Luminescence properties of Sr$_{2}$La$_{8-x}$Tm$_{x}$(GeO$_{4}$)$_{6}$O$_{2}$ apatites ($x$ = 0.1 – 1.0) in the visible and short-wave ir spectral ranges

For the first time, the Sr$_{2}$La$_{8-x}$Tm$_{x}$(GeO$_{4}$)$_{6}$O$_{2}$ ($x$ = 0.1 – 1.0) solid solution with the apatite structure were synthesized by the solid-phase method, and their spectral–luminescence properties were studied. The prospects of using these compounds as phosphors in the visible and short-wave infrared ranges were demonstrated. The luminescence of Sr$_{2}$La$_{8-x}$Tm$_{x}$(GeO$_{4}$)$_{6}$O$_{2}$ germanates, which occurs under ultraviolet radiation, is characterized by the high purity of blue color; the chromaticity coordinates are close to commercially available phosphors. The Sr$_{2}$La$_{8-x}$Tm$_{x}$(GeO$_{4}$)$_{6}$O$_{2}$ compounds efficiently convert 808 nm laser radiation into a series of emission lines in the 1.3 – 2.2 $\mu$m spectral range, caused by sequential ${}^{3}H_{4}\to{}^{3}F_4$ и ${}^{3}F_{4}\to{}^{3}H_{6}$ transitions in Tm$^{3+}$ ions. Germanate Sr$_{2}$La$_{8-x}$Tm$_{x}$(GeO$_{4}$)$_{6}$O$_{2}$ with a maximum emission intensity in the short-wave infrared region shows high thermal stability of luminescence in the 30–220$^\circ$C range.