Bi12SiO20 Single Crystals Research Articles

Characterization of Bi12SiO20 single crystal: understanding structural and thermal properties

Characterization of Bi12SiO20 single crystal: understanding structural and thermal properties

Thermally induced effects on optical absorption in Ag-doped Bi12SiO20 single crystals

The spectral-temperature dependences of optical absorption of Bi12SiO20 crystals doped with Ag ions were measured in the visible range of photon energy hν. The temperature of the samples was varied in heating-cooling cycles in the interval T = 280 – 680 K. It was shown that the spectra fulfilled Urbach rule for hν > 2.1 eV at the forbidden zone width of 3.3 eV. The Urbach rule parameters, calculated within the frame of the electron-phonon interaction model, showed anomalous behavior in the interval T = 389 – 500 K. The observed peaks in the temperature dependences of optical absorption were attributed to the competition of thermally induced processes of color centers formation and destruction. The color centers were assumed in the form of Ag2+ – 2O- and Ag+ – O- complexes that are created due to thermal activation energy Ea1 = 0.1 eV and Ea2 = 0.145 eV, respectively. The spectrum of thermochromic effect characterizing non-reversible thermally induced weakening of optical absorption was detected and analyzed.

Excitation wavelength dependent nonlinear absorption mechanisms and optical limiting properties of Bi12SiO20 single crystal

Nonlinear absorption mechanisms (NA), excitation wavelength dependence, and defect states of Bi12SiO20 (BSO) single crystal were investigated. The band gap and Urbach energies were found to be 2.51 and 0.4 eV from the absorption spectra. To evaluate the effect of excitation energy on the NA mechanism of the BSO single crystal, open aperture Z-scan experiment with 4 ns laser pulse at 532 and 1064 nm wavelengths with different intensities was performed. Obtained data were analyzed with a theoretical model considering the contributions of one photon absorption (OPA), two photon absorption (TPA) and free carrier absorption (FCA) to NA. The results indicated that the NA behavior decreased with increasing of the pump intensity as the defect states at around 2.32 eV by OPA at 532 nm, and TPA at 1064 nm excitations. The dominant NA mechanisms are OPA and sequential TPA at 532 nm as compared to the 1064 nm. A higher NA coefficient was obtained at 532 nm as compared to 1064 nm excitation. This observation was attributed to higher contribution of OPA at 532 nm even at lower input intensities compared to TPA contribution at 1064 nm. Onset optical limiting thresholds were found as 0.34 and 0.68 mJ/cm2 for 532 and 1064 nm input beams, respectively. In the light of the results, the BSO single crystal may be used as a saturable absorber or an optical limiter at convenient input intensity by effectively adjusting defect states and excitation wavelength.

Effect of Laser Heating on Partial Decomposition of Bi12SiO20 (BSO) Single Crystal: Raman Study

The effect of laser (532 nm line of Verdi G) heating during the Raman measurements, on partial decomposition of Bi12SiO20 single crystal, was addressed in this study. The degree of decomposition directly depends on the power density and duration of the laser treatment, which are registered by the phonon Raman spectra. After laser treatment, AFM measurements register additional small spherical islands on the surface. Analysis performed on irradiated and unirradiated samples showed significant changes in transmission spectra, X-ray diffraction (XRD) pattern, Verdet constant, magneto-optical property, and absorption coefficient. The material obtained after laser irradiation can be described as specific nanocomposite consisting of bismuth oxide and silicon oxide-based nano-objects (dimensions below 15 nm in diameter), which are arranged in a matrix of Bi12SiO20.

Structural properties of femtosecond laser irradiation induced bismuth oxide based nano-objects in Bi12SiO20 (BSO) single crystal

Structural properties of femtosecond laser irradiation induced bismuth oxide based nano-objects in Bi12SiO20 (BSO) single crystal

Thermally induced effects in the optical absorption of pure and doped Bi12SiO20 single crystals

Thermally induced effects in the optical absorption of pure and doped Bi12SiO20 single crystals

Linear and nonlinear optical characteristics of Bi12SiO20 single crystals

Bi12SiO20 single crystals grown by Czochralski method were optically investigated in detail in the present paper. Transmission and reflection measurements were performed at room temperature in the 400–800 nm spectral range on the (111) plane. Linear and nonlinear optical characteristics of the Bi12SiO20 crystal were determined analyzing the transmission and reflection spectra. The spectral dependencies of absorption coefficient, skin depth, refractive index, optical and electrical conductivities, real and imaginary parts of dielectric function were plotted. Analyses of optical parameters presented the direct band gap and Urbach energies as 2.55 and 0.33 eV, respectively. Static refractive index and dielectric constant, oscillator strength, dispersion and single oscillator energies, nonlinear refractive index, first- and third-order nonlinear susceptibilities were revealed. Structural properties of the Bi12SiO20 crystal were investigated by x-ray diffraction and scanning electron microscopy measurements.

Investigation of defect levels in Bi12SiO20 single crystals by thermally stimulated current measurements

Bi12SiO20 (BSO) single crystal belongs to the sillenite semiconducting family known as defective compounds. The present paper investigates the defect centers in BSO grown by Czochralski method by means of thermally stimulated current (TSC) measurements performed in the 10–260 K range. The TSC glow curve obtained at heating rate of β = 0.1 K s−1 presented several peaks associated with intrinsic defect centers. The activation energies of defect centers were revealed as 0.09, 0.15, 0.18, 0.22, 0.34, 0.70 and 0.82 eV accomplishing the curve fit analyses method. The peak maximum temperatures and orders of kinetics of each deconvoluted peak were also determined as an outcome of fitting process. TSC experiments were expanded by making the measurements at various heating rates between 0.1 and 0.3 K s−1 to get information about the heating rate dependent peak parameters.

Evaluation of mechanical properties of Bi12SiO20 sillenite using first principles and nanoindentation

ABSTRACT The mechanical and anisotropic elastic properties of Bi12SiO20 (BSO) were investigated using density functional theory (DFT) calculations and nanoindentation. The calculated and experimentally observed XRD patterns of the compound were reported and the crystal structure of the BSO was determined to be cubic with the lattice constant of a = 1.025 nm. The second-order elastic constants and related polycrystalline elastic moduli (e.g. shear modulus, Young’s modulus, Poisson’s ratio, linear compressibility and hardness) were calculated. The calculated elastic constants indicated that BSO is mechanically stable and exhibits anisotropic characteristics. Moreover, the directional dependencies of sound wave velocities were investigated in three dimensions. Pressure-dependent bulk modulus was plotted at temperatures between 0 and 800 K. Hardness and Young’s modulus were also determined by performing nanoindentation experiments on (222) and (631) planes of the BSO single crystal. The analyses of the experimental nanoindentation data resulted in hardness and Young’s modulus values of 7.2 and 97.0 GPa, respectively. The results of DFT and nanoindentation were discussed throughout the paper. The results of the present paper would provide valuable information on the mechanical behaviours of the BSO for the optoelectronic device applications.

Optical characteristics of Bi12SiO20 single crystals by spectroscopic ellipsometry

Structural and optical characteristics of Bi12SiO20 single crystal grown by the Czochralski method were investigated by virtue of X-ray diffraction (XRD) and spectroscopic ellipsometry measurements. XRD analysis indicated that the studied crystal possesses cubic structure with lattice parameters of a = 1.0107 nm. Spectral dependencies of several optical parameters like complex dielectric constant, refractive index, extinction and absorption coefficients were determined using ellipsometry experiments performed in the energy region of 1.2–6.2 eV. The energy band gap of Bi12SiO20 crystals was found to be 3.25 eV by utilizing absorption coefficient analysis. Moreover, critical point energies were calculated as 3.54, 4.02, 4.82 and 5.58 eV from analyses of the second energy derivative spectra of the complex dielectric constant.

Photodielectric Effect in Bi12SiO20 Sillenite Crystals

The results of studies of the effect of illumination on the frequency dependence of the electrical parameters of bismuth silicate Bi12SiO20 single crystals are presented. Illumination in the visible spectral region induces a change in the dielectric parameters (the photodielectric effect) and the manifestation of photoconductivity in the low-frequency region under study. The hopping character of conduction in the dark and upon excitation with light is established. The possible mechanisms of the photodielectric effect and charge transport in the crystals are discussed.

Temperature-dependent band gap characteristics of Bi12SiO20 single crystals

Bi12SiO20 single crystals have attracted interest due to their remarkable photorefractive characteristics. Since bandgap and refractive index are related theoretically to each other, it takes much attention to investigate temperature dependency of bandgap energy to understand the behavior of photorefractive crystals. The present study aims at investigating structural and optical characteristics of photorefractive Bi12SiO20 single crystals grown by the Czochralski method. The structural characterization methods indicated that atomic composition ratios of constituent elements were well-matched with the chemical compound Bi12SiO20, and grown crystals have a cubic crystalline structure. Optical properties of crystals were investigated by room temperature Raman spectroscopy and temperature-dependent transmission measurements between 10 and 300 K. The analyses of transmittance spectra by absorption coefficient and derivative spectrophotometry techniques resulted in energy bandgaps decreasing from 2.61 to 2.48 eV and 2.64 to 2.53 eV as temperature was increased from 10 to 300 K. The Varshni model was applied to analyze temperature-bandgap energy dependency.

Influence of light on the magnetoelectric effect in Fe-doped Bi12SiO20

We report an extraordinary oxidation state of iron in the Fe-doped Bi12SiO20 single crystal. Magnetoelectric effect and changes of this effect under illumination of the sample were investigated in magnetic fields up to 32 T. Moreover, an absorption line and its shift to higher energy caused by magnetic field (the Zeeman effect) were seen in the optical measurements. Obtained results show that the iron dopant is in unexpected, +4 oxidation state and it changes to +5 after illumination with blue light.

Impedance spectra of doped bismuth silicate Bi12SiO20: Ge crystals

The specific features of the behavior of the impedance spectra of germanium-doped Bi12SiO20 single crystals with the sillenite structure have been studied. It has been found that the obtained dependences exhibit a dispersion corresponding to the distribution of the relaxation times. An analysis of the experimental data performed by the graphical-analytic method has made it possible to separate the contributions to the conductivity due to the crystal bulk and the sample-electrode interface. The role played by the impurity factor and lone electron pairs of trivalent bismuth ions in the formation of the defect structure of the crystal has been demonstrated.

Raman spectroscopy of bismuth silicon oxide single crystals grown by the Czochralski technique

In this work, single crystals of bismuth silicon oxide (BSO; Bi12SiO20) have been grown by the Czochralski method. The growth conditions were studied. The critical diameter and the critical rate of rotation were calculated. Suitable polishing and etching solutions were determined. The structure of the Bi12SiO20 has been investigated by x-ray diffraction (XRD), and Raman and Fourier transform infrared spectroscopy (FTIR) spectroscopy. The results obtained are discussed and compared with the published data. The pale yellow Bi12SiO20 single crystals prepared were without cores. Using spectroscopic measurements 19 Raman and 5 IR modes were observed.

Synthesis of Bismuth Silicate Powders by Molten Salt Method

The bismuth silicate powders were prepared by reaction of Bi2O3 and SiO2 as raw materials in KCl-K2CO3, NaCl-Na2CO3, K2CO3-Na2CO3, KCl-NaCl, NaCl-Na2SO4, and KCl-K2SO4 molten salts. Pure Bi12SiO20 powders were synthesized in KCl-K2CO3 flux at 635°C for 1 h, which was lower than that of conventional solid state reaction. X-ray diffraction reveals that the phases of the samples are different in various molten salts. Only Bi12SiO20 phase can be observed in the molten salts with ions. However, a mixture of Bi12SiO20, Bi2SiO5, and Bi4Si3O12 phase are observed in the molten salts without ions. Therefore, the carbonates are not only used as the flux and reaction medium, but also inhibit the formation of other bismuth silicates in the synthesis of Bi12SiO20 powders by molten salt synthesis. The scanning electronic microscopy image indicates that the mechanism of molten salt synthesis in the case of KCl-K2CO3 and NaCl-Na2CO3 are “dissolution-precipitation mechanism.” UV-Vis spectra reveals the absorption edge for the sample is shifted to longer wavelengths compared with Bi12SiO20 single crystal, and the band gap energy (Eg) is 2.82 eV.

Growth and characterization of Nd:Bi12SiO20 single crystal

A Nd:Bi12SiO20 crystal was grown by the Czochralski method. The thermal properties of the crystal were systematically studied. The thermal expansion coefficient was measured to be α=11.42×10−6K−1 over the temperature range of 295–775K, and the specific heat and thermal diffusion coefficient were measured to be 0.243Jg−1k−1 and 0.584mm2/s, respectively at 302K. The density was measured to be 9.361g/cm3 by the buoyancy method. The thermal conductivity of Nd:Bi12SiO20 was calculated to be 1.328Wm−1K−1 at room temperature (302K). The refractive index of Nd:Bi12SiO20 was measured at room temperature at eight different wavelengths. The absorption and emission spectra were also measured at room temperature. Continuous-wave (CW) laser output of a Nd:Bi12SiO20 crystal pumped by a laser diode (LD) at 1071.5nm was achieved with an output power of 65mW. To our knowledge, this is the first time LD pumped laser output in this crystal has been obtained. These results show that Nd:Bi12SiO20 can serve as a laser crystal.

Solubility and optical activity of Bi12SiO20 crystals

In this paper the solubility and optical activity of Bi12SiO20 (BSO) single crystals grown in aqueous NaOH under hydrothermal conditions were reported. BSO was found to have a positive solubility coefficient from 350 to 400°C in 0.5–3M NaOH, as well as a positive dependence on mineralizer concentration. The reason why additional SiO2 should be introduced in the mineralizer to grow high quality BSO was analyzed. High quality and colorless BSO crystals were grown using 4M NaOH as a mineralizer and additional 3wt% SiO2 introduced in the mineralizer. Results showed that the optical activity of hydrothermal colorless BSO was superior to that of BSO grown by the Czochralski (Cz) method.

Effect of axial vibration on Bi12SiO20 crystal growth by vertical Bridgman technique

AbstractBi12SiO20 single crystals have been grown successfully by vertical Bridgman technique. During the crystal growth process, different axial vibration amplitudes of 50 μm, 70 μm and 100 μm were applied with the same vibration frequency of 50 Hz. The effect of different axial vibration amplitudes on quality of the as‐grown Bi12SiO20 single crystals was discussed. The crystals have been characterized by X‐ray rocking curve optical and absorption spectrum. The experimental results reveal that the axial vibration amplitude has a pronounced effect on quality of the as‐grown Bi12SiO20 single crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparison of space- and ground-grown Ce: Bi12SiO20 single crystals

Ce doped Bi12SiO20 single crystals were grown either on board of the Chinese Spacecraft-Shenzhou No.3 (SZ-3) or on the ground at the same conditions with the exception of microgravity. The surface morphology of crystals clearly showed significant differences between the space- and ground-grown portions. The space- and ground-grown crystals have been measured by X-ray rocking curve, Ce concentration distribution in growth direction, dislocation density, absorption spectrums. These results show that the compositional homogeneity and structural perfection of Ce doped crystal grown in space are obviously improved.