大功率发光二极管可靠性和寿命评价试验方法

介绍了发光二极管（LED）的发展简史。提出可能影响LED可靠性的几种因素,主要有封装中的散热问题和LED本身材料缺陷。对于LED可靠性,主要方法是通过测试其寿命来分析其可靠性,一般采取加速实验的方法来测试推导LED寿命。介绍了根据加速应力(主要分为单一加速应力和复合加速应力2种)评价LED寿命的测试方法。在不同加速试验应力条件下测试了大功率LED可靠性,并建立了LED寿命的几种数学模型。最后根据具体实例,通过选择加速应力和试验方法,给出具体推导LED寿命的数学公式。     

Feasibility study of laser cooling of InF molecule

By employing ab initio quantum chemistry method, we investigate the feasibility of laser cooling InF molecule. Four low-lying electronic states (X¹Σ⁺, C¹Π, ³Π and 2³Π) of InF have been calculated using the multi-reference configuration interaction (MRCI) method. The spin-orbit coupling effects are also taken into account in the electronic structure computation at the MRCI level. The highly diagonal Franck-Condon factors for C¹Π → X¹Σ⁺ transitions are estimated. The radiative lifetime of the C¹Π (v′ = 0) state is about 2.22 ns, which is found to be enough short for rapid laser cooling. Though the cooling wavelength of InF is located in the short-wavelength ultraviolet light (UVC), a frequency quadrupled Ti: sapphire laser (189–235 nm) could be capable of generating laser transition wavelength of InF. Furthermore, the C¹Π → X¹Σ⁺ transitions perhaps can be followed by the B³Π₁ → X¹Σ⁺_0⁺ transitions to attain a lower Doppler temperature. Meanwhile, for achieving quasi-closed transition cycle of InF molecule, we investigate the hyperfine structure of the lowest state X¹Σ⁺. Overall, the present results indicate the possibility of laser cooling InF molecules.     

Improvement of the spin polarization lifetime in the 85Rb vapor cell by octadecyltrichlorosilane coating

Effective surface coatings allow for long spin polarization in alkali metal cells, suppressing the magnetic field gradient effect and providing an improvement in atomic magnetometer sensitivity. In this work, the effect of an octadecyltrichlorosilane (OTS) surface coating on the longitudinal and transverse spin polarization lifetime of an optically pumped ⁸⁵Rb vapor cell has been studied. Our results showed that the spin polarization lifetime significantly increased in the OTS lined cell compared to the unlined cell. The relaxation rate due to alkali metal atoms wall collisions and the magnetic field gradient has been decreased by using an OTS surface coating. A longer spin polarization lifetime in the lined cell causes a narrower magnetic resonance line width and subsequently a more sensitive atomic magnetometer.     

铂原子高激发态能级自然辐射寿命测量研究

运用时间分辨激光诱导荧光技术和激光诱导等离子体方法测量了铂原子的15条奇宇称高激发态能级的自然辐射寿命．测量结果处于6.1到116 ns之间,且误差低于10%．经比较,与前人结果在误差范围内符合很好．据文献调研所知,结果中有5条高度接近60000 cm−1的高激发态能级的寿命值是未见报道的．     

降温速率对升级冶金硅定向凝固生长多晶硅少子寿命的影响

对经过前期提纯的冶金级硅料进行一次性定向凝固生长多晶硅铸锭,研究了长晶阶段降温速率对多晶硅少子寿命的影响。结果显示降温速率越低,获得多晶硅少子寿命越高,但降温速率低到一定程度时,少子寿命反而会降低。通过测试生长多晶硅硅锭曲率半径、晶体结构等数据,分析了该现象的产生原因。这将有助于升级冶金硅一次性定向凝固生长多晶硅铸锭的生产应用。     

GaAs光生载流子动力学机制的超快光谱学分析

利用飞秒激光泵浦探测技术,通过改变光学参数,如中心波长、功率,分别对未故意掺杂高纯n型砷化镓的差分反射谱进行研究,进而分析室温下砷化镓光生载流子动力学过程.首先,当泵浦光功率恒为100mW,探测光功率恒为10mW时,随着中心波长的增大,差分反射率峰值随之增大,信噪比也随之增加.其次,通过拟合不同延迟时间下泵浦光功率和差分反射率的实验曲线,并和理论模型比较后发现,在一定范围内的泵浦功率和差分反射率呈线性相关,未故意掺杂高纯n型砷化镓的饱和载流子浓度为(3.590 1±0.310 3)×1017 cm~(-3).在此基础上,把光生载流子动力学过程分为3个过程:804±67fs的光激发过程、134~268fs的初始散射过程、1ps和3~6ps的复合过程.研究表明,差分反射率与探测功率不存在显著的依赖性,但差分反射谱的信噪比与探测功率存在相关性.     

Determination of the transport lifetime limiting scattering rate in InSb/AlxIn1−x Sb quantum wells using optical surface microscopy

We report magnetotransport measurements of InSb/Al_1−xIn_xSb quantum well structures at low temperature (3 K), with evidence for 3 characteristic regimes of electron carrier density and mobility. We observe characteristic surface structure using differential interference contrast DIC (Nomarski) optical imaging, and through use of image analysis techniques, we are able to extract a representative average grain feature size for this surface structure. From this we deduce a limiting low temperature scattering mechanism not previously incorporated in transport lifetime modelling of this system, with this improved model giving strong agreement with standard low temperature Hall measurements. We have demonstrated that the mobility in such a material is critically limited by quality from the buffer layer growth, as opposed to fundamental material scattering mechanisms. This suggests that the material has immense potential for mobility improvement over that reported to date.     

Eu3+:LaF3纳米晶体-液体悬浮系统中荧光弛豫的局域场效应

为研究Eu3+:LaF3纳米晶体-液体悬浮系统中局域场效应对荧光辐射寿命的影响,首先用水热法成功制得了粒径均匀、分散性良好的Eu3+:LaF3纳米晶体,通过将其悬浮在各种液体介质中测出了532 nm脉冲激光激发下Eu3+的5D0能级的荧光寿命,该能级的荧光衰减曲线呈明显的二阶指数衰减特征,对荧光寿命的分析表明其中快速荧光衰减部分源于纳米晶体表面附近的稀土离子.荧光衰减的长寿命部分与各种局域场效应理论模型中的最小二乘法拟合结果表明,忽略表面效应并考虑实际的量子效率时,实腔模型是解释本文的研究系统中荧光弛豫的局域场效应的最佳理论模型.     

CdTe@TiO2复合纳米微粒的制备与表征

利用溶胶-凝胶法合成了CdTe@TiO2复合纳米微粒. 采用扫描和透射电镜对复合微粒的形貌和结构进行了表征, 并探讨了其形成机理. 通过对复合微粒的光谱性质研究发现, 与TiO2复合后, CdTe纳米微粒的荧光有减弱的趋势, 但却具有相似的荧光寿命, 其荧光寿命都短于原CdTe纳米微粒水溶液中的荧光寿命, 说明该材料作为新一代太阳能电池具有非常大的潜力.     

聚(2-甲氧基-5-辛氧基)对苯乙炔/Tb4O7纳米复合材料的制备及其光物理性能研究

采用原位脱氯化氢缩合聚合法制备了聚(2-甲氧基-5-辛氧基)对苯乙炔/氧化铽(PMOCOPV/Tb₄O₇)纳米复合材料. 红外光谱证实了在Tb₄O₇表面的包覆层为PMOCOPV. 紫外-可见吸收光谱表明随着Tb₄O₇含量增加, PMOCOPV/Tb₄O₇的最大吸收峰发生红移且强度提高. 荧光光谱研究表明随着Tb₄O₇含量增加, PMOCOPV/Tb₄O₇的最大发射波长发生蓝移且强度提高, 荧光寿命得到增强, Tb₄O₇与PMOCOPV之间形成了光致电子转移体系, 使得π电子离域程度增加, 并且导致荧光量子效率提高. 根据E_g与入射光子能量hν的关系, 拟合了PMOCOPV/Tb₄O₇薄膜的光学禁带宽度, 发现随着Tb₄O₇含量增加, E_g减小. 采用简并四波混频方法测试它们的三阶非线性极化率χ⁽³⁾, 结果发现随着Tb₄O₇含量增加, PMOCOPV/Tb₄O₇纳米复合体的非线性光学响应逐渐增强, 这说明PMOCOPV与Tb₄O₇之间形成了分子间光致电子转移体系, 产生了复杂的分子间离域π电子非线性运动.