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 Ca 4– x F 2 Si 2 O 7: x Ce 3+ phosphor and violet-light-emitting oxyfluoride Ca 4 F 2 Si 2 O 7 host were synthesized by solid-state reaction. Ca 4– x F 2 Si 2 O 7: x Ce 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 nm excitation, a narrow blue emission was observed. The Ca 4 F 2 Si 2 O 7 host synthesized under the same reduction conditions exhibited violet emission due to the formation of anion-deficient nonstoichiometric Ca 4 F 2−δ Si 2 O 7+δ/2 species. The broad emission of Ca 4 F 2 Si 2 O 7: x Ce 3+ phosphor is attributed to Ce 3+ occupying two crystallographic calcium sites available in the host. A white LED device was fabricated using Ca 4 F 2 Si 2 O 7:Ce 3+ 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 Ca 4 F 2 Si 2 O 7:Ce 3+ suggest the promising application of the single activator phosphor that could produce white light under near-UV-based LEDs.