Deep-red photoluminescence from enhanced D-F transition in Eu doped CaGaGeO phosphors.

In order to explore diverse luminescence properties of Eu in inorganic phosphors, a series of novel deep-red-emitting CaGaGeO phosphors were successfully synthesized by solid-state reactions. The phase formation was verified by the X-ray diffraction patterns and Rietveld refinement and there is only one kind of Ca site in CaGaGeO. The excitation spectrum shows typical excitation peaks of Eu and the broad band ranging from 200 nm to 300 nm was composed of the charge transfer band of O-Eu and Ga-O transition band. The emission spectrum depicts that the intensity of the peak located at 704 nm (D → F) is higher than that of 618 nm (D → F), which finally leads to the deep-red emission of the phosphor with high color saturation. The coordination dodecahedron of EuO8 distorted from a cubic geometry to the square antiprism is responsible for the unusual emission of Eu. The research of the concentration quenching behavior, lifetime and luminescence decay curves imply that the energy transfer between Eu ions finally leads to the concentration quenching, and the interaction type is d-d interaction. The charge compensation, quantum efficiency and the thermal stability of CaGaGeO:Eu were also studied.