单斜结构的Yb:KLu(WO4)2晶体光谱和激光性质的各向异性

研究了Yb:KLu(WO4):晶体对非偏振抽运光的吸收以及连续波激光振荡性质.晶体结构的低对称性导致晶体光谱呈强烈各向异性,最强的吸收和发射都发生在平行于Nm.主轴的偏振方向上.Ng切向晶体具有最高的非偏振抽运光吸收效率和最大的激光功率产生潜力,2mm长的晶体产生的最高连续波输出功率为11 W,相对于吸收抽运功率,光一光转换效率为68%,而斜率效率则达80%.     

Er/Yb∶KY(WO_4)_2晶体的各向吸收光谱和上转换发光特性

测试了Er/Yb∶KY(WO4)2晶体在室温下3个轴Ng,Np,Nm方向上的吸收光谱,分析比较光谱特性,并计算出各能级跃迁的吸收截面,其中沿Np轴方向有最强的吸收和较大的吸收截面,这有利于激光上能级的粒子数堆积,增大跃迁几率,加强荧光输出。由于掺入Yb3+离子,晶体在980 nm附近有很强的吸收和较大的半峰宽。该晶体在980 nm激光泵浦下有上转换绿光和红光,3个晶轴Np,Ng,Nm轴方向的上转换荧光,波峰位置相差甚微,强弱区别明显,且呈现的各向异性,其中Np方向最强。     

Luminescence of Ln3+ and WO 2 2+ ions in wolframylphosphate glasses

We investigate the luminescent properties of potassium wolframylphosphate glasses doped with Eu³⁺, Tb³⁺, and Dy³⁺ ions whose luminescence is excited by donor-acceptor interaction between the active WO ₂ ²⁺ and Ln³⁺ ions, as well as the migration of energy in the subsystems of each type of the active ions. Comparison of the obtained data with the results of investigation of the spectroscopic properties of Ln³⁺ in uranylphosphate materials shows that a sufficiently high degree of the ionicity of bonds of Ln³⁺ with the atoms of its first coordination sphere is preserved in wolframylphosphate matrices. We show that three stages of the decomposition of electron excitations are typical of the WO ₂ ²⁺ ions in wolframylphosphate glasses doped with Ln³⁺ and two stages in nonactivated glasses. The electron excitation energy transfer in the WO ₂ ²⁺ −Ln³⁺ system occurs due to induction-resonance interaction. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 620–625, September–October, 1997.     

Color centres and polymorphism in pure WO3 and mixed (1−x)WO3−y·xReO2 powders

The relationship between structural transformations and colour centres creation is discussed for deeply coloured hydrogen tungsten bronzes and for pure WO₃ powders, acquiring less intense colour after mechanical treatments of variable duration. A comparative study on coloration is made also for mixed compounds (1−x)WO_3−y·xReO₂, where an evidence of a resonance effect for a particular Raman band at 970 cm⁻¹, attributed to the color centres, is observed. Besides, it is found that even moderate milling treatments result in a quite different structural evolution of tungsten trioxide upon cooling. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Mixed state ultrasonic attenuation in clean niobium near Hc2

Both longitudinal and shear ultrasonic attenuations and magnetization were measured as a function of magnetic field in the mixed state of two niobium single crystal samples with residual resistivity ratios of 68 and 2665 respectively. Particular attention was paid to the behavior of the attenuation at fields near H_c2. The higher purity sample showed marked frequency dependence of normalized attenuation at frequencies from 10 to 110 MHz. The other sample showed qualitatively similar but less pronounced frequency dependence at frequencies ranging from 10 to 435 MHz. Frequency dependence in both samples was in qualitative agreement with the theoretical results of Cerdeira and Houghton[1]. The attenuation changes near H_c2 at the lowest experimental frequencies were compared quantitatively with the frequency independent theoretical results of Houghton and Maki[2]. Agreement in the less pure sample was within a factor of two of the Houghton-Maki results at both 4·2 and 1·4 K. Quantitative comparison to theory for the purer sample must be qualified by the large observed frequency dependence. However, agreement between theory and experiment was excellent at 4·2 K. At 1·4 K in the purer sample, the theoretical predictions differed from experimental results by factors from two to six for various configurations of magnetic field and ultrasonic propagation and polarization directions. Houghton-Maki predictions of the dependence of ultrasonic attenuation on the geometry of magnetic field and ultrasonic propagation and polarization direction were also examined.     

WO3 oxide film formation on tungsten in O2/H2 discharges

The features of tungsten oxidation in a flowing O₂ or O₂/H₂ mixture glow discharge with a hollow cathode are investigated in the cathode, plasma, and afterglow regions at T = 300–350 K. The structure and composition of the samples are analyzed via reflection high-energy electron diffraction, reflection X-ray diffraction, electron probe microanalysis, and X-ray photoelectron spectroscopy. The results of analysis show that the metal surface is covered by a thin film (5–10 nm thick) of amorphous porous hydrated tungsten oxide (WO₃) after its exposure to the discharge and storage in air. The study of the film composition using a time-of-flight mass spectrometer indicates that the WO₃ film contains (WO₃) _n (n = 1–6) clusters and water molecules adsorbed in the pores. After exposure of the polycrystals to the O₂/H₂ discharge, the selective intense oxidation of individual grains is detected in the cathode region; the surrounding areas are subjected to weaker oxidation. The thicknesses of the WO₃ films on neighbouring grains differ by more than tenfold. Such grains can be the source of tungsten dust in plasma installations.     

87Rb NMR investigations on binary and ternary fullerene compounds: Rb3C60, K2RbC60 and Rb2CsC60

Results of¹³C MAS NMR and⁸⁷Rb NMR measurements on Rb₃C₆₀, K₂RbC₆₀ and Rb₂CsC₆₀ are presented. The⁸⁷Rb NMR spectra show generally the same characteristics as already reported by other authors. For the ternary compound the degree of site preferential order of the alkali metal ions agrees with the analysis of X-ray absorption data. Furthermore, in the room temperature⁸⁷Rb NMR spectra of all samples an additional broadened line is detected indicating that at least for the samples prepared from sublimed C₆₀ a considerable amount of the Rb ions is located on sites with symmetry lower than cubic.