Synthesis, crystal structure and photoluminescence of Eu-α-SiAlON

Eu-α-SiAlON (Eum/2Si12−m−nAlm+nOnN16−n) was synthesized with nominal compositions having small m and n values, by firing the powder mixture of Eu2Si5N8, α-Si3N4, AlN, and Al2O3 at 1900 °C for 6 h under 1 MPa nitrogen atmosphere. The ratio of the oxidation state of Eu2+/Eu3+ was estimated from the X-ray absorption fine structure (XAFS) measurement. The observed X-ray absorption near edge spectrum (XANES) showed that the Eu ion in Eu-α-SiAlON was mainly in divalent state but also coexisted with a small amount of Eu in the trivalent state. The crystal structure of Eu-α-SiAlON was refined by the Rietveld analysis of the X-ray powder diffraction patterns. The lattice constants of the samples increased with increasing m and n values. The excitation band of Eu-α-SiAlON ranged from the ultraviolet to the visible light region and a broad emission band centered at about 590 nm were observed. The emission intensity decreased significantly with increasing the ratio of trivalent Eu ion, suggesting that the trivalent Eu could be one of the luminescent killer centers.