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

Abstract

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.

Controlling of Structural Ordering and Rigidity of β-SiAlON:Eu through Chemical Cosubstitution to Approach Narrow-Band-Emission for Light-Emitting Diodes Application

“…The obtained reliability factors Rwp, Rp, and x 2 all imply a good fitting quality and no secondary phase was detected. Meanwhile, the refined NPD data also indicate that O shows an overwhelmingly preferential occupation of the N2 (2c sites), in line with the result of the literature 14 . This occurrence provides abundant microenvironment around Eu 2+ with different ratios of O/N in the second coordination zone ( Figure S3).…”

“…To date, in β-SiAlON:Eu, the consensus is that a single crystallographic site existed in the highly symmetric hexagonal channel for the Eu 2+ dopant, coordinated by nine (N,O) atoms. [14][15][16] However, it was still absent of direct evidences to prove the precise microenvironment of Eu 2+ in β-SiAlON. This fundamental question enables us to consider using the exhaustive photoluminescence measurements, such as high pressure and time-resolved spectroscopy, as an option to probe it.…”

“…The covalency of the Eu-N bond is almost not affected by the adjacent O and Al atoms due to Eu occupying almost the same symmetrical EuN9 polyhedron. 14 The magnitude of the crystal field splitting of 5d levels is sensitive to the shape and size of the local polyhedron, which can be further described by the average bond length (lav) and distortion index (D) of the activator-anion polyhedron. Previous work has shown that a shorter lav and a higher polyhedron distortion may increase the crystal field splitting.…”

Critical Review—Narrow-Band Nitride Phosphors for Wide Color-Gamut White LED Backlighting

“…1a tells that the densely packed, corner-sharing (Si,Al)(N,O) 4 tetrahedra form a three-dimensional network with a one-dimensional channel running along the c-axis. 22,23 Density functional theory (DFT) calculations based on the Vienna ab initio Simulation Package (VASP) are used to generate the potential energy surface, as illustrated in Fig. 1b.…”

“…Wang 23 et al demonstrated that z value (Si/Al ratios or oxygen concentrations) could have a significant effect on the local environment of Eu 2+ in β-SiAlON. As shown in Fig.…”