Optical properties of undoped and Ho3+, Er3+, and Tm3+-doped BaAl2S4 and BaAl2Se4 single crystals

The optical energy band gaps of BaAl2S4 and BaAl2Se4 single crystals at 300 K were found to be 3.98 and 3.35 eV, respectively, and the optical energy band gaps of Ho3+, Er3+, and Tm3+-doped BaAl2S4 and BaAl2Se4 single crystal s were smaller than those of the undoped single crystals. Photoluminescence spectra peaked at 459 and 601 nm in the BaAl2S4 and at 486 and 652 nm in t he BaAl2Se4. The photoluminescence emission peaks were attributed to donor- acceptor pair recombinations. Photoluminescence spectra of the Ho3+, Er3+, and Tm3+-doped BaAl2S4 and BaAl2Se4 at 5 K were measured in the wavelength range of 400-900 nm. Sharp emission peaks due to Ho3+, Er3+, and Tm3+ ions were observed and their transition mechanisms were proposed. (C) 2000 Ameri can Institute of Physics. [S0021-8979(00)06619-6].