Deep-red photoluminescence from enhanced 5D0-7F4 transition in Eu3+ doped Ca2Ga2GeO7 phosphors

In order to explore diverse luminescence properties of Eu3+ in inorganic phosphors, a series of novel deep-red-emitting Ca2Ga2GeO7 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 Ca2+ site in Ca2Ga2GeO7. The excitation spectrum shows typical excitation peaks of Eu3+ and the broad band ranging from 200 nm to 300 nm was composed of the charge transfer band of O2–-Eu3+ and Ga3+-O2– transition band. The emission spectrum depicts that the intensity of the peak located at 704 nm (5D0 → 7F4) is higher than that of 618 nm (5D0 → 7F2), 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 Eu3+. The research of the concentration quenching behavior, lifetime and luminescence decay curves imply that the energy transfer between Eu3+ 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 Ca2Ga2GeO7:Eu3+ were also studied.