Elucidating Structure-Composition-Property Relationships of the β-SiAION:Eu2+ Phosphor

In this work, we performed a systematic investigation of structure-composition-property relationships in Eu2+-activated beta-SiAlON, one of the most promising narrow-band green phosphors for high-power light-emitting diodes and liquid crystal display backlighting with wide color gamut. Using first-principles calculations, we identified and confirmed various chemical rules for Si-Al, O-N, and Eu activator ordering within the beta-SiAlON structure. Through the construction of energetically favorable models based on these chemical rules, we studied the effect of oxygen content and Eu2+ activator concentrations on the local EuN9 activator environment, and its impact on important photoluminescence properties such as emission peak position (using the band gap as a proxy), bandwidth, and thermal quenching resistance. Increasing oxygen content is shown to lead to an increase in Eu-N bond lengths and distortion of the EuN9 coordination polyhedron, modifying the crystal field environment of the Eu2+ activator, and resulting in red-shifting and broadening of the emission. We also show that the calculated excited band structure of beta-SiAION exhibits a large gap between the 5d levels and the conduction band of the host, indicating a large barrier toward thermal ionization (>0.5 eV) and, hence, excellent thermal quenching stability. Based on these insights, we discuss potential strategies for further composition optimization of beta-SiAlON.