Luminescence properties of Eu2+ and Ce3+ ions in calcium lithio-germanate Li2CaGeO4

The Eu2+-doped Li2CaGeO4 samples have been prepared by the solid state reaction method and by thermolysis of the complex precursor. It was shown that Eu2+ ions in Li2CaGeO4 exhibit an intense emission with a maximum at 473 nm. The Stokes shift (820 cm−1) and full-width at half-maximum (1415 cm−1) of the emission band are close to those of the Eu2+ emission in Li2CaSiO4. Values of the crystal field splitting and the centroid shift of the Ce3+ 5d configuration in Li2CaGeO4 were also determined and compared with those of Ce3+ ions in Li2CaSiO4. Although the spectral positions of the Ce3+ lowest excitation band for Li2CaRO4 (R=Si, Ge) are practically the same, the magnitudes of the Ce3+ crystal field splitting appeared to be unexpectedly very different. This effect is tentatively attributed to a strong distortion of the calcium site in Li2CaSiO4 caused by the presence of the trivalent lanthanide ion.