A novel negative-thermal quenching Ca9ZnK(VO4)7:Sm3+ phosphor for a 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 VO₄^3- 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 VO₄^3- 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 VO₄^3- 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 S_a-max reaching 0.0871 K^-1, S_r-max attaining 2.059% K^-1, and a minimum δ_T 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.