Crystal structures and photoluminescences of Ce-activated polymer-derived silicon oxynitride phosphors

Abstract

A series of cerium (Ce)-activated silicon oxynitride samples with various amounts of Ce (x, wt%) was prepared by employing the polymer-derived method with polycarbosilane and Ce acetylacetonate as starting materials. The photoluminescence spectra of the samples were measured. The chemical compositions and states, phase structures, and microstructures of the samples were investigated. It was found that β-Si3N4:Ce phase existed in all the samples, accompanied by α-Si3N4:Ce and CeSi3N5 phases in the samples with x ≤ 6.42, and by CeSiO2N and CeSi3N5 phases in the samples with x > 6.42. All samples showed excitation peaks in the region of 225–400 nm and blue emissions in the range of 420–450 nm. Among them, the sample with x = 6.42 exhibited the strongest blue emission at 445 nm with the excitation at 360 nm, and consisted of both crystalline and amorphous phases. The major crystalline phase β-Si3N4:Ce appeared in two space groups P63 and P63/m, leading Ce ions to be either six or nine coordinated by N/O atoms. The amorphous component contained Si-Si, Si-C, Si-O, and C-C bonds. By analyzing effects of crystalline phase on emission intensity, the difference in contributions of crystalline phases on emission intensity of the samples is discussed.