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

A white powder of oxonitridosilicate Ca3Si2O4N2 was synthesized at 1450 degrees 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 (3) over bar (no. 205), cell parameters a = 15.0739(2) angstrom 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 Si-29 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).