Absorption and photoluminescence spectroscopy of diffusion-doped ZnSe:Cr2+
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ZnSe:Cr2+ is an attractive candidate as a room-temperature tunable solid-state laser with output in the 2–3 µm range. Passive absorption losses in this emission range currently limit laser performance. In this study, we use absorption and photoluminescence spectroscopies at 5 and 296K to address the origin of these optical losses. A series of diffusion-doped ZnSe:Cr single-crystal samples with Cr2+ concentrations in the range from 2×1017 cm−3 to 9×1019 cm−3 were obtained using CrSe powder as the dopant source. We find that trace amounts of Fe2+ produce absorption in the 2–3 µm 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 Cr2+. In our series of samples, the relative intensities of the 680 nm absorption band do not track the relative intensities of the 1.8 µm band (known to be due to Cr2+), although excitation near 680 nm does produce weak Cr2+ luminescence. Our absorption data do not support the current assignment of the 680 nm absorption as being an internal transition of the Cr2+ ion.