Crystal and Electronic Structures, Photoluminescence Properties of Eu2+-Doped Novel Oxynitride Ba4Si6O16-3x/2Nx

The crystal structure and the photoluminescence properties of novel green Ba4-yEuySi6O16-3x/2Nx phosphors were investigated. The electronic structures of the Ba4Si6O16 host were calculated by first principles pseudopotential method based on density functional theory. The results reveal that the top of the valence bands are dominated by O-2p states hybridized with Ba-6s and Si-3p states, while the conduction bands are mainly determined by Ba-6s states for the host, which is an insulator with a direct energy gap of 4.6 eV at Gamma. A small amount of nitrogen can be incorporated into the host to replace oxygen and forms Ba4-yEuySi6O16-3x/2Nx solid solutions crystallized in a monoclinic (space group P2(1)/c, Z = 2) having the lattice parameters a = 12.4663(5) angstrom, b = 4.6829(2) angstrom, c = 13.9236(6) angstrom, and beta = 93.61(1)degrees, with a maximum solubility of nitrogen at about x = 0.1. Ba4Si6O16-3x/2Nx:Eu2+ exhibits efficient green emission centered at 515-525 nm varying with the Eu2+ concentration when excited under UV to 400 nm. Furthermore, the incorporation of nitrogen can slightly enhance the photoluminescence intensity. Excitation in the UV-blue spectral range (lambda(exc) = 375 nm), the absorption and quantum efficiency of Ba4-yEuySi6O16-3x/2Nx (x = 0.1, y = 0.2) reach about 80% and 46%, respectively. Through further improvement of the thermal stability, novel green phosphor of Ba4-yEuySi6O16-3x/2Nx is promising for application in white UV-LEDs.