Optical study of CdSe_xS_1-x crystals doped with Cr

Solid-state broadband lasers emitting in the 2-4-μm region are of interest for a variety of applications. However, conventional lasers for these wavelengths have limitations, such as the complexity and cryogenic operation. Recently, alternative materials for the mid-IR lasers - Cr²⁺-doped II-VI chalcogenide crystals - have been proposed. The RT mid-IR absorption in these crystals is due to the effective Cr²⁺ intracenter transitions. We present the results of an investigation of the CdSe_xS _1-x:Cr²⁺ crystals. The crystals were grown from the CdSe source by seeded physical vapor transport in the helium atmosphere with a wafer of CdSe_xS_1-x as a seed. A CrSe source was used for the growth-time doping. The changing sulfur content along the growth axis was determined by energy dispersive x-ray microanalysis. An absorption peak in the IR range of 1.5-2.2 μm due to the Cr²⁺ intracenter transition ⁵T₂ → ⁵E of ions was revealed. The maximum peak absorption was determined to be 4.5 cm^-1. The concentration of the Cr²⁺ ions in the samples calculated from the IR absorption was found to vary from 1×10¹⁷ to 3×10¹⁸ cm ^-3. With the sulfur content, the intracenter absorption peak shifts to shorter wavelengths.