Synthesis And Optical Properties Study Of Ce ³⁺ - Doped , Ce³⁺ , Tb ³⁺ -codoped 12CaO·7Al₂O ₃

The novel blue-emitting phosphors of Cerium doped 12CaO·7Al₂O₃ (C12A7:Ce³⁺) and green-emitting phosphors of Cerium/Terbium codoped 12CaO·7Al₂O₃:Ce³⁺, Tb³⁺ (C12A7:Ce³⁺,Tb³⁺) powders were synthesized by a solid-state reaction method. The microstructure and optical properties were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL), photoluminescence excitation (PLE). Besides, the energy transfer from Ce³⁺ to Tb³⁺ in C12A7:Ce³⁺, Tb³⁺ was studied in details by the Dexter transfer theory.All diffraction peaks of C12A7:Ce³⁺ and C12A7:Ce³⁺, Tb³⁺ are in good agreement with the standard powder diffraction data of C12A7, indicating that all samples crystallize to a single phase of mayenite C12A7 structure. C12A7:Ce³⁺, Tb³⁺ powders exhibit a homogeneous structure, and the average size was 2μm from the SEM micrographs.C12A7:Ce³⁺ phosphors could be effectively excited in the range of 312-386 nm. Under 350 nm excitation, the phosphors show a broad asymmetric emission band (380– 590 nm) centered at 432 nm, due to the transitions of 5d¹â†'²F_5/2å'Œ²F_7/2 of Ce³⁺.The emission spectra of C12A7:Ce³⁺ are fitted properly by sum of two Gaussian functions, and the energy difference of the two ground states is 1550 cm^-1. With increasing Ce³⁺ concentration from 0.5% to 1.5%, the PL and PLE spectra were similar and no red shift was observed reported by others.Upon the efficient excitation of Ce³⁺ at 350 nm, the C12A7:Ce³⁺,Tb³⁺ phosphors show intense green emission centered at 543 nm assigning to ⁵D₄â†'⁷F_J (J=6,5,4,3) transitions of Tb³⁺ ions, and weak blue emission centered at 434 nm, indicating the effective energy transfer occurred from Ce³⁺ to Tb³⁺ in C12A7:Ce³⁺,Tb³⁺. Based on Dexter's ET theory, we have demonstrated that the efficient ET is a resonant type via dipole-dipole mechanism with an energy transfer critical distance of 4.02 (A|°). The ET efficiency between Ce³⁺ and Tb³⁺ in the optimum composition reaches to 99%.Our results demonstrated that the promising applicability of C12A7:Ce³⁺ as a blue-emitting phosphor, and C12A7: Ce³⁺, Tb³⁺ phosphor would be a novel green-emitting phosphor for UV-converting white light-emitting diodes. In addition, C12A7 is an excellent candidate of luminescence compounds that doped with rare earth ions, and has interesting applicability in display technology and lighting industry.