Abstract

A high-quality Cr<sup>3+</sup>:CdWO<sub>4</sub> single crystal at a size of approximately Φ 25 × 80 mm is grown using the Bridgman method with CdO, WO<sub>3</sub>, and Cr<sub>2</sub>O<sub>3</sub> as raw materials and their molar ratio of 100:100:0.5. The temperature gradient of solid-liquid interface at growth is approximately 50 °C/cm and the growth rate is 0.05 mm/h. The X-ray diffraction (XRD), absorption, excitation, and emission spectra of different parts of the as-grown and O<sub>2</sub>-annealed crystals are investigated. Two strong broad optical absorption bands of about 472 and 708 nm are observed, and they are associated with the transitions <sup>4</sup>A<sub>2</sub>→<sup>4</sup>T<sub>1</sub> and <sup>4</sup>A<sub>2</sub>→<sup>4</sup>T<sub>2</sub>. The weak <sup>4</sup>T<sub>2</sub>→<sup>2</sup>E transition (the R-line) at 632 nm is also observed. The crystal-field parameter Dq and the Racah parameters B and C are estimated to be 1 412.4, 776.8, and 3 427.6 cm<sup>-1</sup>, respectively, according to the absorption spectra and crystal-splitting theory. A broadband fluorescence at about 1 000 nm due to <sup>4</sup>T2→<sup>4</sup>A<sub>2</sub> transition is produced by exciting the samples at 675 nm. After being annealed in an O<sub>2</sub> atmosphere, the crystals become more transparent, while the effective light absorption of Cr<sup>3+</sup> ions is evidently enhanced and the emission intensity is also strengthened due to the reduction of oxygen vacancies in the CdWO<sub>4</sub> crystal after annealing.

© 2012 Chinese Optics Letters

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