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

In this work, we performed a systematic investigation of structure–composition–property relationships in Eu 2+ -activated β-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 β-SiAlON structure. Through the construction of energetically favorable models based on these chemical rules, we studied the effect of oxygen content and Eu 2+ activator concentrations on the local EuN 9 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 EuN 9 coordination polyhedron, modifying the crystal field environment of the Eu 2+ activator, and resulting in red-shifting and broadening of the emission. We also show that the calculated excited band structure of β-SiAlON 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 β-SiAlON.