Absorption and photoluminescence spectroscopy of diffusion-doped ZnSe:Cr²⁺

Abstract

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.