OPTICAL-SPECTRA OF DOPED BI12TIO20 CRYSTALS

Single crystals of Bi12TiO20, both 'pure' and doped with various conce ntrations of V, W, Mo, Nd and Cr, have been studied. Absorption spectr a in the energy range 2.0-2.8 eV have been obtained from classical ref lection and transmission measurements. The constant-photocurrent metho d has also been employed in order to study absorption spectra in a wid er energy range (1.3-2.8 eV). A well expressed absorption decrease at energies hv > 2.2 eV has been observed for Bi12TiO20: 0.056 wt% V and Bi12TiO20: 0.013 wt% Mo crystals. Also, a considerable absorption decr ease has been measured at energies hv < 2 eV for Bi12TiO20: 0.056 wt% V and Bi12TiO20: 0.008 wt% W. The origin of some new absorption bands observed in doped Bi12TiO20 crystals as well as some differences in th e effect of impurities on the optical absorption of Bi12TiO20 and Bi12 SiO20 crystals have been discussed.