Na5Eu(WO4)4单晶的光学性质研究

本文测定了Na5Eu(WO4)4单晶的吸收光谱,荧光寿命和荧光分支比,并计算了5D0→7FJ,的辐射跃迁几率、量子效率和发射截面。     

高压下Na5Tb(WO4)4单晶的光谱

研究了Na5Tb(WO4)4单晶的高压发光规律,化学计量的Na5Tb(WO4)4基质发光单晶的发光来源于基质中高浓度Tb3+.用金刚石对顶砧显微光谱系统在0-4GPa范围内研究了Na5Tb(WO4)4的室温高压光谱,确定了各发射谱线的高压移动率.对Tb3+的5D4→7Fj(j=0,1,2,3,4,5),测到18条谱线高压移动率中除一条(5D4→7F2,常压峰值15509cm-1)蓝移外,都红移,红移率最大为-19.5cm-1/GPa(对应谱线5D4→7F4,常压峰值16876cm-1),与Tb3+在其它基质中相比,此移动率很大.     

Increase of the stimulated Raman scattering threshold at droplets by spectral broadening of nanosecond laser pulses

We show that the threshold of stimulated Raman scattering (SRS) from single micro‐droplets increases with the bandwidth of the pulsed excitation laser radiation. SRS thresholds were experimentally investigated for two droplet sizes and two excitation bandwidths. For the narrowband excitation, a frequency doubled Nd:YAG laser with a central wavelength of 532 nm, a full width half maximum (FWHM) bandwidth of 0.05 nm and a repetition rate of 10 Hz was used. For the comparison with the broadband excitation, a dye resonator containing Rhodamine 6G being pumped by the Nd:YAG laser was utilized with a central wavelength of 566 nm and a FWHM bandwidth of 4 nm. Droplets of 89 and 116 µm diameters, respectively, were illuminated by a vertical light sheet. If the broadband excitation is applied instead of the narrowband excitation ‐ for both droplet sizes ‐ the pulsed excitation energies can be increased by a factor of approximately 5 before the SRS threshold is reached. The multiplication register of an emCCD detector was used to detect low signals. The gain factor of the detector was calibrated and adapted to different excitation energies and signal intensities. Copyright © 2012 John Wiley & Sons, Ltd.     

WO4- 团簇的氧原子和分子吸附

采用密度泛函方法研究了WO4团簇阴离子和中性分子的性质．WO4-的最稳定的两个构型对称性为C2v和D2h，两者的四个氧原子都是以原子吸附的形式直接接在钨上的．还发现以前实验上预言的WO4 团簇的双氧分子吸附构型其实是WO4-团簇的一个亚稳态同分异构体．这个同分异构体的几何、振动和电子结构性质与实验结果符合的很好．同时还利用含时密度泛函来计算WO4中性分子的低能激发态，并对光电子能谱做了指认．为了解释实验上为什么可以观测到这个亚稳态，提出了合成WO4时的两种可能的反应机制．     

纳米WO_3块体材料的电致变色效应

WO3薄膜能够通过电、光、热变色 .实验发现纳米WO3块材具有明显的常规块材不具有的电致变色特性 ,即当样品中有电流通过时 ,样品从负极到正极颜色由黄色变为深蓝色 .变色前后样品的显微形貌和相结构都没有明显变化 .x射线光电子能谱说明变色后的样品中出现了低价的钨离子 (W5 ) .根据实验结果 ,变色过程被认为是一种电子注入效应 .纳米样品中的高价钨离子 (W6 )因为纳米材料的表面效应而具有足够大的活性 ,能与电子结合生成低价的离子 ,从而使样品变色     

电致变色氧化钨薄膜锂离子阈值注入量的研究

探讨了ＷＯ３薄膜与１ＭＬｉＣｌＯ４－ＰＣ溶液之间的界面电位差的变化规律及测量方法，制备了三种具有不同电致变色性能的ＷＯ３薄膜，并对它们进行了界面电位差随Ｌｉ＾＋注入量大小变化的测量，通过实验发现，界面电位差的变化趋势能够反映出氧化钨薄膜的Ｌｉ＾＋离子阈值注入量的大小。进而找到了用电阻热蒸发方法制备了电致变色氧化钨薄膜的最佳工艺条件。     

钨酸锌晶体的受激拉曼散射和光致发光研究

采用皮秒532nm 激光激发，研究了ZnWO₄晶体的受激拉曼散射和本征荧光发射.在SRS光谱中观察到一级(558.7nm)和二级(588.6nm)斯托克斯光，线宽分别为130和77cm^－1, 一级斯托克斯光的抽运阈值为6.8mJ.在532nm激光抽运下ZnWO₄晶体的荧光光谱呈现出由能量为2.30，2.45和2.83eV的3个高斯分量组成的独特结构.光致发光表明晶体具有从400nm到650nm的宽带本征发光，其峰值波长为472.0nm，相应于钨氧之间的辐射跃迁. 关键词： 晶体 钨酸锌 受激拉曼散射 闪烁体     

PbWO4晶体发光强度的温度依赖

对X射线激发下的PbWO4晶体发光强度的温度依赖关系(110-300K)进行了研究,对其I-T曲线中的结构结合热释光进行讨论,利用陷阱解释了I-T曲线中'反常'结构存在的原因.     

Eu^3＋的掺杂浓度对NaLa（WO4）2：Eu^3＋发光性能的影响

采用水热法,合成了NaLa（WO4）2：Eu^3＋纳米发光材料。利用激发光谱和发射光谱研究了材料的发光特性。结果表明,Eu^3＋离子的掺杂浓度为3%时,样品有较好的发光特性。样品的激发光谱有3个主激发峰,分别位于270、392nm和464nm处。发射光谱主峰为614nm线谱,此为Eu3＋的发光。     

Tb3+和Na2WO4共掺杂SiO2材料的制备及其发光性质

通过溶胶-凝胶技术制备了稀土离子Tb3 和Na2WO4共掺杂的SiO2材料,利用DTA-TG,IR,XRD等测试手段研究了材料的结构。材料属于非晶态,800℃退火后Tb3 和Na2WO4共掺杂样品的主要结构为SiO2的网状结构。通过三维荧光光谱,荧光激发光谱和发射光谱,分析探讨了Na2WO4对掺稀土离子的SiO2体系发光性质的影响。结果显示,在230nm激发下,样品显示Tb3 的5D4—7Fj(j=4,5,6)和5D3—7Fj(j=4,5,6)发射光谱,在紫外灯的照射下,发射均匀的蓝绿色荧光,说明样品掺杂均匀且分散性较好。Na2WO4的掺入,并不影响Tb3 在SiO2基质中的发射峰的主要位置,但对发光强度有很大的影响,敏化了5D4—7F6蓝色跃迁而猝灭了5D4—7F5绿色跃迁,使材料发射蓝绿色荧光。文章通过所得的能级图,对样品的跃迁机理进行了分析。     

PbWO4晶体空位型缺陷电子结构的研究

采用基于密度泛函理论的相对论性离散变分和嵌入团簇方法计算了PbWO4晶体中与氧空位和铅空位相关缺陷的态密度分布,并运用过渡态方法计算了其激发能.结果表明:PbWO4晶体中WO3+VO缺陷的O2p→W5d跃迁可引起350nm和420nm附近的吸收,并且发现VPb的存在可以使WO42基团的禁带宽度明显变小 关键词： PbWO4晶体 密度泛函 氧空位和铅空位 态密度分布     

Transient stimulated raman scattering in crystals during motion of populations of vibrational states

Transient stimulated Raman scattering (SRS) in crystals is analyzed taking into account the motion of populations of vibrational states under the action of subpicosecond (shorter than the dephasing time) pump pulses. Analytic expressions describing the dynamics of excitation of vibrations in SRS are derived. It is found that for a small wavelength of SRS interaction and high intensities of pump radiation observed for femtosecond SRS in crystals, avalanche excitation of vibrations can be responsible for SRS suppression. It is shown that when phase matching of Stokes-anti-Stokes parametric coupling in transient SRS is ensured, it is possible to elevate the efficiency of frequency conversion under conditions of motion of populations of vibrational states; this explains recent successful results in the experimental implementation of femtosecond SRS in crystals pumped by a Bessel beam.     

YVO4晶体的高效受激拉曼散射

报道了YVO4晶体在532 nm、30 ps脉冲下的的高效受激拉曼散射。采用腔外单次通过方式测量了不同长度YVO4晶体1阶斯托克斯受激拉曼散射的阈值,并得到该晶体的稳态增益系数为16.0±0.5 cm/GW。实验中观察到2阶斯托克斯线(558.6 nm5、87.8 nm)和1阶反斯托克斯线(508.0 nm),受激拉曼散射的整体转换效率高于50%。     

钨-硅基红色荧光粉的制备及其能量传递

通过溶胶-凝胶技术制备了以稀土离子Eu3＋为激活剂的硅基发光材料,并考察了Na2WO4的掺杂对体系发光性能的影响。主要通过研究三维荧光光谱,荧光激发光谱和发射光谱,分析探讨了Na2WO4的掺入对发光中心Eu3＋发光性质的影响,结果发现,三维荧光光谱高斯图像充分表明了Na2WO4的掺杂有效地提高了Eu3＋的5D0→7F2特征跃迁。用荧光激发光谱图和发射光谱图进一步详细的表征了基质和Eu3＋的f→f跃迁及其强度变化情况。通过能级图、位形坐标图和敏化过程示意图等理论对这个影响的原因进行了进一步的说明和探讨。结果表明,O→W的电荷迁移带吸收了大量的能量,并有效地将能量传递给Eu3＋,促使发光中心的发光强度增大。但由于Na2WO4的掺杂还增加了硅基质的能量吸收而使整体材料的发光效率下降。     

Frequency comb expansion in a monolithic self‐mode‐locked laser concurrent with stimulated Raman scattering

The discovery of a novel phase‐locked frequency comb generated from a monolithic laser with the concurrent processes of self‐mode locking (SML) and stimulated Raman scattering (SRS) is reported. It is experimentally shown that the width of the Raman gain can be exploited to considerably expand the frequency comb of a monolithic SML crystal laser via the SRS process. At a pump power of 6.5 W, an output power of 140 mW in the Stokes wave with a pulse width as narrow as 2.9 ps at a pulse repetition rate of 6.615 GHz is obtained. The present finding not only provides useful insights into the monolithic intracavity SRS process but also paves the way for generating mode‐locked pulses based on monolithic self‐Raman crystals.     

Two-photon absorption of high-power picosecond pulses in PbWO<Subscript>4</Subscript>, ZnWO<Subscript>4</Subscript>, PbMoO<Subscript>4</Subscript>, and CaMoO<Subscript>4</Subscript> crystals

The nonlinear process of two-photon interband absorption is studied in tungstate and molybdate oxide crystals excited by a sequence of high-power picosecond pulses with a wavelength of 523.5 nm. The transmission of the crystals is measured for the excitation pulse intensity up to 100 GW/cm². The pulse intensity in the crystals initially transparent at a wavelength of 523.5 nm is strongly limited due to two-photon absorption (TPA), and the reciprocal transmission in PbWO₄ and ZnWO₄ crystals reaches 50–60. In all crystals, TPA induces long-lived one-photon absorption, which affects the nonlinear process dynamics and leads to a hysteresis in the dependence of the transmission on the laser excitation intensity. Absorption dichroism manifests itself in a significant difference in the transmission intensities when the principal orthogonal optical axes of the crystals are excited. The TPA coefficients are determined during the excitation of two optical axes of the crystals. TPA coefficients β for the crystals vary over a wide range, namely, from β = 2.4 cm/GW for PbMoO₄ to β = 0.14 cm/GW for CaMoO₄, and the values of β can differ almost threefold when different optical axes of a crystal are excited. Good agreement is achieved between the measured intensities limited by TPA and the estimates calculated from the measured nonlinear coefficients. Stimulated Raman scattering (SRS) upon excitation at a wavelength of 523.5 nm is only detected in two of the four crystals under study. The experimental results make it possible to explain the suppression of SRS by its competition with TPA, and the measured nonlinear coefficients are used to estimate this suppression.     

He／K系统两步激励产生极紫外相干辐射机制中的斯托克斯及反斯托克斯竞争过程

讨论了Ｈｅ／Ｋ混合蒸汽中两步激励产生极紫外（ＸＵＶ）相干辐射机制中存在的斯托克斯及反斯托克斯跃迁过程．计算了有关跃迁的振子强度、极紫外辐射过程及其竞争过程的受激拉曼散射增益系数和阈值．结果表明，其中６４．３ｎｍ极紫外相干辐射的产生过程与其竞争过程相比，具有最大的增益及最小的阈值；但到能级Ｋ［３ｐ５４ｓ２２Ｐ１／２，３／２］的反斯托克斯跃迁及到能级Ｋ［３ｐ５３ｄ（３Ｐ）４ｓ２２Ｐ１／２，３／２］的斯托克斯跃迁将对其中５９．８ｎｍ极紫外相干辐射的产生构成严重竞争．     

Stimulated Raman Scattering in a Weakly Polar Ⅲ-Ⅴ Semiconductor： Effect of dc Magnetic Field and Free Carrier Concentration

Using the hydrodynamic model of semiconductor plasmas, we perform an analytical investigation of stimulated Raman scattering （SITS） of an electromagnetic pump wave in a transversely magnetized weakly polar semicon- ductor arising from electron-density perturbations and molecular vibrations of the medium both produced at the longitudinal optical phonon frequency. Assuming that the origin of SItS lies in the third-order susceptibility of the medium, we investigate the growth rate of Stokes mode. The dependence of stimulated Raman gain on the external dc magnetic field strength and free carrier concentration is reported. The possibility of the occurrence of optical phase conjugation via SItS is also studied. The steady-state Raman gain is found to be greatly enhanced by the presence of the strong external dc magnetic field.     

YbVO4晶体的受激拉曼散射

采用腔外单次通过方式,研究了一种新型晶体YbVO₄的受激拉曼散射.当抽运激光为532 nm皮秒脉冲时获得了3级斯托克斯线(558.47 nm, 587.92 nm, 620.67 nm)和1级反斯托克斯线(507.58 nm),测得YbVO₄晶体1级斯托克斯受激拉曼散射的稳态增益系数为17.8±0.2 cm/GW,受激拉曼散射的整体转换效率达到37%.实现了YbVO₄晶体对355 nm皮秒激光的受激拉曼散射,观察到1级斯托克斯线(366.1 关键词： 受激拉曼散射 稳态增益系数 转换效率 4晶体')" href="#">YbVO₄晶体     

Brechzahländerungen durch Schwingungsanregung beim stimulierten Raman-Effekt

The influence of stimulated Raman scattering (SRS) on refractive index due to excitation of vibrational levels of molecules has been estimated for Hydrogen and carbon disulphide. A comparison is given between the changes of refractive index caused by SRS, orientation of molecules and electrostriction. There are shown conditions under which it should be possible to observe such changes and therefore polarizabilities of excited levels.