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⁺ (⁴G_5/2→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 (S_r-max) values of the former are 1.55%/K (460 K, 290 nm excitation) and 0.82%/K (506 K, 347 nm excitation). The S_r-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.