Defect-Enabled Superior Negative Thermal Quenching in Palmierite Ba9La(VO4)7:Eu3+ for WLED In Situ Temperature Measuring

Negative thermal quenching (NTQ) of the phosphors is critically important for both scientific research and practical applications, but the design of efficient NTQ phosphors is still a challenging task. Herein, we report a new strategy for developing NTQ materials by cation-vacancy engineering. Specifically, a new color-tunable Ba₉La_1–x(VO₄):xEu³⁺ (BLVO:xEu³⁺) phosphor with abundant intrinsic cation vacancy was developed, exhibiting superior NTQ behavior under 365 nm excitation. The NTQ performance can be modulated via adjusting Eu³⁺ doping levels, and the emission intensity of Eu³⁺ ions in the BLVO:0.20Eu³⁺ phosphor increased by 275% at 473 K compared to room temperature. Furthermore, the reported material emitting bright white light under 365 nm excitation was well-suited for use in white light-emitting diode (WLED) phosphor and fluorescent temperature sensors, exhibiting outstanding color-rendering index (90.1) in lighting and high sensitivity (S_a = 11.83% K^–1, S_r = 2.33% K^–1) in temperature detecting. Lastly, the operating temperature of WLED at different currents can be monitored and displayed in real time through emission spectroscopy. All of the results demonstrated that the designed NTQ BLVO:xEu³⁺ can be used as a single-phase white phosphor and optical thermometry. This work provides a fresh perspective for designing high-efficient NTQ phosphors and expands the application of phosphors in WLED in situ temperature detection.