Phonon-Assisted Thermally Enhanced Up-conversion Fluorescence Lifetime Thermometry and Visualized Temperature Warning in Yb 3+ –Ho 3+ -Codoped Lu 2 Mo 3 O 12

Fluorescence thermometers have been plagued by the problem of thermal quenching (TQ) for a long time when operating at higher temperatures, which seriously hindered their performances in practical application. Ho 3+ –Yb 3+ -codoped Lu 2 Mo 3 O 12 phosphors were synthesized for designing TQ-immune fluorescence thermometers. Temperature-sensitive upconversion (UC) fluorescence lifetime (FL) and fluorescence color were modulated by utilizing appropriate phonon-assisted energy transfer (PAET) from Yb 3+ ( 2 F 5/2 ) to Ho 3+ ( 5 I 5 ) based on Lu 2 Mo 3 O 12 with negative thermal expansion (NTE) properties. Under a 980 nm laser excitation, the FL of the 5 F 4 → 5 I 8 (Ho 3+ ) transition extended from 35.65 to 52.94 μs (280 to 480 K) and the corresponding fluorescence color changed from green to red in Lu 2 Mo 3 O 12: Ho 3+, Yb 3+ . Accordingly, a dual-mode self-calibration fluorescence thermometer based on Lu 2 Mo 3 O 12: Ho 3+, Yb 3+ was constructed through FL technology ( 5 F 4 → 5 I 8 transition) and Commission Internationale de Eclairage chromaticity coordinate ratio (CIER) technology. Ultimately, the feasibility of the thermometer was verified to have high stability and temperature sensitivity (δT = 0.9 K, CIER), indicating that it is a prospective candidate for visualized temperature warning and sensing.