Photoluminescence properties and energy transfer of blue-green CaAl2O4: Tb3+, Bi3+ phosphors

A series of Tb3+ (or Bi3+) doped and Tb3+, Bi3+ co-doped CaAl2O4 phosphors were successfully prepared by the conventional solid state reaction method. The properties of the as-prepared samples, including the crystal structure, morphology, composition and photoluminescence properties are characterized by the X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), energy dispersive spectrometer (EDS), high-angle annular dark field (HAADF) image and spectroscopy technology, etc. The diffraction patterns of the doped samples display the peaks corresponding to the CaAl2O4 phase. The EDS and HAADF indicate that the Ca, Al, O, Tb and Bi elements are distributed uniformly in the Tb single-doped and the Tb, Bi co-doped CaAl2O4 samples. In order to investigate the energy transfer from Bi3+ to Tb3+, the critical (or optimal) doped concentrations of Tb and Bi in CaAl2O4 are obtained experimentally in sequential order. The critical doped concentrations (single-doped: 3 mol%Tb3+, and co-doped: 3 mol%Tb3+, 0.3 mol%Bi3+) for CaAl2O4 hosts have been determined. A strong bluegreen luminescence corresponding to D-5(4) -> F-7(5) transition of Tb3+ by near ultra-violet (367 nm) excitation and the obvious energy transfer from Bi3+ to Tb3+ in the co-doped CaAl2O4 can be observed. The energy transfer mechanism has been discussed. The CIE coordinates and decay lifetimes for the typical samples have also been investigated. It is found that CaAl2O4: Tb3+, Bi3+ is a blue-green emitting phosphor and has higher efficiency for the operation with near ultra-violet excitation.