BaYb$_{2-x}$Er$_{x}$Ge$_{3}$O$_{10}$ and BaY$_{2-10y}$Yb$_{9y}$Er$_{y}$Ge$_{3}$O$_{10}$: luminescent properties and prospects for applications in remote temperature determination

Triorthogermanates BaYb$_{2-x}$Er$_{x}$Ge$_{3}$O$_{10}$ ($x$ = 0.1–0.3) and BaY$_{2-10y}$Yb$_{9y}$Er$_{y}$Ge$_{3}$O$_{10}$ ($y$ = 0.015–0.15) have been synthesized by the solid-state method. According to X-ray powder diffraction data, the compounds crystallize in the monoclinic system, S.G. $P2_1/m$, $Z$ = 2. The concentration and power pump dependences studies have been carried out for the lines in the 510–720 nm spectral range under 980 nm excitation. The mechanisms of energy transfer between optical centers have been also proposed and the optimal composition of the phosphor has been determined. The influence of temperature on the intensity ratio of the luminescence bands with maxima at 521 nm and 552 nm ($^{2}H_{11/2}\to^{4}I_{15/2}$ and $^4S_{3/2}\to^{4}I_{15/2}$ transitions in Er$^{3+}$) has been investigated, and conclusions about the possibility of using the germanates as materials for optical temperature sensors have been drawn.