Optical and Structural Analysis of BaSi2O2N2:Eu Green Phosphor for High-Color-Rendering Lighting

Abstract

Green BaSi2O2N2:0.02Eu2+ phosphor is synthesized through a two-step solid state reaction method. The first firing is for crystallization, and the second firing is for reduction of Eu3+ into Eu2+ and growth of crystal grains. By thermal analysis, the three-time endothermic reaction is confirmed: pyrolysis reaction of BaCO3 at 900 ºC and phase transitions at 1,300 ºC and 1,400 ºC. By structural analysis, it is confirmed that single phase [BaSi2O2N2] is obtained with Cmcm space group of orthorhombic structure. After the first firing the morphology is rod-like type and, after the second firing, the morphology becomes round. Our phosphor shows a green emission with a peak position of 495 nm and a peak width of 32 nm due to the 4f65d1→4f7 transition of Eu2+ ion. An LED package (chip size 5.6 x 3.0 mm) is fabricated with a mixture of our green BaSi2O2N2, and yellow Y3Al5O12 and red Sr2Si5N8 phosphors. The color rendering index (90) is higher than that of the mixture without our green phosphor (82), which indicates that this is an excellent green candidate for white LEDs with a deluxe color rendering index.