ABSORPTION-SPECTRA OF ZIRCON CRYSTALS DOPED WITH CR(IV) - ZRSIO4-CR4+

Crystals of ZrSiO4 'doped' with Cr4+ have been prepared from oxide fluxes. The polarized absorption spectra (alpha,sigma,pi) of single crystals have been recorded in the range 6000-25000 cm(-1) at various temperatures from 10 K to room temperature. The polarized absorption spectra present three main wide bands in the regions 9600-14000 (pi), 15 000-19500 (alpha,sigma) and 20500-24000 (alpha,sigma) cm(-1). It is shown that with these spectra only the hypothesis of a replacement of Si4+ with Cr4+ is acceptable. An explanation and assignment of the bands are proposed by considering their polarizations and the site symmetry perturbation related to the distortion T-d --> D-2d of the oxygen coordination. In particular the first band is assigned to the transition (3)A(2)(T-3(1),et(2)) <-- B-3(1) and the next two bands to the transitions (3)E(T-3(1),et(2)) <-- B-3(1) and (3)E(T-3(1),t(2)) <-- B-3(1). This result agrees with a recent investigation on Y3Al5O12:Cr4+.