Differentiated thermal quenching behavior enabling high-performance FIR optical thermometry in Bi3+-Eu3+ garnet phosphors

The optical thermometry method based on fluorescence intensity ratio (FIR) technology has emerged as a research hotspot in the field of temperature sensing in recent years due to its prominent advantages such as high sensitivity and operational convenience. In this work, a series of novel NaGd 2 Ga 2 InTi 2 O 12 : x Bi 3+ , y Eu 3+ (abbreviated as NGGIT: x Bi 3+ , y Eu 3+ ) optical thermometric phosphors were developed, and their crystal structures, optical properties, and temperature-sensing characteristics were systematically and in-depth characterized and analyzed. Under excitation at 310 nm, Bi 3+ emitted a characteristic broadband green luminescence centered at 500 nm with the optimal doping concentration determined to be x  = 1.5%, and the introduction of Eu 3+ into NGGIT:Bi 3+ enabled the construction of an efficient Bi 3+ -Eu 3+ energy transfer channel. Crucially, Bi 3+ and Eu 3+ exhibited significantly differentiated thermal quenching behaviors during temperature variation, laying an excellent foundation for FIR thermometry. The thermometric performance of NGGIT:1.5%Bi 3+ ,0.25%Eu 3+ phosphor was evaluated using FIR technology, and the results showed that its maximum absolute sensitivity ( S a ) and relative sensitivity ( S r ) reached 2.61% K −1 and 2.60% K −1 , respectively, accompanied by distinct luminescent color transition with temperature changes. This study demonstrated NGGIT:Bi 3+ ,Eu 3+ phosphors possessed excellent temperature-sensing performance and held broad application prospects in FIR-based non-contact thermometry.