Trapping of electrons by H⁺ in the X-ray storage phosphor Ba₃(PO₄)₂:Eu²⁺, La³⁺

When co-doped with La³⁺, Ba₃(PO₄)₂:Eu²⁺ shows an intense thermally stimulated luminescence after X-ray irradiation. The phosphor is also optically stimulable. The stimulated emission is due to the Eu²⁺ ion. In the absence of Eu²⁺ a broad emission band is observed which is tentatively ascribed to a phosphate group close to the La³⁺ ion. EPR reveals the presence of H⁰ after irradiation. It is concluded that the substitution of La³⁺ on a Ba²⁺ site is accompanied by the introduction of H⁺ into the lattice. The latter ion acts as an electron trap; detrapping yields the stimulated luminescence.