Luminescence properties of Eu3+-doped Ca4Gd(BO3)3O phosphors

Eu3+-doped and -undoped Ca4Gd(BO3)3O phosphors were synthesized by high temperature solid-state reaction. Single phase formation of Ca4Gd(BO3)3O was confirmed by X-ray powder diffraction analysis. The vacuum ultraviolet (VUV)-ultraviolet (UV) excitation and emission spectra together with decay curves at different temperatures are investigated. The excitation spectra exhibit that Ca4Gd(BO3)3O:Eu3+ is effectively excited by VUV and UV irradiations. Emission lines of Gd3+ at around 314 nm due to the 6P7/2 → 8S7/2 transitions are observed under the VUV and UV excitations in which the line intensity depends strongly on Eu3+ concentration in Ca4Gd(BO3)3O:Eu3+. It is found that the energy transfer occurs from host absorption band to Gd3+ and Eu3+ ions in Ca4Gd(BO3)3O:Eu3+. The energy transfer efficiency from Gd3+ to Eu3+ is calculated in terms of the concentration dependent decay curves. The temperature dependent lifetimes of 5D1(Eu3+) are investigated to calculate the radiative transition rate of 5D1 → 7FJ and the multiphonon relaxation rate of 5D1 → 5D0. Cross relaxation rates among Eu3+ ions for different Eu3+-doped samples are also calculated based on the concentration and temperature dependent decay curves. It is found that the cross relaxation rates are sensitive to the Eu3+ concentration in Ca4Gd(BO3)3O.