Abstract

Objective To address the growing demands for excitation-free optical temperature sensing in modern engineering and anticounterfeiting technologies， it is crucial to improve the persistent luminescence and optical temperature-sensing performance of near-infrared（ NIR） long persistent luminescence phosphors， broadening their application scenarios.

Methods The ZnGa_2-x（Mg-Zr）_xO₄∶Cr³⁺（ZGMZC， x=0-0. 2） NIR long persistent luminescence phosphors were synthesized via a high-temperature solid-state method by co-doping Mg²⁺and Zr⁴⁺into ZnGa₂O₄∶Cr³⁺ . A systematic analysis was conducted to investigate the effects of different Mg²⁺-Zr⁴⁺doping amounts on the phase structure， luminescence， and persistent luminescence performance of the ZnGa₂O₄ system. Moreover， the material’s potential for temperature sensing under natural light excitation was explored.

Results and Discussion The maximum doping amount of Mg²⁺-Zr⁴⁺was 10%. An increase in Mg²⁺-Zr⁴⁺doping content was observed to enlarge the grain size while progressively widening the band gap. After high-temperature calcination， the samples exhibited strong capability for visible light absorption. The Mg²⁺-Zr⁴⁺doping facilitated the formation of anti-site defects， thereby increasing defects in the matrix. Consequently， the R-line emission and its Stokes and anti-Stokes phonon sidebands （PSB）gradually weakened in the emitted light， while the N-line emission gradually strengthened. However， excessive doping enhanced energy transfer between Cr³⁺and defects， which promoted more non-radiative transitions， causing energy loss and weakened luminescence. Furthermore， as the Mg²⁺-Zr⁴⁺doping amount rose， the sample's persistent luminescence initially increased and then decreased， with the x=0. 05 sample exhibiting the optimal luminescence performance. Under dark conditions， the NIR persistent luminescence of the phosphors was enhanced with increasing temperature.

Conclusion The persistent luminescence performance of NIR phosphors is significantly enhanced through Mg²⁺-Zr⁴⁺co-doping.The synthesized materials exhibit temperature-dependent long persistent luminescence characteristics， which can be effectively charged under natural light and subsequently emit NIR light. The properties indicate their potential as natural light rechargeable materials for optical temperature sensing.

Keywords：near-infrared luminescence； long persistent luminescence phosphors； optical temperature sensing； performance regulation