CdS_xSe_(1-x)/ZnS(核/壳)量子点的光谱截面及其掺杂光纤的传光特性

测量了不同组份比例x的CdS_xSe_(1-x)/ZnS(核/壳)量子点的吸收谱和发射谱,确定了量子点的吸收系数、吸收截面和发射截面.量子点吸收截面随粒径的增大而增大、随x的增大而减小.采用紫外固化胶,制备了掺杂浓度为0.1~5mg/mL的CdS_(0.4)Se_(0.6)/ZnS量子点光纤,测量了不同掺杂浓度量子点光纤中473nm泵浦功率的吸收衰减速率.吸收衰减速率和吸收截面弱关联于掺杂浓度.测量了光致荧光光谱强度随光纤长度和量子点浓度的变化.量子点光纤的光致荧光峰值强度随掺杂浓度和光纤长度变化而变化,且存在一个与最大峰值强度对应的饱和掺杂浓度和光纤长度.本文的实验结果有助于进一步构建新型的CdS_xSe_(1-x)/ZnS量子点增益型光电子器件.     

掺铁近化学配比铌酸锂晶体的紫外光致吸收和弛豫过程的研究

生长了系列掺杂低铁(质量分数分别为0×10-6,3×10-6,5×10-6,10×10-6,25×10-6,50×10-6、100×10-6)的近化学配比铌酸锂(SLN)晶体,测量了它们的紫外-可见光谱,并通过477nm处的线性吸收系数估算晶体中Fe2+和Fe3+的浓度。利用抽运(365nm)-探测(632.8nm)法测量不同掺杂浓度晶体光致吸收的动态过程和稳态特性,结果表明光致吸收是以扩展指数的形式衰减的,其衰减时间常数(即小极化子的寿命)随掺杂浓度和抽运光强增加而减小,扩展指数因子随抽运光强的增加而减少。根据电子的输运方程,利用四阶龙格-库塔方法对电子输运过程进行数值求解,模拟了掺铁铌酸锂(Fe:SLN)晶体的光致吸收的全过程,与实验所得结果符合得很好。     

偶氮染料掺杂PVA的全光开关特性研究

光开关是光通信、光计算机、光信息处理等领域的重要光学元件。利用半导体激光(473nm)作为泵浦光,He-Ne激光(632.8nm)作为探测光,实验研究了偶氮染料掺杂PVA薄膜材料光致双折射效应信号的生长、擦除、衰减特性,分析了泵浦光偏振方向与探测光偏振方向夹角、泵浦光功率对光致双折射效应和全光开关特性的影响,探讨了该材料在光开关方面的应用前景。     

掺杂的Bi4Ge3O12晶体的近红外发光性能

生长了Mg、Ca离子掺杂(提拉法)和Cl离子掺杂(坩埚下降法)的Bi₄Ge₃O₁₂(BGO)晶体,测试了晶体样品的吸收谱、光致发光谱和发光衰减时间等。这些掺杂的BGO晶体的可见光发光比纯BGO有所减弱,但在808 nm和980 nm激光二极管(LD)激发下出现了纯BGO几乎没有的近红外发光,归因于改变了能级的Bi离子或可能出现的低价态Bi离子。掺杂对近红外发光的影响跟掺杂离子价态有关,同价态的掺杂离子对近红外发光的影响相差不大。     

偶氮类有机材料光致双折射的测量

研究了2种偶氮聚合物薄膜的光致双折射效应,并探讨了泵浦光偏振态和光强对光致双折射的影响.采用远离共振区的He-Ne光(633nm)作为探测光,用Ar+激光(488nm)作为泵浦光,通过测量相关参量得到了样品的光致双折射值.实验结果表明:改变泵浦光的偏振态可以控制光致双折射值和探测光的透过信号强度,在0°～45°范围内,泵浦光光强存在最佳值,此时偶氮薄膜实验样品具有最大的双折射值.     

甲基橙偶氮染料掺杂聚乙烯醇薄膜的光存储特性研究

研究了甲基橙(MO)偶氮染料掺杂聚乙烯醇(PVA)薄膜的光致双折射和全息光存储特性.利用YAG激光二倍频(532nm)作为写入光,He-Ne激光(632.8nm)作为读出光,考察了不同染料浓度薄膜的光致双折射,探讨了光致双折射和泵浦光功率的关系,并实现了全息光存储.阐明了MO/PVA光存储的物理机制.     

掺铒、镱铒共掺杂硅酸盐玻璃光致发光强度随泵浦波长的变化

利用半导体激光器的红移特性,测量了掺饵、镱铒共掺杂硅酸盐玻璃样品的光致发光强度随泵浦波长的变化。实验结果表明,掺铒硅酸盐玻璃样品的最佳泵浦波长为981.6nm,镱铒共掺杂硅酸盐玻璃样品的最佳泵浦波长为972.1nm;两种样品的-3dB带宽分别为3 6nm和7.4nm。     

方波激发下Er~(3+)上转换红光激发机理的研究

用方波电源驱动808 nm激光二极管(LD)激发Er3+掺杂的亚碲酸盐氟氧化物玻璃,测量4F9/2能级上转换发光的上升和衰减,根据上升的时间常数确定中间能级的寿命,从而确定4F9/2能级粒子数积累的过程。通过建立速率方程模型分析4F9/2能级的上升和衰减特性与中间能级的关系,确定808 nm LD激发下上转换红光的激发机理,同时提供了一种通过上转换发光,用光电倍增管测量红外能级寿命的方法。     

Tm,Ho双掺杂YVO4晶体中Tm对HO敏化发光现象

摘要报道了对Tm,Ho双掺YVO4晶体光谱性能的测量结果,包括用UV-365型分光光度计测出单掺TmYVO4及HoYVO4吸收谱以及双掺TmHoYVO4的吸收谱;用Ar离子激光器488nm,LD激光器激发测量样品荧光光谱;用J-O理论进行光谱参数计算及对能级结构进行分析;研究了在λ=805nm的激光二极管激发下Tm对Ho的敏化发光过程。发现与YAG,YLF为基质的Tm,Ho双掺材料相比,该材料中的Tm3+离子具有大而均匀的吸收宽度(～26nm),大的峰位吸收截面和积分吸收截面(～1.4×10-20cm2和274.5×10-20 cm),能量转换效率高(可达87％),且泵浦阈值低(～15mW)。表明了YVO4晶体中Tm能有效地敏化Ho,并产生2μm的发射。文中对发射强度与泵浦功率及Tm,Ho之间掺杂浓度的关系进行了初步的分析与讨论。光谱的观察结果表明在实现LD泵浦,全固体化,小型,高效的,2μm激光振荡的探索中,TmHoYVO4晶体将是一种很有实际应用潜力的材料。     

泵浦光偏振态的改变对SO/PMMA薄膜光致双折射的影响

在紫外光伴随下,用偏振态分别为s和p的HeNe激光器发出的632.8nm红光(均为10mW)交替激发螺恶嗪掺杂的聚甲基丙烯酸甲脂薄膜(SO/PMMA),用532nm的绿光(0.1mW)作为探测光记录光致双折射的动力学过程.实验发现透射信号被周期性调制,而且每次调制的最大值随时间逐渐减小并最终趋于稳定.指出了泵浦过程中的异构动态平衡与取向动态平衡并存的物理机制.     

Conductivity and light-induced absorption in BaTiO3

A charge transport model including deep and shallow traps explains both the nonlinear relation between photoconductivity and light intensity and the light-induced absorption in BaTiO₃. A correlation between measurements of photoconductivity and light-induced absorption as a function of temperature yields parameters for the shallow center, among them thermal activation energy and generation rate.     

Photoconductivity and light-induced absorption in KNbO3:Fe

Measurements of photoconductivity and light-induced absorption in KNbO₃: Fe are performed at different light intensities and crystal temperatures. The results are interpreted in terms of a two-center charge transport model. Different model parameters may be evaluated from the experimental data. A complete set of parameters is suggested explaining the dependences of photoconductivity and light-induced absorption on light intensity and temperature for the KNbO₃: Fe crystal investigated.     

Ultra-Fast Decay Process of Electrons in LiNbO3 Crystal Induced by Femtosecond Pulse

Temporal evolution of absorption induced by single femtosecond pulse （13Ors, 800nm） with high intensity in LiNbO3 is obtained using the probe shadow imaging technique in order to investigate light-induced electron relaxation processes. By saturating the polaron density with a high intensity laser pulse, ultra-fast decay process on picosecond time scale is observed. The decay time constant is about 141 ps and it is attributed to the direct interband electron-hole recombination process.     

TEMPORAL CHARACTERISTICS OF DECAY OF LIGHT-INDUCED ABSORPTION IN PHOTOREFRACTIVE BaTiO3 CRYSTALS

We report the observations of the decay processes of light-induced absorption in one undoped and two Ce-doped BaTiO₃ crystals. Two decay times were found, they had not a strong dependence on intensity in our experiment. We present a model with two different shallow trap centers to explain the experimental results. The theoretical and experimental resales agree well with each other. The light-induced absorption coefficients and decay times corresponding to the two shallow levels are also given.     

TEMPORAL CHARACTERISTICS OF DECAY OF LIGHT-INDUCED ABSORPTION IN PHOTOREFRACTIVE BaTiO3 CRYSTALS

We report the observations of the decay processes of light-induced absorption in one undoped and two Ce-doped BaTiO₃ crystals. Two decay times were found, they had not a strong dependence on intensity in our experiment. We present a model with two different shallow trap centers to explain the experimental results. The theoretical and experimental resales agree well with each other. The light-induced absorption coefficients and decay times corresponding to the two shallow levels are also given.     

Photoconductivity and photovoltaic behaviour of LiNbO3 and LiNbO3 waveguides at high optical intensities

The photoconductivity and photovoltaic currents of pure LiNbO₃ and proton exchanged waveguides in LiNbO₃ have been measured as a function of the optical intensity up to about several kW/cm² by the use of surface electrodes. For pure LiNbO₃ the observed dependences are a simple extrapolation of the well known low intensity behaviour. The photoconductivity of proton exchanged waveguides is considerably increased compared with pure LiNbO₃ and the curves are strongly nonlinear in the high intensity region. These results can explain, at least qualitatively, the previously observed characteristic time and intensity dependence of light-induced refractive index changes in this type of waveguides. Both the time and temperature behaviour of the dark conductivity of all proton exchanged waveguides give strong evidence of ionic charge transport in the proton exchanged region.     

Photoluminescence and photoconductive characteristics of hydrothermally synthesized ZnO nanoparticles

In the present paper, ZnO nanoparticles (NPs) with particle size of 20–50 nm have been synthesized by hydrothermal method. UV-visible absorption spectra of ZnO nanoparticles show absorption edge at 372 nm, which is blue-shifted as compared to bulk ZnO. Photoluminescence (PL) and photoconductive device characteristics, including field response, light intensity response, rise and decay time response, and spectral response have been studied systematically. The photoluminescence spectra of these ZnO nanoparticles exhibited different emission peaks at 396 nm, 416 nm, 445 nm, 481 nm, and 524 nm. The photoconductivity spectra of ZnO nanoparticles are studied in the UV-visible spectral region (366–691 nm). In spectral response curve of ZnO NPs, the wavelength dependence of the photocurrent is very close to the absorption and photoluminescence spectra. The photo generated current, I_pc = (I_total - I_dark) and dark current I_dc varies according to the power law with the applied field I_pcαV^r and with the intensity of illumination I_pcαI_L ^r, due to the defect related mechanism including both recombination centers and traps. The ZnO NPs is found to have deep trap of 0.96 eV, very close to green band emission. The photo and dark conductivities of ZnO NPs have been measured using thick film of powder without any binder.     

Light–induced charge transport processes in photorefractive barium titanate crystals doped with iron

3 ) are annealed in a hydrogen atmosphere at various temperatures. After these reducing treatments, absorption, light–induced absorption changes, two–beam coupling direction, photo electron paramagnetic resonance (photo EPR), dark and photoconductivity as well as bulk photovoltaic current density are investigated. The samples are electron conductive and the charge transport is governed by only one level, which is identified by photo EPR as Fe²⁺/Fe³⁺. The photoconductivity exceeds the dark conductivity for intensities above 1 kWm^-2. A relation between the absorption constant and the Fe²⁺ concentration is derived. From the known charge transport parameters the advantageous photorefractive properties of optimized reduced BaTiO₃:Fe are deduced; possible response times in the millisecond range at an intensity of 10 kWm^-2 are estimated. Received: 22 January 1997/Accepted: 23 January 1997     

Influence of post-growth treatment on the holographic storage properties of In:Fe:LiNbO3

The congruent In (3 mol%):Fe (0.03 wt%): LiNbO₃ crystal has been grown by Czochralski method in air. Some crystal samples were reduced in Li₂CO₃ powder, and others were oxidized in Nb₂O₅ powder. The defects and ions location in crystal were investigated by infrared (IR) transmission spectrum. The photorefractive properties were measured by two-wave coupling and light-induced scattering resistance experiments. In the oxidized sample, the photovoltaic effect was the dominant process during recording. However, for the as-grown sample as well as the reduced, the photorefractive effect was governed by the diffuse field and the photovoltaic field, together. In addition, the reduction treatment made the photoconductivity increase, which resulted in shorter erasure time and lower diffraction efficiency, but higher light-induced scattering resistance ability. The oxidation treatment caused the inverse effect.