Defect-Enabled\nSuperior Negative Thermal Quenching\nin Palmierite Ba<sub>9</sub>La(VO<sub>4</sub>)<sub>7</sub>:Eu<sup>3+</sup> for WLED In Situ Temperature Measuring

Negative thermal quenching (NTQ) of the phosphors is\ncritically\nimportant for both scientific research and practical applications,\nbut the design of efficient NTQ phosphors is still a challenging task.\nHerein, we report a new strategy for developing NTQ materials by cation-vacancy\nengineering. Specifically, a new color-tunable Ba<sub>9</sub>La<sub>1–<i>x</i></sub>(VO<sub>4</sub>):<i>x</i>Eu<sup>3+</sup> (BLVO:<i>x</i>Eu<sup>3+</sup>) phosphor\nwith abundant intrinsic cation vacancy was developed, exhibiting superior\nNTQ behavior under 365 nm excitation. The NTQ performance can be modulated\nvia adjusting Eu<sup>3+</sup> doping levels, and the emission intensity\nof Eu<sup>3+</sup> ions in the BLVO:0.20Eu<sup>3+</sup> phosphor increased\nby 275% at 473 K compared to room temperature. Furthermore, the reported\nmaterial emitting bright white light under 365 nm excitation was well-suited\nfor use in white light-emitting diode (WLED) phosphor and fluorescent\ntemperature sensors, exhibiting outstanding color-rendering index\n(90.1) in lighting and high sensitivity (<i>S</i><sub>a</sub> = 11.83% K<sup>–1</sup>, <i>S</i><sub>r</sub> =\n2.33% K<sup>–1</sup>) in temperature detecting. Lastly, the\noperating temperature of WLED at different currents can be monitored\nand displayed in real time through emission spectroscopy. All of the\nresults demonstrated that the designed NTQ BLVO:<i>x</i>Eu<sup>3+</sup> can be used as a single-phase white phosphor and\noptical thermometry. This work provides a fresh perspective for designing\nhigh-efficient NTQ phosphors and expands the application of phosphors\nin WLED in situ temperature detection.