optical, electrical properties and the associated photoluminescence (PL) responses of selected films were analysed. After annealing, the electrical conductivity of all thin films was improved and the optical transmittance remained above 70%. Room temperature PL revealed that the annealed IAZO thin film had a strong green emission than that of IZO film.

  5. Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass

    NASA Astrophysics Data System (ADS)

    Kochanowicz, Marcin; Żmojda, Jacek; Miluski, Piotr; Ragin, Tomasz; Jeleń, Piotr; Sitarz, Maciej; Dorosz, Dominik

    2015-12-01

    The near-infrared emission of low phonon (805 cm-1) germanate glasses from GeO2-Ga2O3-BaO system co-doped with 0.7Yb2O3/(0.07-0.7)Ho2O3 ions has been investigated. Luminescence at 2.1 μm corresponding to 5I7 → 5I8 transition in holmium was obtained by energy transfer between Yb3+ and Ho3+ ions. The optimization of the activator content and the concentration ratio were conducted with the purpose of maximizing the efficiency of energy transfer and as a consequence luminescence intensity at 2mm. The highest value of the luminescence intensity was obtained in glass codoped with 0.7Yb2O3/0.15 Ho2O3.

  6. Efficient visible upconversion luminescence in Er3+ and Er3+/Yb3+ co-doped Y2O3 phosphors obtained by solution combustion reaction

    NASA Astrophysics Data System (ADS)

    Singh, Vijay; Haritha, P.; Venkatramu, V.; Kim, S. H.

    Combustion derived Er3+ -doped Y2O3 and Er3+/Yb3+co-doped Y2O3 powders have been characterized by X-ray diffraction, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy and laser excited spectroscopy. Formation of Y2O3 phosphor was confirmed by X-ray diffraction and energy dispersive X-ray analysis. The vibrational properties of Y2O3 powder was studied by Fourier transform infrared spectroscopy. The luminescence spectra of Er3+ -doped and Er3+/Yb3+ co-doped Y2O3 powders were studied under 379 nm excitation. The strong up-conversion luminescence for Er3+ -doped and Er3+/Yb3+ co-doped Y2O3 powders have been observed under 978 nm laser excitation. The effect of Yb3+ addition on optical and luminescence properties of Er3+:Y2O3 powders were studied. The ratio of red to green intensity has been enhanced when Er3+ -doped Y2O3 is co-doped with Yb3+ ions. The effect of co-doping of Yb3+ ions on the visible luminescence intensity of Er3+ has been studied and the mechanism responsible for the variation in the green and red intensity is discussed.

  7. Efficient visible upconversion luminescence in Er3+ and Er3+/Yb3+ co-doped Y2O3 phosphors obtained by solution combustion reaction.

    PubMed

    Singh, Vijay; Haritha, P; Venkatramu, V; Kim, S H

    2014-05-21

    Combustion derived Er(3+) -doped Y2O3 and Er(3+)/Yb(3+)co-doped Y2O3 powders have been characterized by X-ray diffraction, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy and laser excited spectroscopy. Formation of Y2O3 phosphor was confirmed by X-ray diffraction and energy dispersive X-ray analysis. The vibrational properties of Y2O3 powder was studied by Fourier transform infrared spectroscopy. The luminescence spectra of Er(3+) -doped and Er(3+)/Yb(3+) co-doped Y2O3 powders were studied under 379nm excitation. The strong up-conversion luminescence for Er(3+) -doped and Er(3+)/Yb(3+) co-doped Y2O3 powders have been observed under 978nm laser excitation. The effect of Yb(3+) addition on optical and luminescence properties of Er(3+):Y2O3 powders were studied. The ratio of red to green intensity has been enhanced when Er(3+) -doped Y2O3 is co-doped with Yb(3+) ions. The effect of co-doping of Yb(3+) ions on the visible luminescence intensity of Er(3+) has been studied and the mechanism responsible for the variation in the green and red intensity is discussed. PMID:24682034

  8. Photocatalytic performance of nitrogen, osmium co-doped TiO2 for removal of eosin yellow in water under simulated solar radiation.

    PubMed

    Kuvarega, Alex T; Krause, Rui W M; Mamba, Bhekie B

    2013-07-01

    Nitrogen, osmium co-doped TiO2 photocatalysts were prepared by a modified sol-gel method using ammonia as the nitrogen source and osmium tetroxide as the source of osmium. The role of rutile phase OsO2 in enhancing the photocatalytic activity of rutile TiO2 towards the degradation of Eosin Yellow was investigated. The materials were characterised by various techniques that include FTIR, Raman, XRD, SEM, EDS, TEM, TGA and DRUV-Vis. The amorphous, oven dried sample was transformed to the anatase and then the rutile phase with increasing calcination temperature. DRUV-Vis analysis revealed a red shift in absorption with increasing calcination temperature, confirmed by a decrease in the band gap of the material. The photocatalytic activity of N, Os co-doped TiO2 was evaluated using eosin yellow degradation and activity increased with increase in calcination temperature under simulated solar irradiation. The rutile phase of the co-doped TiO2 was found to be more effective in degrading the dye (k(a) = 1.84 x 10(-2) min(-1)) compared to the anatase co-doped phase (k(a) = 9.90 x 10(-3) min(-1)). The enhanced photocatalytic activity was ascribed to the synergistic effects of rutile TiO2 and rutile OsO2 in the N, Os co-doped TiO2. PMID:23901525

  9. Influence of Li-N and Li-F co-doping on defect-induced intrinsic ferromagnetic and photoluminescence properties of arrays of ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Ghosh, Shyamsundar; Gopal Khan, Gobinda; Varma, Shikha; Mandal, Kalyan

    2012-08-01

    The role of N/F co-doping on the defect-driven room-temperature d0 ferromagnetism in group-I element Li doped ZnO nanowire arrays has been investigated. The ferromagnetic signature of pristine ZnO nanowires has enhanced significantly after Li doping but the Li-N co-doping has found to be more effective in the stabilization and enhancement in room-temperature ferromagnetism in ZnO nanowires. Saturation magnetization in Li-doped ZnO nanowires found to increase from 0.63 to 2.52 emu/g and the Curie temperature rises up to 648 K when 10 at. % N is co-doped with 6 at. % Li. On the other hand, Li-F co-doping leads to exhibit much poor room-temperature ferromagnetic as well as visible luminescence properties. The valance state of the different dopants is estimated by x-ray photoelectron spectroscopy while the photoluminescence spectra indicate the gradual stabilization of Zn vacancy defects or defect complexes in presence of No acceptor states, which is found to be responsible for the enhancement of intrinsic ferromagnetism in ZnO:Li matrix. Therefore, the Li-N co-doping can be an effective parameter to stabilize, enhance, and tune zinc vacancy-induced room-temperature d0 ferromagnetism in ZnO nanowires, which can be an exciting approach to prepare new class of spintronic materials.

  10. Co-doping of CVD diamond with boron and sulfur

    NASA Astrophysics Data System (ADS)

    Eaton, Sally Catherine

    Boron is well-established as a p-type dopant in diamond, but attempts to find a viable n-type dopant remain unsuccessful. In 1999, sulfur was reported to give n-type conductivity. However, later measurements indicated that the samples contained boron and were p-type. Recently, we showed that diamond co-doped with sulfur and small quantities of boron shows n-type conductivity, which was established by Mott-Schottky analyses, thermoelectric effect, Hall measurements, scanning tunneling spectroscopy (STS), and UV open-circuit photo-potential. At higher boron concentrations, a transition to p-type behavior is observed due to overcompensation. Experiments performed without boron in the feed gas or without residual boron in the reactor chamber showed no sulfur incorporation and no change in conductivity. There is evidence that the excess sulfur concentration in the near-surface region is not stable. At room temperature and below, the activation energies range from 0.06 to 0.12 eV. Above 400K there is an irreversible loss in conductivity and the activation energy increases to approximately 1.3 eV. Additionally, we observed by SIMS that there exists a concentration gradient in sulfur with film depth. This sulfur concentration gradient is also observed in our electrical measurements. STS shows a decrease in conductivity with film depth and Hall effect measurements show both p-type and n-type coefficients for samples which are n-type in the near-surface region. The flat-band potential obtained from the Mott-Schottky experiments is only 1 to 1.5 V more negative on the electrochemical scale than that for boron-doped diamond. This implies that the Fermi level is only 1 to 1.5 eV higher than the Fermi level in boron-doped diamond. This observation implies that the n-type conductivity is not by excitation of electrons to the conduction band, but by an alternate mechanism that occurs in the middle of the band gap. One such possibility is an acceptor impurity band. Electrons from

  11. Highly piezoelectric co-doped AlN thin films for wideband FBAR applications.

    PubMed

    Yokoyama, Tsuyoshi; Iwazaki, Yoshiki; Onda, Yosuke; Nishihara, Tokihiro; Sasajima, Yuichi; Ueda, Masanori

    2015-06-01

    We report piezoelectric materials composed of charge-compensated co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) thin films. The effect of the dopant element into AlN on the crystal structure, and piezoelectric properties of co-doped AlN was determined on the basis of a first-principles calculation, and the theoretical piezoelectric properties were confirmed by experimentally depositing thin films of magnesium (Mg) and zirconium (Zr) co-doped AlN (Mg-Zr-doped AlN). The Mg-Zrdoped AlN thin films were prepared on Si (100) substrates by using a triple-radio-frequency magnetron reactive co-sputtering system. The crystal structures and piezoelectric coefficients (d33) were investigated as a function of the concentrations, which were measured by X-ray diffraction and a piezometer. The results show that the d33 of Mg-Zr-doped AlN at total Mg and Zr concentrations (both expressed as β) of 0.35 was 280% larger than that of pure AlN. The experimentally measured parameter of the crystal structure and d33 of Mg-Zr-doped AlN (plotted as functions of total Mg and Zr concentrations) were in very close agreement with the corresponding values obtained by the first-principle calculations. Thin film bulk acoustic wave resonators (FBAR) employing (Mg,Zr)0.13Al0.87N and (Mg, Hf)0.13 Al0.87N as a piezoelectric thin film were fabricated, and their resonant characteristics were evaluated. The measured electromechanical coupling coefficient increased from 7.1% for pure AlN to 8.5% for Mg-Zr-doped AlN and 10.0% for Mg- Hf-doped AlN. These results indicate that co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) films have potential as piezoelectric thin films for wideband RF applications. PMID:26067035

  12. Solubility control in dilute magnetic semiconductors by using the co-doping method

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori; Fujii, Hitoshi; Bergqvist, Lars; Dederichs, Peter H.; Katayama-Yoshida, Hiroshi

    2009-03-01

    To overcome low solubility limit of magnetic impurities in dilute magnetic semiconductors (DMS) and realize room temperature ferromagnetism, we propose a co-doping method to increase solubility of magnetic impurities in DMS [1]. We calculate electronic structure of (Ga, Mn)As, (Ga, Mn)N, (Ga, Cr)N and (Zn, Cr)Te with interstitial impurities, such as Li, Na and Cu, from first-principles by using the Korringa-Kohn- Rostoker coherent potential approximation (KKR-CPA) method. From the total energy results, it is shown that the mixing energy of magnetic impurity becomes negative and the solubility of magnetic impurities is strongly enhanced under the existence of interstitials [1]. In general, the co-dopants compensate hole carriers, thus the system becomes paramagnetic. However, owing to the large diffusivity of these interstitial impurities, we can anneal out the co-dopants after the crystal growth to recover the ferromagnetism. As an example, kinetic Monte Carlo simulations for the diffusion of interstitial co-dopants in DMS will be shown. [1] K. Sato et al., Jpn. J. Appl. Phys. 46 L1120 (2007)

  13. Piezoelectric Franz-Keldysh effect in a GaN/InGaN/AlGaN multilayer structure

    NASA Astrophysics Data System (ADS)

    Hou, Yong T.; Teo, Kie L.; Li, Ming Fu; Uchida, Kazuo; Tokunaga, Hiroki; Akutsu, Nakao; Matsumoto, Koh

    1999-11-01

    Contactless electroreflectance (CER) of a GaN/InGaN/AlGaN multilayer structure grown on sapphire has been measured in the temperature range of 15K and 450K. Except for the GaN exciton structures, well-defined Franz-Keldysh Oscillations are observed above the AlGaN band gap. An electomodulational model based on complex Airy functions is used to analyze the FKOs line shape. The temperature dependence of transition energies is obtained both for GaN and AlGaN. The magnitude of the built in electric field in AlGaN layer is also determined. The temperature dependence of the electric field is found to be consistent with the variation of thermal strain in the epilayer. It is demonstrated that the built-in electric field can be identified to be due to the piezoelectric effect.

  14. White luminescence of Tm-Dy ions co-doped aluminoborosilicate glasses under UV light excitation

    SciTech Connect

    Liu Shimin; Zhao Gaoling; Lin Xiaohua; Ying Hao; Liu Junbo; Wang Jianxun; Han Gaorong

    2008-10-15

    Tm{sup 3+} and Dy{sup 3+} ions co-doped aluminoborosilicate glasses were prepared in this study. The luminescence properties of the glasses were analyzed. A combination of blue, green, yellow, and red emission bands was shown for these glasses, and white light emission could be observed under UV light excitation. White light luminescence color could be changed by varying the excitation wavelength. Concentration quenching effect was investigated in this paper. Furthermore, the dependence of luminescence properties on glass compositions was studied. Results showed that the luminescence intensity changed with different network modifier oxides, while the white color luminescence was not affected significantly. - Graphical abstract: Tm{sup 3+} and Dy{sup 3+} ions co-doped aluminoborosilicate glasses, which emit white light under UV light excitation, were prepared. The dependence of luminescence properties on glass compositions was studied, and results showed that the white color luminescence was not affected significantly with different network modifier oxides. This adjustability could broaden application areas.

  15. Thermoelectric performance of co-doped SnTe with resonant levels

    NASA Astrophysics Data System (ADS)

    Zhou, Min; Gibbs, Zachary M.; Wang, Heng; Han, Yemao; Li, Laifeng; Snyder, G. Jeffrey

    2016-07-01

    Some group III elements such as Indium are known to produce the resonant impurity states in IV-VI compounds. The discovery of these impurity states has opened up new ways for engineering the thermoelectric properties of IV-VI compounds. In this work, resonant states in SnTe were studied by co-doping with both resonant (In) and extrinsic (Ag, I) dopants. A characteristic nonlinear relationship was observed between the Hall carrier concentration (nH) and extrinsic dopant concentration (NI, NAg) in the stabilization region, where a linear increase of dopant concentration does not lead to linear response in the measured nH. Upon substituting extrinsic dopants beyond a certain amount, the nH changed proportionally with additional dopants (Ag, I) (the doping region). The Seebeck coefficients are enhanced as the resonant impurity is introduced, whereas the use of extrinsic doping only induces minor changes. Modest zT enhancements are observed at lower temperatures, which lead to an increase in the average zT values over a broad range of temperatures (300-773 K). The improved average zT obtained through co-doping indicates the promise of fine carrier density control in maximizing the favorable effect of resonant levels for thermoelectric materials.

  16. Optical and spectroscopic characterization of Er3+-Yb3+co-doped tellurite glasses and fibers

    NASA Astrophysics Data System (ADS)

    Narro-García, R.; Desirena, H.; Chillcce, E. F.; Barbosa, L. C.; Rodriguez, E.; De la Rosa, E.

    2014-04-01

    Optical and spectroscopic properties of Er3+-Yb3+ co-doped TeO2-WO3-Nb2O5-Na2O-Al2O3 glasses and fibers were investigated. Emission spectra and fluorescence lifetimes of 4I13/2 level of Er3+ion as a function of rare earth concentration and fiber length were measured in glasses. Results show that the self-absorption effect broadens the spectral bandwidth of 4I13/2→4I15/2 transition and lengthens the lifetime significantly from 3.5 to 4.6 ms. Fibers were fabricated by the rod-in-tube technique using a Heathway drawing tower. The emission power of these Er3+-Yb3+ co-doped Step Index Tellurite Fibers (SITFs; lengths varying from 2 to 60 cm) were generated by a 980 nm diode laser pump and then the emission power spectra were acquired with an OSA. The maximum emission power spectra, within the 1530-1560 nm region, were observed for fiber lengths ranging from 3 to 6 cm. The highest bandwidth obtained was 108 nm for 8 cm fiber length around 1.53 µm.

  17. Bioinspired synthesis of nitrogen/sulfur co-doped graphene as an efficient electrocatalyst for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Zhang, Huanhuan; Liu, Xiangqian; He, Guangli; Zhang, Xiaoxing; Bao, Shujuan; Hu, Weihua

    2015-04-01

    Efficient electrocatalyst of oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and heteroatom-doped carbon materials have demonstrated promising catalytic performance towards ORR. In this paper we report a bioinspired method to synthesize nitrogen/sulfur (N/S) co-doped graphene as an efficient ORR electrocatalyst via self-polymerization of polydopamine (PDA) thin layer on graphene oxide sheets, followed by reacting with cysteine and finally thermal annealing in Argon (Ar) atmosphere. As-prepared N/S co-doped graphene exhibits significantly enhanced ORR catalytic activity in alkaline solution compared with pristine graphene or N-doped graphene. It also displays long-term operation stability and strong tolerance to methanol poison effect, indicating it a promising ORR electrocatalyst.

  18. Cobalt and sulfur co-doped nano-size TiO2 for photodegradation of various dyes and phenol.

    PubMed

    Siddiqa, Asima; Masih, Dilshad; Anjum, Dalaver; Siddiq, Muhammad

    2015-11-01

    Various compositions of cobalt and sulfur co-doped titania nano-photocatalyst are synthesized via sol-gel method. A number of techniques including X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), Rutherford backscattering spectrometry (RBS), thermal gravimetric analysis (TGA), Raman, N2 sorption, electron microscopy are used to examine composition, crystalline phase, morphology, distribution of dopants, surface area and optical properties of synthesized materials. The synthesized materials consisted of quasispherical nanoparticles of anatase phase exhibiting a high surface area and homogeneous distribution of dopants. Cobalt and sulfur co-doped titania demonstrated remarkable structural and optical properties leading to an efficient photocatalytic activity for degradation of dyes and phenol under visible light irradiations. Moreover, the effect of dye concentration, catalyst dose and pH on photodegradation behavior of environmental pollutants and recyclability of the catalyst is also examined to optimize the activity of nano-photocatalyst and gain a better understanding of the process. PMID:26574093

  19. The influence of Er, Ti co-doping on the multiferroic properties of BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Ma, Yinina; Xing, Wenyu; Chen, Jieyu; Bai, Yulong; Zhao, Shifeng; Zhang, Hao

    2016-02-01

    The pure and Er, Ti co-doped BiFeO3 thin films were prepared by chemistry solution deposition. Enhanced ferroelectric and ferromagnetic properties were obtained, which is mainly attributed to that the effect of co-doping Er and Ti leads to the drastic crystal structural transformation from rhombohedral phase to orthorhombic phase. Thus crystal structural transformation not only changes the switching behavior of the polarization path to improve the ferroelectric polarization, but also suppresses the original spiral spin structure to release the locked magnetization. At the same time, the leakage current density is decreased after doping Er3+ and Ti4+, which results from that the crystal structural transformation changes the leakage current mechanism. The present work provides an available way on improving the multiferroic properties of BiFeO3 thin films.

  20. Preparation and characterization of zinc and copper co-doped WO3 nanoparticles: Application in photocatalysis and photobiology.

    PubMed

    Mohammadi, Sanaz; Sohrabi, Maryam; Golikand, Ahmad Nozad; Fakhri, Ali

    2016-08-01

    In this study, pure, Zn, Cu, Zn,Cu co-doped WO3 nanoparticles samples were prepared by precipitation and co-precipitation methods. These nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), Dynamic light scattering (DLS), UV-visible and photoluminescence (PL) spectroscopy. The synthesized pure, Zn, Cu, Zn,Cu co-doped WO3 nanoparticles have smart optical properties and average sizes with 3.2, 3.12, 3.08 and 2.97eV of band-gap, 18.1, 23.2, 25.7 and 30.2nm, respectively. Photocatalytic activity of four nanoparticles was studying towards degradation of gentamicin antibiotic under ultraviolet and visible light irradiation. The result showed that Zn,Cu co-doped WO3 possessed high photocatalytic activity. The photocatalytic activity of WO3 nanoparticles could be remarkably increased by doping the Zn and Cu impurity. This can be attributed to the fact that the red shift of absorption edge and the trapping effect of the mono and co-doped WO3 nanoparticles. The research result presents a general and effective way to prepare different photocatalysts with enhanced visible and UV light-driven photocatalytic performance. Antibacterial activity of four different WO3 nanoparticles against Escherichia coli bacterium has been assessed by the agar disc method under light irradiation and dark medium. It is concluded from the present findings that WO3 nanoparticles can be used as an efficient antibacterial agent. PMID:27262854

  1. Nitrogen and cobalt co-doped zinc oxide nanowires - Viable photoanodes for hydrogen generation via photoelectrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Patel, Prasad Prakash; Hanumantha, Prashanth Jampani; Velikokhatnyi, Oleg I.; Datta, Moni Kanchan; Hong, Daeho; Gattu, Bharat; Poston, James A.; Manivannan, Ayyakkannu; Kumta, Prashant N.

    2015-12-01

    Photoelectrochemical (PEC) water splitting has been considered as a promising and environmentally benign approach for efficient and economic hydrogen generation by utilization of solar energy. Development of semiconductor materials with low band gap, high photoelectrochemical activity and stability has been of particular interest for a viable PEC water splitting system. In this study, Co doped ZnO, .i.e., (Zn0.95Co0.05)O nanowires (NWs) was selected as the composition for further co-doping with nitrogen by comparing solar to hydrogen efficiency (SHE) of ZnO NWs with that of various compositions of (Zn1-xCox)O NWs (x = 0, 0.05, 0.1). Furthermore, nanostructured vertically aligned Co and N-doped ZnO, .i.e., (Zn1-xCox)O:N NWs (x = 0.05) have been studied as photoanodes for PEC water splitting. An optimal SHE of 1.39% the highest reported so far to the best of our knowledge for ZnO based photoanodes was obtained for the co-doped NWs, (Zn0.95Co0.05)O:N - 600 NWs generated at 600 °C in ammonia atmosphere. Further, (Zn0.95Co0.05)O:N-600 NWs exhibited excellent photoelectrochemical stability under illumination compared to pure ZnO NWs. These promising results suggest the potential of (Zn0.95Co0.05)O:N-600 NWs as a viable photoanode in PEC water splitting cell. Additionally, theoretical first principles study conducted explains the beneficial effects of Co and N co-doping on both, the electronic structure and the band gap of ZnO.

  2. Growth and Characterization of Co-Doped Fluorine and Antimony in Tin Oxide Thin Films Obtained by Ultrasonic Spray Pyrolysis

    NASA Astrophysics Data System (ADS)

    Gaewdang, Thitinai; Wongcharoen, Ngamnit

    Fluorine (F)-doped, antimony (Sb)-doped, fluorine and antimony co-doped tin oxide (SnO2) thin films were prepared by ultrasonic spray pyrolysis technique using SnCl2, NH4F and SbCl3 as precursors of Sn, F and Sb elements respectively. F and Sb doping concentrations carried out from 1 to 20 wt% and 1 to 4 wt% in F-doped and Sb-doped SnO2 films respectively. In F and Sb co-doped SnO2 films, the proportions of F and Sb to Sn in starting solution were 15 and 2 wt% respectively. XRD patterns showed that the preferred orientation of SnO2:F, SnO2:Sb and SnO2:F, Sb is dependent on the doping concentration. The variation of doping concentration and preferred orientation of the films was reflected in their morphology as investigated by SEM. The electrical properties of the films were performed by Hall effect measurements in van der Pauw configuration. The minimum resistivity values of SnO2:F and SnO2:Sb were found in the films doped with 15 wt% of F and 2 wt% of Sb. However, The minimum of resistivity value of F and Sb co-doped SnO2 films is not better than neither the one of F-doped nor the one of Sb-doped SnO2 films. The optical transmission of SnO2:F films was found to increase with increasing in F doping concentration. Whereas the optical transmission of SnO2:Sb was found to decrease with increasing in Sb concentration. The F and Sb co-doped SnO2 films annealed in three different conditions at 500°C show the lower transmission values than the value obtained in the as-prepared SnO2:F, Sb films.

  3. Structural, Optical, and Magnetic Properties of Solution-Processed Co-Doped ZnS Thin Films

    NASA Astrophysics Data System (ADS)

    Goktas, A.; Mutlu, İ. H.

    2016-07-01

    Co-doped ZnS thin films have been grown on glass substrates using solution-processing and dip-coating techniques, and the impact of the Co doping level (0% to 5%) and film thickness on certain characteristics examined. X-ray diffraction study revealed that all the films possessed hexagonal crystal structure. Energy-dispersive x-ray analysis confirmed presence of Zn, Co, and S in the samples. Scanning electron microscopy showed that the film surface was homogeneous and dense with some cracks and spots. X-ray photoelectron spectroscopy confirmed introduction and integration of Co2+ ions into the ZnS thin films. Compared with undoped ZnS, optical studies indicated a reduction in optical bandgap energy (E g) while the refractive index (n), extinction coefficient (k), and dielectric constants (ɛ 1, ɛ 2) increased with film thickness (t) and Co doping level (except for 5%). Photoluminescence spectra showed enhanced luminescence intensity as the Co concentration was increased, while the dependence on t showed an initial increase followed by a decrease. The origin of the observed low-temperature (5 K and 100 K) ferromagnetic order may be related to point defects such as zinc vacancies, zinc interstitials, and sulfide vacancies or to the grain-boundary effect.

  4. Structural, optical, and ferromagnetic properties of Co-doped TiO2 films annealed in vacuum

    NASA Astrophysics Data System (ADS)

    Xu, Jianping; Shi, Shaobo; Li, Lan; Zhang, Xiaosong; Wang, Yaxin; Chen, Ximing; Wang, Jianfeng; Lv, Liya; Zhang, Fengming; Zhong, Wei

    2010-03-01

    Polycrystalline anatase Ti1-xCoxO2 (x =0-0.06) films have been fabricated by sol-gel spin coating. The effects of Co doping on the structural, optical, and magnetic properties are investigated. It is shown that oxygen vacancies and/or defects in the films are generated during thermal treatment in vacuum. Co doping reduces crystal quality and inhibits crystalline grain growth. Due to the introduction of Co, photoluminescence (PL) spectra become weak and the band gap emission has a blueshift. PL spectra reveal that the solubility of Co is lower than 0.02. At 300 K, the saturated magnetization is around 1.8 μB/Co, which is independent of the concentration of Co. This value is approximately equivalent to the average magnetic moment of bulk metallic cobalt (1.75 μB/Co). Zero-field-cooling/field-cooling measurements indicate that room temperature ferromagnetism in Co-doped TiO2 films is not an intrinsic property of the material. The presence of Co metal is identified by x-ray photoelectron spectroscopy and scanning electron microscopy.

  5. RETRACTED: Investigation of structural, optical and electronic properties in Al-Sn co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Pan, Zhanchang; Tian, Xinlong; Wu, Shoukun; Yu, Xia; Li, Zhuliang; Deng, Jianfeng; Xiao, Chumin; Hu, Guanghui; Wei, Zhigang

    2013-01-01

    This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Figures 3 and 4 of this paper have also been presented as belonging to other materials in other publications. This observation is evidence of fraud and therefore it is not certain that the described research and conclusions of this paper belong to the presented images. Figures 3 and 4 of this paper can also be found in: Effect of annealing on the structures and properties of Al and F co-doped ZnO nanostructures, Materials Science in Semiconductor Processing, 2014, 17, 162-167, http://dx.doi.org/10.1016/j.mssp.2013.09.023 Highly transparent and conductive Sn/F and Al co-doped ZnO thin films prepared by sol-gel method, Journal of Alloys and Compounds, 2014,583, 32-38, http://dx.doi.org/10.1016/j.jallcom.2013.06.192 Properties of fluorine and tin co-doped ZnO thin films deposited by sol-gel method, Journal of Alloys and Compounds, 2013,576, 31-37, http://dx.doi.org/10.1016/j.jallcom.2013.04.132

  6. Selective substitution and tetragonality by Co-doping of dysprosium and thulium on dielectric properties of barium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Kim, Jungdae; Kim, Dowan; Kim, Jinseong; Kim, Yong-Nam; Hui, K. N.; Lee, Heesoo

    2011-06-01

    Barium titanate (BaTiO3) ceramics co-doped with rare-earth elements were investigated in terms of selective substitution and tetragonality. The dielectrics were designed by addition of various Dy2O3 and Tm2O3 contents, for a total of 1 mol. % concentration, and analyzed in a temperature range from -55°C to 150°C. The dielectric constant of the 0.7 mol. % Dy2O3 and the 0.3 mol. % Tm2O3 co-doped BaTiO3 was 2250, which was about 27% higher than those of specimens doped with 1 mol. % Tm2O3 and 1 mol. % Dy2O3 at room temperature. The tendency of dielectric properties was verified through the changes of lattice parameters and binding energy. The substitution of Dy3+ led to a decrease of tetragonality and grain growth; however, amphoteric substitution caused by the co-doping of Dy2O3 and Tm2O3 compensated for those adverse effects. It can be concluded that the improvement of dielectric properties originated from the increase of the site substitution rate of Dy3+ and Tm3+ ions according to the ionic size the in rare-earth doped BaTiO3 system.

  7. Improving the ethanol gas-sensing properties of porous ZnO microspheres by Co doping

    SciTech Connect

    Xiao, Qi Wang, Tao

    2013-08-01

    Graphical abstract: - Highlights: • Co-doped porous ZnO microspheres were synthesized. • 3 mol% Co-doped ZnO sensor showed the highest response to ethanol. • 3 mol% Co-doped ZnO sensor exhibited fast recovery property. • 3 mol% Co-doped ZnO sensor exhibited good selectivity and long-term stability. - Abstract: Porous Co-doped ZnO microspheres were prepared by a simple hydrothermal method combined with post-annealing. Co species existed as a form of divalent state in the sample and substituted Zn{sup 2+} sites in ZnO crystal lattice, which was affirmed by X-ray diffraction, UV–vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The gas-sensing measurements demonstrated that the 3 mol% Co-doped ZnO sample showed the highest response value to 100 ppm ethanol at 350 °C, which were 5 folds higher than that of the pure ZnO sample. In addition, the 3 mol% Co-doped ZnO sensor exhibited fast recovery property, good quantitative determination, good selectivity and long-term stability. The superior sensing properties were contributed to high specific surface area combined with the large amount of oxygen vacancies originating from Co doping.

  8. Synthesis and characterization of aluminum–boron co-doped ZnO nanostructures

    SciTech Connect

    Kumar, Vinod; Singh, R.G.; Singh, Neetu; Kapoor, Avinashi; Mehra, R.M.; Purohit, L.P.

    2013-02-15

    Graphical abstract: In this paper, we have reported the development of aluminum boron co-doped ZnO (AZB) nanostructures deposited by sol–gel method using spin coating technique. The structure of AZB nanostructure films has been found to exhibit the hexagonal wurtzite structure. The shape of nanostructures has been changed from seed structure to tetra-pods, tetra-pods to nanorods and finally nanorods to nanofiber with variation in Al concentration. The structural, electrical and optical properties of AZB nanostructures are tuned with shape and size of the nanostructures. The effect of Al concentration on the resistivity (ρ), carrier concentration (n) and mobility (μ) of nanostructure films is shown in graph below. A minimum resistivity of 6.8 × 10{sup −4} Ω cm is obtained in AZB films at doping concentration of B 0.6 at.% and Al 0.4 at.% with a sheet resistance of 24 Ω/□ and transmittance of ∼88% for nanorods structure. These nanostructures could be applicable for a various nano-regime devices such as photovolatics, gas sensing and field emission device. Display Omitted Highlights: ► Synthesis of Al and B co-doped ZnO (AZB) nanostructures. ► Minimum resistivity (ρ) of 6.8 × 10{sup −4} Ω cm in AZB films. ► Minimum sheet resistance (R{sub s}) 24 Ω/□ in nanorods (NRs). ► Maximum transmittance ∼88% in NRs. ► Application in nano-electronic devices. -- Abstract: In this paper, we have reported the development of aluminum boron co-doped ZnO (AZB) nanostructures deposited by sol–gel method using spin coating technique. The structure of AZB nanostructure films has been found to exhibit the hexagonal wurtzite structure. The shape of AZB nanostructures has changed from seed structure to tetra-pods, tetra-pods to nanorods and finally to nanofibers with increase in aluminum concentration. The structural, electrical and optical properties of AZB films are tuned with shape and size of the nanostructures. These AZB nanostructures could be

  9. Synthesis of SrAl2O4:Eu2+ phosphors co-doped with Dy3+, Tb3+, Si4+ and optimization of co-doping amount by response surface method

    NASA Astrophysics Data System (ADS)

    Wang, Huan; Liang, Xiaoping; Liu, Kai; Zhou, Qianqian; Chen, Peng; Wang, Jun; Li, Jianxin

    2016-03-01

    Dy3+ doped SrAl2O4:Eu2+ phosphors were synthesized by high temperature solid phase method in a weak reducing atmosphere (5% H2 + 95% N2). The relationship between the crushed granularity and the phosphors brightness was studied. The effect of co-doping amount of Dy3+, Tb3+ and Si4+ on the structure and properties of SrAl2O4:Eu2+ via response surface method was investigated. Photoluminescence measurement results showed that the initial afterglow brightness of 0.002 mol% Dy3+ doped SrAl2O4:Eu2+0.002 phosphors decreased after first increased within the sintering temperature range from 1150 to 1400 °C, which created the highest value of 12,101 mcd/m2 at 1300 °C. Numerous coarse particles in the powder ought to be crushed for the practical application, however, the brightness became lower accompanied by the decrease of the granularity. The luminescence property of SrAl2O4:Eu2+ sintered at 1200 °C improved by co-doping Dy3+-Tb3+-Si4+. The results of response surface method showed that the influence extent on the luminescence property was Dy3+ > Tb3+ > Si4+. When the co-doping amount in SrAl2O4:Eu2+0.002 phosphors of Dy3+, Tb3+ and Si4+ was 0.001 mol%, 0.0005 mol% and 0.002 mol%, respectively, the initial afterglow brightness of SrAl2O4 was up to the highest value of 12,231 mcd/m2, which was in good agreement on the predicted maximum value of 12,519 mcd/m2 with the optimum co-doping amount of 0.0015 mol% Dy3+, 0.0005 mol% Tb3+ and 0.0017 mol% Si4+. The brightness of co-doped phosphors not only increased by 56.79% than that of SrAl2O4:Eu2+0.002, Dy3+0.002 sintered at 1200 °C, but also was above that of 1300 °C. The emission spectra results showed that, compared with 0.001 mol% Dy3+ doped phosphor, the emission peak of 0.001 mol% Dy3+-0.001 mol% Tb3+ co-doped phosphor generated red shift and increased by 9.3% in emission intensity; 0.001 mol% Dy3+-0.004 mol% Si4+ and 0.001 mol% Dy3+-0.001 mol% Tb3+-0.004 mol% Si4+ co-doped SrAl2O4:Eu2+0.002 emission peak created blue

  10. Slow/fast light using a very short Er3+/Yb3+ co-doped fiber.

    PubMed

    Gan, Jiulin; Chen, Jiali; Xu, Shanhui; Yang, Zhongmin; Jiang, Zhonghong

    2013-03-01

    A slow/fast light device with a sealed size of 130 mm×30 mm×3 mm has been demonstrated. Ultraslow propagation and superluminal propagation with group velocity values from 8.4 to -14.7 m/s are observed in a 3.86 cm long Er3+/Yb3+ co-doped single-mode phosphate glass fiber. The dependence of pump power, modulation frequency, and wavelength on the slow/fast light effect in this fiber is investigated in detail. These results suggest that this compact slow/fast device is more suitable for all-fiber applications than those made by traditional methods. PMID:23455260

  11. Aqueous synthesis and characterization of Ni, Zn co-doped CdSe QDs

    NASA Astrophysics Data System (ADS)

    Thirugnanam, N.; Govindarajan, D.

    2016-01-01

    Ni, Zn co-doped CdSe quantum dots (QDs) were synthesized by chemical precipitation method through aqueous route. The prepared QDs were characterized by X-ray diffraction (XRD) technique, UV-Vis absorption spectroscopy, photoluminescence (PL) spectroscopy and high resolution transmission electron microscopy (HRTEM). XRD technique results indicate that the prepared samples have a zinc blende cubic phase. From UV-Vis absorption spectroscopy technique, the prepared samples were blue shifted with respect to their bulk counter part due to quantum confinement effect. Among different doping ratios examined, a maximum PL emission intensity was observed for CdSe:Ni(1 %):Zn(1 %) QDs. HRTEM pictures show that the prepared QDs were in spherical shape.

  12. Hydrothermal fabrication of multi-functional Eu3+ and Tb3+ co-doped BiPO4: Photocatalytic activity and tunable luminescence properties

    NASA Astrophysics Data System (ADS)

    Wang, Yao; Huang, Hongwei; Quan, Chaoming; Tian, Na; Zhang, Yihe

    2016-01-01

    We demonstrated for first time the tunable photoluminescence (PL) properties and photocatalytic activity of the Tb3+ and Eu3+ co-doped BiPO4 assemblies. They are fabricated via a facile hydrothermal approach. Through co-doping of Eu3+ and Tb3+ ions and changing the doping ratio, the emission color of the co-doped BiPO4 phosphors can be tuned precisely from green to yellow and red. Meanwhile, a very efficient energy transfer from Tb3+ to Eu3+ can be observed. Fascinatingly, a warmwhite color has been realized in the co-doped sample by tuning the ratio of Tb3+/Eu3+ to a certain value as displayed in the CIE chromaticity diagram. The doped BiPO4 samples also exhibit significantly enhanced photocatalytic activity compared to the pristine BiPO4 pertaining to Rhodamine (RhB) degradation under UV light. This enhancement should be attributed to the trapping electron effect induced by ion doping that endows BiPO4 with high separation of photoinduced electron-hole pairs, thereby greatly promoting the photocatalytic reactivity. It was corroborated by the electrochemical impedance spectra (EIS). Moreover, the crystal structure, microstructure and optical properties of as-prepared samples were investigated in details.

  13. Dynamics of iron-acceptor-pair formation in co-doped silicon

    SciTech Connect

    Bartel, T.; Gibaja, F.; Graf, O.; Gross, D.; Kaes, M.; Heuer, M.; Kirscht, F.; Möller, C.; Lauer, K.

    2013-11-11

    The pairing dynamics of interstitial iron and dopants in silicon co-doped with phosphorous and several acceptor types are presented. The classical picture of iron-acceptor pairing dynamics is expanded to include the thermalization of iron between different dopants. The thermalization is quantitatively described using Boltzmann statistics and different iron-acceptor binding energies. The proper understanding of the pairing dynamics of iron in co-doped silicon will provide additional information on the electronic properties of iron-acceptor pairs and may become an analytical method to quantify and differentiate acceptors in co-doped silicon.

  14. Enhancement of luminescence emission from GdVO{sub 4}:Er{sup 3+}/Yb{sup 3+} phosphor by Li{sup +} co-doping

    SciTech Connect

    Gavrilović, Tamara V.; Jovanović, Dragana J. Lojpur, Vesna M.; Đorđević, Vesna; Dramićanin, Miroslav D.

    2014-09-15

    This paper demonstrates the effects of Li{sup +} co-doping on the structure, morphology, and luminescence properties of GdVO{sub 4}:Er{sup 3+}/Yb{sup 3+} phosphor prepared using a high-temperature solid-state chemistry method. The GdVO{sub 4}:Er{sup 3+}/Yb{sup 3+} powders synthesized with the Li{sup +} co-dopant (in concentrations of 0, 5, 10, and 15 mol%) are characterized by X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectroscopy. Structural analysis showed that powders co-doped with Li{sup +} have larger crystallite sizes and slightly smaller crystal lattice parameters than powders prepared without Li{sup +} ions. Photoluminescence down-conversion (345-nm excitation) and up-conversion (980-nm excitation) spectra show characteristic Er{sup 3+} emissions, with the most intense bands peaking at 525 nm ({sup 2}H{sub 11/2}→{sup 4}I{sub 15/2} transition) and 552 nm ({sup 4}S{sub 3/2}→{sup 4}I{sub 15/2}). The intensity of up-conversion emission from GdVO{sub 4}:Er{sup 3+}/Yb{sup 3+} is enhanced (by a factor of four) by co-doping with 5 mol% of Li{sup +} ions. The mechanisms responsible for this emission enhancement are discussed. - Graphical abstract: UC emission spectra for GdVO{sub 4}:1.5-mol% Er{sup 3+}/20-mol% Yb{sup 3+} powders co-doped with different concentrations of Li{sup +} ions, recorded under 980-nm excitation. - Highlights: • 5-mol% Li{sup +} co-doped powders have 400% enhanced up-conversion emission intensity. • 15-mol% Li{sup +} co-doping produces 40% higher emission in down-conversion. • Li{sup +} co-doped powders have larger crystallite size and smaller lattice parameters.

  15. AlGaN/GaN field effect transistors for power electronics—Effect of finite GaN layer thickness on thermal characteristics

    SciTech Connect

    Hodges, C. Anaya Calvo, J.; Kuball, M.; Stoffels, S.; Marcon, D.

    2013-11-11

    AlGaN/GaN heterostructure field effect transistors with a 150 nm thick GaN channel within stacked Al{sub x}Ga{sub 1−x}N layers were investigated using Raman thermography. By fitting a thermal simulation to the measured temperatures, the thermal conductivity of the GaN channel was determined to be 60 W m{sup −1} K{sup −1}, over 50% less than typical GaN epilayers, causing an increased peak channel temperature. This agrees with a nanoscale model. A low thermal conductivity AlGaN buffer means the GaN spreads heat; its properties are important for device thermal characteristics. When designing power devices with thin GaN layers, as well as electrical considerations, the reduced channel thermal conductivity must be considered.

  16. Tuning the metal-insulator transition via epitaxial strain and Co doping in NdNiO3 thin films grown by polymer-assisted deposition

    NASA Astrophysics Data System (ADS)

    Yao, Dan; Shi, Lei; Zhou, Shiming; Liu, Haifeng; Zhao, Jiyin; Li, Yang; Wang, Yang

    2016-01-01

    The epitaxial NdNi1-xCoxO3 (0 ≤ x ≤ 0.10) thin films on (001) LaAlO3 and (001) SrTiO3 substrates were grown by a simple polymer-assisted deposition technique. The co-function of the epitaxial strain and Co doping on the metal-insulator transition in perovskite nickelate NdNiO3 thin films is investigated. X-ray diffraction and scanning electron microscopy reveal that the as-prepared thin films exhibit good crystallinity and heteroepitaxy. The temperature dependent resistivities of the thin films indicate that both the epitaxial strain and Co doping lower the metal-insulator (MI) transition temperature, which can be treated as a way to tune the MI transition. Furthermore, under the investigated Co-doping levels, the MI transition temperature (TMI) shifts to low temperatures with Co content increasing under both compressive and tensile strain, and the more distinction is in the former situation. When x is increased up to 0.10, the insulating phase is completely suppressed under the compressive strain. With the strain increases from compression to tension, the resistivities are enhanced both in the metal and insulating regions. However, the Co-doping effect on the resistivity shows a more complex situation. As Co content x increases from zero to 0.10, the resistivities are reduced both in the metal and insulating regions under the tensile strain, whereas they are enhanced in the high-temperature metal region under the compressive strain. Based on the temperature dependent resistivity in the metal regions, it is suggested that the electron-phonon coupling in the films becomes weaker with the increase of both the strain and Co-doping.

  17. Improving the oxidation potential of Sb-doped SnO2 electrode by Zn/Sb co-doping

    NASA Astrophysics Data System (ADS)

    Chen, Aqing; Bin Li, Bin; Miljkovic, Bojan; Souza, Christina; Zhu, Kaigui; Ruda, Harry E.

    2014-07-01

    Inorganic oxides are recognized as attractive materials for developing anodes for wastewater treatment, potentially offering a cost effective solution for electro-oxidation. A key parameter in measuring the effectiveness of different anode materials is the oxygen over potential. In this paper, we study the role of Zn and Sb co-doping of SnO2 thin films to achieve enhanced oxidation potentials, suitable for use in wastewater treatment. The morphology, chemical, and electrochemical properties of the films were characterized, and as a result of an optimization study, suitable anode materials for wastewater treatment are identified.

  18. Effect of Temperature on GaGdO/GaN Metal Oxide Semiconductor Field Effect Transistors

    SciTech Connect

    Abernathy, C.R.; Baca, A.; Chu, S.N.G.; Hong, M.; Lothian, J.R.; Marcus, M.A.; Pearton, S.J.; Ren, F.; Schurman, M.J.

    1998-10-14

    GaGdO was deposited on GaN for use as a gate dielectric in order to fabricate a depletion metal oxide semiconductor field effect transistor (MOSFET). This is the fmt demonstration of such a device in the III-Nitride system. Analysis of the effect of temperature on the device shows that gate leakage is significantly reduced at elevated temperature relative to a conventional metal semiconductor field effeet transistor (MESFET) fabricated on the same GaN layer. MOSFET device operation in fact improved upon heating to 400 C. Modeling of the effeet of temperature on contact resistance suggests that the improvement is due to a reduction in the parasitic resistances present in the device.

  19. Effect of Fe and Co doping on electrical and thermal properties of La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}(Fe, Co){sub x}O{sub 3} manganites

    SciTech Connect

    Varshney, Dinesh; Mansuri, Irfan; Shaikh, M.W.; Kuo, Y.K.

    2013-11-15

    Graphical abstract: - Highlights: • Low temperature resistivity minimum contributes to Coulomb and Kondo scattering. • Metallic resistivity shows electron, magnon and phonon scattering are significant. • At high temperatures small polaron conduction mechanism is viable. • Susceptibility measurements show ferromagnetic–paramagnetic transition. - Abstract: The effect of Fe and Co doping on structural, electrical and thermal properties of half doped La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}(Fe, Co){sub x}O{sub 3} is investigated. The structure of these crystallizes in to orthorhombically distorted perovskite structure. The electrical resistivity of La{sub 0.5}Ce{sub 0.5}MnO{sub 3} exhibits metal-semiconductor transition (T{sub MS} at ∼225 K). However, La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}TM{sub x}O{sub 3} (TM = Fe, Co; 0.0 ≤ x ≤ 0.1) manganites show semiconducting behavior. The thermopower measurements infer hole as charge carriers and electron–magnon as well spin wave fluctuation mechanism are effective at low temperature domain and SPC model fits the observed data at high temperature. The magnetic susceptibility measurement confirms a transition from paramagnetic to ferromagnetic phase. The observed peaks in the specific heat measurements, shifts to lower temperatures and becomes progressively broader with doping of transition metals on Mn-site. The thermal conductivity is measured in the temperature range of 10–350 K with a magnitude in between 10 and 80 mW/cm K.

  20. Piezotronic Effect in Polarity-Controlled GaN Nanowires.

    PubMed

    Zhao, Zhenfu; Pu, Xiong; Han, Changbao; Du, Chunhua; Li, Linxuan; Jiang, Chunyan; Hu, Weiguo; Wang, Zhong Lin

    2015-08-25

    Using high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NWs with an atomic force microscopy tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by the piezotronic effect. In contrast, the normal compressive force cannot change the electron transport characteristics in m-plane GaN NWs whose piezoelectric polarization axis is turned in the transverse direction. This observation provided solid evidence for clarifying the difference between the piezotronic effect and the piezoresistive effect. We further demonstrated a high sensitivity of the m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in any direction. PMID:26256533

  1. All-inorganic colloidal silicon nanocrystals—surface modification by boron and phosphorus co-doping

    NASA Astrophysics Data System (ADS)

    Fujii, Minoru; Sugimoto, Hiroshi; Imakita, Kenji

    2016-07-01

    Si nanocrystals (Si-NCs) with extremely heavily B- and P-doped shells are developed and their structural and optical properties are studied. Unlike conventional Si-NCs without doping, B and P co-doped Si-NCs are dispersible in alcohol and water perfectly without any surface functionalization processes. The colloidal solution of co-doped Si-NCs is very stable and no precipitates are observed for more than 5 years. The co-doped colloidal Si-NCs exhibit size-controllable photoluminescence (PL) in a very wide energy range covering 0.85 to 1.85 eV. In this paper, we summarize the structural and optical properties of co-doped Si-NCs and demonstrate that they are a new type of environmentally-friendly nano-light emitter working in aqueous environments in the visible and near infrared (NIR) ranges.

  2. All-inorganic colloidal silicon nanocrystals-surface modification by boron and phosphorus co-doping.

    PubMed

    Fujii, Minoru; Sugimoto, Hiroshi; Imakita, Kenji

    2016-07-01

    Si nanocrystals (Si-NCs) with extremely heavily B- and P-doped shells are developed and their structural and optical properties are studied. Unlike conventional Si-NCs without doping, B and P co-doped Si-NCs are dispersible in alcohol and water perfectly without any surface functionalization processes. The colloidal solution of co-doped Si-NCs is very stable and no precipitates are observed for more than 5 years. The co-doped colloidal Si-NCs exhibit size-controllable photoluminescence (PL) in a very wide energy range covering 0.85 to 1.85 eV. In this paper, we summarize the structural and optical properties of co-doped Si-NCs and demonstrate that they are a new type of environmentally-friendly nano-light emitter working in aqueous environments in the visible and near infrared (NIR) ranges. PMID:27189818

  3. Structural, magnetic and electronic structure properties of Co doped ZnO nanoparticles

    SciTech Connect

    Kumar, Shalendra; Song, T.K.; Gautam, Sanjeev; Chae, K.H.; Kim, S.S.; Jang, K.W.

    2015-06-15

    Highlights: • XRD and HR-TEM results show the single phase nature of Co doped ZnO nanoparticles. • XMCD and dc magnetization results indicate the RT-FM in Co doped ZnO nanoparticles. • Co L{sub 3,2} NEXAFS spectra infer that Co ions are in 2+ valence state. • O K edge NEXAFS spectra show that O vacancy increases with Co doping in ZnO. - Abstract: We reported structural, magnetic and electronic structure studies of Co doped ZnO nanoparticles. Doping of Co ions in ZnO host matrix has been studied and confirmed using various methods; such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersed X-ray (EDX), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, magnetic hysteresis loop measurements and X-ray magnetic circular dichroism (XMCD). From the XRD and HR-TEM results, it is observed that Co doped ZnO nanoparticles have single phase nature with wurtzite structure and exclude the possibility of secondary phase formation. FE-SEM and TEM micrographs show that pure and Co doped nanoparticles are nearly spherical in shape. O K edge NEXAFS spectra indicate that O vacancies increase with Co doping. The Co L{sub 3,2} edge NEXAFS spectra revealed that Co ions are in 2+ valence state. DC magnetization hysteresis loops and XMCD results clearly showed the intrinsic origin of temperature ferromagnetism in Co doped ZnO nanoparticles.

  4. Ga content and thickness inhomogeneity effects on Cu(In, Ga)Se2 solar modules

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaobo; Cheng, Tzu-Huan; Liu, Chee Wee

    2016-07-01

    The fluctuation of Ga content and absorption layer thickness of Cu(In, Ga)Se2 (CIGS) solar modules is investigated by 3-dimensional numerical simulation. The band gap of CIGS is increased by the increasing Ga content, and the residual compressive strain. Strain effect worsens the degradation of the power conversion efficiency of CIGS module in addition to Ga fluctuation. The intracell Ga fluctuation degrades the open circuit voltage due to the minimum open circuit voltage in the parallel configuration, and also affects the short circuit current due to the Ga-dependent light absorption. The intercell Ga fluctuation leads to a more significant degradation for CIGS solar module efficiency than the intracell Ga fluctuation due to the additional degradation of the fill factor. The thickness fluctuation has a small effect on open circuit voltage, but causes strong degradation of short circuit current and fill factor, which leads to a more significant degradation on power conversion efficiency than Ga fluctuation to the same fluctuation percentage. In reality, the thickness can be tightly controlled within the fluctuation of 5% or less. [Figure not available: see fulltext.

  5. Luminescence characteristics of ZnS nanoparticles co-doped with Ni 2+ and Mn 2+

    NASA Astrophysics Data System (ADS)

    Yang, Ping; Lü, Mengkai; Xu, Dong; Yuan, Duorong; Song, Chunfeng; Liu, Suwen; Cheng, Xiufeng

    2003-12-01

    ZnS nanoparticles doped with Ni 2+ and Mn 2+ have been prepared by co-precipitation from homogeneous solutions of Zn, Ni and Mn salt compounds, with S 2- as precipitating anion formed by decomposition of thioacetamide (TAA). X-ray diffraction analysis shows that the average crystalline particle size of the doped and undoped ZnS nanometer scale samples is about 2-4 nm. A novel luminescent property has been observed in the photoluminescence (PL) spectra of the ZnS nanoparticles co-doped with Ni 2+ and Mn 2+. The ZnS nanoparticles can be doped with Ni 2+ and Mn 2+ during synthesis without altering the X-ray diffraction pattern. However, the emission wavelengths (with a color range from blue to green, λem=475-540 nm) and PL intensities of the co-doped samples vary with changing the impurity mole ratios of Ni 2+ and Mn 2+ in the co-doped samples. When the mole ratios of Ni 2+ and Mn 2+ in the co-doped sample are 0.3% and 2.0%, respectively, the relative fluorescence intensity of the co-doped samples is about four times of that of un-doped ZnS nanocrystals. The PL properties of the co-doped samples are dramatically different from those of Ni 2+- and Mn 2+-doped ZnS nanocrystals.

  6. Soft x-ray absorption spectroscopy on Co doped ZnO: structural distortions and electronic structure

    NASA Astrophysics Data System (ADS)

    Kowalik, I. A.; Guziewicz, E.; Godlewski, M.; Arvanitis, D.

    2016-05-01

    We present soft x-ray absorption spectra from a series of Co doped ZnO films. We discuss systematic variations of the Co L-edge white line intensity and multiplet features for this series of samples. We document sizeable differences in the electronic state of the Co ionic cores, as well as in the local environment of the host lattice atoms, characterised by means of x-ray absorption spectra at the O K-edge and Zn L-edges. Model calculations allow to correlate the observed effects to small structural distortions of the ZnO lattice.

  7. Effective mass from microwave photoresistance measurements in GaAs/AlGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Hatke, A. T.; Zudov, M. A.; Watson, J. D.; Manfra, M. J.; Pfeiffer, L. N.; West, K. W.

    2013-08-01

    We have performed microwave photoresistance measurements in high mobility GaAs/AlGaAs quantum wells and investigated the value of the effective mass. The effective mass, obtained from the period of microwave-induced resistance oscillations (MIRO), was found to be about 12 % lower than the band mass in GaAs, m*b. In contrast, the measured magneto-plasmon dispersion (MPR) revealed an effective mass which is close to m*b, in accord with previous studies. These findings suggest that, in contrast to MPR, the MIRO dispersion contains corrections due to electron-electron interaction effects.

  8. Rutile-type Co doped SnO2 diluted magnetic semiconductor nanoparticles: Structural, dielectric and ferromagnetic behavior

    NASA Astrophysics Data System (ADS)

    Mehraj, Sumaira; Shahnawaze Ansari, M.; Alimuddin

    2013-12-01

    Nanoparticles of basic composition Sn1-xCoxO2 (x=0.00, 0.01, 0.03, 0.05 and 0.1) were synthesized through the citrate-gel method and were characterized for structural properties using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). XRD analysis of the powder samples sintered at 500 °C for 12 h showed single phase rutile type tetragonal structure and the crystallite size decreased as the cobalt content was increased. FT-IR spectrum displayed various bands that came due to fundamental overtones and combination of O-H, Sn-O and Sn-O-Sn entities. The effect of Co doping on the electrical and magnetic properties was studied using dielectric spectroscopy and vibrating sample magnetometer (VSM) at room temperature. The dielectric parameters (ε, tan δ and σac) show their maximum value for 10% Co doping. The dielectric loss shows anomalous behavior with frequency where it exhibits the Debye relaxation. The variation of dielectric properties and ac conductivity with frequency reveals that the dispersion is due to the Maxwell-Wagner type of interfacial polarization in general and hopping of charge between Sn2+ and Sn4+ as well as between Co2+ and Co3+ ions. The complex impedance analysis was used to separate the grain and grain boundary contributions in the system which shows that the conduction process in grown nanoparticles takes place predominantly through grain boundary volume. Hysteresis loops were observed clearly in M-H curves from 0.01 to 0.1% Co doped SnO2 samples. The saturation magnetization of the doped samples increased slightly with increase of Co concentration. However pure SnO2 displayed paramagnetism which vanished at higher values of magnetic field.

  9. Evidence for effective mass reduction in GaAs/AlGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Hatke, A. T.; Zudov, M. A.; Watson, J. D.; Manfra, M. J.; Pfeiffer, L. N.; West, K. W.

    2013-04-01

    We have performed microwave photoresistance measurements in high mobility GaAs/AlGaAs quantum wells and investigated the value of the effective mass. Surprisingly, the effective mass, obtained from the period of microwave-induced resistance oscillations, is found to be about 12% lower than the band mass in GaAs, mb. This finding provides strong evidence for electron-electron interactions which can be probed by microwave photoresistance in very high Landau levels. In contrast, the measured magnetoplasmon dispersion revealed an effective mass which is close to mb, in accord with previous studies.

  10. Simultaneous enhancement of magnetic and ferroelectric properties in Dy and Cr co-doped BiFeO3 nanoparticles.

    PubMed

    Mao, Weiwei; Wang, Xingfu; Chu, Liang; Zhu, Yiyi; Wang, Qi; Zhang, Jian; Yang, Jianping; Li, Xing'ao; Huang, Wei

    2016-03-01

    Multiferroic BiFeO3 (BFO), Bi0.95Dy0.05FeO3 and Bi0.95Dy0.05Fe0.95Cr0.05O3 samples were successfully synthesized by a carbon microsphere-assisted sol-gel (CSG) method. X-ray diffraction analysis confirmed a lattice distortion from a rhombohedral structure to a tetragonal structure upon doping Dy and Cr in BFO. The morphology of BFO and doped BFO could be effectively controlled to form nanoparticles, due to the nucleation sites of the carbon microspheres. The co-doping of Dy and Cr in BFO had a significant improvement effect on the magnetic properties, with the remnant magnetization being 0.557 emu g(-1), due to the structural phase transition, size effects and the strong ferromagnetic interaction between Fe(3+)-O-Cr(3+) ions arising from Cr substitution. Meanwhile, the doping of Dy into BFO effectively reduced the leakage current and enhanced the ferroelectric properties. The simultaneous enhancement of magnetic and ferroelectric properties shows the great potential application of Dy- and Cr-co-doped BFO in future multifunctional devices. PMID:26862599

  11. Effect of doping (C or N) and co-doping (C+N) on the photoactive properties of magnetron sputtered titania coatings for the application of solar water-splitting.

    PubMed

    Rahman, M; Dang, B H Q; McDonnell, K; MacElroy, J M D; Dowling, D P

    2012-06-01

    The photocatalytic splitting of water into hydrogen and oxygen using a photoelectrochemical (PEC) cell containing titanium dioxide (TiO2) photoanode is a potentially renewable source of chemical fuels. However, the size of the band gap (-3.2 eV) of the TiO2 photocatalyst leads to its relatively low photoactivity toward visible light in a PEC cell. The development of materials with smaller band gaps of approximately 2.4 eV is therefore necessary to operate PEC cells efficiently. This study investigates the effect of dopant (C or N) and co-dopant (C+N) on the physical, structural and photoactivity of TiO2 nano thick coating. TiO2 nano-thick coatings were deposited using a closed field DC reactive magnetron sputtering technique, from titanium target in argon plasma with trace addition of oxygen. In order to study the influence of doping such as C, N and C+N inclusions in the TiO2 coatings, trace levels of CO2 or N2 or CO2+N2 gas were introduced into the deposition chamber respectively. The properties of the deposited nano-coatings were determined using Spectroscopic Ellipsometry, SEM, AFM, Optical profilometry, XPS, Raman, X-ray diffraction UV-Vis spectroscopy and tri-electrode potentiostat measurements. Coating growth rate, structure, surface morphology and roughness were found to be significantly influenced by the types and amount of doping. Substitutional type of doping in all doped sample were confirmed by XPS. UV-vis measurement confirmed that doping (especially for C doped sample) facilitate photoactivity of sputtered deposited titania coating toward visible light by reducing bandgap. The photocurrent density (indirect indication of water splitting performance) of the C-doped photoanode was approximately 26% higher in comparison with un-doped photoanode. However, coating doped with nitrogen (N or N+C) does not exhibit good performance in the photoelectrochemical cell due to their higher charge recombination properties. PMID:22905523

  12. Resistive switching: An investigation of the bipolar–unipolar transition in Co-doped ZnO thin films

    SciTech Connect

    Santos, Daniel A.A.; Zeng, Hao; Macêdo, Marcelo A.

    2015-06-15

    Highlights: • A purely bipolar behavior on a Co-doped ZnO thin film has been demonstrated. • We have shown what can happen if a unipolar test is performed in a purely bipolar device. • An explanation for how a sample can show a purely bipolar switching behavior was suggested. • An important open issue about resistive switching effect was put in debate. - Abstract: In order to investigate the resistive switching effect we built devices in a planar structure in which two Al contacts were deposited on the top of the film and separated by a small gap using a shadow mask. Therefore, two samples of 10% Co-doped ZnO thin films were sputtered on glass substrate. High resolution X-ray diffraction (HRXRD) revealed a highly c-axis oriented crystalline structure, without secondary phase. The high resolution scanning electron microscopy (HRSEM) showed a flat surface with good coverage and thickness about 300 nm. A Keithley 2425 semiconductor characterization system was used to perform the resistive switching tests in the bipolar and unipolar modes. Considering only the effect of compliance current (CC), the devices showed a purely bipolar behavior since an increase in CC did not induce a transition to unipolar behavior.

  13. Near-infrared multi-wavelengths long persistent luminescence of Nd3+ ion through persistent energy transfer in Ce3+, Cr3+ co-doped Y3Al2Ga3O12 for the first and second bio-imaging windows

    NASA Astrophysics Data System (ADS)

    Xu, Jian; Tanabe, Setsuhisa; Sontakke, Atul D.; Ueda, Jumpei

    2015-08-01

    We developed a persistent phosphor of Y3Al2Ga3O12 doped with Nd3+, Ce3+, Cr3+ ions (YAGG:Nd-Ce-Cr) exhibiting long (>10 h) persistent luminescence at multi-wavelengths of around 880, 1064, and 1335 nm due to f-f transitions of Nd3+ and at 505 nm due to Ce3+:5d1→4f transition. The intense near-infrared (NIR) persistent luminescence bands from Nd3+ match well with the first (650-950 nm) and second (1000-1400 nm) bio-imaging windows. The NIR persistent radiance of the YAGG:Nd-Ce-Cr phosphor (0.33 × 10-1 mW/Sr/m2) at 60 min after ceasing blue light illumination was over 2 times higher than that of the widely used ZnGa2O4:Cr3+ red persistent phosphor (0.15 × 10-1 mW/Sr/m2).

  14. Ce(3+) /Tb(3+) non-/single-/co-doped K-Lu-F materials: synthesis, optical properties, and energy transfer.

    PubMed

    Cao, Chunyan; Xie, An; Noh, Hyeon Mi; Jeong, Jung Hyun

    2016-08-01

    Using a hydrothermal method, Ce(3+) /Tb(3+) non-/single-/co-doped K-Lu-F materials have been synthesized. The X-ray diffraction (XRD) results suggest that the Ce(3+) and/or Tb(3+) doping had great effects on the crystalline phases of the final samples. The field emission scanning electron microscopy (FE-SEM) images indicated that the samples were in hexagonal disk or polyhedron morphologies in addition to some nanoparticles, which also indicated that the doping also had great effects on the sizes and the morphologies of the samples. The energy-dispersive spectroscopy (EDS) patterns illustrated the constituents of different samples. The enhanced emissions of Tb(3+) were observed in the Ce(3+) /Tb(3+) co-doped K-Lu-F materials. The energy transfer (ET) efficiency ηT were calculated based on the fluorescence yield. The ET mechanism from Ce(3+) to Tb(3+) was confirmed to be the dipole-quadrupole interaction inferred from the theoretical analysis and the experimental data. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26669301

  15. Thermally and optically stimulated radiative processes in Eu and Y co-doped LiCaAlF6 crystal

    NASA Astrophysics Data System (ADS)

    Fukuda, Kentaro; Yanagida, Takayuki; Fujimoto, Yutaka

    2015-06-01

    Yttrium co-doping was attempted to enhance dosimeter performance of Eu doped LiCaAlF6 crystal. Eu doped and Eu, Y co-doped LiCaAlF6 were prepared by the micro-pulling-down technique, and their dosimeter characteristics such as optically stimulated luminescence (OSL) and thermally stimulated luminescence (TSL) were investigated. By yttrium co-doping, emission intensities of OSL and TSL were enhanced by some orders of magnitude. In contrast, scintillation characteristics of yttrium co-doped crystal such as intensity of prompt luminescence induced by X-ray and light yield under neutron irradiation were degraded.

  16. Structural, optical, magnetic and photocatalytic properties of Co doped CuS diluted magnetic semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Sreelekha, N.; Subramanyam, K.; Amaranatha Reddy, D.; Murali, G.; Ramu, S.; Rahul Varma, K.; Vijayalakshmi, R. P.

    2016-08-01

    Pristine and Co doped covellite CuS nanoparticles were synthesized in aqueous solution by facile chemical co-precipitation method with Ethylene Diamine Tetra Acetic Acid (EDTA) as a stabilizing agent. EDAX measurements confirmed the presence of Co in the CuS host lattice. Hexagonal crystal structure of pure and Co doped CuS nanoparticles were authenticated by XRD patterns. TEM images indicated that sphere-shape of nanoparticles through a size ranging from 5 to 8 nm. The optical absorption edge moved to higher energies with increase in Co concentration as indicated by UV-vis spectroscopy. Magnetic measurements revealed that bare CuS sample show sign of diamagnetic character where as in Co doped nanoparticles augmentation of room temperature ferromagnetism was observed with increasing doping precursor concentrations. Photocatalytic performance of the pure and Co doped CuS nanoparticles were assessed by evaluating the degradation rate of rhodamine B solution under sun light irradiation. The 5% Co doped CuS nanoparticles provide evidence for high-quality photocatalytic activity.

  17. 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.

  18. Fluorine and boron co-doped diamond-like carbon films deposited by pulsed glow discharge plasma immersion ion processing

    NASA Astrophysics Data System (ADS)

    He, Xiao-Ming; Hakovirta, M.; Peters, A. M.; Taylor, B.; Nastasi, M.

    2002-05-01

    Fluorine (F) and boron (B) co-doped diamond-like carbon (FB-DLC) films were prepared on different substrates by the plasma immersion ion processing (PIIP) technique. A pulse glow discharge plasma was used for the PIIP deposition and was produced at a pressure of 1.33 Pa from acetylene (C2H2), diborane (B2H6), and hexafluoroethane (C2F6) gas. Films of FB-DLC were deposited with different chemical compositions by varying the flow ratios of the C2H2, B2H6, and C2F6 source gases. The incorporation of B2H6 and C2F6 into PIIP deposited DLC resulted in the formation of F-C and B-C hybridized bonding structures. The levels of the F and B concentrations effected the chemical bonding and the physical properties as was evident from the changes observed in density, hardness, stress, friction coefficient, and contact angle of water on films. Compared to B-doped or F-doped DLC films, the F and B co-doping of DLC during PIIP deposition resulted in the formation of films that possessed a reduced hydrogen concentration and stress, while maintaining a high hardness, low friction coefficient, and high wetting contact angle.

  19. Synergistic enhancement of nitrogen and sulfur co-doped graphene with carbon nanospheres insertion for electrocatalytic oxygen reduction reaction

    DOE PAGESBeta

    Wu, Min; Xin, Huolin L.; Wang, Jie; Wu, Zexing; Wang, Deli

    2015-03-13

    A nitrogen and sulfur co-doped graphene/carbon black (NSGCB) nanocomposite for the oxygen reduction reaction (ORR) was synthesized through a one-pot annealing of a precursor mixture containing graphene oxide, thiourea, and acidized carbon black (CB). The NSGCB showed excellent performance for the ORR with the onset and half-way potentials at 0.96 V and 0.81 V (vs. RHE), respectively. It is significantly improved over that of the catalysts derived from only graphene (0.90 V and 0.76 V) or carbon nanosphere (0.82 V and 0.74 V). The enhanced catalytic activity on the NSGCB electrode could be attributed to the synergistic effect of N/Smore » co-doping and the enlarged interlayer space resulted from the insertion of carbon nanosphere into the graphene sheets. The four-electron selectivity and the limiting current density of the NSGCB nanocomposite are comparable to that of the commercially Pt/C catalyst. Furthermore, the NSGCB nanocomposite was superior to Pt/C in terms of long-term durability and tolerance to methanol poisoning.« less

  20. Investigation of structural and optical properties of ZnO films co-doped with fluorine and indium

    NASA Astrophysics Data System (ADS)

    Keskenler, E. F.; Turgut, G.; Doğan, S.

    2012-07-01

    Undoped ZnO film and ZnO films, which are co-doped with F and In (FIZO) at different concentrations, were synthesized by sol-gel technique and the effects of co-doping of F and In on structural and optical properties of ZnO thin films were investigated. The concentration ratio of [F]/[Zn] was altered from 0.25 to 1.75 with 0.50 step at.% mole and [In]/[Zn] was altered from 0.25 to 1.00 with 0.25 step at.% mole. X-ray diffraction analysis indicates that the films have polycrystalline nature and the (0 0 2) preferred orientation is the stronger peak. No extra phases involving zinc, fluorine and indium compounds were observed even at high F and In content. The grain size of undoped ZnO and FIZO thin films varied between 15 and 20 nm with a small fluctuation. From the SEM images, although the undoped ZnO had a smooth and particle-shaped surface, FIZO films had nanofiber-networks shapes over the surface with average size of 500 nm. The surface morphologies and crystallite sizes for the F and In doped films were slightly different from than those of undoped film. From the optical study, a slight shrinkage of band gap was backwardly observed from 3.36 to 3.25 eV with the increasing of F and In content.

  1. A sensitive and label-free photoelectrochemical aptasensor using Co-doped ZnO diluted magnetic semiconductor nanoparticles.

    PubMed

    Li, Hongbo; Qiao, Yunfei; Li, Jing; Fang, Hailin; Fan, Dahe; Wang, Wei

    2016-03-15

    Co-doped ZnO diluted magnetic semiconductor as a novel photoelectric beacon was first constructed for photoelectrochemical (PEC) aptasensor of acetamiprid. The fabricated PEC sensing is based on the specific binding of acetamiprid and its aptamer, which induces the decreasement of enhanced photocurrent produced by the electron donor of quercetin. Co(2+) doping has a beneficial effect in extending the band width of light absorption of ZnO into the visible region and to promote the separation of the photoinduced carriers due to the sp-d exchange interactions existing between the band electrons and the localized d electrons of Co(2+). The fabricated aptasensor was linear with the concentration of acetamiprid in the range of 0.5-800 nmolL(-1) with the detection limit of 0.18 nmolL(-1). The presence of same concentration of other conventional pesticides did not interfere in the detection of acetamiprid and the recovery is between 96.2% and 103.7%. This novel PEC aptasensor has good performances with high sensitivity, good selectivity, low cost and portable features. The strategy of Co-doped ZnO diluted magnetic semiconductor paves a new way to improve the performances of PEC aptasensor. PMID:26436325

  2. Enhanced rate performance of LiFePO4/C by co-doping titanium and vanadium

    NASA Astrophysics Data System (ADS)

    Long, Yun-Fei; Su, Jing; Cui, Xiao-Ru; Lv, Xiao-Yan; Wen, Yan-Xuan

    2015-10-01

    V and Ti co-doped LiFePO4/C composites were synthesized by a wet milling assisted carbothermal reduction technology. The structure, morphology and electrochemical performance of the samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), magnetic susceptibility, positron annihilation lifetime spectra (PAS), scanning electron microscope (SEM), charge/discharge tests, electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV). The results showed that the V and Ti co-doped samples kept the olivine structure of LiFePO4, but the synergistic effects between V3+ and Ti4+ in the lattice can increase the disorder degree of the lattice and create Li+ vacancies in LiFePO4/C, thus improve electronic conductivity and Li+ diffusion coefficient. LiV0.069Ti0.025Fe0.905PO4/C delivers an initial discharge capacity of 144.1 mAh g-1 with a capacity retention ratio of 99.4%, 96.3% and 93.6% after 100, 200 and 300 cycles at 10C, respectively. Remarkably, it still gives a high discharge capacity of 124.8 mAh g-1 even at a high rate of 20C.

  3. Synergistic enhancement of nitrogen and sulfur co-doped graphene with carbon nanospheres insertion for electrocatalytic oxygen reduction reaction

    SciTech Connect

    Wu, Min; Xin, Huolin L.; Wang, Jie; Wu, Zexing; Wang, Deli

    2015-03-13

    A nitrogen and sulfur co-doped graphene/carbon black (NSGCB) nanocomposite for the oxygen reduction reaction (ORR) was synthesized through a one-pot annealing of a precursor mixture containing graphene oxide, thiourea, and acidized carbon black (CB). The NSGCB showed excellent performance for the ORR with the onset and half-way potentials at 0.96 V and 0.81 V (vs. RHE), respectively. It is significantly improved over that of the catalysts derived from only graphene (0.90 V and 0.76 V) or carbon nanosphere (0.82 V and 0.74 V). The enhanced catalytic activity on the NSGCB electrode could be attributed to the synergistic effect of N/S co-doping and the enlarged interlayer space resulted from the insertion of carbon nanosphere into the graphene sheets. The four-electron selectivity and the limiting current density of the NSGCB nanocomposite are comparable to that of the commercially Pt/C catalyst. Furthermore, the NSGCB nanocomposite was superior to Pt/C in terms of long-term durability and tolerance to methanol poisoning.

  4. Enhanced electrical properties in multiferroic BiFeO3 ceramics co-doped by La3+ and V5+

    NASA Astrophysics Data System (ADS)

    Yu, Benfang; Li, Meiya; Wang, Jing; Pei, Ling; Guo, Dongyun; Zhao, Xingzhong

    2008-09-01

    La3+ and V5+ co-doped Bi0.85La0.15Fe1-xVxO3 (BLFVx, x = 0-0.1) ceramics were prepared by a rapid liquid sintering technique. The effects of the V5+-doping content on the structure and electrical properties of BLFVx ceramics were investigated. In the range of the V5+ content x from 0 to 0.03, BLFVx ceramics had a polycrystalline perovskite structure with tiny residual Bi2O3, while an impurity phase appeared for x > 0.03. As the x increased from 0 to 0.1, both the leakage current density and the dielectric loss (tan δ) for BLFVx ceramics decreased gradually, while the dielectric constant (ɛr) first increased and then decreased gradually in this process, reaching a maximum value of 273 for x = 0.03. Among the BLFVx ceramics, the BLFVx=0.01 ceramic showed a well-saturated hysteresis loop with large remanent polarization (Pr) of 39.4 µC cm-2 and a low coercive electric field (Ec) of ±43.1 kV cm-1 under an applied electric field of ±75 kV cm-1. In addition, these ceramics exhibited good anti-fatigue characteristics after 2 × 1010 read/write polarization cycles. These suggested that La3+ and V5+ co-doping was beneficial for enhancing the dielectric, ferroelectric and anti-fatigue properties of the BLFVx ceramics.

  5. Annealing in tellurium-nitrogen co-doped ZnO films: The roles of intrinsic zinc defects

    SciTech Connect

    Tang, Kun Gu, Ran; Gu, Shulin Ye, Jiandong; Zhu, Shunming; Yao, Zhengrong; Xu, Zhonghua; Zheng, Youdou

    2015-04-07

    In this article, the authors have conducted an extensive investigation on the roles of intrinsic zinc defects by annealing of a batch of Te-N co-doped ZnO films. The formation and annihilation of Zn interstitial (Zn{sub i}) clusters have been found in samples with different annealing temperatures. Electrical and Raman measurements have shown that the Zn{sub i} clusters are a significant compensation source to holes, and the Te co-doping has a notable effect on suppressing the Zn{sub i} clusters. Meanwhile, shallow acceptors have been identified in photoluminescence spectra. The N{sub O}-Zn-Te complex, zinc vacancy (V{sub Zn})-N{sub O} complex, and V{sub Zn} clusters are thought to be the candidates as the shallow acceptors. The evolution of shallow acceptors upon annealing temperature have been also studied. The clustering of V{sub Zn} at high annealing temperature is proposed to be a possible candidate as a stable acceptor in ZnO.

  6. Structural and optical properties of highly crystalline Ce, Eu and co-doped ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Murugadoss, G.; Jayavel, R.; Rajesh Kumar, M.

    2015-06-01

    Different concentrations of europium (Eu), cerium (Ce) doped and co-doped ZnO:Eu (1%), Ce (1%) nanorods were successfully synthesized by chemical method using Polyvinylpyrrolidone as a surfactant. Crystalline phase, morphology, functional groups, optical absorption, emission and thermal properties of prepared samples were investigated by X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), Scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HR-TEM), Fourier transform infra-red (FT-IR), UV-visible, Photoluminescence (PL) spectrophotometer and thermogravimetry (TG) and differential thermal analysis (DTA) analysis. The XRD study showed high crystalline nature of the products with nanoscale regime. Optical study showed shifting the absorption and emission spectra toward higher wavelength side when increasing the doping concentrations. Mainly, this is first time observed a red emission peak at 660 nm for Ce (3%) doped ZnO. Additionally, co-doped ZnO:Eu (1%), Ce (1%) nanorods were synthesized and studied their optical properties. This work demonstrates that simply modified their optical absorption and emission of ZnO by introducing rare earth ions can be used as an effective electrode material in solar cell applications, optoelectronic devices and photocatalysis analysis.

  7. The effect of seeds on GA metabolism in pea pericarp

    SciTech Connect

    Ozga, J.A.; Brenner, M.L. )

    1990-05-01

    To determine the effect of seeds on GA metabolism in pea (Pisum sativum) pericarp tissue, a method was developed that allowed access to the seeds while maintaining pericarp growth. Pericarp tissue of ovaries (3 DAA) was split down the across from the seeds, and seeds were removed. After 24 h. ({sup 14}C)-GA{sub 12} was applied to the inside surface of the pericarp of opened ovaries with or without seeds and to intact ovaries (control). Pericarp tissue was harvested 24 h after ({sup 14}C)-GA{sub 12} application, extracted and chromatographed on C18 HPLC. Wounding (opening ovaries) reduced accumulation of ({sup 14}C)-GA{sub 20}. Notably, removal of seeds significantly decreased ({sup 14}C)-GA{sub 20} accumulation when compared to the wounded controls. ({sup 14}C)-GA{sub 53} was present int he highest amount in the control ovaries attached to the plant, 1.5 {plus minus} 1.0% was found in opened ovaries with seeds and none was detected in ovaries without seeds. Metabolism of ({sup 14}C)-GA{sub 12} was similar in ovaries attached or removed from the plant. Application of GA{sub 3} (2.5 {mu}g/ml) to the ovaries in each treatment did not affect ({sup 14}C)-GA{sub 12} metabolism. These results suggest that the presence of seeds may stimulate GA metabolism in the pericarp.

  8. Sulfur and nitrogen co-doped, few-layered graphene oxide as a highly efficient electrocatalyst for the oxygen-reduction reaction.

    PubMed

    Xu, Jiaoxing; Dong, Guofa; Jin, Chuanhong; Huang, Meihua; Guan, Lunhui

    2013-03-01

    S and N co-doped, few-layered graphene oxide is synthesized by using pyrimidine and thiophene as precursors for the application of the oxygen reduction reaction (ORR). The dual-doped catalyst with pyrrolic/graphitic N-dominant structures exhibits competitive catalytic activity (10.0 mA cm(-2) kinetic-limiting current density at -0.25 V) that is superior to that for mono N-doped carbon nanomaterials. This is because of a synergetic effect of N and S co-doping. Furthermore, the dual-doped catalyst also shows an efficient four-electron-dominant ORR process, which has excellent methanol tolerance and improved durability in comparison to commercial Pt/C catalysts. PMID:23404829

  9. Effect of composite collector design on the breakdown behavior of InGaP/GaAs double heterojunction bipolar transistor

    NASA Astrophysics Data System (ADS)

    Lew, K. L.; Yoon, S. F.

    2003-01-01

    A series of experiments and calculations has been carried out to study the effect of different composite collector designs on InGaP/GaAs/InGaP double heterojunction bipolar transistor breakdown characteristics. A comparison between uncorrected and dead-space corrected models was carried out, and it was found that the dead-space effect is dominant for collector thickness below 300 nm. However, this effect can be neglected for collector thickness larger than 500 nm. The role of lightly doped GaAs (n--GaAs) and heavily doped InGaP (N+-InGaP) spacer layers is discussed systematically to establish a criterion for designing the composite collector structure. The experimental and theoretical results show that it is necessary to keep the sum of n--GaAs and N+-InGaP spacer layer thickness below 50 nm to avoid significant degradation of the device breakdown characteristics.

  10. Ferromagnetism and Conductivity in Hydrogen Irradiated Co-Doped ZnO Thin Films.

    PubMed

    Di Trolio, A; Alippi, P; Bauer, E M; Ciatto, G; Chu, M H; Varvaro, G; Polimeni, A; Capizzi, M; Valentini, M; Bobba, F; Di Giorgio, C; Amore Bonapasta, A

    2016-05-25

    Impressive changes in the transport and ferromagnetic properties of Co-doped ZnO thin films have been obtained by postgrowth hydrogen irradiation at temperatures of 400 °C. Hydrogen incorporation increases the saturation magnetization by one order of magnitude (up to ∼1.50 μB/Co) and increases the carrier density and mobility by about a factor of two. In addition to the magnetic characterization, the transport and structural properties of hydrogenated ZnO:Co have been investigated by Hall effect, local probe conductivity measurements, micro-Raman, and X-ray absorption spectroscopy. Particular care has been given to the detection of Co oxides and metal Co nanophases, whose influence on the increase in the transport and ferromagnetic properties can be excluded on the ground of the achieved results. The enhancement in ferromagnetism is directly related to the dose of H introduced in the samples. On the contrary, despite the shallow donor character of H atoms, the increase in carrier density n is not related to the H dose. These apparently contradictory effects of H are fully accounted for by a mechanism based on a theoretical model involving Co-VO (Co-O vacancy) pairs. PMID:27123761

  11. Structural and photoluminescence properties of Cd and Cu co-doped zinc oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Samuel, T.; Sujatha, K.; Rao, K. Ramachandra; Rao, M. C.

    2016-05-01

    Cd and Cu co-doped ZnO nanoparticles were synthesized by Polyol method and subsequently have been characterized by their structure, optical and photoluminescence studies. XRD and PSA results revealed the formation of Cd and Cu co-doped ZnO nanoparticles with an average crystallite size of 50 nm and average particle size of 246 nm. From Zeta Potential measurements the Zeta Potential was found to be - 29.2 eV indicating the stability of prepared nanoparticles. From Uv-Vis studies, it is found that the absorption of undoped ZnO is less compared with Cd and Cu co-doped ZnO and the absorbance increases with increase in dopant concentration. Photoluminescence studies revealed that the samples are with high structural and optical quality.

  12. Charge Compensated (Al, N) Co-Doped Zinc Oxide (ZnO) Films for Photlelectrochemical Application

    SciTech Connect

    Shet, S.

    2012-01-01

    ZnO thin films with significantly reduced bandgaps were synthesized by doping N and co-doping Al and N at 100oC. All the films were synthesized by radio-frequency magnetron sputtering on F-doped tin-oxide-coated glass. We found that co-doped ZnO:(Al,N) thin films exhibited significantly enhanced crystallinity as compared to ZnO doped solely with N, ZnO:N, at the same growth conditions. Furthermore, annealed ZnO:(Al,N) thin films exhibited enhanced N incorporation over ZnO:N films. As a result, ZnO:(Al,N) films exhibited improved photocurrents than ZnO:N films grown with pure N doping, suggesting that charge-compensated donor-acceptor co-doping could be a potential method for bandgap reduction of wide-bandgap oxide materials to improve their photoelectrochemical performance.

  13. Inverse spin Hall effect in Pt/(Ga,Mn)As

    SciTech Connect

    Nakayama, H.; Chen, L.; Chang, H. W.; Ohno, H.; Matsukura, F.

    2015-06-01

    We investigate dc voltages under ferromagnetic resonance in a Pt/(Ga,Mn)As bilayer structure. A part of the observed dc voltage is shown to originate from the inverse spin Hall effect. The sign of the inverse spin Hall voltage is the same as that in Py/Pt bilayer structure, even though the stacking order of ferromagnetic and nonmagnetic layers is opposite to each other. The spin mixing conductance at the Pt/(Ga,Mn)As interface is determined to be of the order of 10{sup 19 }m{sup −2}, which is about ten times greater than that of (Ga,Mn)As/p-GaAs.

  14. Phosphorus/sulfur Co-doped porous carbon with enhanced specific capacitance for supercapacitor and improved catalytic activity for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Zhou, Yao; Ma, Ruguang; Candelaria, Stephanie L.; Wang, Jiacheng; Liu, Qian; Uchaker, Evan; Li, Pengxi; Chen, Yongfang; Cao, Guozhong

    2016-05-01

    Phosphorus (P)/sulfur (S) co-doped porous carbon derived from resorcinol and furaldehyde are synthesized through one-step sol-gel processing with the addition of phosphorus pentasulfide as P and S source followed with freeze-drying and pyrolysis in nitrogen. The P/S co-doping strategy facilitates the pore size widening both in micropore and mesopore regions, together with the positive effect on the degree of graphitization of porous carbon through elimination of amorphous carbon through the formation and evaporation of carbon disulfide. As an electrode for supercapacitor application, P/S co-doped porous carbon demonstrates 43.5% improvement on specific capacitance of the single electrode compared to pristine porous carbon in organic electrolyte at a current of 0.5 mA due to the P-induced pseudocapacitive reactions. As for electrocatalytic use, promoted electrocatalytic activity and high resistance to crossover effects of oxygen reduction reaction (ORR) in alkaline media are observed after the introduction of P and S into porous carbon. After air activation, the specific capacitance of the single electrode of sample PS-pC reaches up to 103.5 F g-1 and an improved oxygen reduction current density.

  15. A first-principles study of co-doping in lanthanum bromide

    NASA Astrophysics Data System (ADS)

    Aberg, Daniel; Sadigh, Babak; Schleife, Andre; Erhart, Paul

    2015-03-01

    It was recently shown that the energy resolution of Ce-doped LaBr3 scintillator radiation detectors can be crucially improved by co-doping with Sr, Ca, or Ba. Here we outline a mechanism for this enhancement on the basis of electronic structure calculations. We show that Sr dopants create and bind to Br vacancies, resulting in stable neutral complexes. The association with Sr causes the deep vacancy level to move toward the conduction band edge. This is essential for reducing the effective carrier density available for Auger quenching during thermalization of hot carriers. Subsequent de-trapping of electrons from the complexes can activate Ce dopants that have previously captured a hole leading to luminescence. This mechanism implies an overall reduction of Auger quenching of free carriers, which is expected to improve the linearity of the photon light yield with respect to the energy of incident electron or photon. Optical properties of the Ce-Sr-vacancy triple complex are discussed and compared to experiment. Prepared by LLNL under Contract DE-AC52-07NA27344. Support from the National Nuclear Security Administration Office of Nonproliferation Research and Development (NA-22) is acknowledged.

  16. Combinatorial optimization of La, Ce-co-doped pyrosilicate phosphors as potential scintillator materials.

    PubMed

    Wei, Qinhua; Wan, Jieqiong; Liu, Guanghui; Zhou, Zhenzhen; Yang, Hua; Wang, Jiacheng; Liu, Qian

    2015-04-13

    A combinatorial method was employed to rapidly screen the effects of La, Ce-co-doping on the luminescent properties of Gd2Si2O7 pyrosilicate using an 8 × 8 library. The candidate formulations (Gd1-x-yLax)2Si2O7:Ce2y were evaluated by luminescence pictures under ultraviolet excitation. The optimal composition was found to be (Gd0.89La0.1)2Si2O7:Ce0.02 after scaled-up preparation and detailed characterization of powder samples, which shows an excellent light output under both ultraviolet and X-ray excitation (about 5.43 times of commercial YAG:Ce powders). The XRD results indicate that the phase structure sequence is tetragonal-orthorhombic-triclinic for different calcination temperatures and doping ions. The (Gd0.89La0.1)2Si2O7:Ce0.02 powder sample also demonstrated excellent temperature stability of luminescence up to 200 °C and a short decay time of several tens of nanoseconds, suggesting that this may represent a new kind of scintillation material, such as single crystals, ceramics, glass, or phosphors. PMID:25679047

  17. Origin of resolution enhancement by co-doping of scintillators: Insight from electronic structure calculations

    SciTech Connect

    Åberg, Daniel Sadigh, Babak; Schleife, André; Erhart, Paul

    2014-05-26

    It was recently shown that the energy resolution of Ce-doped LaBr{sub 3} scintillator radiation detectors can be crucially improved by co-doping with Sr, Ca, or Ba. Here, we outline a mechanism for this enhancement on the basis of electronic structure calculations. We show that (i) Br vacancies are the primary electron traps during the initial stage of thermalization of hot carriers, prior to hole capture by Ce dopants; (ii) isolated Br vacancies are associated with deep levels; (iii) Sr doping increases the Br vacancy concentration by several orders of magnitude; (iv) Sr{sub La} binds to V{sub Br} resulting in a stable neutral complex; and (v) association with Sr causes the deep vacancy level to move toward the conduction band edge. The latter is essential for reducing the effective carrier density available for Auger quenching during thermalization of hot carriers. Subsequent de-trapping of electrons from Sr{sub La}–V{sub Br} complexes can activate Ce dopants that have previously captured a hole leading to luminescence. This mechanism implies an overall reduction of Auger quenching of free carriers, which is expected to improve the linearity of the photon light yield with respect to the energy of incident electron or photon.

  18. Visible-Light-Induced Bactericidal Activity of Titanium Dioxide Co-doped with Nitrogen and Silver

    PubMed Central

    Wu, Pinggui; Xie, Rongcai; Imlay, Kari; Shang, Jian-Ku

    2011-01-01

    Titanium dioxide nanoparticles co-doped with nitrogen and silver (Ag2O/TiON) were synthesized by the sol-gel process and found to be an effective visible light driven photocatalyst. The catalyst showed strong bactericidal activity against Escherichia coli (E. coli) under visible light irradiation (λ> 400 nm). In x-ray photoelectron spectroscopy and x-ray diffraction characterization of the samples, the as-added Ag species mainly exist as Ag2O. Spin trapping EPR study showed Ag addition greatly enhanced the production of hydroxyl radicals (•OH) under visible light irradiation. The results indicate that the Ag2O species trapped eCB− in the process of Ag2O/TiON photocatalytic reaction, thus inhibiting the recombination of eCB− and hVB+ in agreement with the stronger photocatalytic bactericidal activity of Ag2O/TiON. The killing mechanism of Ag2O/TiON under visible light irradiation is shown to be related to oxidative damages in the forms of cell wall thinning and cell disconfiguration. PMID:20726520

  19. Ni, Fe Co-doped ZnO nanoparticles synthesized by solution combustion method

    SciTech Connect

    Dhiman, Pooja Chand, Jagdish Verma, S. Sarveena, Singh, M.

    2014-04-24

    This paper outlines the synthesis and characterization of Ni-Fe co-doped ZnO nanoparticles by facile solution combustion method. The structural characterization by XRD confirmed the phase purity of the samples. Surface morphology studied by scanning electron microscope revealed cubic type shape of grains. EDS analysis conformed the elemental composition. Higher value of DC electrical conductivity and less band gap for co-doped ZnO from UV-Vis studies confirmed the change in defect chemistry of ZnO Matrix.

  20. Local structure investigation of Co doped ZnO thin films prepared by RF sputtering technique

    NASA Astrophysics Data System (ADS)

    Yadav, A. K.; Haque, S. Maidul; Shukla, D.; Phase, D. M.; Jha, S. N.; Bhattacharyya, D.

    2016-05-01

    Co doped ZnO thin films have been prepared using rf magnetron sputtering technique with varying Co doping concentration. GIXRD has been used to probe long range order and Zn, Co and Oxygen K-edge XAFS measurements have been used for investigating local structure around Zn and Co atoms. GIXRD results show wurzite structure of the samples while XANES and EXAFS results at Zn and Co K edge show that Co is going at Zn site in ZnO matrix and no other phase is present. These results are further confirmed by O K edge and Co L2,3 edge XANES measurements.

  1. InGaAs/GaAs Quantum Dots: Effects of Ensemble Interactions, Interdiffusion, Segregation and Proton Irradiation

    NASA Technical Reports Server (NTRS)

    Leon, R.

    2000-01-01

    A sumary or recent experimental findings on the effects of interdiffusion, segregation, strained ensemble interactions and proton irradiation on the optical properties of InGaAs/GaAs quantum dots (QDs) are presented.

  2. Auger effect in yellow light emitters based on InGaN–AlGaN–GaN quantum wells

    NASA Astrophysics Data System (ADS)

    Huong Ngo, Thi; Gil, Bernard; Valvin, Pierre; Damilano, Benjamin; Lekhal, Kaddour; De Mierry, Philippe

    2016-05-01

    The Auger effect and its impact on the internal quantum efficiency (IQE) of yellow light emitters based on silicon-doped InGaN–AlGaN–GaN quantum wells are investigated by power dependence measurement and using an ABC model. Photoluminescence intensity recorded as a function of excitation power density follows a linear dependence up to a threshold P T that depends on the design of the sample. Above this threshold, the variation of the intensity becomes sublinear, which is characteristic of the onset of Auger recombination processes. After extracting the evolution of IQE with pump power from the experimental data, we use a modified ABC modeling that includes the residual n-type doping to estimate the contribution of different recombination channels. We find that the Auger effect dominates in the high-excitation regime. In addition, we find that intercalating an AlGaN-strain-compensating layer reduces not only the coefficient of nonradiative recombination rates but also reduces the onset of Auger recombination.

  3. On the AlGaInP-bulk and AlGaInP/GaAs-superlattice confinement effects for heterostructure-emitter bipolar transistors

    SciTech Connect

    Tsai, Jung-Hui

    2015-02-09

    The confinement effect and electrical characteristics of heterostructure-emitter bipolar transistors with an AlGaInP bulk-confinement layer and an AlGaInP/GaAs superlattice-confinement layer are first demonstrated and compared by experimentally results. In the two devices, the relatively large valence band discontinuity at AlGaInP/GaAs heterojunction provides excellent confinement effect for holes to enhance current gain. As to the AlGaInP/GaAs superlattice-confinement device, part of thermionic-emission electrons will be trapped in the GaAs quantum wells of the superlattice. This will result in lower collector current and current gain as compared with the bulk-confinement device. Nevertheless, the superlattice-confinement device exhibits a larger current-gain cutoff frequency, which can be attributed that the tunneling behavior is included in the carrier transportation and transporting time across the emitter region could be substantially reduced.

  4. Synthesis, characterization and degradation of Bisphenol A using Pr, N co-doped TiO 2 with highly visible light activity

    NASA Astrophysics Data System (ADS)

    Yang, Juan; Dai, Jun; Li, Jiantong

    2011-08-01

    Praseodymium and nitrogen co-doped titania (Pr/N-TiO 2) photocatalysts, which could degrade Bisphenol A (BPA) under visible light irradiation, were prepared by the modified sol-gel process. Tetrabutyl titanate, urea and praseodymium nitrate were used as the sources of titanium, nitrogen and praseodymium, respectively. The resulting materials were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-vis absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), N 2 adsorption-desorption isotherm and Fourier transform infrared spectra (FTIR). It was found that Pr doping inhibited the growth of crystalline size and the transformation from anatase to rutile. The degradation of BPA under visible light illumination was taken as probe reaction to evaluate the photo-activity of the co-doped photocatalyst. In our experiments, the optimal dopant amount of Pr was 1.2 mol% and the calcination temperature was 500 °C for the best photocatalytic activity. Pr/N-TiO 2 samples exhibited enhanced visible-light photocatalytic activity compared to N-TiO 2, undoped TiO 2 and commercial P25. The nitrogen atoms were incorporated into the crystal of titania and could narrow the band gap energy. Pr doping could slow the radiative recombination of photogenerated electrons and holes in TiO 2. The improvement of photocatalytic activity was ascribed to the synergistic effects of nitrogen and Pr co-doping.

  5. Ultrasonic-assisted sol-gel synthesis of samarium, cerium co-doped TiO2 nanoparticles with enhanced sonocatalytic efficiency.

    PubMed

    Eskandarloo, Hamed; Badiei, Alireza; Behnajady, Mohammad A; Ziarani, Ghodsi Mohammadi

    2015-09-01

    In this work, pure TiO2 and samarium, cerium mono-doped and co-doped TiO2 catalysts were synthesized by an ultrasonic-assisted sol-gel method and their sonocatalytic efficiency studied toward removal of Methyl Orange as a model organic pollutant from the textile industry. The relationship of structure and sonocatalytic performance of catalysts was established by using various techniques, such as XRD, TEM, SEM, EDX, DRS, and PL. A comparison on the removal efficiency of sonolysis alone and sonocatalytic processes was performed. The results showed that the samarium, cerium co-doped TiO2 catalyst with narrower band gap energy and smaller particle size leads to a rapid removal of pollutant. It was believed that Sm(3+) and Ce(4+) ions can serve as superficial trapping for electrons at conduction band of TiO2 and prolonged the lifetime of electron-hole pairs. Finally, the effect of synthesis and operational variables on the sonocatalytic activity of co-doped TiO2 catalyst was studied and optimized using response surface methodology as a statistical technique. The results showed that the maximum removal efficiency (96.33%) was achieved at the optimum conditions: samarium content of 0.6 wt%, cerium content of 0.82 wt%, initial pollutant concentration of 4.31 mg L(-1), catalyst dosage of 0.84 mg L(-1), ultrasonic irradiation power of 700 W, and irradiation time of 50 min. PMID:25682738

  6. Fabrication of the C-N co-doped rod-like TiO{sub 2} photocatalyst with visible-light responsive photocatalytic activity

    SciTech Connect

    Li, Liang-Hai; Lu, Juan; Wang, Zuo-Shan; Yang, Lu; Zhou, Xiu-Feng; Han, Lu

    2012-06-15

    Highlights: ► Novel synthesis of C-N co-doped TiO{sub 2}. ► Self-assembly of C-N co-doped TiO{sub 2} nanorods by nanoparticles. ► Excellent photocatalytic efficiency. -- Abstract: The C-N co-doped TiO{sub 2} nanorods were synthesized by the vapor transport method of water molecules, and urea was used as the carbon and nitrogen source. The samples were characterized by X-ray diffraction and photoelectron spectroscopy analysis. The scanning electron microscope images showed that as-prepared TiO{sub 2} powders were nanorods, which were formed by the stacking of nanoparticles with a uniform size around 40 nm. The degradation of methylene blue with the prepared nanorods demonstrated the photocatalytic activities of TiO{sub 2} under visible light are improved by doping with C and N elements. The main reasons were discussed: doping with C and N elements could enhance the corresponding visible-light absorption of TiO{sub 2}. On the other hand, doping C and N could create more oxygen vacancies in the TiO{sub 2} crystals, which could capture the photogenerated electrons more effectively. Thus, more photogenerated holes could be left to improve the photocatalytic activity of TiO{sub 2}.

  7. Co-Doped MoS₂ Nanosheets with the Dominant CoMoS Phase Coated on Carbon as an Excellent Electrocatalyst for Hydrogen Evolution.

    PubMed

    Dai, Xiaoping; Du, Kangli; Li, Zhanzhao; Liu, Mengzhao; Ma, Yangde; Sun, Hui; Zhang, Xin; Yang, Ying

    2015-12-16

    Highly active and low-cost catalysts for hydrogen evolution reaction (HER) are crucial for the development of efficient water splitting. Molybdenum disulfide (MoS2) nanosheets possess unique physical and chemical properties, which make them promising candidates for HER. Herein, we reported a facile, effective, and scalable strategy by a deposition-precipitation method to fabricate metal-doped (Fe, Co, Ni) molybdenum sulfide with a few layers on carbon black as noble metal-free electrocatalysts for HER. The CoMoS phase after thermal annealing in Co-doped MoS2 plays a crucial role for the enhanced HER. The optimized Co-doped MoS2 catalyst shows superior HER performance with a high exchange current density of 0.03 mA·cm(-2), low onset potential of 90 mV, and small Tafel slope of 50 mV·dec(-1), which also exhibits excellent stability of 10000 cycles with negligible loss of the cathodic current. The superior HER activity originates from the synergistically structural and electronic modulations between MoS2 and Co ions, abundant defects in the active edge sites, as well as the good balance between active sites and electronic conductivity. Thanks to their ease of synthesis, low cost, and high activity, the Co-doped MoS2 catalysts appear to be promising HER catalysts for electrochemical water splitting. PMID:26599427

  8. Self-interaction effects in (Ga,Mn)As and (Ga,Mn)N

    NASA Astrophysics Data System (ADS)

    Filippetti, Alessio; Spaldin, Nicola A.; Sanvito, Stefano

    2005-02-01

    The electronic structures of Mn-doped zincblende GaAs and wurtzite GaN are calculated using both standard local-spin density functional theory (LSDA), and a novel pseudopotential self-interaction-corrected approach (pseudo-SIC), able to account for the effects of strong correlation. We find that, as expected, the self-interaction is not strong in (Ga,Mn)As, because the Fermi energy is crossed by weakly correlated As p-Mn d hybridized bands and the Mn 3d character is distributed through the whole valence band manifold. This result validates the extensive literature of LSDA studies on (Ga,Mn)As, including the conclusion that the ferromagnetism is hole-mediated. In contrast, the LSDA gives a qualitatively incorrect band structure for (Ga,Mn)N, which is characterized by localized Mn 3d bands with very strong self-interaction. Our pseudo-SIC calculations show a highly confined hole just above the Fermi energy in the majority band manifold. Such a band arrangement is consistent with (although by no means conclusive evidence for) a recent suggestion [Phys. Rev. B 033203 (2002)] that formation of Zhang-Rice magnetic polarons is responsible for hole-mediated ferromagnetism in (Ga,Mn)N.

  9. HgNO3 sensitivity of AlGaN/GaN field effect transistors functionalized with phytochelating peptides

    NASA Astrophysics Data System (ADS)

    Rohrbaugh, Nathaniel; Hernandez-Balderrama, Luis; Kaess, Felix; Kirste, Ronny; Collazo, Ramon; Ivanisevic, Albena

    2016-06-01

    This study examined the conductance sensitivity of AlGaN/GaN field effect transistors in response to varying Hg/HNO3 solutions. FET surfaces were covalently functionalized with phytochelatin-5 peptides in order to detect Hg in solution. Results showed a resilience of peptide-AlGaN/GaN bonds in the presence of strong HNO3 aliquots, with significant degradation in FET ID signal. However, devices showed strong and varied response to Hg concentrations of 1, 10, 100, and 1000 ppm. The gathered statistically significant results indicate that peptide terminated AlGaN/GaN devices are capable of differentiating between Hg solutions and demonstrate device sensitivity.

  10. Effects of Ga ion-beam irradiation on monolayer graphene

    NASA Astrophysics Data System (ADS)

    Wang, Quan; Mao, Wei; Ge, Daohan; Zhang, Yanmin; Shao, Ying; Ren, Naifei

    2013-08-01

    The effects of Ga ion on the single layer graphene (SLG) have been studied by Raman spectroscopy (RS), SEM, and field-effect characterization. Under vacuum conditions, Ga ion-irradiation can induce disorders and cause red shift of 2D band of RS, rather than lattice damage in high quality SLG. The compressive strain induced by Ga ion decreases the crystalline size in SLG, which is responsible for the variation of Raman scattering and electrical properties. Nonlinear out-put characteristic and resistance increased are also found in the I-V measurement. The results have important implications during CVD graphene characterization and related device fabrication.

  11. Effects of Ga ion-beam irradiation on monolayer graphene

    SciTech Connect

    Wang, Quan; Mao, Wei; Zhang, Yanmin; Shao, Ying; Ren, Naifei; Ge, Daohan

    2013-08-12

    The effects of Ga ion on the single layer graphene (SLG) have been studied by Raman spectroscopy (RS), SEM, and field-effect characterization. Under vacuum conditions, Ga ion-irradiation can induce disorders and cause red shift of 2D band of RS, rather than lattice damage in high quality SLG. The compressive strain induced by Ga ion decreases the crystalline size in SLG, which is responsible for the variation of Raman scattering and electrical properties. Nonlinear out-put characteristic and resistance increased are also found in the I-V measurement. The results have important implications during CVD graphene characterization and related device fabrication.

  12. Effects of Annealing on GaAs/GaAsSbN/GaAs Core-Multi-shell Nanowires.

    PubMed

    Kasanaboina, Pavan; Sharma, Manish; Deshmukh, Prithviraj; Reynolds, C Lewis; Liu, Yang; Iyer, Shanthi

    2016-12-01

    The effects of ex-situ annealing in a N2 ambient on the properties of GaAs/GaAsSbN/GaAs core-multi-shell nanowires on Si (111) substrate grown by self-catalyzed molecular beam epitaxy (MBE) are reported. As-grown nanowires exhibit band edge emission at ~0.99 eV with a shoulder peak at ~0.85 eV, identified to arise from band tail states. A large red shift of 7 cm(-1) and broadened Raman spectra of as-grown nanowires compared to that of non-nitride nanowires confirmed phonon localization at N-induced localized defects. On annealing nanowires to 750 °C, there was no change in the planar defects in the nanowire with respect to the as-grown nanowire; however, vanishing of the photoluminescence (PL) peak corresponding to band tail states along with enhanced band edge PL intensity, recovery of the Raman shift and increase in the Schottky barrier height from 0.1 to 0.4 eV clearly point to the efficient annihilation of point defects in these GaAsSbN nanowires. A significant reduction in the temperature-induced energy shift in the annealed nanowires is attributed to annihilation of band tail states and weak temperature dependence of N-related localized states. The observation of room temperature PL signal in the 1.3 μm region shows that the strategy of adding small amounts of N to GaAsSb is a promising route to realization of efficient nanoscale light emitters with reduced temperature sensitivity in the telecommunication wavelength region. PMID:26831685

  13. Effects of Annealing on GaAs/GaAsSbN/GaAs Core-Multi-shell Nanowires

    NASA Astrophysics Data System (ADS)

    Kasanaboina, Pavan; Sharma, Manish; Deshmukh, Prithviraj; Reynolds, C. Lewis; Liu, Yang; Iyer, Shanthi

    2016-02-01

    The effects of ex-situ annealing in a N2 ambient on the properties of GaAs/GaAsSbN/GaAs core-multi-shell nanowires on Si (111) substrate grown by self-catalyzed molecular beam epitaxy (MBE) are reported. As-grown nanowires exhibit band edge emission at ~0.99 eV with a shoulder peak at ~0.85 eV, identified to arise from band tail states. A large red shift of 7 cm-1 and broadened Raman spectra of as-grown nanowires compared to that of non-nitride nanowires confirmed phonon localization at N-induced localized defects. On annealing nanowires to 750 °C, there was no change in the planar defects in the nanowire with respect to the as-grown nanowire; however, vanishing of the photoluminescence (PL) peak corresponding to band tail states along with enhanced band edge PL intensity, recovery of the Raman shift and increase in the Schottky barrier height from 0.1 to 0.4 eV clearly point to the efficient annihilation of point defects in these GaAsSbN nanowires. A significant reduction in the temperature-induced energy shift in the annealed nanowires is attributed to annihilation of band tail states and weak temperature dependence of N-related localized states. The observation of room temperature PL signal in the 1.3 μm region shows that the strategy of adding small amounts of N to GaAsSb is a promising route to realization of efficient nanoscale light emitters with reduced temperature sensitivity in the telecommunication wavelength region.

  14. Magnetic field dependence of magnetic domains in Co doped Mn2Sb using magnetic force microscopy

    NASA Astrophysics Data System (ADS)

    Singh, Vikram; Saha, Pampi; Kushwaha, Pallavi; Thamizhavel, A.; Rawat, Rajeev

    2016-05-01

    Magnetic domains in the ferrimagnetic state of Co doped Mn2Sb single crystal has been visualized using Magnetic Force Microscopy. It shows fractal like domain structure. With the application of magnetic field, single domain state is achieved around 2000 Oe. The MFM images collected during field increasing and decreasing cycles show different morphology for same field value.

  15. Yb-Er co-doped phosphate fiber with hexagonal inner cladding

    NASA Astrophysics Data System (ADS)

    Wen, Lei; Wang, Longfei; He, Dongbing; Chen, Danping; Hu, Lili

    2016-04-01

    An Yb-Er co-doped phosphate glass double-clad fiber with hexagonal inner cladding was fabricated by stack-and-draw method. Output power of 4.9 W was extracted with slope efficiency of 30 % from the fiber with 55 cm in length.

  16. Enhanced ferromagnetism in co-doped BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Trivedi, Harsh; Singh, Deepa; Gupta, Rajeev; Garg, Ashish

    2012-02-01

    BiFeO3 (BFO) is the most studied multiferroic material with high ferroelectric polarization as well above room temperature transition temperatures. Studies have shown significant improvements in the electrical and magnetic properties of BFO upon atomic substitutions at Bi (A) and Fe (B) sites. While enhanced ferromagnetism upon A-site doping is attributed to the suppression of cycloidal spin ordering of Fe moments, B site substitution reduces leakage current by eliminating oxygen vacancies. This study aims to combine these two aspects by co-doping the material at A- and B- sites using La^3+ and V^3+/V^+5 respectively and to investigate the electrical and magnetic characteristics of co-doped BFO. La-doped LaxBi1-xFeO3 and co-doped LaxBi1-xVyFe1-yO3 (x = .05, 0.1, 0.15, 0.2; y = 0.03) samples were prepared solid-state reaction method. While La-doped samples show only reduced leakage without any discernible change in the magnetic characteristics, co-doped samples (La^3+ & V^5+ ) show significant enhancements in magnetic properties in addition to reduced leakage attributed to the elimination of oxygen vacancies. Improvement in the magnetic characteristics can be understood as a consequence of enhanced double exchange interaction between adjacent Fe ions. This argument is further strengthened by our observation that co-doped samples made by substitution of Fe with V^+3 show a magnetic response equivalent to that of only La-doped BFO samples.

  17. Scaling performance of Ga2O3/GaN nanowire field effect transistor

    NASA Astrophysics Data System (ADS)

    Li, Chi-Kang; Yeh, Po-Chun; Yu, Jeng-Wei; Peng, Lung-Han; Wu, Yuh-Renn

    2013-10-01

    A three-dimensional finite element solver is applied to investigate the performance of Ga2O3/GaN nanowire transistors. Experimental nanowire results of 50 nm gate length are provided to compare with the simulation, and they show good agreement. The performance of a shorter gate length (<50 nm) is studied and scaling issues of the short-channel effect are analyzed. With a better surrounding gate design and a recessed gate approach, the optimal conditions for a 20 nm gate length are explored in this paper.

  18. Effect of Proton Irradiation on 2DEG in AlGaN/GaN Heterostructures

    NASA Astrophysics Data System (ADS)

    Abderrahmane, A.; Koide, S.; Tahara, T.; Sato, S.; Ohshima, T.; Okada, H.; Sandhu, A.

    2013-04-01

    Low temperature Hall effect measurements were carried on AlGaN/GaN micro-Hall effect sensors before and after irradiation with 380 keV and fluence of 1014 protons/cm2 protons. The sheet electron density after irradiation did not show significant changes but there was a dramatic decrease in the electron mobility of the heterostructures. Prior to irradiation, the observation of well-defined Landau plateaus in the Hall resistance and Shubnikov-de Haas oscillations (SdH) at 4.5 T was indicative of the high quality the heterojunction confining the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface of micro-Hall effect sensors. In contrast, the Landau plateaus disappeared after irradiation and the threshold magnetic field required for the observation of the SdH increased, which was accompanied by a decrease of the electron mobility. Temperature dependent magnetoresistance measurements were used to deduce the effective mass and the quantum scattering time before irradiation. A negative magnetoresistance was observed at low magnetic fields which is related to weak localization and parabolic negative magnetoresistance attributed to electron-electron interaction in both samples.

  19. Sustained phase separation and spin glass in Co-doped KxFe2-ySe2 single crystals

    DOE PAGESBeta

    Ryu, Hyejin; Wang, Kefeng; Opacic, M.; Lazarevic, N.; Warren, J. B.; Popovic, Z. V.; Bozin, Emil S.; Petrovic, C.

    2015-11-19

    We describe Co substitution effects in KxFe2-y-zCozSe2 (0.06 ≤ z ≤ 1.73) single crystal alloys. By 3.5% of Co doping superconductivity is suppressed whereas phase separation of semiconducting K2Fe4Se5 and superconducting/metallic KxFe2Se2 is still present. We show that the arrangement and distribution of superconducting phase (stripe phase) is connected with the arrangement of K, Fe and Co atoms. Semiconducting spin glass is found in proximity to superconducting state, persisting for large Co concentrations. At high Co concentrations ferromagnetic metallic state emerges above the spin glass. This is coincident with changes of the unit cell, arrangement and connectivity of stripemore » conducting phase.« less

  20. Sonocatalytic degradation of azo fuchsine in the presence of the Co-doped and Cr-doped mixed crystal TiO2 powders and comparison of their sonocatalytic activities.

    PubMed

    Wang, Jun; Lv, Yanhui; Zhang, Zhaohong; Deng, Yingqiao; Zhang, Liquan; Liu, Bin; Xu, Rui; Zhang, Xiangdong

    2009-10-15

    In order to degrade some pollutants effectively under ultrasonic irradiation, the Co-doped and Cr-doped mixed crystal TiO(2) powders, with high sonocatalytic activity, were prepared as sonocatalyst. The Co-doped and Cr-doped mixed crystal TiO(2) powders as sonocatalyst were prepared through sol-gel and heat-treated methods from tetrabutylorthotitanate, and then were characterized by XRD and TG-DTA technologies. In order to compare and evaluate the sonocatalytic activity of the Co-doped and Cr-doped mixed crystal TiO(2) powders, the low power ultrasound was as an irradiation source and the azo fuchsine was chosen as a model compound to be degraded. The degradation process was investigated by UV-vis, TOC, ion chromatogram and HPLC techniques. The results indicated that the sonocatalytic activity of Cr-doped mixed crystal TiO(2) powder was higher than that of Co-doped and undoped mixed crystal TiO(2) powder during the sonocatalytic degradation of the azo fuchsine in aqueous solution. These results may be of great significance for driving sonocatalytic method to treat non- or low-transparent industrial wastewaters. PMID:19467773

  1. High temperature ferromagnetism and optical properties of Co doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Pal, Bappaditya; Giri, P. K.

    2010-10-01

    We report on the occurrence of high temperature ferromagnetism (FM) in ZnO nanoparticles (NPs) doped with Co-atoms. ZnO NPs of two different initial sizes are doped with 3% and 5% Co using ball milling and FM is studied at room temperature and above. X-ray diffraction and high-resolution transmission electron microscopy analysis confirm the absence of metallic Co clusters or any other phase different from würtzite-type ZnO. UV-visible absorption studies show change in band structure and photoluminescence studies show green emission band at 520 nm indicating incorporation of Co-atoms and presence of oxygen vacancy defects, respectively in ZnO lattice. Micro-Raman studies of doped samples shows defect related additional bands at 547 and 574 cm-1. XRD and Raman spectra provide clear evidence for strain in the doped ZnO NPs. The field dependence of magnetization (M-H curve) measured at room temperature exhibits the clear FM with saturation magnetization (Ms) and coercive field (Hc) of the order of 3-7 emu/g and 260 Oe, respectively. Temperature dependence of magnetization (M-T) measurement shows sharp ferromagnetic to paramagnetic transition with a high Curie temperature (Tc) of ˜800 K for 3% Co doped ZnO NPs. It is found that doping at 5% and higher concentration does not exhibit a proper magnetic transition. We attempt to fit the observed FM data with the bound magnetic polaron (BMP) model involving localized carriers and magnetic cations. However, calculated concentration of the BMPs is well below the typical percolation threshold in ZnO. We believe that observed high temperature FM is primarily mediated by defects in the strained NPs. ZnO NPs of lower initial size show enhanced FM that may be attributed to size dependent doping effect.

  2. Characterization of partially ordered GaInP/GaAs heterointerfaces by the quantum Hall effect

    NASA Astrophysics Data System (ADS)

    Uchida, Kazuo; Satoh, Kiwamu; Asano, Keita; Koizumi, Atsushi; Nozaki, Shinji

    2013-05-01

    The new approach to the characterization of semiconductor interfacial properties by the quantum Hall effect (QHE) and the scanning near field optical microscopy (SNOM) is demonstrated to the heterointerfaces of partially ordered GaInP/GaAs grown by low-pressure Metal Organic Vapor Phase Epitaxy. The Shubnikov de-Haas (SdH) oscillations and the Hall plateaus are observed in the heterointerfaces of both the less-ordered and more-ordered GaInP/GaAs samples with a large clover-shape, but these samples exhibit both 2D and 3D electron behaviors. In contrast to large clover-shaped samples, the distinct SdH oscillations and the Hall plateaus in the less-ordered sample, while the single SdH oscillation and the corresponding large plateau in the more-ordered small Hall-bar sample are observed. These results suggest that there may be many domains, each having a different carrier density and sizes in the less-ordered sample, while one or few large domains with uniform carrier concentration and sizes in the more-ordered sample. In SNOM measurements, PL intensity varies in the mapping of the more-ordered sample and it is concluded that the variation of the PL intensity may result from an inhomogeneous distribution of non-radiative recombination centers in the more-ordered sample.

  3. Neutron irradiation effects in GaAs

    SciTech Connect

    Patel, J.U.

    1992-01-01

    Changes in electrical properties of n-GaAs as a result of irradiations with fast neutron have been studied, after epitaxial layers doped with Si at concentrations in the range 1.35 x 10[sup 15] to 1.60 x 10[sup 16] cm[sup [minus]3] were irradiated with reactor neutron fluences up to 1.31 x 10[sup 15] cm [sup [minus]2]. When the changes in carrier concentration, Hall mobility and resistivity were more than 25% of their initial values, nonlinear dependence on neutron fluence was apparent. New theory is proposed which explains the changes in electrical properties in terms of rates of trapping and release of charges. A theoretical relationship is derived for the change in carrier concentration as a function of neutron fluence and Fermi level shift was found to be consistent with the observed changes in carrier concentration. A correlation has been found between the changes in carrier concentration and mobility with neutron fluence using newly defined physically meaningful parameters in the case of two pairs of samples. The correlation has been explained in terms of the increased scattering of charge carriers from the defects created by neutrons that trap the free carriers. Mobility changes were measured at temperatures from 15 K to 305 K in n-GaAs van-der Pauw samples irradiated by fast reactor neutrons. The inverse mobility values obtain versus temperature, from the variable temperature Hall measurements, in the case of irradiated and in-irradiated samples were fitted using the relation [mu][sup [minus]1] = T[sup [minus]3/2] + B T[sup 3/2]. The inverse mobility increased as a result of neutron irradiations over the whole range of temperature, the increase being attributed to the increased scattering from neutron induced charged defects.

  4. Synthesis, structural, optical, and magnetic properties of Co doped, Sm doped and Co+Sm co-doped ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Poornaprakash, B.; Poojitha, P. T.; Chalapathi, U.; Subramanyam, K.; Park, Si-Hyun

    2016-09-01

    The compositional, structural, optical and magnetic properties of ZnS, Zn0.98Co0.02S, Zn0.98Sm0.02S and Zn0.96Co0.02Sm0.02S nanoparticles synthesized by a hydrothermal method are presented and discussed. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies revealed that all the samples exhibited cubic structure without any impurity phases. X-ray photoelectron spectroscopy (XPS) results revealed that the Co and Sm ions existed in +2 and +3 states in these samples. The photoluminescence (PL) spectra of all the samples exhibited a broad emission in the visible region. The room temperature magnetization versus applied magnetic field (M-H) curves demonstrated that the Sm+Co doped nanoparticles exhibited enhanced ferromagnetic behavior compare to Co and Sm individually doped ZnS nanoparticles, which is probably due to the exchange interaction between conductive electrons with local spin polarized electrons on the Co2+ or Sm3+ ions. This study intensifies the understanding of the novel performances of co-doped ZnS nanoparticles and also provides possibilities to fabricate future spintronic devices.

  5. Effect of photocatalytic oxidation technology on GaN CMP

    NASA Astrophysics Data System (ADS)

    Wang, Jie; Wang, Tongqing; Pan, Guoshun; Lu, Xinchun

    2016-01-01

    GaN is so hard and so chemically inert that it is difficult to obtain a high material removal rate (MRR) in the chemical mechanical polishing (CMP) process. This paper discusses the application of photocatalytic oxidation technology in GaN planarization. Three N-type semiconductor particles (TiO2, SnO2, and Fe2O3) are used as catalysts and added to the H2O2-SiO2-based slurry. By optical excitation, highly reactive photoinduced holes are produced on the surface of the particles, which can oxidize OH- and H2O absorbed on the surface of the catalysts; therefore, more OH* will be generated. As a result, GaN MRRs in an H2O2-SiO2-based polishing system combined with catalysts are improved significantly, especially when using TiO2, the MRR of which is 122 nm/h. The X-ray photoelectron spectroscopy (XPS) analysis shows the variation trend of chemical composition on the GaN surface after polishing, revealing the planarization process. Besides, the effect of pH on photocatalytic oxidation combined with TiO2 is analyzed deeply. Furthermore, the physical model of GaN CMP combined with photocatalytic oxidation technology is proposed to describe the removal mechanism of GaN.

  6. Preparation of superior lubricious amorphous carbon films co-doped by silicon and aluminum

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoqiang; Hao, Junying; Yang, Jun; Zheng, Jianyun; Liang, Yongmin; Liu, Weimin

    2011-09-01

    Silicon (Si) and aluminum (Al) co-doped amorphous carbon films ((Si, Al)-C:H) were deposited on Si and stainless steel substrates by radio frequency (13.56 MHz) magnetron sputtering. The Al and Si were found to jointly regulate the hybridized carbon bonds. Mechanical properties of the films were detected by nano-indention and scratch tests. The nano-indention results revealed that all the samples exhibited good elastic recovery rate, among which the highest one was beyond 84%. Besides co-regulating the hybridizations of carbon, the co-doped Si and Al also had a common regulation on the mechanical and tribological properties. Especially, the film containing 1.6 at. % of Si and 0.9 at. % of Al showed a super-low friction (< 0.01) and a superior wear resistance in ambient air.

  7. Low-temperature ferromagnetic properties in Co-doped Ag{sub 2}Se nanoparticles

    SciTech Connect

    Yang, Fengxia E-mail: xia9020@hust.edu.cn; Yu, Gen; Han, Chong; Liu, Tingting; Zhang, Duanming; Xia, Zhengcai E-mail: xia9020@hust.edu.cn

    2014-01-06

    β-Ag{sub 2}Se is a topologically nontrivial insulator. The magnetic properties of Co-doped Ag{sub 2}Se nanoparticles with Co concentrations up to 40% were investigated. The cusp of zero-field-cooling magnetization curves and the low-temperature hysteresis loops were observed. With increasing concentration of Co{sup 2+} ions mainly substituting Ag{sub I} sites in the Ag{sub 2}Se structure, the resistivity, Curie temperature T{sub c}, and magnetization increased. At 10 T, a sharp drop of resistance near T{sub c} was detected due to Co dopants. The ferromagnetic behavior in Co-doped Ag{sub 2}Se might result from the intra-layer ferromagnetic coupling and surface spin. This magnetic semiconductor is a promising candidate in electronics and spintronics.

  8. Enhanced dielectric, impedance and magnetic characteristics of Co doped multiferroic Bi2Fe4O9

    NASA Astrophysics Data System (ADS)

    Mohapatra, S. R.; Sahu, B.; Kaushik, S. D.; Singh, A. K.

    2016-05-01

    Multiferroic Bi2Fe4(1-x)Co4xO9 (x = 0, 0.05) were prepared by conventional solid state reaction route. X-ray diffraction (XRD) result indicated the decrease in lattice parameters due to 5% Co doping. Grain growth in the doped composition was confirmed from surface morphology characterization. Frequency dependent real part of dielectric constant (ɛ') at room temperature showed an enhancement of ~70% in doped sample at 1 kHz. A decrease in peak height with doping was noticed from the modulus study. Lastly, room temperature M-H measurement upto 9 T showed induced ferromagnetism in Bi2Fe4O9 due to 5% Co doping. The values of remnant magnetization (Mr) and coercive field (Hc) in Bi2Fe3.8Co0.2O9 was found to be 0.007 µB/f.u. and 0.295 kOe respectively.

  9. Upconversion luminescence of Yb 3+/Tb 3+ co-doped tellurite glasses

    NASA Astrophysics Data System (ADS)

    Kochanowicz, Marcin; Zmojda, Jacek; Dorosz, Dominik; Miluski, Piotr; Dorosz, Jan

    2014-05-01

    In the article the upconversion luminescence ofTeO2- GeO2 - PbO - PbF2- BaO - Nb2O5 - LaF3 glass system co-doped withYb 3+ /Tb 3+ under 976 nm laser diode excitation was investigated. The influence of Tb2O3concentration on the luminescent properties was determined. Measured strong luminescence at492, 547, 588, 622 nm correspond to 5D4→7FJ (J=6, 4, 3) transitions. Energy transfer (ET) mechanism involved in observed emission was discussed. The highest upconversion emission intensity was obtained in the tellurite glass co-doped with 0.5 Yb2O3/0.5 Tb2O3 (mol%).

  10. Enhanced electrical activation in In-implanted Ge by C co-doping

    SciTech Connect

    Feng, R. Kremer, F.; Mirzaei, S.; Medling, S. A.; Ridgway, M. C.; Sprouster, D. J.; Decoster, S.; Pereira, L. M. C.; Glover, C. J.; Russo, S. P.

    2015-11-23

    At high dopant concentrations in Ge, electrically activating all implanted dopants is a major obstacle in the fulfillment of high-performance Ge-channel complementary metal oxide semiconductor devices. In this letter, we demonstrate a significant increase in the electrically-active dopant fraction in In-implanted Ge by co-doping with the isovalent element C. Electrical measurements have been correlated with x-ray absorption spectroscopy and transmission electron microscopy results in addition to density functional theory simulations. With C + In co-doping, the electrically active fraction was doubled and tripled at In concentrations of 0.2 and 0.7 at. %, respectively. This marked improvement was the result of C-In pair formation such that In-induced strain in the Ge lattice was reduced while the precipitation of In and the formation of In-V clusters were both suppressed.

  11. High field effects of GaN HEMTs.

    SciTech Connect

    Barker, Joy; Shul, Randy John

    2004-09-01

    This report represents the completion of a Laboratory-Directed Research and Development (LDRD) program to develop and fabricate geometric test structures for the measurement of transport properties in bulk GaN and AlGaN/GaN heterostructures. A large part of this study was spent examining fabrication issues related to the test structures used in these measurements, due to the fact that GaN processing is still in its infancy. One such issue had to do with surface passivation. Test samples without a surface passivation, often failed at electric fields below 50 kV/cm, due to surface breakdown. A silicon nitride passivation layer of approximately 200 nm was used to reduce the effects of surface states and premature surface breakdown. Another issue was finding quality contacts for the material, especially in the case of the AlGaN/GaN heterostructure samples. Poor contact performance in the heterostructures plagued the test structures with lower than expected velocities due to carrier injection from the contacts themselves. Using a titanium-rich ohmic contact reduced the contact resistance and stopped the carrier injection. The final test structures had an etch constriction with varying lengths and widths (8x2, 10x3, 12x3, 12x4, 15x5, and 16x4 {micro}m) and massive contacts. A pulsed voltage input and a four-point measurement in a 50 {Omega} environment was used to determine the current through and the voltage dropped across the constriction. From these measurements, the drift velocity as a function of the applied electric field was calculated and thus, the velocity-field characteristics in n-type bulk GaN and AlGaN/GaN test structures were determined. These measurements show an apparent saturation velocity near to 2.5x10{sup 7} cm/s at 180 kV/cm and 3.1x10{sup 7} cm/s, at a field of 140 kV/cm, for the bulk GaN and AlGaN heterostructure samples, respectively. These experimental drift velocities mark the highest velocities measured in these materials to date and confirm

  12. Giant temperature coefficient of resistance in Co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Zhou, X. F.; Zhang, H.; Yan, H.; He, C. L.; Lu, M. H.; Hao, R. Y.

    2014-03-01

    A novel high-performance thermistor material based on Co-doped ZnO thin films is presented. The films were deposited by the pulsed laser deposition technique on Si (111) single-crystal substrates. The structural and electronic transport properties were correlated as a function of parameters such as substrate temperature and Co-doped content for Zn1- x Co x O ( x=0.005,0.05,0.10 and 0.15) to prepare these films. The Zn1- x Co x O films were deposited at various substrate temperatures between 20 and 280 °C. A value of 20 %/K for the negative temperature coefficient of resistance (TCR) with a wide range near room temperature was obtained. It was found that both TCR vs. temperature behavior and TCR value were strongly affected by cobalt doping level and substrate temperature. In addition, a maximal TCR value of over 20 % K-1 having a resistivity value of 3.6 Ω cm was observed in a Zn0.9Co0.1O film near 260 °C, which was deposited at 120 °C and shown to be amorphous by X-ray diffraction. The result proved that the optimal Co concentration could help us to achieve giant TCR in Co-doped ZnO films. Meanwhile, the resistivities of the films ranged from 0.4 to 270 Ω cm. A Co-doped ZnO/Si film is a strong candidate of thermometric materials for non-cooling and high-performance bolometric applications.

  13. Structural, optical and dielectric property of Co doped Bi{sub 2}Fe{sub 4}O{sub 9}

    SciTech Connect

    Swain, Smita Mohapatra, S. R. Sahoo, B. Singh, A. K.

    2014-04-24

    Multiferroic Bi{sub 2}Fe{sub 4}O{sub 9} and Co doped Bi{sub 2}Fe{sub 4}O{sub 9} are prepared by solid state route reaction method using bismuth oxide(Bi{sub 2}O{sub 3}), iron oxide(Fe{sub 2}O{sub 3}) and cobalt oxide (Co{sub 3}O{sub 4}). Their structural optical and dielectric properties are studied and compared. X-ray diffraction (XRD) results confirm that there is no change in crystal structure due to Co doping. From dielectric constant measurement we conclude that dielectric constant increases due to Co doping. UV-Visible plot shows due to Co doping bang gap energy increases.

  14. Luminescence Properties of Sm3+/Eu3+ Co-Doped ZnO Quantum Dots.

    PubMed

    Liu, Fengyi; Li, Hong; Hu, Yajing; Na, Jin; Mou, Yun; Yang, Kun; Ye, Zuhu; Li, Mingyue; Xie, Ya-Hong

    2016-04-01

    In order to improve luminescence properties of semiconductor ZnO quantum dots (QDs), Sm3+/Eu3+ co-doped ZnO QDs have been controllably synthesized by sol-gel method in this paper. ZnO QDs have a spherical shape with mean diameter at about 5-6 nm, which was characterized by high-resolution transmission electron microscopy (HRTEM). ZnO QDs have hexagonal wurtzite structure with parts of Sm3+ and Eu3+ incorporated into the lattice, which was demonstrated by X-ray Diffraction (XRD). Luminescence properties at room temperature (RT) of different amount of Sm3+ and 2 mol% Eu3+ doped ZnO QDs were examined in-depth by optical spectra. In contrast to the Pr3+/Eu3+ co-doped fluorescent performance researched in our previous study, the photoluminescence (PL) spectra indicates the unique luminescence properties of Sm3+/Eu3+ co-doped ZnO QDs. In addition, fluorescence lifetimes were obtained to illustrate the luminous mechanism. PMID:27451672

  15. Local investigation of hyperfine interactions in pure and Co-doped ZnO

    NASA Astrophysics Data System (ADS)

    Mercurio, M. E.; Carbonari, A. W.; Cordeiro, M. R.; Saxena, R. N.; D'Agostino, L. Z.

    2010-05-01

    In the present work bulk samples of pure as well as Co-doped ZnO with different concentrations were prepared by sol-gel method from highly pure metallic Zn (99.9999%) and Co (99.9999%). The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray microanalysis (EDS) and perturbed gamma-gamma angular correlation (PAC) spectroscopy. Carrier-free 111In nuclei were introduced during preparation of the samples and used as probe nuclei at Zn sites for PAC measurements. PAC results show that both pure and Zn1-xCoxO ( x≤0.15) samples have the same electric quadrupole frequency when Co-doped samples are annealed in air, argon or nitrogen atmosphere at 1173 K. SEM and EDS results showed that Co-doped samples are homogeneous without any secondary Co phases. These observations indicate that Co ions are substituted for Zn ions and have a similar electronic structure of Zn ions. A weak local magnetism was observed at temperatures below about 300 K for Co concentration of 10% when sample was annealed in Nitrogen.

  16. Gain dynamics in Er(3+):Yb(+) co-doped fiber amplifiers.

    PubMed

    Steinke, M; Neumann, J; Kracht, D; Wessels, P

    2015-06-01

    Understanding the gain dynamics of fiber amplifiers is essential for the implementation and active stabilization of low noise amplifiers or for coherent beam combining schemes. The gain dynamics of purely Er3+ or Yb3+ doped fiber amplifiers are well studied, whereas no analysis for co-doped systems, especially for Er3+:Yb3+ co-doped fiber amplifiers has been performed, so far. Here, we analyze for the first time the gain dynamics of Er3+:Yb3+ co-doped fiber amplifiers theoretically and experimentally. It is shown that due to the energy transfer between the Yb3+ and Er3+ ions a full analytical solution is not possible. Thus, we used numerical simulations to gain further insights. Comparison of experimental and numerical results shows good qualitative agreement. In addition, we were able to determine the Yb3+-Er3+ transfer function of the energy transfer experimentally. PMID:26072851

  17. Photoluminescence properties of ZnS nanoparticles co-doped with Pb 2+ and Cu 2+

    NASA Astrophysics Data System (ADS)

    Yang, Ping; Lü, Mengkai; Xü, Dong; Yuan, Duolong; Zhou, Guangjun

    2001-03-01

    Nanometer-scale ZnS, ZnS:Cu, ZnS:Pb, and ZnS co-doped with Cu 2+ and Pb 2+ have been synthesized using a chemical precipitation method. X-ray diffraction analysis shows that the diameter of the particles is 2-4 nm. These nanocrystals can be doped with copper and lead during the synthesis without altering the X-ray diffraction pattern. However, doping has shifted the luminescence to 530 nm (Cu 2+-doped) and 500-550 nm (co-doped with Cu 2+ and Pb 2+). In the case of ZnS:Pb nanocrystals, a relatively broad emission band (color range from blue to yellow) has been observed and its excitation wavelength shows a red shift. The photoluminescence intensity increases as the ZnS nanoparticles co-doped with Pb 2+ and Cu 2+. The results strongly suggest that doped ZnS nanocrystals, especially two kinds of metals activated ZnS nanocrystals, form a new class of luminescent materials.

  18. Valence band structure and magnetic properties of Co-doped Fe3O4(100) films

    NASA Astrophysics Data System (ADS)

    Ran, F. Y.; Tsunemaru, Y.; Hasegawa, T.; Takeichi, Y.; Harasawa, A.; Yaji, K.; Kim, S.; Kakizaki, A.

    2011-06-01

    Structural and magnetic properties, and the valence band structure of pure and Co-doped (up to 33%) Fe3O4(100) films were investigated. Reconstruction of the Fe3O4(100) surface is found to be blocked by Co doping. Doped Co ions in Fe3O4 are in a charge state of 2 + and substitute the Fe2+ in the B site of Fe3O4. All the films exhibit room temperature ferromagnetism. Co doping changes the coercivity and reduces saturation magnetization. The density of states near the Fermi level is reduced by Co doping due to the decrease of Fe2+ in the B site, which might responsible for the decrease in conductivity and magnetoresistance of Co-doped Fe3O4. The Verwey transition in the range of 100-120 K is observed for the pure Fe3O4 film, while no transition could be detected for Co-doped Fe3O4 films.

  19. Effect of the thickness of InGaN interlayer on a-plane GaN epilayer

    NASA Astrophysics Data System (ADS)

    Wang, Jian-Xia; Wang, Lian-Shan; Zhang, Qian; Meng, Xiang-Yue; Yang, Shao-Yan; Zhao, Gui-Juan; Li, Hui-Jie; Wei, Hong-Yuan; Wang, Zhan-Guo

    2015-02-01

    In this paper, we use the a-plane InGaN interlayer to improve the property of a-plane GaN. Based on the a-InGaN interlayer, a template exhibits that a regular, porous structure, which acts as a compliant effect, can be obtained to release the strain caused by the lattice and thermal mismatch between a-GaN and r-sapphire. We find that the thickness of InGaN has a great influence on the growth of a-GaN. The surface morphology and crystalline quality both are first improved and then deteriorated with increasing the thickness of the InGaN interlayer. When the InGaN thickness exceeds a critical point, the a-GaN epilayer peels off in the process of cooling down to room temperature. This is an attractive way of lifting off a-GaN films from the sapphire substrate. Project supported by the National Natural Science Foundation of China (Grant Nos. 91233111, 61274041, and 11275228), the Special Funds for Major State Basic Research Project of China (Grant No. 2012CB619305), the National High Technology R & D Program of China (Grant Nos. 2014AA032603 and 2014AA032609), and the Guangdong Provincial Special Fund for LED Industrial Development, China (Grant No. 2012A080302003).

  20. Co-doping induced coexistence of superconductivity and ferromagnetism in Bi3.9Co0.1O4S3

    NASA Astrophysics Data System (ADS)

    Yu, Chuan; Feng, Zhenjie; Yin, Xunqing; Li, Qing; Kang, Baojuan; Lu, Bo; Jing, Chao; Cao, Shixun; Zhang, Jincang

    2016-09-01

    The effects of Co doping on the physical properties of the Bi4O4S3 system was studied. We discovered that stable Bi3.9Co0.1O4S3 compound exhibits both long-range ferromagnetism and enhanced superconductivity with thermodynamic evidences for Tc ∼ 5.5 K. We found that there is an anomalous feature which represents superconducting transition in the hysteretic M-vs.-H loops for Bi3.9Co0.1O4S3 at T = 3 K.

  1. Preparation and upconversion emission modification of Yb, Er co-doped Y2SiO5 inverse opal photonic crystals.

    PubMed

    Yan, Dong; Zhu, Jialun; Yang, Zhengwen; Wu, Hangjun; Wang, Rongfei; Qiu, Jianbei; Song, Zhiguo; Zhou, Dacheng; Yang, Yong; Yin, Zhaoyi

    2014-05-01

    Yb, Er co-doped Y2SiO5 inverse opal photonic crystals with three-dimensionally ordered macroporous were fabricated using polystyrene colloidal crystals as the template. Under 980 nm excitation, the effect of the photonic stopband on the upconversion luminescence of Er3+ ions has been investigated in the Y2SiO5:Yb, Er inverse opals. Significant suppression of the green or red UC emissions was detected if the photonic band-gap overlaps with the Er3+ ions emission band. PMID:24734639

  2. Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; Kravchenko, I. I.; Zhang, Ming-Lan

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersion observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.

  3. Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

    DOE PAGESBeta

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; et al

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersionmore » observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.« less

  4. Surface passivation of tellurium-doped GaAs nanowires by GaP: Effect on electrical conduction

    SciTech Connect

    Darbandi, A.; Salehzadeh, O.; Watkins, S. P.; Kuyanov, P.; LaPierre, R. R.

    2014-06-21

    We report on the surface passivation of Au-assisted Te-doped GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy. The electrical properties of individual free standing NWs were assessed using a tungsten nano-probe inside a scanning electron microscope. The diameter independent apparent resistivity of both strained and relaxed passivated NWs suggests the unpinning of the Fermi level and reduction of sidewalls surface states density. Similar current-voltage properties were observed for partially axially relaxed GaAs/GaP NWs. This indicates a negligible contribution of misfit dislocations in the charge transport properties of the NWs. Low temperature micro-photoluminescence (μ-PL) measurements were also carried out for both uncapped and passivated GaAs NWs. The improvement of the integrated (μ-PL) intensity for GaAs/GaP NWs further confirms the effect of passivation.

  5. Overshoot effects of electron on efficiency droop in InGaN/GaN MQW light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Huang, Yang; Liu, Zhiqiang; Yi, Xiaoyan; Guo, Yao; Wu, Shaoteng; Yuan, Guodong; Wang, JunXi; Wang, Guohong; Li, Jinmin

    2016-04-01

    To evaluate electron leakage in InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs), analytic models of ballistic and quasi-ballistic transport are developed. With this model, the impact of critical variables effecting electron leakage, including the electron blocking layer (EBL), structure of multiple quantum wells (MQWs), polarization field, and temperature are explored. The simulated results based on this model shed light on previously reported experimental observations and provide basic criteria for suppressing electron leakage, advancing the design of InGaN/GaN LEDs.

  6. Effect of wet oxidized AlxGa1-xAs layer on the interdiffusion of InGaAs/GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Choe, Joong-Seon; Ryu, Sang-Wan; Choe, Byung-Doo; Lim, H.

    1998-06-01

    The effect of wet oxidized AlAs cap layer and AlGaAs interlayer on the thermal stability of In0.2Ga0.8As/GaAs quantum well (QW) is studied. The QW interdiffusion rate is observed to increase with the Al composition of the AlxGa1-xAs interlayer until x reaches about 0.5 and then saturate for x⩾0.5. When the oxidation is performed at 380 °C for 15 min, the threshold value of x for the enhancement of QW interdiffusion is found to be 0.3. It is also confirmed that the QW interdiffusion can only be explained when the strain effect in InGaAs is taken into account.

  7. Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability

    SciTech Connect

    Liu, L.; Xi, Y. Y.; Ren, F.; Pearton, S. J.; Laboutin, O.; Cao, Yu; Johnson, Wayne J.; Kravchenko, Ivan I

    2012-01-01

    AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 lm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were 100 V, however, this degraded to 50 60V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600 700 V), while a much smaller Viso of 200V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

  8. White light emission from Tm{sup 3+}/Dy{sup 3+} co-doped oxyfluoride germanate glasses under UV light excitation

    SciTech Connect

    Lakshminarayana, G.; Yang Hucheng; Qiu Jianrong

    2009-04-15

    In this paper, we report on the absorption and photoluminescence properties of Tm{sup 3+}/Dy{sup 3+} ions co-doped oxyfluoride germanate glasses for white light emission. The X-ray diffraction (XRD) and differential thermal analysis (DTA) profiles of the host glass have been carried out to confirm its structure and thermal stability. From the measured absorption spectra, Judd-Ofelt (J-O) intensity parameters (OMEGA{sub 2}, OMEGA{sub 4} and OMEGA{sub 6}) have been evaluated for Tm{sup 3+} and Dy{sup 3+} ions. A combination of blue, yellow and red emissions has emerged in these glasses, which allows the observation of bright white light when the glasses are excited by the ultraviolet light. The white light luminescence colour could be changed by varying the excitation wavelength. Also, various colours of luminescence, including white light, can be easily tuned by adjusting the concentrations of Tm{sup 3+} or Dy{sup 3+} ions in the co-doped glasses. Concentration quenching effect was also investigated and possible energy transfer mechanism from Dy{sup 3+}->Tm{sup 3+} ions was explained which is also confirmed by the decay lifetime measurements. - Graphical Abstract: A combination of blue, yellow and red emissions has emerged from Tm{sup 3+}/Dy{sup 3+} co-doped glasses, which allows the observation of bright white light and makes them as excellent candidates applicable in the solid-state multi-colour three-dimensional display.

  9. Humidity effects on tribochemical removal of GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Yu, Bingjun; Gao, Jian; Jin, Chenning; Xiao, Chen; Wu, Jiang; Liu, Huiyun; Jiang, Shulan; Chen, Lei; Qian, Linmao

    2016-06-01

    Defect-free tribochemical removal of gallium arsenide (GaAs) was demonstrated in vacuum, dry air, and various humidity environments by scratching with a SiO2 tip. The removal depth increases with increasing relative humidity (1–90%), and reaches its maximum value in water. A perfect crystal matrix without defects was observed in the cross section of the scratched groove using a transmission electron microscope. A model based on reactive tip scratching-induced oxidation, water solubility of debris, and adhesion effect was proposed to interpret tribochemical removal of GaAs surface. This study provides new insights into defect-free and site-controlled nanofabrication of GaAs.

  10. Effect of high density H 2 plasmas on InGaP/GaAs and AlGaAs/GaAs HEMTs

    NASA Astrophysics Data System (ADS)

    Ren, F.; Kopf, R. F.; Kuo, J. M.; Lothian, J. R.; Lee, J. W.; Pearton, S. J.; Shul, R. J.; Constantine, C.; Johnson, D.

    1998-05-01

    InGaP/GaAs and AlGaAs/GaAs high electron mobility transistors have been exposed to inductively coupled plasma or electron cyclotron resonance H 2 plasmas as a function of pressure, source power and rf chuck power. The transconductance, gate ideality factor and saturated drain-source current are all degraded by the plasma treatment. Two mechanisms are identified: passivation of Si dopants in the InGaP or AlGaAs donor layers by H 0 and lattice disorder created by H + and H 2+ ion bombardment. HEMTs are found to be more susceptible to plasma-induced degradation than heterojunction bipolar transistors.

  11. Effect of the Yb3+ Concentration in Up-Conversion and Electrical Properties of Ho3+/Yb3+ Co-doped (0.94Na0.5Bi0.5TiO3-0.06BaTiO3) Ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Qian; Li, Yanxia; Li, Jun; Chai, Xiaona; Zhao, Haifeng; Wang, Xusheng; Yao, Xi

    2016-07-01

    Ho3+/Yb3+ co-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-BT:Ho3+/Yb3+) ceramics were synthesized by solid-state reaction and characterized by x-ray diffraction (XRD), luminescent, dielectric, ferroelectric and piezoelectric measurements. The XRD diffraction data showed that all the ceramics were single phase with a perovskite structure. Bright green up-conversion (UC) emission bands (545 nm) and weak red UC emission bands (660 nm) corresponded to the transitions from (5F4, 5S2) → 5I8 and 4I5 → 5I8, respectively. Furthermore, optimized UC emission intensity was observed in the NBT-BT:0.005Ho3+/0.03Yb3+ samples. The thermal behavior of UC emission in the ceramics was also investigated and the maximum sensitivity based on fluorescence intensity ratio (FIR) technology was approximately 0.0042 K-1 at 100 K. Moreover, relatively good dielectric properties ( ɛ = 4475) and ferroelectric properties ( P r = 32 μ/cm2 and E c = 37 kV) were obtained in NBT-BT:0.005Ho3+/0.005Yb3+. As a multi-functional material, NBT-BT:Ho3+/Yb3+ ceramics may be useful in electro-optical devices.

  12. Effect of the Yb3+ Concentration in Up-Conversion and Electrical Properties of Ho3+/Yb3+ Co-doped (0.94Na0.5Bi0.5TiO3-0.06BaTiO3) Ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Qian; Li, Yanxia; Li, Jun; Chai, Xiaona; Zhao, Haifeng; Wang, Xusheng; Yao, Xi

    2016-04-01

    Ho3+/Yb3+ co-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-BT:Ho3+/Yb3+) ceramics were synthesized by solid-state reaction and characterized by x-ray diffraction (XRD), luminescent, dielectric, ferroelectric and piezoelectric measurements. The XRD diffraction data showed that all the ceramics were single phase with a perovskite structure. Bright green up-conversion (UC) emission bands (545 nm) and weak red UC emission bands (660 nm) corresponded to the transitions from (5F4, 5S2) → 5I8 and 4I5 → 5I8, respectively. Furthermore, optimized UC emission intensity was observed in the NBT-BT:0.005Ho3+/0.03Yb3+ samples. The thermal behavior of UC emission in the ceramics was also investigated and the maximum sensitivity based on fluorescence intensity ratio (FIR) technology was approximately 0.0042 K-1 at 100 K. Moreover, relatively good dielectric properties (ɛ = 4475) and ferroelectric properties (P r = 32 μ/cm2 and E c = 37 kV) were obtained in NBT-BT:0.005Ho3+/0.005Yb3+. As a multi-functional material, NBT-BT:Ho3+/Yb3+ ceramics may be useful in electro-optical devices.

  13. Understanding the infrared to visible upconversion luminescence properties of Er{sup 3+}/Yb{sup 3+} co-doped BaMoO{sub 4} nanocrystals

    SciTech Connect

    Adhikari, Rajesh; Choi, Jinhyuk; Narro-García, R.; De la Rosa, E.; Sekino, Tohru; Lee, Soo Wohn

    2014-08-15

    In this paper we report the infrared to visible upconversion luminescence properties of Er{sup 3+}/Yb{sup 3+} co-doped BaMoO{sub 4} nanocrystals synthesized via microwave assisted sol–gel processing route. Structural, morphological and upconversion luminescence properties were investigated by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and Upconversion Photoluminescence spectra analysis. Results revealed that the oval shaped BaMoO{sub 4} nanocrystals ranging in size from 40 to 60 nm having tetragonal scheelite crystal structure were obtained by sol–gel route. The infrared to visible upconversion luminescence has been investigated in Er{sup 3+}/Yb{sup 3+} co-doped in BaMoO{sub 4}with different Yb{sup 3+} concentrations. Intense green upconversion emissions around 528, 550 nm, and red emission at 657 nm corresponding to the {sup 2}H{sub 11/2}, {sup 4}S{sub 3/2}, and {sup 4}F{sub 9/2} transitions, respectively to the {sup 4}I{sub 15/2} ground state were observed when excited by CW laser radiation at 980 nm. The green emissions were greatly enhanced after the addition of sensitizer (Yb{sup 3+} ions). The effect of Yb{sup 3+} on the upconversion luminescence intensity was analyzed and explained in terms of the energy transfer process based. The reported work establishes the understanding of molybdates as an alternative host material for upconversion luminescence. - Graphical abstract: Infrared to visible upconversion luminescence of Er{sup 3+}/Yb{sup 3+} co-doped BaMoO{sub 4} nanocrystals. - Highlights: • Nanocrystals were synthesized by microwave assisted sol–gel processing route. • Strong green emissions were observed in Er{sup 3+}/Yb{sup 3+} co-doped BaMoO{sub 4} nanocrystals. • Provides an insight on Upconversion luminescence properties of oxides host materials.

  14. Effects of spontaneous polarization on GaInN/GaN quantum well structures

    SciTech Connect

    Thomsen, M.; Joenen, H.; Rossow, U.; Hangleiter, A.

    2011-06-15

    Using electron beam irradiation, cathodoluminescence, and photoluminescence under ultrahigh vacuum conditions, we study the effect of spontaneous polarization on polar (0001) and nonpolar (1100) GaInN/GaN quantum well structures. We use cathodoluminescence measurements with an electron beam irradiation time of up to several hours. A drastic blueshift of the quantum well emission accompanied by a 100-fold increase of intensity is observed in polar samples. These changes can be described by an activation of the spontaneous polarization field due to the desorption of surface charges, which counteracts the piezoelectric field in the quantum well. Etching or annealing of the surface leads to similar effects. The influence of the sample structure was investigated by varying the cap thickness of the samples. A different time- dependent behavior of changes in the quantum well emission energy and the intensity depending on cap thickness and acceleration voltage was observed. This can be explained by de-screening and screening effects induced by the electron beam which are discussed in detail. For nonpolar (1100) samples, no change in quantum well emission energy or intensity was observed. This is consistent with a spontaneous-polarization-induced surface field in the c-plane case and verifies the absence of the spontaneous polarization field in the nonpolar (1100) direction.

  15. Surfactant effects on GaAs-Ge heterostructures

    NASA Astrophysics Data System (ADS)

    Karlina, L. B.; Vlasov, A. S.; Ber, B. Y.; Kazanthev, D. Yu.; Marukhina, E. P.

    2013-10-01

    A study of the effect of isoelectronic surfactants (In and P) on the photoluminescence and photovoltaic characteristics of GaAs-Ge heterostructures is presented. The surfactants were introduced into the structure by simultaneous post-growth diffusion. A GaAs photoluminescence spectra analysis was performed via a layer-by-layer etching procedure. It is shown that the effect of the surfactants is observed over a wide concentration range from 3×1017 to 1×1020 cm-3. The effects of the In and P passivation of nonradiative recombination centers are observed. A p-n junction was formed via phosphorus diffusion. PV conversion efficiency of 3.2% for the 900-1840 nm wavelength region has been registered under 40-400x concentrated sunlight (AM1.5D low-AOD).

  16. Preparation and properties of sliver and nitrogen co-doped TiO{sub 2} photocatalyst

    SciTech Connect

    Zhang, Ying; Zhang, Jin; Zhu, Zhongqi; Yan, Ningning; Liu, Qingju

    2013-11-15

    Graphical abstract: - Highlights: • The silver and nitrogen co-doped TiO{sub 2} photocatalysts were prepared and characterized. • The light absorption threshold wavelength of Ag–N–TiO{sub 2} is red-shifted to visible light. • The recombination of the photo-generated electrons and holes of Ag–N–TiO{sub 2} is inhibited. • The photocatalytic activity of Ag–N–TiO{sub 2} is remarkable improved. - Abstract: TiO{sub 2} photocatalysts co-doped with different content of Ag and N were prepared by sol–gel method combined with microwave chemical method. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), ultraviolet–visible diffuse reflectance spectrum (UV–vis) and photo-luminescence emission spectrum (PL). The photocatalytic activity was investigated by photocatalytic degradation of methylene blue (MB) under irradiation of fluorescent lamp. The results indicate that Ag and N co-doping can restrain the increase of grain size, broaden the absorption spectrum to visible light region, and inhibit the recombination of the photo-generated electron–hole pairs. Moreover, the photocatalytic activity of Ag–N–TiO{sub 2} in MB degradation is remarkable improved. The degradation rate of the sample with Ag:TiO{sub 2} = 0.05 at%, N:TiO{sub 2} = 18.50 wt% in 5 h is 93.44%, which is much higher than that of Degussa P25 (39.40%)

  17. Degradation and annealing effects caused by oxygen in AlGaN/GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Jiang, R.; Shen, X.; Chen, J.; Duan, G. X.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Kaun, S. W.; Kyle, E. C. H.; Speck, J. S.; Pantelides, S. T.

    2016-07-01

    Hot-carrier degradation and room-temperature annealing effects are investigated in unpassivated ammonia-rich AlGaN/GaN high electron mobility transistors. Devices exhibit a fast recovery when annealed after hot carrier stress with all pins grounded. The recovered peak transconductance can exceed the original value, an effect that is not observed in control passivated samples. Density functional theory calculations suggest that dehydrogenation of pre-existing ON-H defects in AlGaN plays a significant role in the observed hot carrier degradation, and the resulting bare ON can naturally account for the "super-recovery" in the peak transconductance.

  18. Ferromagnetism in Co-doped (La,Sr)TiO3

    SciTech Connect

    Fix, T.; Liberati, M.; Aubriet, H.; Sahonta, S.-L.; Bali, R.; Becker, C.; Ruch, D.; MacManus-Driscoll, J.L.; Arenholz, E.; Blamire, M.G.

    2009-04-21

    The origin of ferromagnetism in Co-doped (La,Sr)TiO{sub 3} epitaxial thin films is discussed. While the as-grown samples are not ferromagnetic at room temperature or at 10 K, ferromagnetism at room temperature appears after annealing the films in reducing conditions and disappears after annealing in oxidizing conditions. Magnetic measurements, x-ray absorption spectroscopy, x-ray photoemission spectroscopy and transmission electron microscopy experiments indicate that within the resolution of the instruments the activation of the ferromagnetism is not due to the presence of pure Co.

  19. Nitrogen and sulfur co-doped carbon dots with strong blue luminescence

    NASA Astrophysics Data System (ADS)

    Ding, Hui; Wei, Ji-Shi; Xiong, Huan-Ming

    2014-10-01

    Sulfur-doped carbon dots (S-CDs) with a quantum yield (QY) of 5.5% and nitrogen, sulfur co-doped carbon dots (N,S-CDs) with a QY of 54.4% were synthesized, respectively, via the same hydrothermal route using α-lipoic acid as the carbon source. The obtained S-CDs and N,S-CDs had similar sizes but different optical features. The QY of N,S-CDs was gradually enhanced when extending the reaction time to increase the nitrogen content. After careful characterization of these CDs, the doped nitrogen element was believed to be in the form of C&z.dbd;N and C-N bonds which enhanced the fluorescence efficiency significantly. Meanwhile, the co-doped sulfur element was found to be synergistic for nitrogen doping in N,S-CDs. The optimal N,S-CDs were successfully employed as good multicolor cell imaging probes due to their fine dispersion in water, excitation-dependent emission, excellent fluorescence stability and low toxicity. Besides, such N,S-CDs showed a wide detection range and excellent accuracy as fluorescent sensors for Fe3+ ions.Sulfur-doped carbon dots (S-CDs) with a quantum yield (QY) of 5.5% and nitrogen, sulfur co-doped carbon dots (N,S-CDs) with a QY of 54.4% were synthesized, respectively, via the same hydrothermal route using α-lipoic acid as the carbon source. The obtained S-CDs and N,S-CDs had similar sizes but different optical features. The QY of N,S-CDs was gradually enhanced when extending the reaction time to increase the nitrogen content. After careful characterization of these CDs, the doped nitrogen element was believed to be in the form of C&z.dbd;N and C-N bonds which enhanced the fluorescence efficiency significantly. Meanwhile, the co-doped sulfur element was found to be synergistic for nitrogen doping in N,S-CDs. The optimal N,S-CDs were successfully employed as good multicolor cell imaging probes due to their fine dispersion in water, excitation-dependent emission, excellent fluorescence stability and low toxicity. Besides, such N,S-CDs showed a

  20. Magnetic and dielectric studies of Li-Cu co-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Vivek, S.; Ajith, S. K.; Chitralekha, C. S.; Nair, Swapna S.

    2016-05-01

    Room temperature ferromagnetism has been observed in Li-Cu co-doped ZnO nanoparticles prepared by sol-gel route. Our studies indicated that the observed ferromagnetism is a surface phenomenon which depends on oxygen vacancy and the nature of the dopants. Dependence of ferromagnetism on the annealing temperature indicated the role of oxygen vacancy, and the decrease in coercivity as the particle size increases indicates the surface dependence of ferromagnetism. It is found that the addition of dopants also enhanced ferromagnetism. Dielectric studies indicated an increase in dielectric constant as the doping concentration is increased.

  1. Luminescence studies of rare-earth doped and Co-doped hydroxyapatite

    NASA Astrophysics Data System (ADS)

    Vasugi, G.; Thamizhavel, A.; Girija, E. K.

    2012-06-01

    Rare-earth doped and co-doped hydroxyapatite (Eu: HA, Eu-Y: HA) were prepared by wet precipitation method by using CTAB as the organic modifier. The synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Photoluminescence spectra (PL). Upon excitation at 350 nm the samples Eu: HA and Eu-Y: HA shows the emission band in the visible region, which makes it suitable for potential application such as bio-imaging.

  2. Preparation of hybrid Josephson junctions on Co-doped Ba-122 single crystals

    NASA Astrophysics Data System (ADS)

    Reifert, D.; Hasan, N.; Döring, S.; Schmidt, S.; Monecke, M.; Feltz, M.; Schmidl, F.; Tympel, V.; Wisniewski, W.; Mönch, I.; Wolf, T.; Seidel, P.

    2014-08-01

    In this paper we present a method for processing a hybrid Josephson junction on Co-doped BaF{{e}_{2}}A{{s}_{2}} (Ba-122) single crystals with a thin film Pb-counter electrode and a barrier layer of Ti{{O}_{x}}. This includes the leveling and polishing of the crystals and structuring them with thin film techniques such as photo lithography, sputtering and ion beam etching. The junctions show hysteretical resistively and capacitively shunted junction-like I-V characteristics with an {{I}_{c}}{{R}_{n}}-product of about 800 \\mu V.

  3. The effects of the porous buffer layer and doping with dysprosium on internal stresses in the GaInP:Dy/por-GaAs/GaAs(100) heterostructures

    SciTech Connect

    Seredin, P. V.; Gordienko, N. N.; Glotov, A. V.; Zhurbina, I. A.; Domashevskaya, E. P.; Arsent'ev, I. N. Shishkov, M. V.

    2009-08-15

    In structures with a porous buffer layer, residual internal stresses caused by a mismatch between the crystal-lattice parameters of the epitaxial GaInP alloy and the GaAs substrate are redistributed to the porous layer that acts as a buffer and is conducive to disappearance of internal stresses. Doping of the epitaxial layer with dysprosium exerts a similar effect on the internal stresses in the film-substrate structure.

  4. 3D coral-like nitrogen-sulfur co-doped carbon-sulfur composite for high performance lithium-sulfur batteries

    NASA Astrophysics Data System (ADS)

    Wu, Feng; Li, Jian; Tian, Yafen; Su, Yuefeng; Wang, Jing; Yang, Wen; Li, Ning; Chen, Shi; Bao, Liying

    2015-08-01

    3D coral-like, nitrogen and sulfur co-doped mesoporous carbon has been synthesized by a facile hydrothermal-nanocasting method to house sulfur for Li-S batteries. The primary doped species (pyridinic-N, pyrrolic-N, thiophenic-S and sulfonic-S) enable this carbon matrix to suppress the diffusion of polysulfides, while the interconnected mesoporous carbon network is favourable for rapid transport of both electrons and lithium ions. Based on the synergistic effect of N, S co-doping and the mesoporous conductive pathway, the as-fabricated C/S cathodes yield excellent cycling stability at a current rate of 4 C (1 C = 1675 mA g-1) with only 0.085% capacity decay per cycle for over 250 cycles and ultra-high rate capability (693 mAh g-1 at 10 C rate). These capabilities have rarely been reported before for Li-S batteries.

  5. 3D coral-like nitrogen-sulfur co-doped carbon-sulfur composite for high performance lithium-sulfur batteries.

    PubMed

    Wu, Feng; Li, Jian; Tian, Yafen; Su, Yuefeng; Wang, Jing; Yang, Wen; Li, Ning; Chen, Shi; Bao, Liying

    2015-01-01

    3D coral-like, nitrogen and sulfur co-doped mesoporous carbon has been synthesized by a facile hydrothermal-nanocasting method to house sulfur for Li-S batteries. The primary doped species (pyridinic-N, pyrrolic-N, thiophenic-S and sulfonic-S) enable this carbon matrix to suppress the diffusion of polysulfides, while the interconnected mesoporous carbon network is favourable for rapid transport of both electrons and lithium ions. Based on the synergistic effect of N, S co-doping and the mesoporous conductive pathway, the as-fabricated C/S cathodes yield excellent cycling stability at a current rate of 4 C (1 C = 1675 mA g(-1)) with only 0.085% capacity decay per cycle for over 250 cycles and ultra-high rate capability (693 mAh g(-1) at 10 C rate). These capabilities have rarely been reported before for Li-S batteries. PMID:26288961

  6. Tailoring the electronic and optical properties of anatase TiO2 by (S, Nb) co-doping from a DFT plus U calculation

    NASA Astrophysics Data System (ADS)

    Ren, Dahua; Li, Huiran; Cheng, Xinlu

    2015-12-01

    The geometrical structure, defect formation, electronic and optical properties of S-doped, Nb-doped, and (S, Nb)-codoped anatase TiO2 were successfully calculated by the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory with plus U method. Firstly, the geometrical structure demonstrates that the (S, Nb) co-doping can effectively induce lattice distortion and reduce the recombination of electron-hole pairs. Note that the (S, Nb)-codoped system further reduces the band gap compared with pure and mono-doped TiO2 due to the mixture of S 2p and Nb 4d states appears in the gap, which results in an obvious red-shift in the optical absorption spectra and improves the photocatalytic activity. Moreover, the (S, Nb) co-doping should be grown under Ti-rich conditions while S or Nb mono-doping is expected to be easier under O-rich conditions. The above results would be beneficial to further developing for titanium dioxide photocatalyst.

  7. Role of glass structure in defining the chemical dissolution behavior, bioactivity and antioxidant properties of zinc and strontium co-doped alkali-free phosphosilicate glasses.

    PubMed

    Kapoor, Saurabh; Goel, Ashutosh; Tilocca, Antonio; Dhuna, Vikram; Bhatia, Gaurav; Dhuna, Kshitija; Ferreira, José M F

    2014-07-01

    We investigated the structure-property relationships in a series of alkali-free phosphosilicate glass compositions co-doped with Zn(2+) and Sr(2+). The emphasis was laid on understanding the structural role of Sr(2+) and Zn(2+) co-doping on the chemical dissolution behavior of glasses and its impact on their in vitro bioactivity. The structure of glasses was studied using molecular dynamics simulations in combination with solid state nuclear magnetic resonance spectroscopy. The relevant structural properties are then linked to the observed degradation behavior, in vitro bioactivity, osteoblast proliferation and oxidative stress levels. The apatite-forming ability of glasses has been investigated by X-ray diffraction, infrared spectroscopy and scanning electron microscopy-energy-dispersive spectroscopy after immersion of glass powders/bulk in simulated body fluid (SBF) for time durations varying between 1h and 14 days, while their chemical degradation has been studied in Tris-HCl in accordance with ISO 10993-14. All the glasses exhibit hydroxyapatite formation on their surface within 1-3h of their immersion in SBF. The cellular responses were observed in vitro on bulk glass samples using human osteosarcoma MG63 cell line. The dose-dependent cytoprotective effect of glasses with respect to the concentration of zinc and strontium released from the glasses is also discussed. PMID:24709542

  8. Anions (N,S) mono-doping and co-doping influences on electronic structures and optical properties of InNbO4

    NASA Astrophysics Data System (ADS)

    Shi, Haifeng; Zhou, Changping; Zhang, Chengliang; Ye, Enjia

    2016-04-01

    In this paper, the electronic structures and optical properties of N-doped, S-doped and N/S-codoped InNbO4 were systematically investigated by first-principles calculations based on density functional theory (DFT). As for N-doped InNbO4, the acceptor N-2p states would introduce on the upper edge of the valence band (O-2p). While S-3p states would mix with O-2p states when O atom was replaced by S atom in InNbO4. As for N/S-codoped InNbO4, N-2p states mixed with S-3p states above the valence band, resulting in the energy bandgap further narrower in contrast to those of the individual N(S)-doped InNbO4. The optical absorption edge of N/S-codoped InNbO4 displayed an obvious redshift and was successfully extended to visible light region due to the synergistic effect of N/S co-doping. This research proposed that N/S co-doping was a promising method to improve the photocatalytic properties of InNbO4.

  9. Synthesis and down-conversion luminescence properties of Er3+/Yb3+ co-doped AlF3-PbF2-CaF2 powders

    NASA Astrophysics Data System (ADS)

    Liu, Fangchao; Han, Qun; Liu, Tiegen; Chen, Yaofei; Du, Yang; Yao, Yunzhi

    2015-08-01

    Er3+/Yb3+ co-doped oxy-fluoride powders with varying Er/Yb concentration were prepared by a melt quenching method at various sintering temperature. The effect of the Er/Yb doped concentration and sintering temperature were analyzed by using optical absorption and emission techniques. The Judd-Ofelt theory has been used to evaluate the three intensity parameters (Ωλ, where λ = 2, 4 and 6) and calculate the oscillator strengths (fc). Ultraviolet-to-visible emissions were observed under the excitation of a 325 nm CW laser. It was found that the down-conversion fluorescence intensity changes with the sintering temperature and Er/Yb content ratio, the results were explained with the level transitions in Er3+/Yb3+ co-doped systems. The intensity ratios (intensity of 437 nm as reference) of the luminescence spectra that the samples sintered at various temperature are relevant to Ω6 parameter which indicates the vibration amplitude of the Er-O distance. The sintering temperature also has an influence on the intensity ratios via affecting the thermalization of the excited 4I15/2 level.

  10. [Preparation and luminescence properties of Tb3+ ion and Na2WO4 co-doped SiO2 materials].

    PubMed

    Wang, Xi-Gui; Li, Xia

    2008-02-01

    Tb3+ and Na2 WO4 co-doped SiO2 materials were prepared by sol-gel method and the structure of materials were measured by DTA-TG, IR and XRD techniques. The results indicate that the materials were in amorphous phase andthe Si-O-Si bond was still observed in samples annealed at 800 degrees C. The influence of Na2 WO4 on luminescence properties of terbium glasses was investigated by three-dimension fluorescence spectra, excitation and emission spectra. It is approve that when sample excited by 230 nm showed the characteristic emission peaks of terbium corresponding to 5D4-(7) Fj (j = 4, 5, 6) and 5 D3 -(7)Fj (j = 4, 5, 6) transitions. Doping Na2 WO4 has less influence with the emission position of SiO2 materials with terbium, but has a great effect with the emission intensity. It is find that the blue transition of 5D4-7F6 was activated and the green transition of 5D4-7F5 was quenched and the materials radiate green blue fluorescence light under ultraviolet light. The mechanism of sample was analyzed by the energy levels of Tb3+ and Na2 WO4 co-doped glasses. PMID:18478999