Spectroscopic properties of Cr-doped melilite crystals

Four kinds of Cr-droped melilite crystals, Ca2MgSi2O7 (akermanite), CaAl2SiO7 (gehlenite), CaGa2SiO7 (Ga-ghlenite) and CaGa2GeO7 (GaGe-gehlenite). with different sizes of the sites for Cr ions to substitute, were grown in series, using both the CZ and FZ techniques. Although Cr++ is regarded as a major species in melilites. the existence of Cr6+ in gehlenite is also suggested from the change in absorption spectra by annealing, and the dependence of distribution coefficient of Cr ions on growth atmosphere. Spectral peak shifts are not obvious if the host crystal field is altered in melilites, because the local environment of the sites for Cr ion is possibly changed by reforming the packing features of the host lattice.