In-depth study of spectroscopic properties of new $P{r}^{3+}$-ion doped low-phonon sesquisulfide $L{u}_2{S}_3$ material for mid-IR laser sources

$L{u}_2{S}_3$ material from the family of sesquisulfide hosts appears to be a promising low-phonon material for use as a laser gain medium allowing for a laser emission over a broad spectral range from ultraviolet to far mid-infrared wavelengths. In this paper, a praseodymium-ion doped $L{u}_2{S}_3$ single crystal grown by micro-pulling down technique is investigated with focus on its spectroscopic properties. The Raman, excitation, and luminescence spectra are presented. By selective excitation of the main energy levels of $P{r}^{3+}$-ions, 26 luminescence transitions of the $Pr:L{u}_2{S}_3$ crystal spanning the 0.49 to 5.5 $\mu$m wavelength range have been identified. The correct assignment of the observed luminescence spectra to the respective $P{r}^{3+}$ energy-level transitions was confirmed by the calculation of the optimized squared reduced-matrix elements for the tensor operators U(k) and L + gS.