A dual-mode optical thermometer based on dual-excitation Bi3+,Sm3+ co-doped Y4GeO8 phosphors

Dual-excitation and dual-emission Y4GeO8:Bi3+,Sm3+ phosphors were manufactured by traditional solid-phase sintering technique. The X-ray diffraction, morphology, photoluminescence, energy transfer process and temperature sensing properties of Y4GeO8:Bi3+,Sm3+ samples were comprehensively evaluated. The Y4GeO8:Bi3+,Sm3+ phosphors exhibit characteristic emissions of Bi3+ (3P1→1S0) and Sm3+ (4G5/2→6H) under both 290 and 347 nm excitations. In fluorescence intensity ratio and Commission International de L'Eclairage coordinates modes, Y4GeO8:Bi3+,Sm3+ samples present excellent temperature measurement performance. The maximum relative sensitivity (Sr-max) values of the former are 1.55 %/K (460 K, 290 nm excitation) and 0.82 %/K (506 K, 347 nm excitation). The Sr-max(x) values of the latter are 0.21 %/K (437 K, 290 nm excitation) and 0.15 %/K (513 K, 347 nm excitation). These results illustrate that Y4GeO8:Bi3+,Sm3+ phosphors can be used as a candidate material for a dual-mode optical thermometer under dual-excitation.