Author Affiliations
Abstract
A high-quality Cr3+:CdWO4 single crystal at a size of approximately \Phi 25 \times 80 mm is grown using the Bridgman method with CdO, WO3, and Cr2O3 as raw materials and their molar ratio of 100:100:0.5. The temperature gradient of solid-liquid interface at growth is approximately 50 oC/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 O2-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 4A2->4T1 and 4A2->4T2. The weak 4T2->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 1 412.4, 776.8, and 3 427.6 cm-1, respectively, according to the absorption spectra and crystal-splitting theory. A broadband fluorescence at about 1 000 nm due to 4T2->4A2 transition is produced by exciting the samples at 675 nm. After being annealed in an O2 atmosphere, the crystals become more transparent, while the effective light absorption of Cr3+ ions is evidently enhanced and the emission intensity is also strengthened due to the reduction of oxygen vacancies in the CdWO4 crystal after annealing.
230.5298 Photonic crystals 260.1180 Crystal optics Chinese Optics Letters
2012, 10(4): 042301