Blue Emitting Ca8La2(PO4)6O2:Ce~(3+)Eu~(2+) Phosphors with High Color Purity and Brightness for White LED: Soft-Chemical Synthesis, Luminescence, and Energy Transfer Properties

摘要

Ce~(3+) and/or Eu~(2+) 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 Ce~(3+) and Eu~(2+) ions at different lattice sites has been identified and discussed. The CLPA:0.04Ce~(3+) 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:0.05Eu~(2+) phosphor also exhibits blue emission with CIE coordinates (0.187, 0.164). The energy transfer from Ce~(3+) to Eu~(2+) in CLPA:Ce~(3+)/Eu~(2+) phosphors has been validated and demonstrated to be a resonant type via a dipole-dipole mechanism. The critical distance (R_c) of Ce~(3+) to Eu~(2+) ions in CLPA was calculated (by the spectral overlap method) to be 26.67 A. The quantum yields of Ce~(3+) and Eu~(2+) coactivated CLPA phosphors are enhanced compared with that of Eu~(2+) activated samples due to energy transfer. The CIE coordinates of CLPA:0.04Ce~(3+), 0.02Eu~(2+) 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.