Luminescence properties of Eu3+ doped CaMoO4 micron phosphors

Eu3+ doped CaMoO4 micron phosphors of different concentrations were prepared by chemical precipitation method. The photoluminescence properties were studied in detail. The X-ray diffraction measurements indicate that the samples are scheelite structure, and doping Eu3+ enlarge the lattice parameter of host material. The scanning electron microscope images show that the particle morphology is near-spherical and the size is 4-5 mu m. The excitation and emission spectra of CaMoO4:Eu show that CaMoO4:Eu can be effectively excited by blue light and near UV-light, and the red light emission of high colour purity can be realized. The electron-phonon coupling properties were also studied. The results indicate that the magnitude of Huang-Rhys factor is 10(-2), so the CaMoO4 : Eu is a weak electron-phonon coupling material. The results also indicate that the Huang-Rhys factor increases with the increase of concentration. It is probably because that increasing the doping concentration enhances the lattice relaxation. The transition intensity parameter Omega(2) of Eu3+ enlarges while the concentration is increasing. Because Omega(2) and the luminescent center environment are closely related, the numerical value of Omega(2) enlarges with the increase of degree of environmental disorder. But Omega(4) doesn't have obvious change. It can be explained that the environmental sensitivity level of Eu3+ D-5(0) -> F-7(2) transition is higher than that of D-5(0) -> F-7(4) transition. The quantum efficiency of Eu3+ D-5(0) energy level decreases with the increase of doping concentration. This can be attributed that the enhancement of Eu3+ doping concentration enlarges the energy transfer rate between luminescent centers, so the energy of excited electrons can be transferred to quenching center more easily and then the nonradiative relaxation rate of excited electrons increases. The best doping concentration of Eu3+ is 25% by drawing the concentration quenching curve. Furthermore, the energy transfer type of Eu3+ in CaMoO4 host is confirmed to be exchange interaction and the critical distance is calculated to be 8.4 angstrom. The chromaticity coordinate of CaMoO4:Eu phosphors is (0.654, 0.334), so the samples have high colour purity. The study indicates that CaMoO4:Eu micron phosphor prepared by chemical precipitation method is a red phosphor material with excellent property.