不同激发密度下CdS晶体的光致发光和受激发射

本文主要研究在77-111K温度范围内、不同激发密度的N2激光器的337.1nm谱线激发下,激子-激子(Ex-Ex)、激子-载流子(Ex-e)的相互作用和发射一个LO声子(Ex-1LO)、两个LO声子(Ex-2LO)的自由激子的辐射复合行为.并在77K温度下观测到由Ex-Ex发射产生的受激发射.     

极性晶体膜中强耦合激子的性质

在强耦合极化子模型基础上,采用Lee-Low-Pines(LLP)变分法研究了极性晶体膜中激子与表面光学(SO)声子强耦合、与体纵光学(LO)声子弱耦合体系的性质.讨论了极性晶体膜中激子的诱生势与膜厚度和温度的变化关系.结果表明:激子的诱生势不仅与电子-空穴间距离有关,而且与极性晶体膜厚度有关,同时温度对激子诱生势的影响十分显著.     

在正向电压激发下ZnSe MIS二极管的自由激子发光

研究了最低温度为20~30K时,在正向电压激发下ZnSe MIS二极管的激子发光光谱,在这一温度下,二极管有可能通过足以产生发光的电流.对于利用通常气相技术生长的高纯晶体所制备的二极管,其电致发光几乎完全由Γ8→Γ6自由激子发光的1LO和2LO声子伴线所组成.根据Gross等人的半经典理论,讨论了两个谱带的形状.结果是谱带的宽度和不对称性归结为激子服从Maxwell-Boltzmann分布,其有效激子温度接近于晶格温度.     

极性晶体膜中强耦合激子的极化子效应和温度依赖性

采用线性组合算符和变分方法研究了极性晶体膜中激子与表面光学(SO)声子强耦合、与体纵光学(LO)声子弱耦合体系的性质,推导出了激子诱生势的表达式,并以AgBr晶体为例进行了数值计算.结果表明:激子的诱生势不仅与电子-空穴间距离有关,而且温度与极性晶体膜厚度对激子诱生势的影响也十分显著.     

极性晶体膜中强耦合激子的极化子效应和温度依赖性

采用线性组合算符和变分方法研究了极性晶体膜中激子与表面光学（SO）声子强耦合、与体纵光学（LO）声子弱耦合体系的性质,推导出了激子诱生势的表达式,并以AgBr晶体为例进行了数值计算.结果表明：激子的诱生势不仅与电子-空穴间距离有关,而且温度与极性晶体膜厚度对激子诱生势的影响也十分显著.     

正向高密度脉冲电流激发下ZnSe MIS二极管中的自由激子发光

本文测量了在77K和正向脉冲电流密度为50～500mA/mm2的激发下,ZnSe MIS二极管的电致发光光谱.首次在高电流密度激发下的ZnSe晶体的电致发光光谱上,观测到自由激子与自由激子间(Ex-Ex)的散射.本中根据自由激子的动能分布,讨论了2LO声子协助的自由激子伴线的形状,发现当激发电流密度增高时,自由激子的有效温度大于晶格温度,这可归结为激子与激子间的非弹性散射.     

高质量纳米ZnO薄膜的光致发光特性研究

报道了利用低压-金属有机物化学气相沉积技术生长纳米ZnS薄膜，然后，将ZnS薄膜在氧气中于800℃温度下进行热氧化制备高质量纳米ZnO薄膜.x射线衍射结果表明，纳米ZnO薄膜具有六角纤锌矿多晶结构.室温下观察到一束强的紫外(3.26 eV) 光致发光和很弱的深能级发射.根据激子峰的半高宽度与温度的关系确定了激子-纵向光学声子（LO）的耦合强度（ГLO）.由于量子限域效应使ГLO减少较多. 关键词： 光致发光 热氧化 激子 纳米ZnO薄膜     

多原子极性晶体中表面激子的性质

本文研究多原子极性晶体中表面激子的性质.采用微扰法导出表面激子的有效哈密顿量.多支LO声子对表面激子的自陷能和有效势的影响是相互独立的.对于Wannier激子,电子、空穴间的相互作用的有效势仍是库仑型的,只是介电常数约化为 .多支LO声子的作用使激子的自陷能更低.并得到激子的自陷条件.     

纳米ZnO薄膜的激子光致发光特性

报道了纳米ZnO薄膜激子光致发光(PL)与温度的关系。首先利用低压金属有机化学气相沉积(LPMOCVD)技术生长ZnS薄膜,然后将ZnS薄膜在氧气中于800℃下热氧化2h获得纳米ZnO薄膜。X射线衍射(XRD)结果表明,纳米ZnO薄膜具有六角纤锌矿多晶结构且具有择优(002)取向。室温下观察到一束强的紫外(326eV)光致发光(PL)和很弱的深能级(DL)发射。根据激子峰的半高宽(FWHM)与温度的关系,确定了激子纵向光学声子(LO)的耦合强度(ГLO)。     

极性晶体中极化子效应对界面强耦合激子性质的影响

在Huybrechts关于强耦合极化子的模型基础上,采用LLP变分法研究了极性晶体中激子与IO声子强耦合、与LO声子弱耦合体系的基态能量,推导出了激子的自陷能和诱生势的表达式,并以AgCl/AgBr晶体为例进行了数值计算,结果表明,激子的自陷能不仅与激子的坐标z有关,而且电子-空穴间距离ρ对激子自陷能的影响也十分显著;激子的诱生势不仅与电子-空穴间距离ρ有关,而且激子距离晶体界面的位置z对诱生势的影响也十分显著.     

Free exciton emission in forward-biased CdS MIS diodes

The radiative decay of free excitons with the emission of 0, 1, or 2LO phonons has been observed in electroluminescence in Cds MIS diodes operated in forward bias at temperatures in the range 40 – 77K. The line shapes and temperature dependence of the ILO and 2LO phonon assisted replicas are discussed in terms of the distribution of kinetic energy of the excitons with an effective temperature equal to that of the lattice.     

Excitonic polaron and phonon assisted photoluminescence of ZnO nanowires

The coupling strength of the radiative transition of hexagonal ZnO nanowires to the longitudinal optic (LO) phonon polarization field is deduced from temperature dependent photoluminescence spectra. An excitonic polaron formation is discussed to explain why the interaction of free excitons with LO phonons in ZnO nanowires is much stronger than that of bound excitons with LO phonons. The strong exciton-phonon coupling in ZnO nanowires affects not only the Haung-Ray S factor but also the FXA-1LO phonon energy spacing, which can be explained by the excitonic polaron formation.     

Fabrication and low-temperature photoluminescence spectra of Mn-doped ZnO nanowires

Mn-doped ZnO nanowires have been fabricated through a high temperature vapor-solid deposition process. The low-temperature photoluminescence spectra of the samples show that there are multipeak emissions at the ultraviolet (UV) region (about 3.4?C3.0?eV). The excitonic and phonon-assisted transitions in Mn-doped ZnO nanowires were investigated. The results show that there is an obvious oscillatory structure emission at the UV region under low temperature from 12?C125?K. The oscillatory structure has an energy periodicity about 70?meV and the oscillatory structure is mainly attributed to longitudinal optical (LO) phonon replicas of free excitons?(FX). The multipeak emissions at 12?K are attributed to a donor-bound exciton (DBX, 3.3617?eV), 1LO-phonon replicas of a free exciton (FX-1LO, 3.3105?eV), 2LO-phonon replicas of a free exciton (FX-2LO, 3.2396?eV), and 3LO-phonon replicas of a free exciton (FX-3LO, 3.1692?eV), respectively. The intensity of UV emission and the efficiency of emission from the Mn-doped ZnO nanowires are improved.     

Dependence of photoluminescence of ZnO/Zn0.85Mg0.15O multi-quantum wells on barrier width

Temperature-dependent photoluminescence (PL) from two multi-quantum well (MQW) structures with different barrier widths has been systematically investigated. The PL band in the well layers is dominated by localized excitons (LE), D⁰X, and D⁰X-1LO. As the temperature increases, luminescence from the excitons localized in the well layers shows an ‘S’-shaped shift in the thin barrier MQW whereas a monotonic redshift is observed from the thick barrier MQW. Quenching of well-related emission is associated with delocalization of the excitons in the potential minima induced by interface fluctuations or alloy disorder. The activation energies correlated with depths of the local potential are deduced to be 7 and 17 meV for the thick and thin barrier MQWs, respectively.     

Multiplasmon replicas of the emission lines of bound excitons in ZnSe crystals

This paper reports on the results of investigations into the cathodoluminescence spectra of ZnSe crystals grown from a vapor phase and annealed in a bismuth melt [ZnSe(Bi) crystals], as well as in a bismuth melt containing aluminum [ZnSe(Bi,Al) crystals], at a temperature of 1200 K for 120 h. The longitudinal optical (LO) phonon replicas of the emission lines of free excitons are dominant in the cathodoluminescence spectra of the samples subjected to annealing in the bismuth melt with subsequent quenching. The emission spectra of all the samples studied, including the initial crystals, contain series of I ₁ ^s,d -nLO lines of bound excitons. It is revealed that plasmon replicas are characteristic not only of the I ₁ ^s -nLO lines. A weak exciton-plasmon interaction manifests itself in the form of single-plasmon Stokes satellites of the I ₁ ^d -nLO spectral lines. A theory describing the multiphoton optical transitions of bound excitons with the participation of mixed plasmonphonon vibrational modes is proposed. This theory makes it possible to calculate the shape function of an emission spectrum without recourse to model concepts. The results of the theoretical calculations are in agreement with the experimental data.     

Temperature-dependent luminescence dynamics for ZnO thin films

The paper presents the photoluminescence investigation of zinc oxide thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz wafers. The films with different thickness (number of layers) were annealed at different temperatures after the preparation process. It was found that high quality, transparent ZnO thin films could be produced on quartz substrates at relatively low annealing temperature (450–550  $^{\circ }\mathrm{C}$ ). The dependence of the ZnO thin film quality was studied by X-ray diffraction and atomic force microscopy techniques. Optical properties were investigated by classic and time-resolved photoluminescence (TRPL) measurements. Photoluminescence spectra allowed us to estimate energy of the free excitons, bond excitons and their longitudinal optical (LO) phonon replicas as a function of the annealing temperature. An innovative TRPL technique let us precisely measure the decay time of the free- and bond excitons’ in the real time. TRPL measurements as a function of temperature reveal a biexponential decay behavior with typical free/bound exciton decay constants of 970/5310 ps for the as-grown sample and 1380/5980 ps after annealing process. Presented spectra confirm high structural and optical quality of investigated films. We proved that the thermal treatment improve both optical and structural quality and extend the photoluminescence’s lifetimes. The obtained experimental results are important for identification of exciton’s peaks and their LO phonon replicas for the investigated ZnO films.     

Exciton–phonon interaction in Al_(0.4)Ga_(0.6)N/Al_(0.53)Ga_(0.47)N multiple quantum wells

The exciton-phonon interaction in Al_(0.4)Ga_(0.6)N/Al_(0.53)Ga_(0.47)N multiple quantum wells(MQWs) is studied by deepultraviolet time-integrated and time-resolved photoluminescence(PL).Up to four longitudinal-optical(LO) phonon replicas of exciton recombination are observed,indicating the strong coupling of excitons with LO phonons in the MQWs.Moreover,the exciton-phonon coupling strength in the MQWs is quantified by the Huang-Rhys factor,and it keeps almost constant in a temperature range from 10 K to 120 K.This result can be explained in terms of effects of fluctuations in the well thickness in the MQWs and the temperature on the exciton-phonon interaction.     

Photoluminescence and time-resolved photoluminescence of star-shaped ZnO nanostructures

Optical properties of star-shaped ZnO nanostructures were studied. The temperature-dependent photoluminescence (PL) was examined up to fourth-order longitudinal optical (LO) phonon assisted emissions of free excitons and confirmed that the nature of the room temperature PL in ZnO is 1-LO phonon assisted emission of free excitons. Low threshold ultraviolet stimulated emissions (SE) were obtained for our powder samples at room temperature. Picosecond time-resolved PL measurements detected a bi-exponential decay behavior which is strongly dependent on the excitation intensity: the slow decay term decreased faster than the fast decay term as the excitation intensity increased and the emission decays were dominated by the fast one. We also found that the emission decays decreased super-linearly before the appearance of the SE. This behavior may be used to deduce the threshold of SE or lasing.