Microwave synthesis of red-emitting Ca₂Si₅N₈:Eu²⁺ phosphor and its photoluminescence properties for white-LEDs

A microwave synthesis method has been developed for synthesis of Ca₂Si₅N₈:Eu²⁺ phosphor and its photoluminescence properties were investigated. Ca, Si, and Eu₂O₃ powders were used as the reactants serving as the sources of the Ca, Si and Eu. Addition of NaN₃ NH₄Cl and Si₃N₄ powders was found to increase significantly the product yield. These powders were mixed and pressed into a compact which was then embedded in AlN powder inside a BN crucible. The crucible was then placed at the center of the microwave cavity (TE103 single-mode). The microwave synthesis was performed at a microwave power (2.45 GHz) of 600 W for 1 h in a flowing 90%N₂-10%H₂ gas at one atmosphere. The effects of process parameters on the product yield were investigated and a reaction mechanism was proposed. The synthesized Ca₂Si₅N₈:Eu²⁺ phosphor absorbs light in the region of 240–520 nm and shows a single broad band emission in the region of 550–700 nm (peaking at 596–606 nm). The peak emission intensity at an optimized Eu₂O₃ molar ratio (0.03) was measured to be ∼106% of the commercial YAG:Ce³⁺ (P46-Y3) phosphor.