Synthesis, structure and luminescence properties of new chloro-germanate phosphors Ca_3GeO_4Cl_2:Eu~(2+)

摘要

A kind of novel blue-emitting chloro-germanate phosphor Ca_3GeO_4Cl_2:Eu~(2+) 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 Ca_3GeO_4Cl_2:Eu~(2+) was investigated in detail. Ca_3GeO_4Cl_2:Eu~(2+) 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 Eu~(2+) ions. The optimum concentration of Eu~(2+) in the Ca_3GeO_4Cl_2 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 ?. Thermal stability studies show that the photoluminescence intensity of the Ca_3GeO_4Cl_2:Eu~(2+) phosphor at 150 °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 Ca_3GeO_4Cl_2:Eu~(2+) phosphor was also discussed to verify different luminescence centers in the lattice.