Design of Dual-Mode Optical Thermometry Based on Thermally\nActivated Efficient Energy\nTransfer in LaNbO<sub>4</sub>/Ln<sup>3+</sup> (Eu<sup>3+</sup>/Sm<sup>3+</sup>/Pr<sup>3+</sup>) Phosph

Exploring methods to achieve high thermal stability in\nphosphors\nis of great significance for their applications in high-temperature\nfields. Currently, energy transfer (ET) from the host to activator\nlanthanide ions (Ln<sup>3+</sup>) is an effective approach to improving\nthe antithermal quenching of phosphors. In this contribution, LaNbO<sub>4</sub> (LNO) with efficient blue emission is used as the host to\nconstruct the host–Ln<sup>3+</sup> dual-emitting LNO/Ln<sup>3+</sup> (Eu<sup>3+</sup>/Sm<sup>3+</sup>/Pr<sup>3+</sup>) phosphor\nsystem, and the ET efficiency under thermal activation is investigated.\nExperimental results indicate that as the temperature rises, the ET\nefficiency from the LNO host to activator Ln<sup>3+</sup> increases,\nresulting in completely opposite luminescent thermal responses between\nthe LNO host and activator Ln<sup>3+</sup>. That is, the emission\nof the LNO host undergoes thermal quenching, while the emission of\nactivator Ln<sup>3+</sup> exhibits antithermal quenching, where the\nintegrated luminescence intensity at 498 K is 2.50–3.73 times\nthat at 298 K. Therefore, based on the differing luminescent thermal\nresponse trends of the emission peaks of the phosphors, a dual-mode\noptical temperature sensing system can be designed using fluorescence\nintensity ratio and fluorescence color change, achieving high relative\nsensitivity. Thus, this work provides new insights into the design\nof host ET phosphors and their applications in optical temperature\nsensing.