Absorption and photoluminescence spectroscopy of diffusion-doped ZnSe:Cr super(2+)

ZnSe:Cr super(2+) is an attractive candidate as a room-temperature tunable solid-state laser with output in the 2-3 mu m range. Passive absorption losses in this emission range currently limit laser performance. In this study, we use absorption and photoluminescence spectroscopies at 5 and 296 K to address the origin of these optical losses. A series of diffusion-doped ZnSe:Cr single-crystal samples with Cr super(2+) concentrations in the range from 2x10 super(17) cm super(-3) to 9x10 super(19) cm super(-3) were obtained using CrSe powder as the dopant source. We find that trace amounts of Fe super(2+) produce absorption in the 2-3 mu m range. Also, we have obtained data on a 680 nm absorption band observed in ZnSe:Cr which has been assigned to an internal transition of Cr super(2+). In our series of samples, the relative intensities of the 680 nm absorption band do not track the relative intensities of the 1.8 mu m band (known to be due to Cr super(2+)), although excitation near 680 nm does produce weak Cr super(2+) luminescence. Our absorption data do not support the current assignment of the 680 nm absorption as being an internal transition of the Cr super(2+) ion.