Synthesis, characterization and luminescence properties of Ca2Si(O,N)4:Ce3+ and Sr2Si(O,N)4:Ce3+ oxonitridosilicate phosphors

Ce3+-activated single phase β-Ca2Si(O,N)4 (CSON) and α′-Sr2Si(O,N)4 (SSON) oxonitridosilicate phosphors were synthesized by a conventional solid state reaction method at 1100 °C using LiF as a flux. For comparative purposes, their oxide equivalents, β-Ca2SiO4 (CSO) and α′-Sr2SiO4 (SSO), doped with Ce3+ were obtained using the same synthesis method. The incorporation of nitrogen in the phosphors was confirmed by Energy Dispersive Spectroscopy (EDS). The formation of Sr-N and Si-N bonds can be observed in the FT-IR spectra. The oxide phosphors showed single intense broad band of Ce3+ emissions centered at 415 (CSO:Ce3+) and 425 nm (SSO: Ce3+) after ultraviolet irradiation. The oxonitridosilicate phosphors exhibited two-band emissions from Ce3+ occupying two Ca2+ or Sr2+ sites. The emissions were red shifted compared to their oxide counterparts, blue-green for CSON:Ce3+ and green for SSON:Ce3+. The thermal stability and quantum yields (QY) of oxonitridosilicate phosphors were significantly improved compared with respective oxide phosphors. Exceptional thermal stability of SSON:Ce3+ phosphor (90% of initial emission intensity at 200 °C) and high QY (85%) means that this phosphor can be used in white light emitting diodes.