Novel ir phosphor based on Sr$_{3}$La$_{2}$(Ge$_{3}$O$_{9}$)$_{2}$ : Nd$^{3+}$, Ho$^{3+}$ germanate

Cyclogermanate Sr$_{3}$La$_{2}$(Ge$_{3}$O$_{9}$)$_{2}$, isostructural to silicate Sr$_{3}$Er$_{2}$(Si$_{3}$O$_{9}$)$_{2}$, activated by neodymium and holmium is obtained for the first time by the precursor method. Ion Nd$^{3+}$ in the structure of Sr$_{3}$La$_{2}$(Ge$_{3}$O$_{9}$)$_{2}$ is a sensitizer of the infrared luminescence of Ho$^{3+}$. Excitation by radiation with a wavelength of 808 nm leads to a series of emission lines in the luminescence spectra of Sr$_{3}$La$_{2-x}$Nd$_{x}$(Ge$_{3}$O$_{9}$)$_{2}$ : Ho$^{3+}$ in the short-wave and middle-IR ranges (1.0–3.4 $\mu$m). The highest intensity of lines at 2.1 and 2.7 $\mu$m, associated with the $^{5}I_{7}\to{}^{5}I_{8}$ и $^{5}I_{6}\to{}^{5}I_{7}$ transitions in the Ho$^{3+}$ ion, is found for compositions containing traces of holmium. Based on the analysis of the concentration dependences of the luminescence intensity, an optimal composition of the phosphor is determined, which ensures the maximum efficiency of conversion of laser radiation energy. The data obtained are interpreted in the assumption of cross-relaxation energy transfer from Nd$^{3+}$ to Ho$^{3+}$.