Blue Emitting Ca8La2(PO4)6O2:Ce3+/Eu2+ Phosphors with High Color Purity and Brightness for White LED: Soft-Chemical Synthesis, Luminescence, and Energy Transfer Properties

Ce3+ and/or Eu2+ activated Ca8La2(PO4)6O2 (CLPA) oxyapatite blue phosphors have been prepared via a Pechini-type sol–gel process. X-ray diffraction (XRD), photoluminescence (PL) spectra, absolute quantum yield, as well as lifetimes were utilized to characterize samples. The emission of Ce3+ and Eu2+ ions at different lattice sites has been identified and discussed. The CLPA:0.04Ce3+ phosphor exhibits bright blue emission with higher quantum yield (67%) and excellent CIE coordinates (x = 0.160, y = 0.115) under UV excitation, and the CLPA:0.05Eu2+ phosphor also exhibits blue emission with CIE coordinates (0.187, 0.164). The energy transfer from Ce3+ to Eu2+ in CLPA:Ce3+/Eu2+ phosphors has been validated and demonstrated to be a resonant type via a dipole–dipole mechanism. The critical distance (R c) of Ce3+ to Eu2+ ions in CLPA was calculated (by the spectral overlap method) to be 26.67 Å. The quantum yields of Ce3+ and Eu2+ coactivated CLPA phosphors are enhanced compared with that of Eu2+ activated samples due to energy transfer. The CIE coordinates of CLPA:0.04Ce3+, 0.02Eu2+ are (0.179, 0.169). The corresponding luminescence and energy transfer mechanisms have been proposed in detail. These blue phosphors might be promising for use in pc-white LEDs.