Optical and holographic properties of Bi4Ge3O12 crystals doped with ruthenium

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.     

Synthesis of a bismuth germanium oxide source material for Bi4Ge3O12 crystal growth

A technique has been developed for the preparation of a modified source material for the crystal growth of bismuth orthogermanate, Bi₄Ge₃O₁₂ (BGO). It includes dispersion of molten bismuth through mixing with germanium oxide (GeO₂) powder in a rotating reactor, followed by oxidation with oxygen. The source material thus prepared contains, in addition to bismuth and germanium oxides, considerable proportions of germanates (Bi₂GeO₅, Bi₄Ge₃O₁₂, and Bi₁₂GeO₂₀), which improve the reactivity of the components of the source material during homogenization before the crystal growth process. After sintering at 880°C, the density of the modified source material (3.9 g/cm³) is a factor of 1.5 higher than that of a source material prepared from Bi₂O₃ and GeO₂ powders. BGO crystals grown using the synthesized source material possess good scintillation characteristics.     

Temperature dependence of Bi4Ge3O12 photoluminescence spectra

Bi₄Ge₃O₁₂ single crystals were obtained using Czochralski growth method. Photoluminescence spectra were analyzed versus temperature from 12 to 295 K. Besides the previously observed emission bands at 610 and 820 nm, the new emission band at 475 nm was found by a careful temperature dependence measurement in the present study. The influence of basic and defect structure on the shape and position of the spectra versus temperature was discussed.     

Optical effects caused by high laser powers in ion-implanted Bi4Ge3O12 waveguides

Abstract

The ‘optical writing’ of permanent channel waveguides in the surface of He⁺ ion-implanted bismuth germanate, Bi₄Ge₃O₁₂, has been studied, using end-coupled argon and Ti:sapphire CW laser beams. Comparisons of the self-focusing effect in waveguides and bulk samples have been made for both Nd³⁺ doped and undoped material. The permanent ‘writing’ effect has been compared with the structural change observed earlier in ion-implanted Bi₄Ge₃O₁₂ waveguides annealed at high temperature.     

Electro-mechanical behaviour of single domain single crystals of bismuth titanate (Bi4Ti3O12)

The piezoelectric constantsd ₁₁,d ₂₂ andd ₃₃ for a single domain single crystal of Bi₄Ti₃O₁₂ have been measured at room temperature using appropriate crystal cuts on a Berlincourtd ₃₃ meter. From the known temperature dependence of the spontaneous polarization, lattice strain and dielectric permittivity, the equivalent piezoelectric constants have been calculated assuming a simple proper ferroelectric in which,P _s, is the order parameter. Constants in the plane of the perovskite-like sheets in the Bi₄Ti₃O₁₂ structure (d ₁₁,d ₂₂) show good agreement with experimental values. The calculated value of the constantd ₃₃ is more than an order of magnitude larger than the experimentally-measured value and gives clear indication of the indirect coupling to the strain in the tetrad axial direction and the need for a more sophisticated phenomenology.     

Effect of High Gamma Doses on the Scintillation and Optical Properties of Bi4Ge3O12 Crystals

Inorganic Materials - We have studied the influence of high gamma doses and dose rates on the light output of bismuth orthogermanate (Bi4Ge3O12) crystals. The results demonstrate that the change in...     

Alteration of amorphous Bi4Ge3O12 by Tl2O and Na2O

Ternary thallium and sodium bismuth germanate glasses were prepared and their densities refractive indices, and infra-red spectra obtained. The effect of univalent cations on the stability of the arrangement of decoupled GeO₄ tetrahedra in amorphous Bi₄Ge₃O₁₂ was compared with the effect of divalent cations. The molar volumes of glasses with the nominal mol% composition 20 M₂O(MO).20 Bi₂O₃.60 GeO₂ are directly related to the size and charge type of M^z+. However, the molar volumes of such glasses are inversely related to the ionic potential (z/r) of M^z+. The infra-red spectra of these ternary glasses exhibitv _Ge?O shifts that reflect the presence of both isolated and small clusters of GeO₄ tetrahedra compared to amorphous Bi₄Ge₃O₁₂. This slight increase in the degree of polymerization appears to be directly related to the ionic potential of M^z+.     

Doping effect on the optical, electro-optic, and photoconductive properties of Bi12MO20 (M = Ge, Si, Ti)

The doping effect on the optical, electro-optic, and photoconductive properties of Czochralski-grown Bi₁₂MO₂₀ (M = Ge, Si, Ti) sillenite-structure single crystals was studied. The dopants were introduced into the growth charge in the form of oxides. Bi₁₂TiO₂₀ crystals were doped with V, Zn, Cu, P, and Nb; and Bi₁₂SiO₂₀ crystals were doped with Cd and Mo. The results indicate that the doping level has a significant effect on the photoconductivity of the Bi₁₂TiO₂₀〈Zn〉, Bi₁₂TiO₂₀〈Cu〉, Bi₁₂SiO₂₀〈Cd〉, and Bi₁₂SiO₂₀〈Bi₂₄CdMoO₄₀〉 crystals, which may exceed that of undoped crystals at low doping levels and may be substantially lower than it, down to zero, at increased dopant concentrations. Niobium doping of bismuth titanate has no effect on its photosensitivity and electro-optic properties. Phosphorus and vanadium enhance the photosensitivity of bismuth titanate over the entire composition range studied but have little effect on its electro-optic coefficient r ₄₁. A slight increase in r ₄₁ was only observed at high vanadium concentrations. The axial impurity distribution in the crystals is shown to be nonuniform, which reflects in their photoresponse: the photoconductivity of the copper-doped crystals near the seed end is 3 times that near the tail end.     

Dielectric properties of bismuth doped CaCu3Ti4O12 ceramics

Ca_1?3x/2Bi_xCu₃Ti₄O₁₂ (x = 0.0–0.3) ceramics were prepared by the conventional solid-state reaction method. X-ray powder diffraction analysis confirmed the formation of cubic CCTO phase except for subtle peaks of CuO. SEM micrographs suggested that the morphologies of doped CCTO ceramics had been sheet-like for high Bi-doping amount, and the dominant grain size decreasing could be seen for the small content of Bi-doping CCTO. Dielectric properties of pure and doped CCTO were investigated in a broad temperature range of 20–420 K. The results showed that bismuth doping could decrease the dielectric loss but suppress the dielectric temperature stability at the same time. Bi doped CCTO ceramics presented different relaxation properties. As to pure CCTO and BCCTO (x = 0.3) only one MW relaxation (Relaxation I) could be found, which moves to higher frequency with temperature increasing. However, two relaxation processes (Relaxation I and II) appear for BCCTO (x = 0.1–0.2). By means of complex impedance spectra analysis and Arrhenius fitting, we successfully separated the different conductive segments and explained the mechanisms of the two relaxation processes. Relaxation I appeared at low temperature could be attributed to the V_O doping energies inside CCTO grains which did not showed significant changing of activation energy after bismuth doping. For Relaxation II at higher temperature than Relaxation I, with activation energy obviously depending on the Bi-ion concentration, may be related with the V_O point defects at the grain boundaries.     

Dielectric properties of Bi4(GeO4)3 and Bi4(SiO4)3

Dielectric constant, dielectric loss and conductivity of Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ single crystals have been measured as a function of frequency and in the temperature range from liquid nitrogen temperature to 400° C. The values of the static dielectric constant at room temperature are 16·4 and 13·7 for Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ respectively. The plots of log (σ) against reciprocal temperature at different frequencies of these crystals merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0·95 eV and 1·2 eV for Bi₄(GeO₄)₃ and Bi₄(SiO₄)₃ respectively.     

Optical study of Mn-doped Bi4Ti3O,12 thin films by spectroscopic ellipsometry

Mn-doped Bi4Ti3O12(B4T3) thin films grown at 400 degrees C on a Pt/Ti/SiO2/Si substrate through pulsed laser deposition (PLD) were analyzed via spectroscopic ellipsometry (SE). The PLD targets were produced through the conventional solid-state sintering method, and the film samples were annealed at 600 degrees C. The SE spectra of B4T3 films were measured using a rotating analyzer type ellipsometer within the 1.12 to 6.52 eV energy range, with the various incidence angles. The optical properties of the B4T3 films with increasing Mn-mol concentration were extracted using a multilayer model for the whole structure and the Tauc-Lorentz (TL) dispersion relation for the B4T3 film layer. The analysis results clearly showed that the significant changes in optical properties of B4T3 films are caused by thermal annealing procedure and the Mn-mol concentrations. X-ray diffraction (XRD) measurement was also performed to confirm the results of SE analysis.     

Phonon spectra of eulytite crystals Bi4M3O12 (M = Ge,Si): ab initio study

In this paper we present the results of ab initio DFT calculation of phonon spectra for bismuth ortho-germanate Bi₄Ge₃O₁₂ and bismuth ortho-silicate Bi₄Si₃O₁₂ crystals, in the center of the first Brillouin zone. First, the geometry optimization was performed using the analytical energy gradients, with respect to atomic coordinates and unit cell parameters. Vibrational frequencies and normal modes were calculated within the harmonic approximation by diagonalizing the mass-weighted Hessian matrix. The IR and Raman spectra of both crystals were simulated with the periodic ab initio Crystal 09 code and B3LYP hybrid functional and the two sets of Transverse-Optical and Longitudinal-Optical frequencies are generated, together with their intensities. Also, the influence of isotopic substitution for Bi, Ge and O in phonon modes and the picture with values of frequencies shift in each mode by isotopic substitution were calculated. The obtained results are discussed and the comparision between the computed spectra and experimental data is quite satisfactory, which justifies the model and simulation scheme used for the title systems.     

Planar optical waveguides in Bi4Ge3O12 crystal fabricated by swift heavy-ion irradiation

We report on the fabrication of the planar waveguides in Bi4Ge3O12 crystal by using 17 MeV C5+ or O5+ ions at a fluence of 2×10(14) ions/cm2. The reconstructed refractive index profiles of the waveguides produced by either C5+ or O5+ irradiation are the "well" + "barrier" pattern distribution. The two-dimensional modal profiles of the planar waveguides, measured by using the end-coupling arrangement, are in good agreement with the simulated modal distributions. After thermal annealing treatment at 260 °C for 30 min, the propagation loss for C5+ and O5+ irradiated waveguides could be reduced down to ~1.1 and ~4.8 dB/cm, respectively, which exhibit acceptable guiding qualities for potential applications in integrated optics.     

Molten salt synthesis and luminescence properties of Bi4Si3O12 powders

In this paper, Bismuth silicate (Bi₄Si₃O₁₂, BSO) powders were prepared by reaction in molten salts (NaCl and KCl) using Bi₂O₃ and SiO₂ powders as raw materials. The effects of salt contents and excessive contents of Bi₂O₃ and SiO₂ were characterized by X-ray diffraction and scanning electron microscopy. The properties of Bi₄Si₃O₁₂ powders were analyzed via fluorescence spectroscopy. Forming mechanism of platelets was discussed. The experimental results suggest that Bi₄Si₃O₁₂ powders are produced at 780 °C for 4 h with 40 wt% salts and 5 wt% excessive content of Bi₂O₃. The peaks of excitation spectrum and emission spectrum for BSO powders are separately located at 266 and 457.6 nm. Compared with crystal materials, the excitation spectrum and emission spectrum of Bi₄Si₃O₁₂ powders indicate blue shift. Interface reacting mechanism can be used to explain the coarsening process of bismuth silicate platelets produced in molten salt synthesis. In addition, dissolution–precipitation mechanism also plays an important role in the synthesis of bismuth silicate platelets.     

Optical properties of Bi12SiO20 (BSO) and Bi12TiO20 (BTO) obtained by mechanical alloying

Mechanical alloying has been used successfully to produce nanocrystalline powders of BTO and BSO. The milled BTO and BSO were studied by x-ray powder diffraction, DTA, infrared and Raman scattering spectroscopy. After 7 hours of milling the formation of BTO and BSO was confirmed by x-ray powder diffraction. The infrared and Raman scattering spectroscopy results suggest that the increase of the milling time lead to the formation of ferroelectric BTO and BSO, as seen by x-ray diffraction analysis. These materials are attractive for various electro-optical devices, including optical data processing. They present a number of attractive features as reversible recording materials for real-time holography and image processing applications. This milling process presents the advantage, that melting is not necessary, and the powder obtained is nanocrystalline with extraordinary mechanical properties. The material, can be compacted and transformed in solid piezoelectric ceramic samples. The high efficiency of the process, opens a way to produce commercial amount of nanocrystalline piezoelectric powders. Due to the nanocrystalline character of this powder, their mechanical properties have changed and for this reason a pressure of 1 GPa is enough to shape the sample into any geometry.