Design of Dual-Mode Optical Thermometry Based on Thermally Activated Efficient Energy Transfer in LaNbO4/Ln3+ (Eu3+/Sm3+/Pr3+) Phosphors

Exploring methods to achieve high thermal stability in phosphors is of great significance for their applications in high-temperature fields. Currently, energy transfer (ET) from the host to activator lanthanide ions (Ln³⁺) is an effective approach to improving the antithermal quenching of phosphors. In this contribution, LaNbO₄ (LNO) with efficient blue emission is used as the host to construct the host-Ln³⁺ dual-emitting LNO/Ln³⁺ (Eu³⁺/Sm³⁺/Pr³⁺) phosphor system, and the ET efficiency under thermal activation is investigated. Experimental results indicate that as the temperature rises, the ET efficiency from the LNO host to activator Ln³⁺ increases, resulting in completely opposite luminescent thermal responses between the LNO host and activator Ln³⁺. That is, the emission of the LNO host undergoes thermal quenching, while the emission of activator Ln³⁺ exhibits antithermal quenching, where the integrated luminescence intensity at 498 K is 2.50-3.73 times that at 298 K. Therefore, based on the differing luminescent thermal response trends of the emission peaks of the phosphors, a dual-mode optical temperature sensing system can be designed using fluorescence intensity ratio and fluorescence color change, achieving high relative sensitivity. Thus, this work provides new insights into the design of host ET phosphors and their applications in optical temperature sensing.