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

Abstract

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 Å. Thermal stability studies show that the photoluminescence intensity of the Ca₃GeO₄Cl₂:Eu²⁺ 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:Eu²⁺ phosphor was also discussed to verify different luminescence centers in the lattice.