Growth of Codoped CdWO4 Crystals by Bridgman Method and Their Optical Spectra
YU Can1，3, XIA Hai-ping1*, WANG Dong-jie2, CHEN Hong-bing2
1. Key Laboratory of Photo-Electronic Materials, Ningbo University, Ningbo 315211, China 2. Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, China 3. Chinese People’s Liberation Army with Number of 92746, Ningbo 315504, China
Abstract：The CdWO4 crystals with good quality in the size of Φ25 mm×120 mm, doped with Co in 0.5% molar fraction in the raw composition, were grown by the Bridgman method by taking ～70 ℃·cm-1 of solid-liquid interface and ~0.50 mm·h-1 growth rate. The crystal presents transparence and deep blue. The X-ray diffraction (XRD) was used to characterize the crystals. Three absorption peaks at 518, 564 and 655 nm respectively, which are attributed to the overlapping of 4T1(4F)→4A2(4F) and 4T1(4F)→4T1(4P) of Co2+ octahedrons, and a wide band centered at 1 863 nm, which is attributed to 4T1(4F)→4T2(4F), was observed. The absorption results indicated that the Co ions presented +2 valence in crystal and located within the distorted oxygen octahedrons. The crystal-field parameter Dq and the Racah parameter B were estimated to be 990 and 726.3 cm-1 respectively based on the absorption spectra. A fluorescence emission at 778 nm (4T1(4P)→4T1(4F)) for codoped CdWO4 crystals was observed under excitation by 520 nm light. It can be deduced from the changes in absorption and emission intensity of different parts of crystal that the concentration of Co2+ ion in crystal increased along growing direction and the effective distribution coefficient of Co2+ ion in CdWO4 crystal is less than 1.
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