First-principles study of thermal quenching mechanism of Mn⁴⁺ − doped fluoride phosphors: Electronic structure, optical properties and phosphor design principles

In this work we use advanced theoretical models and currently available experimental data to investigate the thermal quenching mechanism of the Mn⁴⁺ ion luminescence in fluorides. Using first-principles calculations on Mn⁴⁺ doped systems, we examine how host lattice fundamental properties, crystal structure, and local coordination environments influence the electronic, optical and thermal quenching behavior of the Mn⁴⁺ ion impurity. A key innovation of this study lies in the incorporation of mechanical and dynamic stability criteria as predictive indicators of host suitability. Mechanical stability was assessed by the calculations of the elastic constants, with the Born stability criteria serving as the benchmark for assessment. The dynamic stability was determined by computing the phonon density of states of the host fluorides. We show that mechanical and dynamic stability is a key predictor of whether a fluoride host can support efficient Mn⁴⁺ luminescence. In stable hosts, thermal quenching follows the ²E → ⁴T₂ → ⁴A₂ crossover process, with the quenching temperature and activation energy correlated to the zero-phonon energy of the ⁴T₂ state and the Stokes shift of the ⁴A₂ ↔ ⁴T₂ transition. Conversely, mechanically and dynamically unstable hosts fail to support efficient Mn⁴⁺ luminescence. This work correlates material's fundamental properties and electronic structure of the Mn⁴⁺ ion to luminescence efficiency, providing insights into phosphor design principles. While multiple approaches to high-throughput screening exist, the methodology presented here offers one such pathway-demonstrating predictive power that can strategically guide materials selection and design of high-performance phosphors.