Luminescent properties of Eu and Ce ions in strontium litho-silicate Li2SrSiO4

The luminescent properties of Eu²⁺ and Ce³⁺ ions in Li₂SrSiO₄ have been studied upon excitation in the 2-20 eV region. Based on the results of luminescent measurements, values of the crystal field splitting and the centroid shift of the Ce³⁺5d configuration in Li₂SrSiO₄ were found and compared with those of Ce³⁺ ions in some other inorganic compounds. The Eu²⁺ ions in Li₂SrSiO₄ exhibit a broad band emission with a maximum at 576 nm, which is due to the 4f⁶5d→4f⁷ transition. It was shown that the long-wavelength position of the Eu²⁺ emission in Li₂SrSiO₄ is caused by the large crystal-field splitting of the Eu²⁺ 4f⁶5d configuration and relatively high degree of covalency of the Eu-O bond. The stabilization of Eu²⁺ ions in Li₂SrSiO₄ during the synthesis process requires a strong reducing agent. Two phenomenological approaches to explain the low stability of Eu²⁺ in Li₂SrSiO₄ are also discussed.