OPTICAL-PROPERTIES OF ALPHA-ZNAL2S4-CR SINGLE-CRYSTALS

The optical properties of the chromium doped spinel type semiconductor alpha-ZnAl2S4 have been examined over the temperature range 2-540 K. The intrinsic photoluminescence (PL) showed an intense ultraviolet pea k at 381 nm at 296 K. From extrinsic absorption and emission spectra t he transitions between the ground state (4)A(2g) and the excited level s E-2(g), T-2(1g), T-2(2g), T-4(2g), and T-4(1g) of Cr3+ ions were obs erved. A fit of the measured temperature dependence of the PL decay, u sing a four level model, yielded the lifetimes of the E-2(g),T- 2(1g), and T-4(2g) levels and the energy gaps between the E-2(g)-T-2(1g) and E-2(g)-T-4(2g) states which were found to be very close to the values obtained from steady-state measurements. A configurational coordinate diagram for Cr3+ ions in a alpha-ZnAl2S4: Cr spinel host has been con structed. Optical gain measurements at 198, 298, and 380 K displayed t wo separate spectral regions associated to the Cr3+ ions and possibly Cr4+ impurity centers. Gain values of up to 25 cm(-1) at 198 K were ob tained. (C) 1998 American Institute of Physics.