Growth and optical properties of Cr3+-doped CdWO4 single crystals

Abstract

A high-quality Cr 3+:CdWO 4 single crystal at a size of approximately Φ 25×80 mm is grown using the Bridgman method with CdO, WO 3, and Cr 2O 3 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 2-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 4A 2 → 4T 1 and 4A 2 → 4T 2. The weak 4T 2 → 2E 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 1412.4, 776.8, and 3427.6 cm -1, respectively, according to the absorption spectra and crystal-splitting theory. A broadband fluorescence at about 1000 nm due to 4T 2 → 4A 2 transition is produced by exciting the samples at 675 nm. After being annealed in an O 2 atmosphere, the crystals become more transparent, while the effective light absorption of Cr 3+ ions is evidently enhanced and the emission intensity is also strengthened due to the reduction of oxygen vacancies in the CdWO 4 crystal after annealing. © 2012 Chinese Optics Letters.