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

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 (E-ads) and charge transfer (Delta Q) 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.