Synthesis and luminescence properties of a novel phosphor Ca2−x/2Si1−xPxO4:Eu2+ for near UV-excited white-light-emitting diodes

A novel green-emitting phosphor, Eu2+-doped Ca2−x/2Si1−xPxO4 (0.25≤x≤0.30), was prepared through a conventional solid- state reaction. X-ray diffraction (XRD), photoluminescence (PL) and decay studies were employed to characterize the sample, which was assigned to P63mc space group in the hexagonal system. The effect of P-doping on the α-Ca2SiO4 was studied and P2O5 broken down by the raw material of (NH4)2HPO4 played an important role in stabilizing α-Ca2SiO4 which can only be stable at high temperature. The XRD patterns of the Ca2−x/2Si1−xPxO4 host were found pure and optimized when the mole fraction of P2O5 was 14.5%. The diffuse reflectance spectra of the Ca1.855Si0.71P0.29O4 and Ca1.845Si0.71P0.29O4:0.01Eu2+ covered the spectral region of 230–400 nm, implying that the phosphor was suitable for UV or near-UV LED excitation. The phosphor could be effectively excited in the near UV region with the maximum at 372 nm. The emission spectrum of the Ca1.845Si0.71P0.29O4:0.01Eu2+ phosphor showed an asymmetrical single intensive band centered at 513 nm, which corresponded to the 4f65d1→4f7 transition of Eu2+. Eu2+ ions might occupy two types of Ca2+ sites in the Ca1.855Si0.71P0.29O4 lattice and form two corresponding emission centers, which led to the asymmetrical emission of Eu2+ in Ca1.855Si0.71P0.29O4. The effects of Eu2+-doped concentration in Ca1.855−xSi0.71P0.29O4:xEu2+ on the PL were also discussed, the optimum doping concentration of Eu2+ was 1 mol.% and the critical distance of the energy transfer was also calculated by the concentration-quenching method. The non-radiative energy transfer between Eu2+ seemed to be caused by the multipole-multipole interaction. The fluorescence lifetime of Eu2+ was found to be 0.55711 μs. The results suggested that these phosphors might be promising candidates used for near UV light excited white LEDs.

XRD patterns of Ca2−x/2Si1−xPxO4 (x=0.25−0.30)Figure optionsDownload full-size imageDownload as PowerPoint slide