O/N ordering in the structure of Ca3Si2O4N2 and the luminescence properties of the Ce3+ doped material

Abstract

A white powder of oxonitridosilicate Ca₃Si₂O₄N₂ was synthesized at 1450 °C from CaCO₃, Si₃N₄ and SiO₂. The crystal structure was refined using X-ray and neutron powder diffraction data with subsequent Rietveld refinements (R_wp = 7.35 for XRD and R_wp = 5.53 for NPD). The phase has a cubic unit cell with space group Pa (no. 205), cell parameters a = 15.0739(2) Å and Z = 24. In contrast with most layered oxonitridosilicates, such as MSi₂O₂N₂ (M = Ca, Sr, Ba), Ba₃Si₆O₉N₄ and Ce₄Si₄O₅N₆, Ca₃Si₂O₄N₂ is constructed of highly corrugated 12-membered rings of [Si₁₂O₂₄N₁₂], which is composed of [SiO₂N₂] tetrahedra. N atoms fully occupy the bridging sites and O atoms fully occupy the terminal sites. This structure is also supported by the ²⁹Si NMR measurement. The photoluminescence of Ce³⁺ doped Ca₃Si₂O₄N₂ shows that the phosphor has a typical shouldered emission band peaking at 470 nm and the phosphor can be efficiently excited in the range 300–400 nm, which makes it an attractive candidate phosphor for the application in phosphor-converted light-emitting diodes (pc-LEDs).