Search

This study presents the photoluminescence characteristic analysis of a series of red phosphors of KAlSiO4:1.5 mol%Sm3+,x mol%Eu3+ (x = 2, 3, 4, 5, 6, 7) prepared via high-temperature solid-phase reaction. The results show that the X-ray diffraction (XRD) refinement results are reliable. The unit cell parameters and volume gradually decrease as the Eu3+ concentration increases, resulting in a grain size reduction of 10.22%. When x = 6, the emission peaks of Sm3+ at 564, 601, and 651 nm disappear completely, and the corresponding full width at half maximum becomes 0. At 610 nm, the emission peak intensity of Eu3+ is increased by a factor of 4.8. The resonant non-radiative energy transfer effect is greater than the co-excitation effect. A maximum energy transfer efficiency of 97.8% is achieved. The integral area at 610 nm is as high as 85%. The color purity of the phosphor is as high as 92.97%, and the internal quantum yield gradually changes from 32% to 51%. Ultimately, these results confirm that the silicate phosphor is suitable for the red component in the three primary color phosphors of white light-emitting diodes.

The effects of TiO 2 / Al 2 O 3 / MgF 2 triple-layer (TL) antireflection (AR) coating on reducing optical loss of GaInP/InGaAs/Ge triple-junction (TJ) solar cell have been investigated by using Essential Macleod Program software and Crosslight Apsys software, and compared to that of TiO 2 / Al 2 O 3 dual-layer (DL) AR coating. The DLAR and TLAR coatings have reduced the average optical reflectivity values of the TJ solar cells by around 18.9% and 22.2%, respectively. The conversion efficiency of TJ solar cell was increased by 21.29% and 29.44% with DLAR and TLAR coatings. External quantum efficiency values of TJ solar cells with DL and TLAR coating increased in full wavelength region due to the increase of photo generated current density caused by the reduction of surface reflectivity. Both simulation and experimental results showed that the TiO 2 / Al 2 O 3 / MgF 2 TLAR coating has better anti-reflecting properties over TiO 2 / Al 2 O 3 DLAR coating, and improved the overall performance of TJ solar cell more.

A new green-emitting phosphor, KAlSiO4:1.5 mol% Tb3+, x mol% Li+, was prepared via a high-temperature solid-phase method, and its crystal structure, diffuse reflectance spectrum, and luminescence were studied. The results show that the Li+ doping shifts the strongest diffraction peak to a high angle direction, reducing grain size by 11.4%. The entry of Li2CO3 improves the luminescence performance of KAlSiO4:1.5 mol% Tb3+. At a Li+ concentration of 1.5 mol%, the sample has strong absorption in the ultraviolet light range from 250 to 400 nm. The luminous intensity of the sample at 550 nm approximately quadruples after Li+ doping. Additionally, the colour purity of the sample and the internal quantum yield increase to 83.3% and 42%, respectively. The sample changes colour with time when exposed to air without an obvious fading phenomenon. The emission intensity at 200 °C is 95.1% of its value at room temperature, indicating that the phosphor has excellent thermal stability when x = 1.5. These results show the feasibility of using the silicate phosphor for generating the green light component of white light-emitting diodes for solid-state lighting.

To understand and control the behavior of electrochemical systems, including batteries and electrocatalysts, we seek molecular-level details of the charge transfer mechanisms at electrified interfaces. Recognizing some key limitations of standard equilibrium electronic structure methods to model materials and their interfaces, we propose applying charge constraints to effectively separate electronic and nuclear degrees of freedom, which are especially beneficial to the study of conversion electrodes, where electronic charge carriers are converted to much slower polarons within a material that is nonmetallic. We demonstrate the need for such an approach within the context of sulfur cathodes and the arrival of Li ions during discharge of a Li-S cell. The requirement that electronic degrees of freedom are arrested is justified by comparison with real-time evolution of the electronic structure. Long-lived metastable configurations provide plenty of time for nuclear dynamics and relaxation in response to the electrification of the interface, a process that would be completely missed without applying charge constraints. This approach will be vital to the study of dynamics at electrified interfaces which may be created deliberately, adding charge to the electrode, or spontaneously, due to finite temperature dynamics in the electrolyte.

Minimizing the impact of radiation-induced degradation in dilute nitride based optoelectronic devices is crucial in its applications. The effects of 1-MeV electron irradiation (of 1 × 1014–1 × 1016 e/cm2 range) on undoped GaInNAs|GaAs single quantum-well (QW) structure has been studied by low-temperature photoluminescence (PL). PL spectra of GaInNAs|GaAs QW are measured before and after electron irradiation. The results show a slight enhancement of the PL intensity in relatively low electron fluence, and then subsequent deterioration of PL with the increase of cumulative electron fluences. The enhancement in PL intensity at low electron doses is explained by recombination-enhanced defect reaction model, and the degradation at high electron doses is explained by irradiation-induced defects in the lattice.

Alkali doping can suppress deleterious antisite defects in kesterite Cu2ZnSnS4 (CZTS) and improve the open-circuit voltage. In this study, the effects of light Na-doping on the performance and the band alignment of CZTS/CdS thin-film solar cells were investigated. CZTS:Na thin films were fabricated by the spin coating with 10% Na doping on the surface of CZTS. The Na-doping led to the narrower FWHM and larger grain size. The hole concentration and the conductivity were improved due to the NaZn shallow acceptor defects. In addition, Na-doping can improve the band alignment of absorber/buffer interface and inhibit SRH recombination by the Na passivation effect and the suppression of SnZn defects. The typical cliff-like conduction band offset (CBO) was reduced from 0.25 eV in CZTS:Na/CdS to 0.1 eV in CZTS/CdS heterojunction. CZTS:Na device exhibited a higher Voc of 653 mV than that of CZTS/CdS device. The maximum conversion efficiency reached 7.46%, increased by 44% after Na-doping. These results clarify the effect of Na-doping on the band structure of the heterojunction in CZTS solar cells and support a new aspect that synthesis of a surface-doping CZTS:Na absorber has great potential for future research.

We employ the recently introduced generalized microcanonical inflection point method for the statistical analysis of phase transitions in flexible and semiflexible polymers and study the impact of the bending stiffness upon the character and order of transitions between random-coil, globules, and pseudocrystalline conformations. The high-accuracy estimates of the microcanonical entropy and its derivatives required for this study were obtained by extensive replica-exchange Monte Carlo simulations. We observe that the transition behavior into the compact phases changes qualitatively with increasing bending stiffness. Whereas the &Theta, collapse transition is less affected, the first-order liquid-solid transition characteristic for flexible polymers ceases to exist once bending effects dominate over attractive monomer-monomer interactions.

In this work, the (Ag,Cu)2ZnSnS4 (ACZTS) thin films were fabricated via sputtering with a multi-target to form different layer stacks, i.e., (S1) ZnS/Sn/Cu/Ag/Mo,(S2) ZnS/Sn/Ag/Cu/Mo and (S3) ZnS/Ag/Sn/Cu/Mo. The stacked precursors were sulfurized through a soft annealing, followed by a two-step sulfurization in a chamber filled with N2 at standard atmospheric pressure. The x-ray photoelectron spectroscopy elemental profile showed a vertical non-uniform distribution of Ag in the film. Based on the results of scanning electron microscopy and electron probe microanalysis, Ag enrichment of the upper surface was beneficial for the grain size. Moreover, a dense, uniform surface could be obtained and the stability of the elemental composition could be maintained. After optimizing the order of the Ag layers, the efficiency of the solar cells increased from 1.30% to 3.65%, an improvement of 181%. The open circuit voltage is increased from 448 mV to 630 mV because of the reduced voids, increased grain size, and reduced CuZn antisite defects.

In this research, a series of Ca2MgSi2O7: 2% Sm3+, x% Eu3+ (x=4, 5, 6, 7, 8) red phosphors were synthesized using the high-temperature solid-phase method. The phase and luminescence properties of the samples were investigated using an X-ray diffractometer and a photoluminescence spectrometer. The results showed that the synthesized samples were of pure phase, and the introduction of small amounts of Sm3+ and Eu3+ had no significant impact on the crystal structure of the phosphors. It is observed from the phosphor spectra that the co-doped samples exhibited intense red-light emission corresponding to that of Eu3+ at 613 nm when excited at the strongest excitation peak of Sm3+ (401 nm); here, the emission peak intensity of Eu3+ increased by a factor of 5.3. It is found that resonant nonradiative energy transfer occurs from Sm3+ to Eu3+ in the sample, and the energy transfer efficiency reaches up to 44%. The calculated critical distance for energy transfer is 16.117 Å and the concentration interrupt mechanism is an electric dipole-dipole (d-d) interaction. The color coordinates of the samples are all located in the red region (0.6319, 0.3676) with a color purity of ~ 89.3%. The samples exhibited thermal stability of up to 68.6% of that at room temperature when heated to 150˚C . The LED samples packaged with the phosphors emitted warm white-light with a color temperature (CCT) of 5553 K and a color rendering index (Ra) of 84.8. The magnesium yellow feldspar silicate phosphor is suitable as the red component in white LED trichromatic phosphors and has potential applications in solid-state lighting.

A 25 nm thick Ag thin film was sputtered between the Cu2ZnSnS4 (CZTS) absorber and Mo electrode to improve the back contact in CZTS solar cells. The CZTS absorber was fabricated via a cost-effective N,N-dimethylformamide-based solution method. X-ray diffraction and Raman spectroscopy demonstrated that Ag diffused into the CZTS and partially substituted Cu, which resulted in an increased lattice constant a and grain size. Ag doping of CZTS (ACZTS) reduced both the Sn-loss and the presence of voids. An ACZTS photovoltaic device (ITO/i-ZnO/CdS/ACZTS/Mo) was fabricated and showed higher EQE than the CZTS device over the wavelength range of 450–800 nm. The open circuit voltage increased (Voc) from 543 to 631 mV, the short circuit current density (Jsc) increased from 10.36 to 14.37 mA, and the efficiency increased from 2.02 to 3.43% after sputtering the Ag layer. This is mainly because Ag functions as a temporary protective layer that made a tighter combination between Mo and the CZTS absorber.

Electron irradiation causes atomic displacement damage and produces point defects in semiconductor materials. The formation and variation of defects determine the optical properties of semiconductors during the irradiation process. In this paper, Te-doped GaSb was irradiated by 1 MeV electrons, with fluence of 1 × 1015 electrons cm−2, and its optical properties investigated by temperature-dependent photoluminescence (PL) before and after irradiation. After irradiation, the peak position had a blue-shift and intensity was significantly enhanced. The carrier concentration increased from 4.14 × 1017 to 7.82 × 1017 cm−3 but mobility decreased from 2690 to 1780 cm2 V−1 s−1. These phenomena could be explained by the complex mechanism of defect decomposition, that is, the VGaGaSbTeSb defect decomposed into two independent VGaGaSb and TeSb defects. To verify this mechanism, undoped GaSb was irradiated under the same conditions and PL results indicated that electron irradiation had little effect on optical properties of undoped GaSb.

The demands for space solar cells are continuously increasing with the rapid development of space technologies and complex space missions. The space solar cells are facing more critical challenges than before: higher conversion efficiency and better radiation resistance. Being the main power supply in spacecrafts, III-V multijunction solar cells are the main focus for space application nowadays due to their high efficiency and super radiation resistance. In multijunction solar cell structure, the key to obtaining high crystal quality and increase cell efficiency is satisfying the lattice matching and bandgap matching conditions. New materials and new structures of high efficiency multijunction solar cell structures are continuously coming out with low-cost, lightweight, flexible, and high power-to-mass ratio features in recent years. In addition to the efficiency and other properties, radiation resistance is another sole criterion for space solar cells, therefore the radiation effects of solar cells and the radiation damage mechanism have both been widely studied fields for space solar cells over the last few decades. This review briefly summarized the research progress of III-V multijunction solar cells in recent years. Different types of cell structures, research results and radiation effects of these solar cell structures under different irradiation conditions are presented. Two main solar cell radiation damage evaluation models—the equivalent fluence method and displacement damage dose method—are introduced.

The epitaxy properties of GaAs-based GaSb thin films were investigated under different growth conditions to identify suitable smooth areas on GaSb epilayer surface for growing high-quality AlInSb metamorphic buffers. The results showed notable reduction in threading dislocation densities (TDDs) and hillocks densities (HDs) of GaSb buffer layer when the temperature of substrates rising to Tc (surface reconstruction conversion temperature) + 110 °C and growth rate decreasing to 0.25 mono layer per second (ML/s). These conditions led to gradual changes in GaSb epilayer surface morphologies from tiny hillocks to near-parallel steps. The AlInSb/GaSb compound buffers were studied by employing five different structures of AlInSb metamorphic buffer layers grown on optimized GaSb layers, and then analyzed by various analytical methods. The influence of various structural buffer layers on defects were evaluated in order to suppress the formation of defects. It was shown that the buffer layer with low-temperature interface layer and superlattice structure presents obvious inhibitory effects on defects. Among these, specimens with superlattice interface exhibits the lowest TDDs of 3.1 × 107 cm−2 and moderate HDs of 2.4 × 107 cm−2.

The electrical parameters and external quantum efficiency (EQE) of 3 MeV and 8 MeV proton beam irradiated upright metamorphic (UMM) GaInP/GaInAs/Ge triple-junction solar cells, grown by metal-organic chemical vapor deposition, have been investigated and compared to lattice-matched (LM) GaInP/GaInAs/Ge solar cells. High-resolution X-ray diffraction was used to study the relaxation of strain by analysing reciprocal space maps. Threading dislocation density was estimated from cathodoluminescence image. SRIM simulation results have been applied for analysing the irradiation induced displacement damage and its effects on cell performance. The results show that the electrical parameters of both UMM and LM cells degraded more by 3 MeV proton compared to 8 MeV proton irradiation. The degradation of V-oc and I-sc depends on each other in both UMM and LM cells but have different features under proton irradiation due to different cell configurations, materials, and parameters etc. EQE spectra of UMM and LM cells mainly degrades in longer wavelength region due to the reduction of minority carrier diffusion length. Top GaInP subcell in UMM cell shows better radiation resistance than LM cell due to the higher In-P composition, and middle GaInAs middle subcell in UMM structure shows weaker radiation resistance because of the relatively higher indium composition.

WOS: 000423981200049, MXenes are the newest class of two-dimensional (2D) materials, and they offer great potential in a wide range of applications including electronic devices, sensors, and thermoelectric and energy storage materials. In this work, we combined the outstanding electrical conductivity, that is essential for battery applications, of graphene with MXene monolayers (M2CX2 where M = Sc, Ti, V and X = OH, O) to explore its potential in Li battery applications. Through first principles calculations, we determined the stable stacking configurations of M2CX2/graphene bilayer heterostructures and their Li atom intercalation by calculating the Li binding energy, diffusion barrier and voltage. We found that: (1) for the ground state stacking, the interlayer binding is strong, yet the interlayer friction is small; (2) Li binds more strongly to the O-terminated monolayer, bilayer and heterostructure MXene systems when compared with the OHterminated MXenes due to the H+ induced repulsion to the Li atoms. The binding energy of Li decreases as the Li concentration increases due to enhanced repulsive interaction between the positively charged Li ions; (3) Ti2CO2/graphene and V2CO2/graphene heterostructures exhibit large Li atom binding energies making them the most promising candidates for battery applications. When fully loaded with Li atoms, the binding energy is -1.43 eV per Li atom and -1.78 eV per Li atom for Ti2CO2/graphene and V2CO2/graphene, respectively. These two heterostructures exhibit a nice compromise between storage capacity and kinetics. For example, the diffusion barrier of Li in Ti2CO2/graphene is around 0.3 eV which is comparable to that of graphite. Additionally, the calculated average voltages are 1.49 V and 1.93 V for Ti2CO2/graphene and V2CO2/graphene structures, respectively; (4) a small change in the in-plane lattice parameters (, Scientific and Technological Research Council of Turkey (TUBITAK); FWO-Flanders; Flemish Science Foundation (FWO-Vl); Methusalem foundation of the Flemish government; Hercules foundation; TUBITAK [115F024, 116F080]; BAGEP Award of the Science Academy, This work was supported by the bilateral project between the Scientific and Technological Research Council of Turkey (TUBITAK) and FWO-Flanders, Flemish Science Foundation (FWO-Vl) and the Methusalem foundation of the Flemish government. Computational resources were provided by the TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRGrid e-Infrastructure), and HPC infrastructure of the University of Antwerp (CalcUA) a division of the Flemish Supercomputer Center (VSC), which is funded by the Hercules foundation. We acknowledge the support from the TUBITAK (Grant No. 115F024 and 116F080). Part of this work was supported by the BAGEP Award of the Science Academy.

The low dose rate response of bipolar ICs and discrete device are evaluated on the basis of different experiments. Based on experiments, a time-saving and conservative approach-temperature switching approach (TSA)-to simulate the enhanced low dose rate sensitivity (ELDRS) of bipolar devices is presented. Good agreement is observed between the predictive curve obtained with the temperature switching approach and the low dose rate data. Moreover, a description of the underling mechanisms of TSA is analyzed in this paper.

The zinc (Zn) diffusion effects on metal–organic chemical vapor deposition grown flexible inverted metamorphic (IMM) GaInP/GaAs/InGaAs triple junction solar cell performance have been investigated. By studying electrical and spectral properties of solar cells with different configuration, it was found out that the Zn diffusion from GaAs middle cell AlGaAs:Zn back surface field (BSF) layer into AlGaAs/GaAs tunnel junction is the main reason for I–V curve inflection and low fill factor. Besides, the thermal annealing effects caused by the long epitaxial growth time also has significant effect on Zn diffusion and degrades the overall cell performance. These adverse effects caused by Zn diffusion was suppressed by replacing Zn with carbon as the p-type dopant source in BSF layer, and the thermal annealing effects was solved by fine tuning InGaAs bottom subcell base layer thickness. A large area, 4 × 2 cm2, flexible IMM GaInP/GaAs/InGaAs triple junction solar cell with 34.52% efficiency under AM 1.5D solar spectrum has been successfully fabricated.

ZAO (ZnO: Al)/Al and ITO/Ag complex back-reflectors were successfully applied to substrate nip and superstrate pin amorphous silicon solar cells respectively. As a result, the short circuit current (Isc) for a cell with a complex back-reflector increases significantly as compared with a cell without a complex back-reflector. For a superstrate pin cell prepared on SnO2 coated glass, the short-circuit current even increases up to 30%.

The degradation characteristic of GaInP/GaAs/In0.3Ga0.7As inverted metamorphic (IMM) triple junction solar cells irradiated by 1 MeV electron and 10 MeV proton have been studied and compared to that of traditional GaInP/InGaAs/Ge lattice matched (LM) triple junction solar cells. Both IMM and LM solar cells exhibited very good radiation resistance upon 3.16 × 1010 MeV/g displacement damage dose electron and proton irradiation level. The remaining factor of maximum output power is 0.86 and 0.85 for electron irradiation and 0.73 and 0.75 for proton irradiation in IMM and LM solar cells, respectively. IMM solar cell showed better properties in current matching in end-of-life condition comparing to that of LM solar cells. 1 MeV electron to 10 MeV proton irradiation relative damage coefficients, R e p , for IMM and LM solar cells are determined as 3.11 and 2.78, respectively, by using equivalent displacement damage dose model. The radiation damage coefficient of diffusion length upon 1 MeV electron and 10 MeV proton irradiation for both types of solar cell structures have been calculated.

In this article, with gold nanoellipsoid, nanocylinder, and nanobar as the research object, we investigated the variation of resonance wavelength and refractive index sensitivity by using discrete dipole approximation. The effects of the particle size and shape on the resonance wavelength and refractive index sensitivity were quantitatively analyzed. We also performed comparative analysis on the refractive index sensitivity of these three gold nanoparticles in order to find gold nanoparticles with high sensitivity. It was found that gold nanocylinder has a greater refractive index sensitivity as compared to the gold nanoellipsoid or gold nanobar of the same dimensions, thus it is more suitable for biosensing applications.

For application in space environments, the effect of 1-MeV electron irradiation on wafer-bonded GaInP/GaAs//InGaAsP/InGaAs four-junction solar cell grown by all solid state molecular beam epitaxy was studied. After exposure to 1-MeV electron irradiation at 1×15 e/cm 2 , an end of life remaining factor of approximately 85% was obtained. The wafer bonding interface was studied by spectral response and transmission electron microscopy. 1-MeV electron irradiation was conducted on the individual InGaAsP and InGaAs single junction cell, respectively. The degradation of the four-junction cell was mainly due to damage on the InGaAsP and InGaAs subcells rather than the bonding interface.

In this study, Tb3+—doped natural sodium feldspar (NaAlSi3O8) phosphors have been successfully prepared using high−temperature solid—state method with natural sodium feldspar as a substrate. Energy—dispersive X—ray spectrometry analysis (EDX) of NaAlSi3O8 showed that 0.03 wt% of Eu element was present, and elemental distribution mapping analysis showed that the distribution of trace Eu in minerals was aggregated. The crystal structure and luminescence properties of the natural sodium Eu—containing feldspar and synthetic sodium feldspar NaAlSi3O8:Eu3+, Tb3+ phosphors are discussed in detail. The crystal structure analysis of the samples showed that the Na+ in the natural matrix was partly replaced by the doped Tb3+. Studies on the photoluminescence properties of the samples indicate that Eu does not form a luminescent center in the natural mineral, however, the strong characteristic peak of Eu3+ at 615 nm appears after doping with Tb3+ and the peak at 615 nm increases with the increase of Tb3+ concentration. According to the above spectral results, the energy transfer from Tb3+ to Eu3+ is obtained. Through the measurement and analysis of color coordinates, it is found that with the increase of Tb3+ concentration, the luminescence color of the samples can be regulated in the green to red region. NaAlSi3O8:Eu3+ Tb3+ phosphors has potential application value.

The CdS film is one of the best candidates for the n-type buffer layer in Cu2ZnSnS4 (CZTS) solar cells. However, the inappropriate band alignment at CdS/CZTS heterojunction result in the high barrier for the photogenerated carriers, which decrease the open-circuit voltage and the short-circuit current. In this paper, the crystallization and the optical bandgap of the Zn-doping Cd0.6Zn0.4S film fabricated by chemical bath deposition were studied. XRD showed that the lattice constant of hexagonal Cd0.6Zn0.4S decreased a little after Zn doping because of the shorter bond length of Zn–S. Photoluminescence and transmittance spectra showed the band gap of Cd0.6Zn0.4S thin film increased from 2.59 to 2.88 eV due to Burstein-Moss shift. The conduction band offset (CBO) obviously decreased from 0.51 eV in CZTS/CdS heterojunction to 0.27 eV in CZTS/Cd0.6Zn0.4S heterojunction which result in the short-circuit current increasing from 12.25 to 15.05 mA/cm2. The conversion efficiency (Eff) and fill factor (FF) of the solar cell based on CZTS/Cd0.6Zn0.4S were increased from 2.31% to 31.06 to 4.88% and 47.45, comparing to CZTS/CdS solar cell.

Recently penta-graphene was proposed as a stable two-dimensional carbon allotrope consisting of a single layer of interconnected carbon pentagons [Zhang et al., PNAS, 2015, 112, 2372]. Its silicon counterpart, penta-silicene, however, is not stable. In this work, we show that multilayers of penta-silicene form stable materials with semiconducting or metallic properties, depending on the stacking mode. We demonstrate their dynamic stability through their phonon spectrum and using molecular dynamics. A particular type of bilayer penta-silicene is found to have lower energy than all of the known hexagonal silicene bilayers and forms therefore the most stable bilayer silicon material predicted so far. The electronic and mechanical properties of these new silicon allotropes are studied in detail and their behavior under strain is investigated. We demonstrate that strain can be used to tune its band gap.

In this study, a high performance TiO 2 / Al 2 O 3 / MgF 2 multilayer anti-reflective (AR) coating, with an average reflectivity of 6.36% in spectral range of 300–1800 nm, applied on GaInP/GaAs/Ge triple-junction solar cell was designed by Essential Macleod Program (EMP) software. Based on the simulation results, TiO 2 , Al 2 O 3 , MgF 2 single layer and TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating samples were grown by Electron Beam Evaporation (EBE) system for 1 MeV electron beam irradiation experiment. The overall reflectivity of TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating is decreased with the increase of electron irradiation fluence due to the change of reflectivity of each AR layer caused by the refractive index changes. This result indicates that the TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating can improve the triple junction solar cell radiation resistance by achieving favorable permeability in the broadband solar spectrum, especially in 750–900 nm region where the main degradation spectral window for triple junction solar cell.

1 meV electron irradiation and post thermal annealing effects of GaInAsN bulk material with bandgap energy of 1 eV was studied by low-temperature photoluminescence (PL). The nitrogen proportion of the samples was confirmed by high-resolution X-ray diffraction measurement as 0.26%. The result shows that the PL intensity and high activation energy non-radiative centers of GaInAsN materials degraded seriously due to the irradiation induced large number of defects. The PL enhancement phenomena were observed in all samples after rapid thermal annealing (RTA) at 650 ∘C for five minutes. The irradiation and RTA caused PL peak red-shift and blue-shift have been discussed.

In this account, a series of InAsSb thin films were grown on GaAs substrates with GaSb as buffer layer by MBE, the effect of nucleation layer grown under different conditions on the quality of InAsSb thin films was studied, and the inhibition effect of AlSb/GaSb superlattice structure (SLS) on defect propagation in heteroepitaxy was evaluated. In this process, the corresponding Sb/As BEP flux ratio changes of As/In BEP flux ratio are studied. The sensitivity of Sb/As BEP flux ratio to As beam change is eliminated by using locked As beam value and Sb/As BEP flux ratio, which improves the repeatability of epitaxial material component control. At the same time, the Sb content of the GaSb/InAsSb interface could be accurately tuned by controlling the opening sequence and time of the sources cell shutter. Released the increase of strain at the interface caused by too large Sb component. It can be used to control the composition of InAsSb materials.

In this investigation, BaAl2Si2O8 (BAS):Eu2+ (BaF2-derived BAS:Eu and BaCO3-derived BAS:Eu) series of blue phosphor samples were synthesized through high-temperature solid-phase method, and their structure and luminescence properties were examined. In the case of BaF2-derived BAS:Eu, hexagonal feldspar (BaAl2Si2O8) was obtained, which exhibited a UV region (λem = 372 nm) fluorescence at 300 nm excitation. In the case of BaCO3-derived BAS:Eu, a monoclinic feldspar (BaAl2Si2O8) was obtained, which exhibited a blue region (λem = 428 nm) fluorescence at 300 nm excitation. The luminescence mechanism was the f-d transition of Eu2+, and the Eu2+ underwent different degrees of 5 d energy level splitting in different crystal field environments. This accounted for the UV region and blue region fluorescence. Considering that the phase transition between the hexagonal and monocline phases is a slow process, fluorescence emissions in UV and blue regions were generated during the two-phase transition period. As a result, phosphor exhibited a controllable spectrum from UV region (λem = 372 nm) to blue region (λem = 428 nm). Furthermore, based on the crystal field splitting formula, the blue-shift phenomenon of the spectrum was shown to occur in the monoclinic phase. Finally, the crystal distortion index of the environment of Eu2+ was calculated.

The degradation characteristics of MOCVD grown InGaAsP/InGaAs dual junction solar cells, irradiated by 1 MeV electron, 3 MeV and 10 MeV proton, have been investigated. Main electrical and optical properties of solar cell degraded seriously with the increase of irradiation fluences due to the irradiation induced defects which are acting as non-radiative recombination centers in the active layers of the solar cell. The remaining factor of P m a x is 0.67, 0.53 and 0.51 for 1 MeV electron, 10 MeV proton, and 3 MeV proton irradiation, respectively, when the displacement damage dose (DDD) is 3 . 16 × 1 0 10 MeV/g. The degradation of external quantum efficiency (EQE) of each subcell mainly occurred in the long wavelength region, the integrated current density J s c of InGaAsP and InGaAs subcells degraded more seriously upon 3 MeV and 10 MeV proton irradiation comparing to 1 MeV electron irradiation. The InGaAsP subcell turned out to be the current limiting unit due to the lower J s c before and post irradiation. By applying equivalent displacement damage dose model, the relative damage coefficient for 3 MeV proton to 10 MeV proton and 1 MeV electron to 10 MeV proton have been calculated.

We designed a compact, widely tunable, high-energy, stable, mid-infrared optical parametric oscillator pumped by a conventional Q-switched Nd:YAG nano-second laser. The idler wavelengths were tuned from 2.2 to 4.8 μm through gratings and temperature control of the multi-grating MgO-doped periodically poled lithium niobite (PPLN) crystal. A maximum idler output energy of 2.15 mJ was obtained at a pump energy of 21 mJ, which corresponded to an optical-optical efficiency in excess of 10%. A broad-spectrum bandwidth of 21 nm of idler radiation in the mid-infrared wavelength range was considered the result of the large grating period of the PPLN crystal.

利用高温固相法合成BaAl2Si2O8：Cr3+，Er3+系列荧光粉，研究了Cr3+和Er3+掺杂对BaAl2Si2O8材料发光特性的影响.BaAl2Si2O8：Er3+荧光样品在393 nm激发波长下只呈现出峰值为550 nm的绿色荧光，来源于2H11/2→4I15/2和4S3/2→4I15/2跃迁的叠加.BaAl2Si2O8：Cr3+荧光样品在550 nm激发波长下呈现峰值为694 nm的红色荧光，来源于2E→4A2的跃迁.在共掺杂样品BaAl2Si2O8：Cr3+，Er3+中，用Cr3+激发峰的凹槽处380 nm作为激发光，得到的发射峰不仅有Er3+的发射峰位，还有Cr3+的发射峰位，说明两个离子之间可能存在辐射能量传递；对共掺杂BaAl2Si2O8：1% Cr3+，x% Er3+样品的荧光光谱进行测试，随着x的增加，Cr3+的激发和发射光谱强度均有所增加，并且当x=0.5时，光谱强度是原来的4倍.另外，当固定Cr3+的浓度时，随着Er3+的浓度增加，Cr3+的荧光寿命逐渐增加；当固定Er3+的浓度时，随着Cr3+的浓度增加，Er3+的荧光寿命逐渐减小.这些现象表明了Er3+和Cr3+之间存在共振能量传递，通过理论计算得到Er3+和Cr3+之间的能量临界距离为4.5 nm，属于电偶极-电偶极相互作用.

We investigate a milli-joule level near-infrared MgO:PPLN optical parametric oscillator. The maximum near-infrared 1.5 μm output energy reached 5.6 mJ at the pump energy of 22.5 mJ, corresponding to a conversion efficiency of 25%.

Tm3+/Dy3+-codoped Ca2Al2SiO7 phosphors have been synthesized using a high-temperature solid-state reaction method. The crystal structure, x-ray diffraction patterns, and photoluminescence (PL) properties of the rare-earth (RE) ions, and energy transfer (ET) processes between RE ions, were investigated in detail. The quenching concentration of Tm3+ and Dy3+ singly doped in Ca2Al2SiO7 was determined to be 0.006 mol and 0.02 mol, respectively. Under excitation at 357 nm, Ca2Al2SiO7:Tm3+ phosphors showed emission lines of Tm3+ corresponding to 1D2 → 3F4 and 1G4 → 3H6 transitions. Efficient ET from Tm3+ to Dy3+ ions was observed, leading to color-tunable emissions of Ca2Al2SiO7:0.006Tm3+,xDy3+ (x = 0 mol to 0.02 mol) phosphors. Theoretical calculations revealed that the efficiency of the ET gradually increased with increase in the Dy3+ ion concentration, reaching a maximum of ∼ 42.1% at Tm3+ ion concentration of 0.006 mol. Furthermore, at 473 K, the quantum efficiency was calculated to be 79.8% at room temperature, confirming the good thermal stability of the Ca2Al2SiO7:0.006Tm3+,xDy3+ phosphors.

Minimizing the impact of radiation-induced degradation in optoelectronic devices based dilute nitride is crucial in applications. The effects of 1MeV electron irradiation (1×1014 e/cm2 ~ 1×1016 e/cm2 range) on undoped GaInNAs/GaAs single quantum well (QW) structure has been studied by low temperature photoluminescence (PL). PL spectra of GaInNAs/GaAs QW are measured before and after electron irradiation. The results show a slight enhancement of the PL intensity in relatively low electron fluence, and then subsequent deterioration of PL with increase of cumulative electron fluence. The enhancement in PL intensity at low electron doses are explained by recombination-enhanced defect reaction model and the degradation at high electron doses are explained by irradiation induced defects in lattice.

We investigate the effects of 1.0MeV electron beam irradiation on the photoluminescence of self-assembled InAs/GaAs quantum dots. After irradiation doses up to 1×1016e-/cm2 , photoluminescence of all samples was degraded dramatically and some additional radiation-induced changes in photo-carrier recombination from QDs, which include a slight increase in PL emission with low electron doses under different photo-injection condition in two samples, are also noticed. Different energy shift was observed in two samples with different Quantum Dot sizes. We attribute this remarkable phenomenon to combination of stress relaxation induced red-shift and In-Ga intermixing caused blue-shift.

Edge functionalization of graphene nanoribbons with nitrogen atoms for various adatom configurations at armchair and zigzag edges are investigated. We provide comprehensive information on the electronic and magnetic properties and investigate the stability of the various systems. Two types of rippling of the nanoribbons, namely edge and bulk rippling depending on the sign of edge stress induced at the edge, are found. They are found to play the decisive role for the stability of the structures. We also propose a type of edge decoration in which every third nitrogen adatom at the zigzag edges is replaced by an oxygen atom. In this way, the electron count is compatible with a full aromatic structure, leading to additional stability and a disappearance of magnetism that is usually associated with zigzag nanoribbons.

WOS: 000432823800002, PubMed ID: 29714168, There is an increasing need to understand interfaces between two-dimensional materials to realize an energy efficient boundary with low contact resistance and small heat dissipation. In this respect, we investigated the impact of charge and substitutional atom doping on the electronic transport properties of the hybrid metallic-semiconducting lateral junctions, formed between metallic (1T and 1T(d)) and semiconducting (1H) phases of MoS2 by means of first-principles and non-equilibrium Green function formalism based calculations. Our results clearly revealed the strong influence of the type of interface and crystallographic orientation of the metallic phase on the transport properties of these systems. The Schottky barrier height, which is the dominant mechanism for contact resistance, was found to be as large as 0.63 eV and 1.19 eV for holes and electrons, respectively. We found that armchair interfaces are more conductive as compared to zigzag termination due to the presence of the metallic Mo zigzag chains that are directed along the transport direction. In order to manipulate these barrier heights we investigated the influence of electron doping of the metallic part (i.e. 1T(d) -MoS2). We observed that the Fermi level of the hybrid system moves towards the conduction band of semiconducting 1H-MoS2 due to filling of 4d-orbital of metallic MoS2, and thus the Schottky barrier for electrons decreases considerably. Besides electron doping, we also investigated the effect of substitutional doping of metallic MoS2 by replacing Mo atoms with either Re or Ta. Due to its valency, Re (Ta) behaves as a donor (acceptor) and reduces the Schottky barrier for electrons (holes). Since Re and Ta based transition metal dichalcogenides crystallize in either the 1T(d) or 1T phase, substitutional doping with these atom favors the stabilization of the 1T(d) phase of MoS2. Co-doping of hybrid structure results in an electronic structure, which facilities easy dissociation of excitons created in the 1H part., Scientific and Technological Research Council of Turkey (TUBITAK); FWO-Flanders; Flemish Science Foundation (FWO-VI); Methusalem foundation of the Flemish government; Hercules foundation; TUBITAK [115F024], This work was supported by the bilateral project between the The Scientific and Technological Research Council of Turkey (TUBITAK) and FWO-Flanders, Flemish Science Foundation (FWO-VI) and the Methusalem foundation of the Flemish government. Computational resources were provided by TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRGrid e-Infrastructure), and HPC infrastructure of the University of Antwerp (CalcUA) a division of the Flemish Supercomputer Center (VSC), which is funded by the Hercules foundation. We acknowledge the support from TUBITAK (Grant No. 115F024).

The electrical parameters and EQE spectral response of 1 MeV electron beam irradiated MOVPE grown lattice-matched (LM) and upright metamorphic (UMM) GaInP/GaInAs/Ge triple-junction solar cells have been investigated with different flux density and fluence range from $5\times 10^{14}$ to $1.5\times 10^{15}\mathbf{cm}^{-2}$ . The overall degradation of electrical parameters of UMM cell was higher than LM cell due to the existence of dislocation within the epitaxy active layers. It was observed that the EQE spectra degrade mainly in top and middle subcells, and top GaInP subcell in UMM cell showed better radiation resistance due to the higher InP composition. An artifact phenomenon was observed in bottom Ge subcell due to the low shunt resistance.

We report a milli-joule level mid-infrared MgO:PPLN optical parametric oscillator. The maximum mid-infrared 3.5 μm idler output energy reached 3.47 mJ at the pump energy of 21 mJ, corresponding to a photon conversion efficiency of 55%.

A series of single-phased Li 2 BaSiO 4 :Ce3+, Eu2+, Sm3+ phosphors were synthesized, investigated the luminescent properties and discussed the energy transfer process. These results indicated that this phosphor has a potential application for ultraviolet white light-emitting diodes.

Properties and passivation effect of ultra-thin AlN films fabricated on InGaAs/GaAs near-surface quantum wells by plasma-enhanced atomic layer deposition are investigated. The role of the coating on the surface is studied by examining the electric field build-up by photoreflectance. Photoluminescence confirms the passivation effect with ultra-thin layers and the reduced electric fields with thicker AlN layers. Atomic force microscopy shows that an ultra-thin AlN layer does not substantially alter the surface morphology.

Low-temperature (T = 30 K) photoluminescence (PL) and post thermal annealing effects on 150 KeV proton irradiated GaInAsN bulk, single quantum well and triple quantum well structures (Eg ~ 1.0 eV) have been investigated. The nitrogen proportion of the samples was confirmed by high-resolution X-ray diffraction (HR-XRD) measurement as 0.26%, 0.30% and 0.20% for GaInAsN bulk, SQW, and MQW samples, respectively. The result shows that the PL intensity of GaInAsN materials degraded seriously by proton irradiation. The PL intensity enhancement were observed for all three types of sample after thermal annealing at 650 °C for 5 min, and MQW sample was recovered by the factor bigger than 100. The irradiation induced red-shift and thermal annealing induced blue-shift phenomena were analyzed by SRIM simulation result and theoretical models of InGaAs band structure.

In this paper we reported the electrical and spectral properties of 1 MeV electron and 3 MeV proton irradiated In0.53Ga0.47As single junction solar cell, which is used as the fourth subcell of wafer bonded GaInP/GaAs//InGaAsP/InGaAs four-junction full spectra solar cell. The equivalent displacement damage dose model was applied to study the radiation effects of solar cell. The results show that the electrical parameters of the solar cell degrade seriously with the increase of irradiation fluences, the reduction of minority carrier life-time and changes of series and shunt resistance caused by irradiation-induced displacement damage are the main reason for the degradation of cell performance. Degradation of spectral response mainly occurred in the long wavelength region of solar cell due to the bigger displacement damage in the base layer of solar cell. Degradation properties of solar cell by electron and proton irradiation can be predicted by electron to proton damage equivalency factor Rep.