A Novel Negative-Thermal Quenching Ca9ZnK(VO4)7:Sm3+ Phosphor for Sensitive Optical Thermometer

Developing new phosphors with negative thermal quenching (NTQ) performance has important significance in both theoretical research and high-temperature applications. Herein, a novel Ca9ZnK(VO4)7:Sm3+ (CZKV:Sm3+) phosphor with NTQ of Sm3+ ions and TQ of VO43- groups was designed by a defect engineering strategy. The heterovalent substitution of Ca2+ by Sm3+ introduces cation vacancy defects in the host. It is found that the defect structures in the CZKV:Sm3+ phosphor help enhance the energy transfer (ET) from VO43- to Sm3+ at high temperatures, thereby achieving the NTQ of Sm3+, as revealed by the charge compensator of Li+ ions. Moreover, based on the NTQ of Sm3+ and TQ of VO43- in the phosphor, an optical thermometer model was constructed to achieve high-precision sensing of temperature. Specifically, within the 300 K-475 K range, the thermometer exhibited high sensitivity, with Sa-max reaching 0.0871 K-1, Sr-max attaining 2.059% K-1, and a minimum δT of 0.016 K. Additionally, the CZKV:Sm3+ phosphor exhibits unique thermochromic properties, enabling ambient temperature estimation through simple observation of its luminescent color. Owing to these exceptional characteristics, the CZKV:Sm3+ phosphor emerges as a highly promising candidate for advanced optical thermometry applications.