Luminescent properties of Eu2+ and Ce3+ 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.