Synthesis, structure and luminescence properties of new chloro-germanate phosphors Ca3GeO4Cl2:Eu2+

A kind of novel blue-emitting chloro-germanate phosphor Ca3GeO4Cl2:Eu2+ has been synthesized via a high temperature solid-state method. The crystal structure of the as-prepared phosphor was discussed from the viewpoint of the doping behaviors of the activators. The luminescence properties and thermal stability of Ca3GeO4Cl2:Eu2+ was investigated in detail. Ca3GeO4Cl2:Eu2+ phosphors exhibit a broad-band excitation band in the near ultra-violet region and a blue emission peak at 428 nm, which are both ascribed to the 4f-5d transitions of the Eu2+ ions. The optimum concentration of Eu2+ in the Ca3GeO4Cl2 phosphor was determined to be 3 mol%, and the concentration quenching mechanism was considered to be the dipole-dipole interaction with a critical distance of R-c = 22.11 angstrom. Thermal stability studies show that the photoluminescence intensity of the Ca3GeO4Cl2:Eu2+ phosphor at 150 degrees C was 77% of the initial value at room temperature. The activation energy, E, was calculated to be 0.163 eV suggesting good thermal stability. The variation in lifetime of Ca3GeO4Cl2:Eu2+ phosphor was also discussed to verify different luminescence centers in the lattice.