Bi2Mo2O9: Yb3+/Tm3+/Ho3+ phosphors for high-sensitivity optical thermometry and white-light upconversion

Bi 2 Mo 2 O 9 : Yb 3+ /Tm 3+ /Ho 3+ phosphors were synthesized via solid-state reaction method. Structural characterization confirmed phase purity and effective rare-earth incorporation into the host lattice. Under 980 nm excitation, the materials exhibited distinct emission bands corresponding to Tm 3+ (477 and 690 nm) and Ho 3+ (542 and 657 nm). Through optimization of Ho 3+ concentration (0.5 mol%), white-light upconversion emission was obtained with CIE 1931 coordinates of (0.3147, 0.2805). Using fluorescence intensity ratio technique based on non-thermally coupled energy levels of Tm 3+ ( 1 G 4 ) and Ho 3+ ( 5 F 5 ), it was found that the material had excellent temperature sensing performance, achieving maximum sensitivities of 21.74 %K −1 (absolute) and 1.892 %K −1 (relative). Remarkably, the material exhibits temperature-dependent chromaticity shifts from white (303 K) to yellow (483 K), enabling visual temperature indication. The findings demonstrate that Bi 2 Mo 2 O 9 : Yb 3+ /Tm 3+ /Ho 3+ phosphors exhibit promising prospects in optical thermometry and thermally-responsive luminescent devices, particularly in scenarios where thermally-driven color variations are advantageous or tolerable.