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

A kind of novel blue-emitting chloro-germanate phosphor Ca3GeO4Cl2: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 Ca3GeO4Cl2:Eu(2+) was investigated in detail. Ca3GeO4Cl2: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 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 Å. Thermal stability studies show that the photoluminescence intensity of the Ca3GeO4Cl2: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 Ca3GeO4Cl2:Eu(2+) phosphor was also discussed to verify different luminescence centers in the lattice.