调制掺杂的应变In0.60Ga0.40As/In0.52Al0.48As多量子阱结构的光致发光谱研究

报道了调制掺杂的应变In_0.60Ga_0.40As/In_0.52Al_0.48As多量子阱中室温光致发光光谱.观察到n=1和2电子子带到n=1重空穴子带的强发光峰.在低温下可以观察到n=1电子子带到n=1轻空穴弱发光肩胛.通过对发光强度随激发功率及温度依赖关系以及理论模型的分析研究,认为该调制掺杂量子阱中辐射复合效率降低的主要机制是应变失配位错对载流子的陷阱作用.界面上的失配位错是陷阱的主要来源.并用静态的光致发光理论模型 关键词：     

Threshold kinetic processes for t-C4F9I

A laser oscillator system was used to study the kinetics of t-C₄F₇I relative to n-C₃F₇I. Modeling shows that the rapid R + I¹ recombination results in near steady state gain levels being achieved for t-C₄F₉I while the n-C₃F₇I exhibits strong transient behavior. The estimated recombination rate for t-C₄F₉I is much larger than the published value.     

Microstructural evolutions of Pr13Fe80B7 alloys during solid HDDR process

Microstructural evolutions of Pr₁₃Fe₈₀B₇ alloys during solid hydrogenation disproportionation desorption recombination (HDDR) process is systematically investigated. The results show that the early-disproportionated products of Pr₁₃Fe₈₀B₇ alloys are mainly characteristic of rod-like morphology, and the rods are PrH₂ while the matrix is Fe. Moreover, all the PrH₂ rods have the same crystallographic orientation, and grow with a definite orientation related to the Fe matrix. However, it is notable that no iron boride phase except for NdH₂ and Fe is found. With the prolonged disproportionation time, the rod-like disproportionated products coarsen, and the Fe₂B come to form. When the disproportionation time is 17 h, the rod-like disproportionation morphology transforms into sphere, and a large amount of Fe₂B is found. Subsequent investigations for the recombination show that the recombination reactions start at the boundaries between PrH₂ rods and Fe matrix, and the rim-like Pr₂Fe₁₄B is formed on the PrH₂ rods. Moreover, the recombined PrFeB powder of the rod-like microstructure has strong magnetic anisotropy.     

Intrinsic ultraviolet luminescence from Lu2O3, Lu2SiO5 and Lu2SiO5:Ce

Radioluminescence and thermally stimulated luminescence measurements on Lu₂O₃, Lu₂SiO₅ (LSO) and Lu₂SiO₅:Ce³⁺ (LSO:Ce) reveal the presence of intrinsic ultraviolet luminescence bands. Characteristic emission with maximum at 256 nm occurs in each specimen and is attributed to radiative recombination of self-trapped excitons. Thermal quenching of this band obeys the Mott-Seitz relation yielding quenching energies 24, 38 and 13 meV for Lu₂O₃, LSO and LSO:Ce, respectively. A second intrinsic band appears at 315 nm in LSO and LSO:Ce, and at 368 nm in Lu₂O₃. Quenching curves for these bands show an initial increase in peak intensity followed by a decrease. Similarity in spectral peak position and quenching behavior indicate that this band has a common origin in each of the samples and is attributed to radiative recombination of self-trapped holes, in agreement with previous work on similar specimens. Comparison of glow curves and emission spectra show that the lowest temperature glow peaks in each specimen are associated with thermal decay of self-trapped excitons and self-trapped holes. Interplay between the intrinsic defects and extrinsic Ce³⁺ emission in LSO:Ce is strongly indicated.     

Geminate and non-geminate recombination in a-As2Se3

Combined zerographic measurements and a delayed-collection field technique has been applied to a-As₂Se₃. The data shows that the zero-field quantum efficiency is 0.45±0.02. The measured field and temperature dependence gives a best fit to the Onsager theory with $\text{r}{}_0\text{=80}\text{A}\text{?}$ for Φ₀=1. Non-geminate recombination was studied using a delayed-collection field technique as a function of the time delay of the collection field. The results indicate a remarkably long recombination lifetime≈1 sec at room temperature which is diffusion-controlled.     

Calculation of radiative transition probabilities and radiative recombination rate coefficients for H2, OH, H 2+ and OH+ molecules

A method is presented to calculate the radiative transition probabilities and the radiative recombination rate coefficients between electronic molecular states. Total transition probabilities are determined from vibrational transition probabilities without considering the detailed rotational structure of the molecular electronic states. Radiative recombination rate coefficients are obtained from the computation of vibrational photo-ionisation cross sections. Concerning spontaneous emission, Lyman (B → X) and Werner (C → X) band systems of H₂ and Meinel (A → X), (B → A) and (B → X) band systems of OH are investigated. For radiative recombination, transitions between H₂⁺ (X) and H₂(X), and between OH⁺(X, a, A, b, and c) and OH(X) are considered. Transition probabilities and recombination rate coefficients are calculated as a function of temperature in the range 1500–15 000 K.     

Preparation,microstructure, and magnetic properties of a nanocrystalline Nd12Fe82B6 alloy by HDDR combined with mechanical milling

Nanocrystalline Nd₁₂Fe₈₂B₆ (atomic ratio) alloy powders with Nd₂Fe₁₄B/α-Fe two-phase structure were prepared by HDDR combined with mechanical milling. The as-cast Nd₁₂Fe₈₂B₆ alloy was disproportionated via ball milling in hydrogen, and desorption–recombination was then performed. The phase and structural change due to both the milling in hydrogen and the subsequent desorption–recombination treatment was characterized by X-ray diffraction (XRD). The desorption–recombination behavior of the as-disproportionated alloy was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The morphology and microstructure of the final alloy powders subject to desorption–recombination treatment were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results showed that, by milling in hydrogen for 20 h, the matrix Nd₂Fe₁₄B phase of the alloy was fully disproportionated into a nano-structured mixture of Nd₂H₅, Fe₂B, and α-Fe phases with average size of about 8 nm, and that a subsequent desorption–recombination treatment at 760 °C for 30 min led to the formation of Nd₂Fe₁₄B/α-Fe two-phase nanocomposite powders with average crystallite size of 30 nm. The remanence B_r, coercivity H_c, and maximum energy product (BH)_max of such nanocrystalline Nd₁₂Fe₈₂B₆ alloy powders achieved 0.73 T, 610 kA/m, and 110.8 kJ/m³, respectively.     

Hole mobility in evaporated layers of As2S3.CdI2

The hole drift mobility in As₂S₃.CdI₂ has been determined using Spear's method. The room-temperature value is 10^?4$\text{cm}{}^2\text{Vs}$, the activation energy 0.2 eV. The hole yield appears to be controlled by geminate recombination.     

Radiated recombination in CdGa2Se4

The photoluminescence of single crystals of CdGa₂Se₄ is studied as a function of temperature, of the excitation intensity, and of the polarization of the exciting light. A possible level scheme for optical transitions in the perfect crystal is given and evidence is also found for donor-acceptor pair recombination luminescence.     

三元异质结构Ag-Bi2MoO6/BiPO4光催化剂高效降解苯酚红

多组分复合体系有利于电荷的有效分离,减少电子空穴对的复合几率。通过低温液相法首次合成Ag-Bi₂MoO₆/BiPO₄三元异质结构光催化剂。利用XRD、SEM、EDX及XPS等技术对样品进行了表征。结果表明,Ag纳米粒子光照积累在Bi₂MoO₆/BiPO₄的表面,通过表面等离子共振增加对可见光的吸收,同时作为电子受体促进了光生电子的转移。Ag、BiPO₄和Bi₂MoO₆形成三元异质结构有效地抑制了光生电子空穴对的复合。Ag-Bi₂MoO₆/BiPO₄表现出优异的光催化性能,其光催化活性较BiPO₄、Bi₂MoO₆和Bi₂MoO₆/BiPO₄样品有较大提高。并且对Ag-Bi₂MoO₆/BiPO₄三元异质结构的光催化机制进行了讨论。光催化过程中反应活性物种捕获实验结果表明h⁺和O₂^·-是主要的活性基团.     

The origin of K2, Rb2 and Cs2 triplet 13Πg−X3Σ+u bands in discharge

The absorption and emission spectra of potassium, rubidium and caesium low-pressure discharges have been studied at the far blue wings of resonance D2-lines. The observed diffuse bands were attributed to the 1³Π_g?X³Σ⁺_u transition. Experiments revealed the recombination ²P + ²S nature of these bands, and the corresponding rate coefficients were obtained. Energies of the higher excited states as well as the X³Σ⁺_u -state well depths for K₂, Rb₂ and Cs₂ molecules were estimated.     

Al2O3增强的Co2-C98/Al2O3/Si异质结的光伏效应

随着能源危机的加剧,太阳能电池作为开发和利用太阳能的一种普遍形式, 日益受到世界各国的重视.随着太阳能电池向着高效率、薄膜化、无毒性和原材料丰富的方向发展, 单纯的硅系太阳能电池已经无法达到这样的要求,因此新的材料和工艺的开发利用迫在眉睫. 本文研究了碳材料在硅异质节上实现光伏效应的改善及其可能在太阳能电池上的应用. 采用脉冲激光沉积方法制备的Co₂-C₉₈/Al₂O₃/Si异质结构在标准日光照射 (AM1.5, 100 mW/cm²)条件下,可获得0.447 V的开路电压和18.75 mA/cm²的电流密度, 转换效率可达3.27%.通过电容电压特性和暗条件下的电输运性能测量, 证明了氧化铝层的引入不但对单晶硅的表面起到了物理钝化作用,减小了反向漏电流, 使异质结界面缺陷、界面能级和复合中心减少,还起到了场效应钝化作用, 增加了异质结界面的势垒高度,增加了开路电压,使异质结的光伏效应显著增强.     

Luminescence in high purity In0.53Ga0.47As

We have investigated luminescence processes in high purity In_0.53Ga_0.47As grown by liquid phase epitaxy on InP substrate. The origins of luminescence processes have been determined by studying the dependence of emission intensity and spectrum on temperature. We show that exciton-ionized donor complex dominates the luminescence at 2K. With increasing temperature, the luminescence spectrum is dominated by donor-valence band and free electron-free hole recombination. Spectrum and bandgap energy are found to be dependent on the excitation position.     

Photoluminescence study of disordering in the cation sublattice of Cu2ZnSnS4

In this study we investigated the influence of the degree of disordering in the cation sublattice on low temperature photoluminescence (PL) properties of Cu₂ZnSnS₄ (CZTS) polycrystals. The degree of disordering was changed by using different cooling rates after post-annealing at elevated temperatures. The results suggest that in the case of higher degree of cation sublattice disorder radiative recombination involving defect clusters dominates at T = 10 K. These defect clusters induce local band gap energy decrease in CZTS. The concentration of defect clusters can be reduced by giving more time for establishing ordering in the crystal lattice. As a result, radiative recombination mechanism changes and band-to-impurity recombination involving deep acceptor defect with ionization energy of about 200 meV starts to dominate in the low temperature PL spectra of CZTS polycrystals.     

应变纤锌矿GaN/A10.15Ga0.85N柱形量子点的光学性质:流体静压力效应

在有效质量近似下,考虑强的内建电场和应变对材料参量的影响,变分研究了流体静压力对有限高势垒应变纤锌矿GaN/Al_0.15Ga_0.85N柱形量子点中重空穴激子的结合能、发光波长和电子空穴复合率的影响.数值结果表明,激子结合能和电子空穴复合率随流体静压力的增大而近线性增大,发光波长随流体静压力的增大而单调减小.在量子点尺寸较小的情况下,流体静压力对激子结合能和电子空穴复合率的影响更明显.由于应变效应,为了获得有效的电子-空穴复合过程,GaN量子点的高度必须小于5.5 nm.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Method for the analysis of saturation effects of cathodoluminescence in phosphors; applied to Zn2SiO4:Mn and Y3Al5O12:Tb

Saturation of the luminescence of phosphors under stationary cathode-ray excitation is due to activator ground-state depletion and an increased importance of higher order recombination processes at high excitation density. A method based on model considerations is presented to determine the kinetics of the dominating superlinear energy-loss process. The method is illustrated to analyse the saturation of the luminescence of Zn₂SiO₄:Mn and the blue ⁵D₃→⁷F emission of Y₃Al₅O₁₂:Tb. Quadratic energy-loss processes related to excited activator ions (Mn, Tb) are found. With this result the emitted optical flux under stationary excitation conditions and the rise time and the decay time of the luminescence can be quantitatively interpreted. When activator ground-state depletion occurs excited-state absorption cannot be excluded.     

Thermoluminescence of pure and doped ThO2

Thermoluminescence (TL) measurements in the temperature range 295–675 K indicate the existence of at least five trapping centres for single crystals of nominally pure “reduced” ThO₂ and three trapping centres for “oxidized” ThO₂. Deliberate doping with Ca²⁺, Y³⁺ and Ta⁵⁺ impurities decreases TL emission. For reduced ThO₂, accidentally incorporated rare-earth impurities, Pr³⁺, Tb³⁺, Er³⁺ act as the electron-hole recombination sites. In oxidized crystals the impurity Fe³⁺ is thought to be involved in the recombination process. In the temperature range 80–295 K an additional eight trapping centres exist for both oxidized and reduced ThO₂. For the reduced crystals the emission is probably associated with Fe in the +2 state, and in the +3 state for oxidized crystals. The differences in the TL glow curve intensities are partially explained by differences in the temperature dependence of the luminescence efficiency of the different recombination centres.     

Texture in a ternary Nd16.2Fe78.2B5.6 powder using a modified hydrogenation–disproportionation–desorption–recombination process

A modified hydrogenation–disproportionation desorption-recombination (HDDR) process consisting of (i) solid disproportionation and (ii) slow recombination under partial hydrogen pressure has been applied to a Nd_16.2Fe_78.2B_5.6 alloy. Scanning electron microscopy shows that an initially fine rod-like structure of NdH_2±x and Fe observed after 15 min of hydrogenation at 900°C is transformed into a granular morphology with prolonged annealing. Simultaneously, finely dispersed tetragonal Fe₃B particles of 10–50 nm diameter exist. XRD studies show that this metastable Fe₃B phase is transformed to Fe₂B and Fe on further annealing. Short solid-disproportionation times result in a higher degree of anisotropy after recombination, whereas long annealing times and conventional processing lead to isotropic material. It is concluded that the formation of the intermediate tetragonal Fe₃B phase after solid disproportionation is pivotal for the inducement of texture in HDDR processed ternary NdFeB-type alloys.     

Dark electrical conductivity and photoconductivity of Ga4Se3S layered single crystals

Ga₄Se₃S layered crystals were studied through the dark electrical conductivity, and illumination- and temperature-dependent photoconductivity in the temperature region of 100-350 K. The dark electrical conductivity reflected the existence of two energy states located at 310 and 60 meV being dominant above and below 170 K, respectively. The photoconductivity measurements revealed the existence of another two energy levels located at 209 and 91 meV above and below 230 K. The photoconductivity was observed to increase with increasing temperature. The illumination dependence of photoconductivity was found to exhibit linear and supralinear recombination above and below 280 K, respectively. The change in recombination mechanism was attributed to the exchange in the behavior of sensitizing and recombination centers.