Revealing The Degradation Mechanism of (Sr,Ca)AlSiN₃:Eu²⁺ Phosphor Aged Under Thermal‐Moisture‐Sulfur Conditions: A Combined Experimental and Ab Initio Study

Abstract

MAlSiN3:Eu2+ (M = Ca, Sr) is commonly used in high‐power phosphor‐converted white‐light‐emitting diodes and laser diodes to promote their color‐rendering index. However, the wide application of this phosphor is limited by the degradation of its luminescent properties in high‐temperature, high‐humidity, and high‐sulfur‐content environment. Here, the degradation mechanism of the (Sr,Ca)AlSiN3:Eu2+ (SCASN) red phosphor under thermal‐moisture‐sulfur coupling conditions is investigated. Furthermore, by performing first‐principles calculations, the hydrolysis mechanism on an atomic scale is assessed. The adsorption energy (Eads) and charge transfer (ΔQ) results showed that H2O chemically adsorbed on the (0 1 0), (3 1 0), and (0 0 1) surfaces of the CaAlSiN3 (CASN) host lattice. The energy barrier for H2O dissociation is only 29.73 kJ mol−1 on the CASN (0 1 0) surface, indicating a high dissociation probability. The formation of NH3, Ca(OH)2, and CaAl2Si2O8 is confirmed by H+ tended to combine with surface N atoms, while OH− combined with the surface Al/Si or Ca atoms. Moreover, ab initio molecular dynamics simulations were performed to further understand the hydrolysis process. This work offers a guidance on the design and applications of luminescent materials in LED packages with higher reliability and stability requirements in harsh environment.