Infrared spectroscopic properties of low-phonon lanthanide-doped KLuS2 crystals

KLuS2 single crystal samples undoped and doped with a low (5 %) or high (38 %) concentration of trivalent thulium or ytterbium ions were synthesized in the form of thin hexagonal plates. The low phonon energy (220 cm(-1)) was confirmed using Raman spectroscopy. Samples were studied also by using optical absorption and emission as well as electron paramagnetic resonance spectroscopy and the observed spectral features are discussed. In particular, the 5 % Yb doped samples demonstrate homogeneous dopant distribution inside the material over the lutetium sites. No other signals either from potassium site or the exchange coupled ions were detected. For infrared transitions the luminescence kinetic was determined. Significantly broad infrared emission bands (at 1.4, 1.8 and 2.3 mu m for Tm3+, 1 mu m for Yb3+) and long decay times (e.g. 0.4 ms from H-3(4) to 19 ms from F-3(4) levels of Tm3+, 1.4 ms from F-2(5/2) level of Yb3+) make those materials perspective for future laser development.