Plasma-assisted coating mitigates degradation of (Sr,Ca)AlSiN3:Eu2+ phosphors under thermal‐moisture‐sulfur condition: from synergistic aging mechanisms to protective strategies

(Sr, Ca)AlSiN 3 :Eu 2+ (SCASN) phosphors are widely used in white LEDs due to their excellent red spectral performance. However, exposure to high temperature, high humidity, and sulfur-containing environments significantly degrades their performance and long-term stability. Herein, a rapid plasma-assisted deposition technique is employed to apply an ultrathin Si-based nanolayer onto SCASN (SCASN-Coated), enhancing its durability under such harsh conditions. Accelerated aging tests conducted at 100 °C, 100 % relative humidity (RH), and in a sulfur-containing atmosphere reveal that unmodified SCASN retains only 24.1 % of its initial luminous intensity after 1008 h, whereas the SCASN-Coated preserves approximately 41.2 % of their original brightness without compromising intrinsic luminescent properties. First-principles calculations and molecular dynamics simulations further elucidate that SCASN has a strong chemical adsorption effect on SO 2 (−3.056  eV). And the combined presence of SO 2 and H 2 O promotes the displacement of Ca 2+ ions, accelerating degradation. The protective SiO 2 nanolayer drastically reduces the SO 2 adsorption energy (−0.124  eV) and inhibits Ca 2+ ion migration. This surface protection strategy not only augments the resilience of SCASN phosphors under extreme conditions but also provides research paradigm into the degradation mechanisms, thereby offering new avenues for extending the service life of LED devices in challenging environments.