Browsing by Author "Marinova, V"

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Effect of ruthenium doping on the optical and photorefractive properties of Bi12TiO20 single crystals
(2002-03-15)
Marinova, V
;
Hsieh, ML
;
Lin, SH
;
Hsu, KY
;
電子物理學系
Bi12TiO20 (BTO) single crystals nominally pure and doped with ruthenium are grown by top-seeded solution growth method. The effect of ruthenium concentration on optical and photorefractive properties is studied. Strong influence of doping on these properties is observed. It is shown that optical transmission of crystal samples with higher ruthenium content is shifted to the near IR spectral region, while the absorption coefficient is considerably increased. The optical activity of Ru doped crystals is further reduced in comparison with undoped BTO. Photochromic effect is observed in strongly doped crystal. Photorefractive properties are experimentally investigated using two-beam coupling. Response time and diffraction efficiency are changed with ruthenium content. (C) 2002 Elsevier Science B.V. All rights reserved.
Light-induced absorption of Ru-doped Bi12TiO20 crystals
(2003)
Piquette, S
;
Marinova, V
;
Lin, SH
;
Hsu, KY
;
光電工程學系
The effect of ruthenium doping on optical properties of Bi12TiO20 (BTO) single crystals is studied. A low concentration of ruthenium do not change absorption behavior of BTO, however higher ruthenium addition significantly shifts the optical absorption to the near infrared spectral region with an absorption shoulder appearing around 1.8 eV. The absorption coefficient increases with increasing the Ru concentration. Light-induced absorption changes are observed and the dynamics of build-up and dark decay processes are investigated. Results show that concentration of shallow levels increase with Ru content. Evolution of the build -up and dark decay of light induced absorption consists of fast and slow components: the first process occurs within few seconds, while the second one needs several hours (or days). It is established that light-induced absorption can be modified by preliminary illumination and thermal treatments thus multilevel lead to the transient and persistent parts of light-induced absorption. A model, assuming one deep and two shallow levels is proposed to explain the bi-exponential behavior of the build-up and the dark decay of light- induced absorption when the crystals are preliminary annealed in oxygen atmosphere.
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.
Light-induced properties of ruthenium-doped Bi4Ge3O12 crystals
(2005-12-01)
Marinova, V
;
Lin, SH
;
Hsu, KY
;
電子物理學系
;
光電工程學系
The influence of ruthenium addition at different doping concentrations on the optical properties and holographic behavior of Bi4Ge3O12 crystals is investigated. Doped Bi4Ge3O12 single crystals are grown by using the Czochralski technique. The distribution coefficient of each crystal is measured to determine the concentration of a doped ruthenium element. Holographic experiments are performed. Ruthenium is found to make Bi4Ge3O12 sensitive in the red spectral range. Thermal annealing and ultraviolet exposure have been used to modify the defect structure and corresponding absorption band of each crystal such that the holographic recording has been influenced. The diffraction efficiency increases with increasing of ruthenium content, especially after irradiation by ultraviolet light. (c) 2005 American Institute of Physics.
Near infrared holographic recording in Ru-doped Bi12TiO20 single crystals
(2003)
Marinova, V
;
Lin, SH
;
Hsu, KY
;
光電工程學系
;
Department of Photonics
Bi12TiO20 (BTO) single crystals doped with high concentration of ruthenium are grown by the Top Seeded Solution Growth Method. Ruthenium addition in BTO crystals shifts the optical absorption to the near IR spectral region in comparison with non-doped one. Measurements on light-induced near infrared absorption and temporal behavior of the dark decay are performed. Holographic gratings at 790 nm and 825 nm are recorded and dynamics of photorefractive index grating build-up and readout process are investigated.
Optical and holographic properties of Bi4Ge3O12 crystals doped with ruthenium
(2003-10-01)
Marinova, V
;
Lin, SH
;
Hsu, KY
;
Hsieh, ML
;
Gospodinov, MM
Bi4Ge3O12 single crystals doped with different concentration of Ru were grown by the Czochralski technique. Optical absorption bands were induced by illumination with ultraviolet light at room temperature. The absorption coefficient values increased with increasing ruthenium concentration. The induced photochromic effect was completely reversible: all samples recovered their transparency after thermal treatment. Preliminary holographic recording experiments showed a fast response time and a relatively slow erase time during the reading process. (C) 2003 Kluwer Academic Publishers.
Photorefractive properties and applications of Ru-doped Bi12TiO20 single crystals
(2001)
Marinova, V
;
Hsieh, ML
;
Lin, SH
;
Hsu, KY
;
光電工程學系
Bi12TiO20 single crystals doped with different concentrations of Ru were grown. Optical transmission spectra were measured. Photorefractive properties were experimentally investigated using two-beam coupling. Applications for optical information processing will be investigated.