Luminescent and lasing characteristics of polycrystalline Cr:Fe:ZnSe exited at 2.09 and 2.94 µm wavelengths

The luminescence of Cr2+ and Fe2+ in Cr:Fe:ZnSe polycrystals excited at room temperature by pulsed lasers at wavelengths of 2.09 and 2.94 m was studied. For comparison, we also studied the luminescence in single crystals and polycrystals of Fe:ZnSe with iron ion concentration in the range from 5.6 × 1018 to 5.7 × 1019 cm−3. Doping of the polycrystalline samples was carried out using a high-temperature diffusion process with subsequent control of the dopants concentration distribution over the crystal depth. The dependence of the luminescence lifetime τlt of Fe2+ ions on the dopants concentration in crystals excited at a wavelength of 2.94 m was obtained. It was found that chromium quenches the luminescence of Fe2+ no less actively (if no more) than iron itself. The τlt values were measured for Fe:ZnSe excited at a wavelength of 2.94 m and Cr:Fe:ZnSe samples with the same maximum Fe2+ ions concentrations ( 0.9 × 1019 cm−3) at wavelengths of 2.94 m and 2.09 m. A noticeable increase in τlt value and luminescence rise time was observed in Cr:Fe:ZnSe crystals excited at a wavelength of 2.09 m (τlt 460 ns) compared to 2.94 m (τlt 240 ns). For comparison, the value of τlt in Fe:ZnSe was about 340 ns. The obtained results confirm the fast energy transfer in Cr:Fe:ZnSe crystals from excited chromium ions to iron ions. The output characteristics of lasers on Fe:ZnSe and Cr:Fe:ZnSe polycrystalline active elements with pumping by HF laser radiation were compared. The slope efficiency with respect to the absorbed energy of Cr:Fe:ZnSe lasers was significantly lower, and the generation threshold was two times higher than for Fe:ZnSe lasers. The prospects for creating a room temperature laser, in which the excitation of iron ions will be carried out through energy transfer from chromium ions, are analyzed.