Browsing by Author "Gospodinov, M"

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Light-induced properties of doped Bi4Ge3O12 single crystals
(2003)
Marinova, V
;
Lin, SH
;
Gospodinov, M
;
Hsu, KY
;
光電工程學系
Optically homogeneous bismuth germanate Bi4Ge3O12 single crystals doped with vanadium, cobalt and vanadium plus cobalt have been successfully grown by Czohralski technique with automatically diameter-weight control. The distribution coefficients for individual doping elements are determined. The effect of doping on the light-induced properties of BGO single crystals is studied. Optical absorption spectrum of annealed samples can be strongly modified under ultraviolet illumination. The photochromic effect is optically or thermally reversible from one state to another. Volt-amper charactersitcs show linear behavour and dark conductivity values are sigma similar to 10(-13) (Omega.cm)(-1). Holographic grating were successfully recorded in all investigated doped crystals at 514 nm.
Light-induced properties of Ru-doped Bi12TiO20 crystals
(2003-11-01)
Marinova, V
;
Lin, SH
;
Sainov, V
;
Gospodinov, M
;
Hsu, KY
Absorption, light-induced absorption, photoconductivity and dark conductivity measurements are performed on Bi12TiO20 (BTO) crystals doped with different concentrations of ruthenium. It is found that a higher ruthenium addition shifts the optical absorption to the near-IR spectral region in comparison with non-doped BTO crystals and the absorption changes increase with increasing Ru content. The dark conductivity follows the Arrhenius law with an activation energy of 0.89 eV. From the measured light-induced absorption and nonlinear photoconductivity the participation of a shallow level in the charge transport mechanism in Ru-doped BTO crystals is suggested. Highly Ru-doped BTO samples possess infrared sensitivity and holographic gratings are successfully recorded at 790 and 825 nm, respectively.