Spectroscopic properties of KPb$_{2}$Cl$_{5}$ and RbPb$_{2}$Br$_{5}$ doped with Er$^{3+}$ and Yb$^{3+}$

Alkali halide crystals doped with Er$^{3+}$ exhibit several properties that make them promising for practical use in optical fibers and converters of the emission spectrum. In this work, we studied the luminescence spectra of crystals as a function of the excitation radiation wavelength and the temperature dependences of the luminescence intensity in the up-conversion mechanism of excitation of the most intense lines (530, 550, and 650 nm) and upon excitation at 980 nm. In KPb$_{2}$Cl$_{5}$ : Er$^{3+}$, RbPb$_{2}$Br$_{5}$ : Er$^{3+}$, and KPb$_{2}$Cl$_{5}$ : Er$^{3+}$+Yb$^{3+}$ crystals, the luminescence kinetics were measured upon excitation at 313 and 365 nm, and the theoretical estimates of lifetimes were made using the Judd–Ofelt theory. The results can be used in the development of laser-based systems and for estimating the degree of approximation of calculations by the Judd–Ofelt method for these crystals.