Photoluminescence of AgGaTe2 single crystals

The temperature dependence of the photoluminescence spectra of AgGaTe₂ single crystals obtained by the Bridgman-Stockbarger method is investigated within the temperature range 10-300 K. The emission bands associated with donor-acceptor recombination and free and bound excitons are detected. The bonding energy of the free exciton and the forbidden gap of the crystals at 10 K are calculated. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 222–224, March–April, 2000. This work is partially sponsored by the British Royal Society, INTAS (grant No. 634), and EPSRC (grant GR/L 62757).     

Photoelectric properties ofp-CuInSe2 crystals

Spectra of the photoelectromotive force of p-CuInSe₂ single crystals obtained by directional crystallization of a stoichiometric-composition melt in an upright ampoule have been investigated by the method of phase-sensitive detection. A difference in the phase shifts between the exciting light and the arising photoelectromotive force in the extrinsic (impurity) and intrinsic regions of optical absorption is determined. The lifetime in the region of optical self-absorption is found to equal τ=15·10⁻⁶ at T=77 K. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 129–131, January–February, 1997.     

The photoluminescence of ZnSe bulk single crystals excited by femtosecond pulse

This paper reports on the photoluminescence spectra of ZnSe single crystal with trace chlorine excited by the femtosecond laser pulse. Three emission bands, including second-harmonic-generation, two-photon-excited peak and a broad band at 500--700nm, were detected. The thermal strain induced by femtosecond pulse strongly influences the photoluminescence of ZnSe crystal. The corresponding strain \va in ZnSe crystal is estimated to be about 8.8 \ti10^-3 at room temperature. The zinc-vacancy, as the main point defect induced by femtosecond pulse, is successfully used to interpret the broad emission at 500--700nm. The research shows that self-activated luminescence possesses the recombination mechanism of donor--vacancy pair, and it is also influenced by a few selenium defects and the temperature. The rapid decrease in photoluminescence intensity of two-photon-excited fluorescence and second-harmonic generation emission at lower temperature is attributed to the fact that more point defects result in the thermal activation of the two-photo-absorption energy converting to the stronger recombination emission of chlorine--zinc vacancy in 500--700nm. The experimental results indicate that the femtosecond exciting photoluminescence shows a completely different emission mechanism to that of He--Cd exciting luminescence in ZnSe single crystal. The femtosecond laser exhibits a higher sensitive to the impurity in crystal materials, which can be recommended as an efficient way to estimate the trace impurity in high quality crystals.     

Influences of excitation power and temperature on photoluminescence in phase-separated InGaN quantum wells

The photoluminescence(PL) properties of a green and blue light-emitting InGaN/GaN multiple quantum well structure with a strong phase separated into quasi-quantum dots(QDs) and an InGaN matrix in the InGaN epilayer are investigated.The excitation power dependences of QD-related green emissions(P_D) and matrix-related blue emissions(P_M) in the low excitation power range of the PL peak energy and line-width indicate that at 6 K both P_m and P_D are dominated by the combined action of Coulomb screening and localized state filling effect.However,at 300 K,P_m is dominated by the non-radiative recombination of the carriers in the InGaN matrix,while P_D is influenced by the carriers transferred from the shallower QDs to deeper QDs by tunnelling.This is consistent with the excitation power dependence of the PL efficiency for the emission.     

离子注入诱导量子阱界面混合效应的光致荧光谱研究

采用多元芯片方法获得了一系列不同离子注入剂量的GaAsAlGaAs非对称耦合量子阱单元,通过光致荧光谱测量,研究了单纯的离子注入导致的界面混合效应.荧光光谱行为与有效质量理论计算研究表明,Al原子在异质结界面的扩散在离子注入过程中已基本完成,而热退火作用主要是去除无辐射复合中心. 关键词： 量子阱 离子注入 光致荧光谱 界面混合     

Effect of electron screening on the photoluminescence in GaAs/AlGaAs quantum wells

Magneto-photoluminescence of one-side-doped GaAs/AlGaAs single quantum well is measured. Dependence of the spectra on the well width revealed that the long range screening effect of two-dimensional electrons on a free hole plays an important role in the process of recombination.     

Temperature dependent photoluminescence studies of ZnSe:I single crystals grown by chemical vapor transport

The single crystal ZnSe:I sample was grown by the chemical vapor transport (CVT) method using iodine as the transporting agent. The iodine incorporates itself effectively as a donor in the lattice. The sample shows a 〈111〉 optical quality surface and has an absorption edge at 2.55 eV due to a deep impurity band nearly 0.15eV below the conduction band. The photoluminescence emission spectra of this crystal have been measured for its temperature dependence as well as for excitation energy dependence. The photoluminescence is in accordance with a donor-acceptor complex formation involving iodine activated donors and self-activated acceptors. The configuration coordinate model has been used to explain the temperature dependent changes in the peak position and the bandwidth of the emission band. The decrease in luminescence efficiency with increasing temperature is explained by using a simple model for thermal quenching. The activation energy at low temperature range (T<200K) is different from that at high temperature range (200K<T<300K).     

Temperature-dependent photoluminescence of size-tunable ZnAgInSe quaternary quantum dots

Colloidal ZnAgInSe (ZAISe) quantum dots (QDs) with different particle sizes were obtained by accommodating the reaction time. In the previous research, photoluminescence (PL) of ZAISe QDs only could be tuned by changing the composition. In this work the size-tunable photoluminescence was observed successfully. The red shift in the photoluminescence spectra was caused by the quantum confinement effect. The time-resolved photoluminescence indicated that the luminescence mechanisms of the ZAISe QDs were contributed by three recombination processes. Furthermore, the temperature-dependent PL spectra were investigated. We verified the regular change of temperature-dependent PL intensity, peak energy, and the emission linewidth of broadening for ZAISe QDs. According to these fitting data, the activation energy (ΔE) of ZAISe QDs with different nanocrystal sizes was obtained and the stability of luminescence was discussed.     

Anomalous temperature dependence of photoluminescence spectra from InAs/GaAs quantum dots grown by formation–dissolution–regrowth method

Two kinds of InAs/GaAs quantum dot(QD) structures are grown by molecular beam epitaxy in formation–dissolution–regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of quantum dots are different for the two samples. The variation tendencies of PL peak energy, integrated intensity, and full width at half maximum versus temperature for the two samples are analyzed, respectively. We find the anomalous temperature dependence of the InAs/GaAs quantum dots and compare it with other previous reports. We propose a new energy band model to explain the phenomenon. We obtain the activation energy of the carrier through the linear fitting of the Arrhenius curve in a high temperature range. It is found that the Ga As barrier layer is the major quenching channel if there is no defect in the material. Otherwise, the defects become the major quenching channel when some defects exist around the QDs.     

Giant enhancement of photoluminescence emission in monolayer WS2 by femtosecond laser irradiation

Monolayer transition metal dichalcogenides have emerged as promising mat erials for opt oelectTonic and nanophotonic devices.However,the low photoluminescence(PL)quantum yield(QY)hinders their various potential applications.Here we engineer and enhance the PL intensity of monolayer WS₂by femtosecond laser irradiation.More than two orders of magnitude enhancement of PL intensity as compared to the as-prepared sample is determined.Furthermore,the engineering time is shortened by three orders of magnitude as compared to the improvement of PL intensity by continuous-wave laser irradiation.Based on the evolution of PL spectra,we attribute the giant PL enhancement to the conversion from trion emission to exciton,as well as the improvement of the QY when exciton and trion are localized to the new-formed defects.We have created microstructures on the monolayer WS₂based on the enhancement of PL intensity,where the engineered structures can be stably stored for more than three years.This flexible approach with the feature of excellent long-term storage stability is promising for applications in information storage,display technology,and opto electronic devices.     

内电场对纳米硅光致发光谱的影响

从量子限制发光中心模型出发，计算了纳米硅的光致发光（PL）特征与发光中心间的关系. 研究发现，纳米硅与发光中心间的内电场对载流子复合率及峰位振荡有着十分重要的影响. 在2—5 nm的尺寸范围内，纳米硅发光中心上的载流子复合概率远大于内部复合概率，仅需考虑发光中心上的载流子复合发光. 还发现发光中心与纳米硅粒子间的内电场对于纳米硅的发光峰位振荡有着显著的影响.发光中心与纳米硅粒子间的内电场的存在会显著减小纳米硅粒子的内部发光效率以及外部相应发光中心上的发光强度，使得纳米硅PL谱的峰位随纳米晶粒尺寸变化而发生 关键词： 内电场 纳米硅 光致发光 量子限制发光中心     

Pool-Frenkel thermoelectric modulation of exciton photoluminescence in GaSe crystals

Effect of external field on the exciton photoluminescence of GaSe crystals has been investigated and it has been observed that the PL is quenched with the applied field. The changes observed in the PL spectra have been analyzed with impact exciton, Franz-Keldysh and Pool-Frenkel effects. From the analyses of the experimental data, it has been found that the intensity of direct free, indirect free and bound exciton peaks decreased exponentially with the square root of applied field as I∼exp-β√E. The energy positions of emission peaks were found to shift to longer wavelength with the applied field as ΔE∼β√E. From these findings, the Pool-Frenkel thermoelectric field effect is seen to be the dominant mechanism in the variation of exciton PL with the applied field even though the impact exciton and Franz-Keldysh effects contribute.     

掺杂对多层Ge/Si(001)量子点光致发光的影响

利用超高真空化学气相沉积设备, 在Si (001) 衬底上外延生长了多个四层Ge/Si量子点样品. 通过原位掺杂的方法, 对不同样品中的Ge/Si量子点分别进行了未掺杂、磷掺杂和硼掺杂. 相比未掺杂的样品, 磷掺杂不影响Ge/Si量子点的表面形貌, 但可以有效增强其室温光致发光; 而硼掺杂会增强Ge/Si量子点的合并, 降低小尺寸Ge/Si量子点的密度, 但其光致发光会减弱. 磷掺杂增强Ge/Si量子点光致发光的原因是, 磷掺杂为Ge/Si量子点提供了更多参与辐射复合的电子. 关键词： Ge/Si量子点 磷掺杂 光致发光     

温度对CdS纳米颗粒形状和光致发光特性的影响

采用反胶束法,在常温和低温下(接近零度)合成了硅土包裹的CdS纳米颗粒.高分辨电镜表明常温下合成的颗粒呈现直径小于5 nm的球形,而在低温下出现了短棒形和长达微米量级的线形.通过对实验过程的分析表明:不仅合成CdS纳米颗粒溶液的浓度,而且温度对CdS纳米颗粒的形状产生了重要的影响.进一步研究了CdS纳米颗粒的光致发光特性.     

Optical properties of InGaAsBi/GaAs strained quantum wells studied by temperature-dependent photoluminescence

The effect of bismuth on the optical properties of InGaAsBi/GaAs quantum well structures is investigated using the temperature-dependent photoluminescence from 12 K to 450 K.The incorporation of bismuth in the InGaAsBi quantum well is confirmed and found to result in a red shift of photoluminescence wavelength of 27.3 meV at 300 K.The photoluminescence intensity is significantly enhanced by about 50 times at 12 K with respect to that of the InGaAs quantum well due to the surfactant effect of bismuth.The temperature-dependent integrated photoluminescence intensities of the two samples reveal different behaviors related to various non-radiative recombination processes.The incorporation of bismuth also induces alloy non-uniformity in the quantum well,leading to an increased photoluminescence linewidth.     

Optical properties of Tl2In2Se3S layered single crystals

The optical properties of Tl₂In₂Se₃S layered single crystals have been analyzed using transmission and reflection measurements in the wavelength region between 500 and 1100 nm. The optical indirect transitions with a band gap energy of 1.96 eV and direct transitions with a band gap energy of 2.16 eV were determined from analysis of absorption data at room temperature. Dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-effective-oscillator model. The refractive index dispersion parameters – oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index – were found to be 4.67 eV, 45.35 eV, 1.38 × 10¹⁴ m ^{? 2} and 3.27, respectively. Transmission measurements were also performed in the temperature range 10–300 K. As a result of temperature-dependent transmission measurements, the rate of change in the indirect band gap with temperature, i.e. γ = ?5.6 × 10^?4 eV/K, and the absolute zero value of the band gap energy, E _gi(0) = 2.09 eV, were obtained.     

Room‐temperature photoluminescence in quasi‐2D TlGaSe2 and TlInS2semiconductors

We reveal the intrinsic band‐to‐band photoluminescence (PL) in Tl‐based anisotropic semiconductors by means of confocal spectroscopy. The PL achieves largest value for k ⊥ c , where c is the layers stacking axis, and is dependent on polarization. In TlGaSe₂, the band edge absorption spectra were determined at different excitation geometry by using techniques of depth‐resolved free‐carrier absorption (FCA) and photoacoustic response (PAR). A strong absorption enhancement is detected in a large spectral area in the near‐surface region lateral to ab plane. The band‐to‐band absorption enhancement is the most probable cause for high PL intensity. The near‐surface behavior, different from the bulk, might implement useful photonic functionality at room temperature (RT). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)