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.