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

A series of Tb 3+ (or Bi 3+ ) doped and Tb 3+ , Bi 3+ co-doped CaAl 2 O 4 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 CaAl 2 O 4 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 CaAl 2 O 4 samples. In order to investigate the energy transfer from Bi 3+ to Tb 3+ , the critical (or optimal) doped concentrations of Tb and Bi in CaAl 2 O 4 are obtained experimentally in sequential order. The critical doped concentrations (single-doped: 3 ​mol%Tb 3+ , and co-doped: 3 ​mol%Tb 3+ , 0.3 ​mol%Bi 3+ ) for CaAl 2 O 4 hosts have been determined. A strong blue-green luminescence corresponding to 5 D 4 → 7 F 5 transition of Tb 3+ by near ultra-violet (367 ​nm) excitation and the obvious energy transfer from Bi 3+ to Tb 3+ in the co-doped CaAl 2 O 4 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 CaAl 2 O 4 : Tb 3+ , Bi 3+ is a blue-green emitting phosphor and has higher efficiency for the operation with near ultra-violet excitation.