The concentration quenching and crystallographic sites of Eu²⁺ in Ca₂BO₃Cl

A yellow phosphor, Ca₂BO₃Cl:Eu²⁺, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f,⁶5d¹→4f,⁷ transition of Eu²⁺. Eu²⁺ ions occupy two types of Ca²⁺ sites in the Ca₂BO₃Cl lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu²⁺ in Ca₂BO₃Cl. The emission intensity of Eu²⁺ in Ca₂BO₃Cl is influenced by the Eu²⁺ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole-dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.