坩埚下降法生长钨酸镉单晶的光学均匀性

采用垂直坩埚下降法生长出大尺寸CdWO₄单晶, 通过DSC/TG、XRD、电子探针、透射光谱和X射线激发发射光谱对单晶进行了测试表征, 分析了单晶生长过程中熔体挥发情况和单晶化学成分变化, 研究了所生长单晶的光学均匀性的变化规律. 结果表明, CdWO₄单晶生长过程存在比较严重的熔体挥发, 且熔体中CdO比WO₃更加易于挥发; CdWO₄单晶的化学组成存在不同程度缺Cd的特征, 初期生长晶体的n(Cd)/n(W)比相对高, 后期生长晶体的n(Cd)/n(W)比持续减小, 相应地单晶在380~550nm区域的光透过率略有降低, X射线激发发光强度有所降低, 且发光波长出现略微红移的趋势. 通过提高多晶料纯度、减少熔体挥发和氧气氛退火处理, 可以改善坩埚下降法生长CdWO₄单晶的光学均匀性.

Optical Homogeneity of CdWO4 Single Crystal Grown by Vertical Bridgman Process

Large size CdWO₄ single crystals were grown by vertical Bridgman process. The crystal was characterized by DSC/TG, XRD, EPMA, optical transmittance and X-ray stimulated luminescence spectra. The melt volatilization in the growth and the chemical composition change of the crystal were analyzed and the optical homogeneity of the grown crystal boule was investigated. It is verified that a serious melt volatilization occurs in the crystal growth, in which CdO in the melt is more prone to volatile. The chemical composition of the grown crystal shows a cadmium lacking characteristics in varying degrees. A higher Cd/W ratio in chemical composition appears in the crystal grown in earlier period, while the Cd/W ratio decreases continuously in the crystal grown afterward. The crystal grown in later period shows somewhat a lower optical transmittance in the wavelength range of 380-550nm and a lower intensity of X-ray stimulated luminescence with a little red-shifted wavelength. By means of purifying the feed material, decreasing the melt volatilization and annealing in oxygen atmosphere, the crystals with better optical homogeneity may be grown by vertical Bridgman process.