Versatile Ca4F2Si2O7 Host from Defect-Induced Host Emission to White-Light-Emitting Ce3+-Doped Ca4F2Si2O7 Phosphor for Near-UV Solid-State Lighting

White-light-emitting Ca4-xF2Si2O7:xCe(3+) phosphor and violet-light emitting oxyfluoride Ca4F2Si2O7 host were synthesized by solid-state reaction. Ca4-xF2Si2O7:xCe(3+) has strong absorption in the near-UV region (370 nm) and shows a broad emission in the range of 390-600 nm centered at 475 nm. Under 315 rim excitation, a narrow blue emission was observed. The Ca4F2Si2O7 host synthesized under the same reduction conditions exhibited-violet emission due to the formation of anion-deficient nonstoichiorrietric Ca4F2-delta Si2O7+delta/2, species. The broad emission of Ca4F2Si2O7:xCe(3+) phosphor is attributed to Ce3+ occupying two crystallographic calcium sites available in the host. A white LED device was fabricated using Ca4F2Si2O7:Ce3+ without any additive phosphor, displaying excellent CIE chromaticity (0.29, 0.35) close to white emission with a color rendering index of 97. These exceptional optical properties of Ca4F2Si2O7:Ce3+ suggest the promising application of the single activator phosphor that could produce white light under near-UV-based LEDs.