Towards a universal ansatz for heat-induced emission peak shifts: insights from M₂SiO₄:Eu²⁺ (M = Sr, Ba, Ca) phosphors

Heat-induced emission peak shift (HIEPS), encompassing both redshift and blueshift, remains mechanistically unresolved in phosphor materials. Using state-of-the-art first-principles calculations of M₂SiO₄:Eu²⁺ (M = Sr, Ba, Ca), we reveal that conventional thermal expansion theory cannot adequately explain these phenomena. Instead, our frozen phonon analysis identifies local electron-phonon coupling as the dominant mechanism, where anisotropic thermal vibrations selectively distort the asymmetric Eu-5d potential well that arises from the dopant’s coordination environment. This distortion manifests through the temperature-sensitive ${\mathrm{\Delta }}_{f-d}$ parameter governing the 5d → 4f transition energy, directly controlling spectral shifts. Our findings establish a universal framework for HIEPS in rare-earth phosphors and enable a ${\mathrm{\Delta }}_{f-d}$ -guided strategy for designing thermally stable phosphors.