锰掺杂近化学计量比铌酸锂晶体的电荷输运过程

用泵浦(350 nm)-探测(780 nm)法研究了轻度锰掺杂近化学计量比铌酸锂晶体的光致吸收的特征,结果表明光致吸收的暗衰减过程以扩展指数的形式衰减,并测量了饱和光致吸收、衰减时间常量和扩展因子对泵浦光光强的依赖关系.在z轴方向上加直流电场测量了紫外光照射下光伏打电流强度和光电导,发现它们与光强之间成超线性关系.实验结果可以用考虑本征缺陷能级和掺杂能级之间激发和复合的修正的双中心电荷输运模型进行定量的解释.     

掺铁铌酸锂晶体的光电导衰减特性研究

利用电化学分析仪对掺铁同成分铌酸锂晶体进行瞬态光电导研究. 以不同掺铁浓度铌酸锂晶体为样品, 在不同强度的纳秒级脉冲光照射下对光电导的研究发现: 铌酸锂晶体的瞬态光电导是由较为复杂的电子迁移过程形成, 其衰减可以用一个指数函数叠加一个扩展指数来拟合. 拟合参数与光强、掺铁浓度存在以下依赖关系: 入射光强增强时, 幅值σ₁^max、σ₂^max、时间常数τ₂和扩展因子β 值增大, 在光强增大到一定时, τ₂和β出现饱和; 晶体的掺铁浓度升高时, σ₁^max、σ₂^max、τ₂ 值增大, 而β值减小. 根据实验结果, 从理论上提出了光电子导带迁移伴随光电子在小极化子上跳跃迁移的复合电荷传输模型. 该模型较好地解释了掺铁同成分铌酸锂晶体的光电导的衰减特点.     

掺铁铌酸锂晶体第一性原理研究

利用第一性原理计算方法研究铁掺杂铌酸锂晶体的电子结构和光学性质，所有计算采用广义梯度近似下的平面波超软赝势方法，得到如下结论：掺杂产生的杂质能级，主要由铁的d轨道贡献。掺杂降低了电子跃迁所需能量，同时也降低了各原子的电子轨道能量。掺杂离子在晶体中既是电子的施主又是受主。铁的掺杂使铌酸锂晶体的能量损失函数有较大的增加，对光存储的效率有一定影响。铁的掺杂使晶体的光学性质在可见光低能范围发生变化，吸收谱在可见光区域产生吸收峰，有利于晶体全息存储的应用。     

近化学计量比双掺铁锰铌酸锂晶体紫外光致吸收特性的研究

研究了不同锂含量的双掺铁锰铌酸锂晶体的紫外光致吸收特性,结果表明,同成分晶体的紫外光致吸收系数较低,随着锂含量的增加,晶体的紫外光致吸收系数逐渐增大,当晶体中的锂含量达到49.57mol%附近时,紫外光致吸收系数达到最大值4.20 cm-1,进一步增加晶体中的锂含量,饱和光致吸收系数开始下降。在此基础上,提出了近化学计量比双掺铁锰铌酸锂晶体的双色非挥发全息存储的三中心模型,即随着晶体锂含量的增加,双掺铁锰晶体的光折变中心除了Fe2+/Fe3+,Mn2+/Mn3+外,还将增加双极化子/小极化子中心。     

近红外PbS量子点掺杂光子晶体光纤的光传输特性

制备了导光波带位于近红外1400～1650nm的硫化铅(PbS)量子点掺杂光子晶体光纤(QD-PCF)。测量了QD-PCF对980nm抽运光和1550nm信号光的吸收。在980nm激光激励下,测量了QD-PCF的光致荧光(PL)光谱,确定了1550nm中心波长处PL光强最强时的量子点掺杂浓度(质量分数)和光纤长度,发现其PL光强远大于普通单纤芯掺杂的量子点光纤(QDF)。实验发现QD-PCF的PL光强会出现间隔距离较短的多光强峰值,该多光强峰值现象与掺杂浓度有关。对比测量了QD-PCF和未掺杂PCF的带隙,表明量子点掺杂没有改变PCF的带隙分布。测量了QD-PCF的抽运激励阈值和抽运饱和功率,其抽运阈值功率与QDF接近,抽运饱和功率大于QDF,这与QD-PCF有较大的光纤截面以及较高的量子点掺杂浓度有关。     

掺铁铌酸锂晶体中光致散射的锂组分和温度依赖关系研究

研究了单掺铁铌酸锂晶体的光致散射行为随锂组分以及温度的变化关系.实验表明,随晶体组分的升高,光致散射得到了大幅抑制;不同组分晶体光致散射被完全抑制的温度不同.由此提出掺铁铌酸锂晶体在48.9 mol%-49.3 mol%范围内可能存在一临界锂组分,当晶体组分超过这一临界组分时,晶体光致散射被大幅抑制,而光致散射行为的温度依赖关系明显改变.     

Fe:Mg:LiNbO3晶体电子结构和吸收光谱的第一性原理研究

基于密度泛函理论的第一性原理, 研究了LiNbO₃晶体以及不同Mg浓度的Fe:Mg:LiNbO₃晶体的电子结构和吸收光谱. 研究结果显示: 掺铁铌酸锂晶体的杂质能级由Fe 的3d轨道和O的2p轨道贡献, 禁带宽度为2.845 eV; 对于Mg, Fe共掺样品, Mg的浓度小于或等于阈值时, 禁带宽度分别为2.901 和2.805 eV; 掺铁铌酸锂晶体的吸收谱在2.3和2.6 eV处分别存在一个吸收峰, 其强度因Mg的浓度不同而发生变化. 研究结果还表明, 不同浓度的Mg对晶体内Fe²⁺和Fe³⁺的浓度以及占位产生了不同的影响. 还提出了光电子的形成不应单独考虑铁的轨道电子态, 而应同时考虑与铁成键的氧的轨道电子态的观点.     

掺Ce,Fe系列LiNbO3晶体光折变效应光存储特性

研究了系列Ce：Fe掺杂以及不同后处理态(生长态、还原态和氧化态)铌酸锂晶体的透过率光谱和光折变全息存储特性。实验结果表明单掺Ce铌酸锂晶体具有较好的图像存储质量和较宽的透过率光谱范围,二波耦合增益相对较低;高掺杂铌酸锂样品的透过率光谱范围较窄,光折变二波耦合增益较低。晶体的后处理对铌酸锂样品的光折变特性影响明显,双掺Ce:Fe还原态铌酸锂晶体具有较高的二波耦合增益;氧化态样品具有较大的透过率光谱范围;还原态样品具有较大的光折变二波耦合增益特性。实验结果还表明在同种样品中难于同时获得大的二波耦合增益和图像存储质量。     

静电染色法在铌酸锂晶体铁电性显示中的应用

我们应用静电复印油墨将铌酸锂铁电畴染色(静电染色法)显示,并扩展到铌酸锂晶体光铁电性的显示,包括单畴铌酸锂光折变区电场电荷分布、单畴掺铁铌酸锂晶体表面电击穿效应和单畴掺铁铌酸锂晶体存储的全息衍射光栅图象的显示等. 上述光铁电性显示图象,与使用其他实验手段所得到的     

同成分掺镁铌酸锂晶体紫外光致吸收阈值效应的研究

研究了同成分掺镁铌酸锂晶体中的紫外光致吸收效应。通过对不同掺Mg浓度铌酸锂晶体的紫外光致吸收系数和双色存储灵敏度的测量,发现同成分掺镁铌酸锂晶体的紫外光致吸收效应具有Mg离子浓度阈值效应。只有当掺Mg摩尔分数大于3．0％时,从近紫外一直延伸到近红外波段的紫外光致吸收效应才显示出来。这一Mg离子浓度阈值效应进一步为双色存储灵敏度的测量结果所证实。该浓度阈值小于掺镁铌酸锂晶体抗光损伤效应的摩尔分数阈值4．6％。这种紫外光致吸收现象可能和掺镁铌酸锂晶体中反位铌NbLi浓度的急剧减少基本消失有关。     

掺杂的AgCl微晶在化学增感条件下的光电子衰减特性

利用微波吸收介电谱技术研究了K₄Fe(CN)₆浅电子陷阱掺杂剂和S+Au增感剂对立方体AgCl微晶光生电子衰减时间分辨特性的影响。结果表明,掺杂浓度为10-8～10-7 mol·mol-1Ag时,在增感之前,掺杂位置越接近表面时,光电子衰减过程会变慢,即衰减时间增加;S+Au增感后的掺杂乳剂中光电子衰减变快,说明了增感中心起深电子陷阱作用,当掺杂位置接近表面90%Ag时,光电子衰减时间突然减小,说明表面掺杂中心和增感中心可能发生了某些反应。     

Investigation of the photoelectron decay of silver halide microcrystal

The microwave absorption dielectric spectrum can be used to study the decay process of free photoelectrons and shallow-trapped electrons in semiconductor crystals. The decay curve of free photoelectrons and shallow-trapped electrons of silver halide grains is measured using this technique. The influence of iodide and K_4Fe(CN)_6 shallow electron trap dopants on the photoelectron lifetime of silver halide grains is studied. For the unsensitized cubic AgCl crystals, when the free photoelectron lifetime (FLT) reaches a maximum, the photographic efficiency is optimal. From our analysis, we conclude that FLT is the longest for the cubic AgCl crystals doped with 0.5% iodide at 80% doping position and 1×10^{-6} mol K_4Fe(CN)_6/molAg, whereas, for the highly photosensitized cubic AgBrCl crystals doped with K_4Fe(CN)_6, the photographic efficiency is optimal when the FLT reaches its minimum. The free photoelectron lifetime reaches minimum and the sensitivity of AgBrCl emulsion reaches maximum when the doping position is 30%Ag at K_4Fe(CN)_6 content of 10^{-6}mol/molAg.     

Spectroscopic properties of thulium ions in bismuth silicate glass

A new type of bismuth silicate glass (Bi2O3-SiO2-ZnO-Al2O3-La2O3) doped with Tm2O3 is prepared by melt-quenching method. The thermal stability of the glass is examined by differential scanning calorimetry. No crystallization peak is found. Using the absorption and emission spectra, the absorption and emission cross-sections are calculated. Their maximum data are 2.9×10-21cm2 at 1663 nm and 4.7×10-21cm2 at 1826 nm, respectively. Using the Judd-Ofelt theory, the radiation transition probabilities and radiative lifetimes are obtained. The extended overlap integral method is applied to analyze energy transfer process among the Tm3+ ions. The transfer constants of cross-relaxation and energy migration among the Tm3+ ions at the 3H4 level are 7.60×10-40 and 14.98×10-40 cm6 /s, respectively. The critical transfer radius for cross-relaxation is 0.99 nm. The cross relaxation process is easy to realize and is favorable for obtaining ～2-μm laser.     

γ射线辐照与O2退火对Bi∶CdWO4单晶体光谱性能的影响

用500和800℃,在氧气下,对掺Bi钨酸镉晶体进行热退火处理,测定了处理后晶体的吸收光谱与发射光谱。随退火处理温度的升高晶体的吸收强度降低,吸收边带发生蓝移。在373与980nm的光激发下,分别观察到发光中心为528nm的CdWO4晶体本征发光与发光中心为1 078nm的Bi 5+发光。晶体样品通过高温氧气处理,发光中心为528nm的荧光带强度增强,但发光中心为1 078nm的荧光带强度变弱。这可能是由于氧退火使Bi 5+转化成Bi 3+所致。经退火处理后,晶体的颜色逐渐变浅,透光率明显提高,这是由于晶体中氧空位减少所致。经γ射线辐照处理后,528nm处的发光增强,而1 078nm处的发光减弱,这可能是由于γ射线辐照后导致Bi 5+变成Bi 3+。     

掺铥钨酸钡单晶生长和光谱研究

采用Czochralski 法生长出光学质量的BaWO₄:Tm³⁺单晶,利用X粉末衍射实验确定了不同掺杂浓度晶体的晶胞参数.测定了晶体的室温吸收光谱,应用Juud-Ofelt理论,拟合了光谱的3个强度参数,其值分别为Ω₂=404×10^-20cm²,Ω₄=0509×10^-20cm²,Ω关键词： 4：Tm³⁺单晶')" href="#">BaWO₄：Tm³⁺单晶 吸收谱 光谱参数 上转换发光     

Dosimeter properties of Ce and Eu doped LiCaAlF6

Optical, scintillation properties, optical stimulated luminescence, and thermally stimulated luminescence of Ce 1, 3, and 5% doped and Eu 1, 1.5, and 2% doped LiCaAlF₆ crystals fabricated by Tokuyama Corp. were investigated. In transmittance, absorption was proportional to dopant concentrations and typical optical quantum yield of Ce and Eu-doped LiCaAlF₆ were 40 and 100%, respectively. Scintillation wavelength and decay time profiles were investigated under X-ray irradiation. Ce³⁺ and Eu²⁺ 5d-4f luminescence appeared around 300 nm and 370 nm with typical decay time of 40 ns and 1.5 μs, respectively. Optically stimulated luminescence of Ce-doped ones appeared under 405 nm stimulation with detectable intensity while those of Eu doped ones were quite weak. Thermally stimulated luminescence of Ce- and Eu-doped LiCaAlF₆ were enough strong and they exhibited good response function from 1 to 1000 mGy exposure.     

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.     

Optical and holographic properties of Fe+Mn co-doped Bi4Ge3O12 crystals

The effect of iron and manganese co-doping on the light-induced, dark- and photoconductivity and holographic properties of Bi₄Ge₃O₁₂ crystals in comparison with Fe- and Mn-single doping is studied. Fe+Mn co-doped crystals exhibited strong photochromic effect at room temperature, the photochromic effect being fully reversible by thermal annealing. The observed light-induced absorption changes and non-linear dependence of photoconductivity on light intensities indicate deep and shallow photoactive levels contribution to the charge transport mechanism of Fe+Mn co-doped BGO. Holographic gratings are successfully recorded at different wavelengths and a possibility to extend the photorefractive sensitivity into the red spectral range is demonstrated. It is found furthermore that Fe+Mn-doping combination leads to faster response time during holographic recording, especially after a preliminary exposure with ultraviolet light, in comparison with Fe- and Mn-single doping.     

Reduction effect on the optical properties of Sm doped in SrB4O7 and SrB6O10 crystals

Reduction effects on the optical properties of Sm²⁺ ions doped in SrB₄O₇ and SrB₆O₁₀ crystals were studied by measurements of luminescence intensity decay as a function of time, X-ray irradiation and laser power effects on the photoluminescence. The fluorescence intensity of Sm²⁺ doped in SrB₄O₇ and SrB₆O₁₀ crystals decreased upon excitation at 488 nm of Ar⁺ laser and this so-called photo-bleaching effect was highly dependent on the sample preparation conditions. The fluorescence intensity of Sm²⁺ doped in SrB₄O₇ decreased about 13%, while it decreased about 55% in the SrB₆O₁₀ crystal irradiated with X-ray for 10 h. Differences of photo-beaching effect and other optical properties of Sm²⁺ doped in SrB₄O₇ and SrB₆O₁₀ are discussed.