连续光条件下对LiNbO3:Fe:Mn晶体全息存储性能的理论研究

以双中心模型为基础,在低光强连续光条件下研究了LiNbO3:Fe:Mn晶体在稳态情况下的非挥发双光双步全息存储性能.采用数值方法.通过比较双中心模型中深(Mn2 /Mn3 )、浅(Fe2 /Fe2 )能级之间所有可能的电子交换过程,发现由隧穿效应引起的深浅能级之间直接电子交换过程对LiNbO3:Fe:Mn晶体总的空间电荷场大小起着决定性的作用.同时.这一电子交换过程对晶体非挥发全息存储性能也起着至关重要的作用.此外.通过相同实验条件下LiNbO3:Fe:Mn晶体与近化学比LiNbO3:Fe晶体总的空间电荷场的比较,显示LiNbO3:Fe:Mn晶体在低抽运光和高记录光光强条件下有着比近化学比LiNbO3:Fe晶体更佳的伞息存储性能.     

连续光条件下对LiNbO3∶Fe∶Mn晶体全息存储性能的理论研究

以双中心模型为基础,在低光强连续光条件下研究了LiNbO3∶Fe∶Mn晶体在稳态情况下的非挥发双光双步全息存储性能。采用数值方法,通过比较双中心模型中深(Mn2+/Mn3+)、浅(Fe2+/Fe3+)能级之间所有可能的电子交换过程,发现由隧穿效应引起的深浅能级之间直接电子交换过程对LiNbO3∶Fe∶Mn晶体总的空间电荷场大小起着决定性的作用。同时,这一电子交换过程对晶体非挥发全息存储性能也起着至关重要的作用。此外,通过相同实验条件下LiNbO3∶Fe∶Mn晶体与近化学比LiNbO3∶Fe晶体总的空间电荷场的比较,显示LiNbO3∶Fe∶Mn晶体在低抽运光和高记录光光强条件下有着比近化学比LiNbO3∶Fe晶体更佳的全息存储性能。     

Ca3Sc2Si3O12:Ce3+的第一性原理研究

对Ca₃Sc₂Si₃O₁₂:Ce³⁺共掺杂N^3-、Sc³⁺、Mn²⁺、Mg²⁺和Na⁺进行第一性原理计算,研究不同的电荷补偿对发光中心Ce³⁺的影响．首先利用密度泛函理论构建超晶胞模型对Ce³⁺周围的局部结构进行了优化,然后通过CASSCF/CASPT2 RASSI-SO计算得到Ce³⁺的4f→5d跃迁能量．计算数据与实验光谱相吻合．实验光谱中的一个未知峰值理论分析确认是Sc³⁺替代Si⁴⁺导致的．     

NaF晶体中电荷补偿掺杂Ce3+离子光谱性质的从头算

用从头算研究NaF晶体中Ce³⁺占据Na⁺格位时的光谱性质,电荷补偿由占据格位第一配位壳层的两个氟原子被氧取代 (O_F^') 或第二配位壳层的两个Na空位(_Na^') 来提供. 首先采用基于DFT的超单胞模型方法优化了Ce³⁺的局域结构,并构造以Ce为中心的镶嵌团簇,对其进行基于波函数理论的CASSCF/CASPT2/RASSI-SO计算,获得Ce³⁺的4f¹和5d¹组态分裂能级能量. 通过将4f→5d跃迁能量计算值与低温实验激发光谱比较,发现实验观测到的最低4f→5d跃迁谱带(390 nm)来自于两个最近邻O_F^'补偿的Ce³⁺离子,并不是文献中的两个次近邻V_Na^' 补偿的Ce³⁺. 最后从5d¹组态能级重心位移和晶场分裂两方面分析了由两个最近邻O_F^'取代造成最低4f→5d 跃迁红移约8000 cm^-1的原因.     

SrBPO5:Ce3+的VUV光谱

研究了Ce³⁺离子激活的SrBPO₅在130—400nm波长范围的光谱性质.在VUV激发光谱上指认了Ce³⁺的5个4f¹→4f⁰5d¹跃迁激发带.发现在SrBPO₅中Ce³⁺的5d轨道能级重心位于43.2×10³cm^－1,这在氧化物基质中是比较高的.此外,还报道和讨论了SrBPO₅的基质吸收带和Ce³⁺的5d轨道在SrBPO₅中的晶体场劈裂及SrBPO₅:Ce³⁺在VUV-UV激发下的发射光谱.     

CdTe太阳电池中起因于Cu的深能级

在CdTe太阳电池中,易引入并形成Cu深能级中心. 本文采用深能级瞬态谱测试法研究了ZnTe背接触和石墨背接触CdTe太阳电池的部分深能级中心. 研究中运用密度泛函相关理论,分析闪锌矿结构CdTe,Cd空位体系和掺Cu体系的电子态密度,计算得出T_d场和C_3v场下Cu²⁺ d轨道的分裂情况. 计算结果表明,CdTe太阳电池中的E_v+0206 eV和E_v+0122 eV两个深中心来源于Cu替代Cd原子. 计算结果还表明,掺入Cu可降低CdTe体系能量.     

Ce3+ 掺杂高密度氧化物玻璃的闪烁性能研究

用高温熔融法制备了以SiO₂-B₂O₃-Al₂O₃-Gd₂O₃为基质系统Ce³⁺掺杂的玻璃样品, 测试样品的密度、紫外——可见透射光谱、紫外激发光谱和主要的闪烁性能, 并且把一部分闪烁性能和PbWO晶体及BGO晶体做比较. 着重研究了不同Ce³⁺掺杂浓度与Gd³⁺ 离子的含量对玻璃样品闪烁性能的影响规律. 结果表明: 玻璃样品具有较大的密度; 样品的X射线激发发射光谱发射峰位置都在390 nm左右, 当Ce³⁺ 离子的掺杂浓度为1.0 mol%(摩尔分数)、Gd₂O₃含量为15 mol%时, 玻璃样品的发光峰强度达到BGO晶体发光强度的90%; 同样验证了Ce³⁺ 离子具有浓度猝灭效应; Gd³⁺可以敏化Ce³⁺离子发光, 但是Gd³⁺离子到达一定浓度时, 反而会产生猝灭效应, 降低了Ce³⁺ 离子的发光. Ce³⁺ 离子掺杂SiO₂-B₂O₃-Al₂O₃-Gd₂O₃系统的闪烁玻璃有望替代闪烁晶体广泛应用于高能物理中.     

Er3+/Ce3+共掺碲铋酸盐玻璃的制备及光谱特性提高研究

采用高温熔融退火法制备了系列 80TeO₂-10Bi₂O₃-10TiO₂-0.5Er₂O₃-xCe₂O₃ (x=0,0.25, 0.5,0.75,1.0 mol%)和(80-y) TeO₂-10Bi₂O₃-10TiO₂-yWO₃-0.5Er₂O₃-0.75Ce₂O₃ (y=3,6,9,12 mol%)的碲铋酸盐玻璃.测试了玻璃样品400-1700 nm范围内的吸收光谱, 975 nm抽运下的上转换发光谱和1.53 μm波段荧光谱, 以及808 nm激励下的Er³⁺离子荧光寿命和无掺杂玻璃样品的Raman光谱, 并结合Judd-Ofelt理论和McCumber理论计算了Er³⁺离子光谱参数.结果表明, 在掺Er³⁺碲铋酸盐玻璃中引入Ce³⁺离子进行Er³⁺/Ce³⁺共掺, 通过Er³⁺离子⁴I_11/2能级与Ce³⁺离子²F_5/2 能级间基于声子辅助的能量传递过程,可以有效抑制Er³⁺离子上转换发光并明显增强其 1.53 μm波段荧光;同时,在现有Er³⁺/Ce³⁺共掺玻璃组分基础上引入WO₃, 可进一步提高1.53 μm波段荧光并展宽其荧光发射谱. 研究结果对于获取优异光谱特性的宽带掺Er³⁺光纤放大器玻璃基质具有实际意义.     

锰氧化物团簇正离子与硫化氢反应的实验与理论研究 (cited: 2)

采用激光溅射法制备了同位素标记的氧化锰团簇正离子Mn_m¹⁸O_n⁺,并研究了其在快速流动反应管中与硫化氢在热碰撞条件下的反应,氧化锰团簇正离子与硫化氢反应前后的质量分布与强度变化由飞行时间质谱仪检测．实验表明,绝大多数氧化锰团簇正离子可与硫化氢发生氧-硫交换反应产生水分子,反应通式为：Mn_m¹⁸O_n⁺+H₂S→Mn_m¹⁸O_n-1S⁺+H₂¹⁸O．通过密度泛函理论计算了氧化锰团簇正离Mn₂O₂⁺、Mn₂O₃⁺和Mn₂O₄⁺与H₂S反应的机理,结果显示,在这些反应体系中氧-硫交换反应通道同时具有热力学和动力学优势,印证了实验中观察到的现象．气相团簇研究发现的氧-硫交换反应与相关凝聚相体系反应结果一致     

金属有机框架材料UiO-66-NH2中的铜离子掺杂位置效应及相关动力学研究

本文通过调控合成构建了两种类型的铜离子掺杂金属有机框架(MOF)材料UiO-66-NH₂：一种是Cu²⁺离子浸渍在MOF孔隙中所形成的Cu@UiO-66-NH₂,另一种则是Cu²⁺离子部分取代Zr-O团簇中的Zr⁴⁺离子所形成的双金属中心Cu-UiO-66-NH₂. 超快光谱与动力学表征表明：与未掺杂的MOF相比,这两个铜离子掺杂的MOF体系均促进了与LCCT态相关的弛豫动力学,其促进程度的顺序为Cu-UiO-66-NH₂>Cu@UiO-66-NH₂UiO-66-NH₂;这与它们在可见光光催化析氢活性测试中所观察到的趋势一致. 该工作揭示了Zr基MOF体系中的铜离子掺杂位置效应及相关动力学,表明可在类似MOF体系中通过合理设计金属掺杂的具体位置来促进光致电荷分离、抑制有害的电荷复合,有利于提高MOF体系的光催化性能.     

Comparison of two-color holography among different doped LiNbO3 crystals at low intensities

The effects of material and experimental parameters on the nonvolatile two-color holographic recording space charge field and sensitivity for different doped LiNbO₃:Fe crystals have been studied theoretically based on a two-center model. When the direct electron transfer between the deep-trap centers and the shallow-trap centers was considered, the near-stoichiometric LiNbO₃:Fe is confirmed theoretically to be of bigger space charge field and higher recording sensitivity than the LiNbO₃:Fe:Mn and LiNbO₃:Cu:Ce in the low intensity region. A further improvement of the recording sensitivity can be achieved by doping concentration, thermal reduction treatment of Fe, appropriate gating and recording wavelengths with large photo-excitation cross sections.     

Ce$lt;sup$gt;3+$lt;/sup$gt;在LiBaBO$lt;sub$gt;3$lt;/sub$gt;中的发光特性及晶体学格位

采用固相法制备了LiBaBO₃：Ce³⁺发光材料.测得LiBaBO₃：Ce³⁺材料的发射光谱为一不对称的单峰宽谱,主峰位于440 nm;监测440 nm发射峰,可得其激发光谱为一主峰位于370 nm的宽谱.利用van Uitert公式计算了Ce³⁺取代LiBaBO₃中Ba²⁺时所占晶体学格位,得出438 nm发射带归属于九配位的Ce³⁺发射,而469 nm发射带起源于八配位的Ce³⁺发射.研究了Ce³⁺浓度对LiBaBO₃：Ce³⁺材料发光强度的影响,结果显示,随Ce³⁺浓度的增大,发光强度呈现先增大后减小的趋势,Ce³⁺浓度为3mol%时强度最大,造成其浓度猝灭的原因为电偶极-偶极相互作用.引入Li⁺,Na⁺或K⁺可增强LiBaBO₃：Ce³⁺材料的发射强度.利用InGaN管芯（370 nm）激发LiBaBO₃：Ce³⁺材料,获得了很好的蓝白光发射,色坐标为（x=0.291,y=0.297）. 关键词： 白光发光二极管 3：Ce³⁺')" href="#">LiBaBO₃：Ce³⁺ 晶体学格位 发光特性     

Strong permanent reversible diffraction gratings in copper-doped lithium niobate crystals caused by a zero-electric-field photorefractive effect

Permanent reversible diffraction gratings with refractive-index modulations of up to 10^-4 and with a grating vector perpendicular to the polar axis are realized in LiNbO₃:Cu crystals by making use of high temperature recording and charge compensation. The index changes do not result from light-induced space-charge fields and the linear electro-optic effect. They are linked to fixed high-contrast narrow-band absorption gratings of Cu⁺/Cu²⁺ ions via the Kramers–Kronig relations. PACS 42.65; 42.70; 72.40; 78.20     

Enhancement of catalytic activity in NH3-SCR reaction by promoting dispersibility of CuCe/TiO2-ZrO2 with ultrasonic treatment

A series of CuCe-modified TiO₂-ZrO₂ catalysts synthesized by stepwise impregnation method and ultrasonic-assisted impregnation method were investigated to research the removal of NO in the simulated flue gas. Results showed that the CuCe/TiO₂-ZrO₂ catalyst prepared by ultrasonic-assisted impregnation method exhibited the superior NO conversion, in which higher than 85% NO was degraded at the temperature range of 250–400 °C and the highest NO conversion of 94% at 350 °C. It proves that ultrasonic treatment can markedly improve the performance of catalysts. The effect of ultrasonic enhancement on CuCe/TiO₂-ZrO₂ was comprehensively studied through being characterized by physicochemical characterization. Results reveal that the ultrasonic cavitation effect improves the distribution of active species and the synergistic interaction between Cu with Ce components (Cu⁺ + Ce⁴⁺ ↔ Cu²⁺ + Ce³⁺) on the catalysts significantly, thus resulting in better dispersibility as well as a higher ratio of Cu²⁺ and Ce³⁺ of the catalysts. Moreover, it was found that the CuCe/TiO₂-ZrO₂ catalyst prepared by the ultrasonic-assisted impregnation method represented a higher degree of ultrafine metal particles and evenness. The above results were described with the generalized dimension and singularity spectra in multifractal analysis and validated by the comparative test. Therefore, it can be concluded that ultrasonic treatment facilitates the particle size and distribution of active sites on the catalysts.     

Thermoluminescence excitation spectroscopy: A versatile technique to study persistent luminescence phosphors

A versatile new facility to study photoionization processes in impurity doped compounds is presented. In this new facility monochromatic light is coupled to a thermoluminescence reader, enabling a fully automated recording of glow curves as a function of photon excitation wavelength. It provides detailed information on the mechanism of trap filling preceding persistent luminescence. The technique is first demonstrated with a study on Lu₂SiO₅:Ce³⁺ and then applied to commercial modern day double lanthanide doped SrAl₂O₄:Eu²⁺,Dy³⁺, Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺, CaAl₂O₄:Eu²⁺,Nd³⁺; and to the classical ZnS:Cu⁺ persistent luminescence phosphors. The presented data provide new insight into the mechanism of persistent luminescence.     

Enhanced nonvolatile holographic properties in Zn,Ru and Fe co-doped LiNbO3 crystals

A series of LiNbO₃ crystals doped with various concentrations of ZnO and fixed concentrations of RuO₂ and Fe₂O₃ have been grown by the Czochralski method from the congruent melts. The type of charge carriers was determined by Kr⁺ laser (476 nm) and He–Ne laser (633 nm). The results revealed that the holes were the dominant charge carriers at blue light irradiation. Dual-wavelength and two-color techniques were employed to investigate the nonvolatile holographic storage properties of Ru:Fe:LiNbO₃ and Zn doped Ru:Fe:LiNbO₃ crystals. The essential parameters of blue nonvolatile holographic storage in Zn:Ru:Fe:LiNbO₃ crystals were enhanced greatly with the increase of Zn concentration. This indicates that the damage resistant dopants Zn²⁺ ions enhance the photorefractive properties at 476 nm wavelength instead of suppressing the photorefraction. The different mechanisms of blue photorefractive and nonvolatile holographic storage properties by dual wavelength recording in Zn:Ru:Fe:LiNbO₃ crystals were discussed.     

双掺杂LiNbO3:Fe:Mn全息存储动力学

建立了包括扩散、漂移和光伏打效应三种输运机制,小信号光强、小调制度近似下描述双掺杂LiNbO₃:Fe:Mn晶体用双色光进行全息存储的动力学的耦合微分方程组,数值求解并解释了晶体光存储的时间动态发展过程.在此基础上,分析了晶体的氧化还原程度对全息存储过程的影响,只有在晶体总的受主数密度N_a(即Fe³⁺和Mn³⁺的数密度之和)大于铁离子数密度N_{2的条件下,双掺杂LiNbO3:Fe:Mn晶体全 关键词：}     

Investigation of the EPR g factors and defect structure for the Cu-VNa center in the X-irradiated NaCl: Cu crystal

The g factors of a tetragonally-compressed Cu²⁺ center in NaCl: Cu⁺ crystal X-irradiated at room temperature are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, the contribution to g factors from both crystal-field (CF) and charge-transfer (CT) mechanisms are included. The calculations are based on the defect model that the tetragonally-compressed Cu²⁺center is assigned to the Cu²⁺ ion (which is caused by Cu⁺ ion (at the Na⁺ site) irradiated by X-ray) associated with a nearest Na⁺ ion vacancy V_Na along C₄ axis due to charge compensation. From the calculations, the g factors g_|| and g_⊥ are explained and the defect structure (charactering by the displacement ΔZ of the Cl⁻ ion intervening in Cu²⁺ and V_Na) of the Cu²⁺ (or Cu²⁺-V_Na) center is obtained. The results are discussed.     

Enhanced hydrogen production by doping Pr into Ce0.9Hf0.1O2 for thermochemical two-step water-splitting cycle

We synthesized (Ce_0.9Hf_0.1)_1−xPr_xO_2−δ (x=0, 0.05 and 0.1) using the polymerized complex method. The synthesized samples, as well as the samples after thermochemical two-step water-splitting cycles have a fluorite structure and Pr exists in the solid solutions with both trivalent and tetravalent states, as suggested by powder X-ray Diffraction (XRD) Patterns. The reduction fraction of Ce⁴⁺ in redox cycles (oxidation step in air) and two-step water-splitting cycles (oxidation step in steam) indicates that the addition of Pr into Ce–Hf oxide solid solution cannot improve the reduction fraction of Ce⁴⁺ during the redox cycles but both the reduction fraction of Ce⁴⁺ and H₂ yield are significantly enhanced during two-step water-splitting cycles. The chemical composition of 10 mol% Pr doped Ce_0.9Hf_0.1O₂ exhibits the highest reactivity for hydrogen production in H₂-generation step by yielding an average amount of 5.72 ml g⁻¹ hydrogen gas, which is much higher than that evolved by Ce_0.9Hf_0.1O₂ (4.50 ml g⁻¹). The enhancement effect of doping Pr on the performance during two-step water-splitting cycles is because of the multivalent properties of Pr, which can: (1) reduce the amount of Ce³⁺ oxidized by contamination air (contamination air eliminated by partial oxidation of Pr³⁺ to Pr⁴⁺) in H₂-generation step; (2) enhance the reaction rate in H₂-generation step by improving the ionic conductivity (extrinsic oxygen vacancies created by the substitution of Ce⁴⁺ by Pr³⁺).