In-depth study of spectroscopic properties of new $Pr^{3+}$-ion doped low-phonon sesquisulfide $Lu_2S_3$ material for mid-IR laser sources

Abstract

$Lu_2S_3$ 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 $Lu_2S_3$ 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 $Pr^{3+}$-ions, 26 luminescence transitions of the $Pr:Lu_2S_3$ 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 $Pr^{3+}$ energy-level transitions was confirmed by the calculation of the optimized squared reduced-matrix elements for the tensor operators U(k) and L + gS.