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/2 Si1-x Px O4(0.25≤x≤0.30),was prepared through a conventional solidstate 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-Ca2 SiO4 was studied and P2 O5 broken down by the raw material of(NH4)2 HPO4 played an important role in stabilizing α-Ca2 SiO4 which can only be stable at high temperature.The XRD patterns of the Ca2-x/2 Si1-x Px O4 host were found pure and optimized when the mole fraction of P2 O5 was 14.5%.The diffuse reflectance spectra of the Ca1.855 Si0.71 P0.29 O4 and Ca1.845 Si0.71 P0.29 O4 :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 Ca1.845 Si0.71 P0.29 O4 :0.01Eu2+phosphor showed an asymmetrical single intensive band centered at 513 nm,which corresponded to the 4f65d1→4f7transition of Eu2+.Eu2+ions might occupy two types of Ca2+sites in the Ca1.855 Si0.71 P0.29 O4 lattice and form two corresponding emission centers,which led to the asymmetrical emission of Eu2+in Ca1.855 Si0.71 P0.29 O4.The effects of Eu2+-doped concentration in Ca1.855-x Si0.71 P0.29 O4 :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.