Luminescence properties of Eu 2+ and Ce 3+ ions in calcium lithio-germanate Li 2 CaGeO 4

Abstract The Eu 2+ -doped Li 2 CaGeO 4 samples have been prepared by the solid state reaction method and by thermolysis of the complex precursor. It was shown that Eu 2+ ions in Li 2 CaGeO 4 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 Eu 2+ emission in Li 2 CaSiO 4 . Values of the crystal field splitting and the centroid shift of the Ce 3+ 5d configuration in Li 2 CaGeO 4 were also determined and compared with those of Ce 3+ ions in Li 2 CaSiO 4 . Although the spectral positions of the Ce 3+ lowest excitation band for Li 2 CaRO 4 (R=Si, Ge) are practically the same, the magnitudes of the Ce 3+ crystal field splitting appeared to be unexpectedly very different. This effect is tentatively attributed to a strong distortion of the calcium site in Li 2 CaSiO 4 caused by the presence of the trivalent lanthanide ion.