Robust and orange-yellow-emitting Sr-rich polytypoid α-SiAlON (Sr 3 Si 24 Al 6 N 40 :Eu 2+ ) phosphor for white LEDs

• Published in: Science and technology of advanced materials Vol. 25; no. 1; p. 2396276
• Main Authors: Estili, Mehdi, Xie, Rong-Jun, Takahashi, Kohsei, Funahashi, Shiro, Suzuki, Tohru S, Hirosaki, Naoto
• Format: Journal Article
• Language: English
• Published: United States Taylor & Francis 02.09.2024; Taylor & Francis Group
• Subjects: nitrides; Optical, Magnetic and Electronic Device Materials; phosphors; photoluminescence; powder synthesis; White light emitting diodes; White light emitting diodes; powder synthesis; photoluminescence; nitrides; phosphors
• ISSN: 1468-6996; 1878-5514
• DOI: 10.1080/14686996.2024.2396276

Nitrides and oxynitrides isostructural to α-Si N ( -α-SiAlON,  = Sr, Ca, Li) possess superb thermally stable photoluminescence (PL) properties, making them reliable phosphors for high-power solid-state lighting. However, the synthesis of phase-pure Sr-α-SiAlON still remains a great challenge and has only been reported for Sr below 1.35 at.% as the large size of Sr ions tends to destabilize the α-SiAlON structure. Here, we succeeded to synthesize the single-phase powders of a unique 'Sr-rich' polytypoid α-SiAlON (Sr Si Al N :Eu ) phosphor with three distinctive Sr/Eu luminescence sites using a solid-state remixing-reannealing process. The Sr content of this polytypoid structure exceeds those of a few previously reported structures by over 200%. The phase purity, composition, structure, and PL properties of this phosphor were investigated. A single phase can be obtained by firing the stoichiometric mixtures of all-nitride precursors at 2050°C under a 0.92 MPa N atmosphere. The Sr Si Al N :Eu shows an intense orange-yellow emission, with the emission maximum of 590 nm and internal/external quantum efficiency of 66%/52% under 400 nm excitation. It also has a quite small thermal quenching, maintaining 93% emission intensity at 150°C. In comparison to Ca-α-SiAlON:Eu , this Sr counterpart shows superior quantum efficiency and thermal stability, enabling it to be an interesting orange-yellow down-conversion luminescent material for white LEDs. The experimental confirmation of the existence of such 'Sr-rich' SiAlON systems, in a single-phase powder form, paves the way for the design and synthesis of novel 'Sr-rich' SiAlON-based phosphor powders with unparalleled properties.