Syntheses and photoluminescence properties of Sr₂Si₅N₈:Eu²⁺ phosphors

Sr₂Si₅N₈:Eu²⁺ phosphors were prepared by carbothermal reduction and nitridation method using Sr₂CO₃, Si₃N₄ and Eu₂O₃ as raw materials, and C as main reduction agent. The influence of C, Sr₂CO₃ and Eu²⁺ contents on phase composition and photoluminescence properties of as-prepared phosphors were investigated. The experimental results indicate that single-phase Sr₂Si₅N₈:Eu²⁺ is produced with molar ratio n_c/n_Si3N4=9/5. Excessive Sr₂CO₃ addition contributes to the N contents of the as-prepared phosphors, which enhances emission intensity. There is an asymmetric wide emission peaks between 550 nm and 700 nm due to the electron transfer of Eu²⁺ from 4f⁶5d¹ to 4f⁷ excited by 450 nm. Increasing Eu²⁺ concentration from 1.5mol% to 20mol%, the luminescence intensity hits the maximum value at Eu²⁺ concentration of 2mol% followed by continuous decline. Meanwhile the emission peak position is red-shifted from 608 nm to 641 nm, and the CIE chromaticity coordinates varies from (0.606, 0.393) to (0.656, 0.343), which indicates that Sr₂Si₅N₈:Eu²⁺ is a promising phosphor for white LEDs.