Millimeter-scale Na2SiF6:Mn4+ red-emitting crystals with intense zero phonon line at 617 nm and enhanced hydrolysis resistance

• Published in: Ceramics international 2024-12
• Main Authors: He, Lulu, Zhang, Mingxin, Dong, Xiaoliang, Zhang, Liying, Shi, Ce, Ji, Haipeng
• Format: Article
• Language: English
• Subjects: Cooling-induced crystallization; Mn4; Photoluminescence; Red phosphor
• ISSN: 0272-8842
• DOI: 10.1016/j.ceramint.2024.12.239

Macroscopic Mn4+-activated fluoride crystals can exhibit improved resistance to hydrolysis and higher quantum efficiency compared to their micro-sized powder counterparts. Among various Mn4+-doped fluorides, Na2SiF6:Mn4+ is exceptional for its dominant photoluminescence at 627 nm, a notably short wavelength for this class of materials. While traditionally available only as micro-sized powder, this paper presents, for the first time, the growth of Na2SiF6:Mn4+ in the form of millimeter-sized crystals. Utilizing a cooling-induced crystallization technique, we have obtained Na2SiF6:Mn4+ crystals that exhibit columnar morphology with single-crystal-like characteristics and pronounced zero phonon line emission at 617 nm. The synthesis was meticulously optimized regarding the cooling protocol, cooling rate, and Mn4+ doping concentration. With increasing dosage of K2MnF6 in the precursor, a phase transformation from Na2SiF6:Mn4+ to (Na,K)2SiF6:Mn4+ and K2SiF6:Mn4+ was observed for the product crystals. The incorporation of Mn4+ was hindered during the cooling-induced crystallization of the crystals as the nominal Si/Mn concentration ratios significantly exceed the measured values. Comparison of the deterioration behavior in water suggests that the as-grown Na2SiF6:Mn4+ crystals displayed significantly improved stability against water attack compared to the Na2SiF6:Mn4+ powder phosphor. This work may inspire the development of more durable phosphor crystals for long-lasting white light LED technologies.