Promising Oxonitridosilicate Phosphor Host Sr3Si2O4N2: Synthesis, Structure, and Luminescence Properties Activated by Eu2+ and Ce3+/Li+ for pc-LEDs

A novel oxonitridosilicate phosphor host Sr3Si2O4N2 was synthesized in N-2/H-2 (6%) atmosphere by solid state reaction at high temperature using SrCO3, SiO2, and Si3N4 as starting materials. The crystal structure was determined by a Rietveld analysis on powder X-ray and neutron diffraction data. Sr3Si2O4N2 crystallizes in cubic symmetry with space group Pa (3) over bar, Z = 24, and cell parameter a = 15.6593(1) angstrom. The structure of Sr3Si2O4N2 is constructed by isolated and highly corrugated 12 rings which are composed of 12 vertex-sharing [SiO2N2] tetrahedra with bridging N and terminal 0 to form three-dimensional tunnels to accommodate the Sr2+ ions. The calculated band structure shows that Sr3Si2O4N2 is an indirect semiconductor with a band gap approximate to 2.84 eV, which is close to the experimental value approximate to 2.71 eV from linear extrapolation of the diffuse reflection spectrum. Sr3-xSi2O4N2:xEu(2+) shows a typical emission band peaking at similar to 600 nm under 460 nm excitation, which perfectly matches the emission of blue InGaN light-emitting diodes. For Ce3+/Li+-doped Sr3Si2O4N2, one excitation band is in the UV range (280-350 nm) and the other in the UV blue range (380-420 nm), which matches emission of near-UV light-emitting diodes. Emission of Sr3-2xSi2O4N2:xCe(3+),xLi(+) shows a asymmetric broad band peaking at similar to 520 nm. The long-wavelength excitation and emission of Eu2+ and Ce3+/Li+-doped Sr3Si2O4N2 make them attractive for applications in phosphor-converted white light-emitting diodes.