OPTICAL-SPECTRA OF SYNTHETIC SPINELS IN THE SYSTEM MGAL2O4-MGCR2O4

Unpolarized optical spectra were measured in the wavelength range 322- 1666 nm by the diffuse reflection technique from spinel powders synthe sized in the system MgAl2O4-MgCr2O4. The spectra were interpreted by t he crystal-field theory on the basis of trigonally distorted spinel oc tahedra with D-3d symmetry. For chromium-rich solid solutions, includi ng the MgCr2O4 end-member, results after peak fittings showed octahedr al D-3d local symmetry around Cr3+ ions, identical to the crystallogra phic site symmetry. For chromium-poor solid solutions, ho Never, octah edral C-3v local symmetry was suggested around Cr3+ ions, different fr om the D-3d crystallographically expected.