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The interaction of two counterpropagating light waves on reflection holographic gratings is studied in cubic photorefractive crystals with the natural optical activity. The anisotropy of contributions from intramode (without a change in the refractive index of natural circularly polarised waves) and intermode processes to the interaction of the waves in a bismuth titanate crystal is considered. It is shown that the polarisation dependences of the effective gain and the polarisation vectors of the interacting light beams measured at a wavelength of 633 nm in a (100) cut Bi12TiO20:Fe, Cu crystal of thickness 2.6 mm well agree with numerical calculations with the use of the two-beam coupling constant equal to 6.8 cm-1.

It is shown that the interaction of counterpropagating coherent light beams at a wavelength of 633 nm in a Bi12TiO20:Ca:Ga crystal leads to the formation of a holographic reflection grating, which is a combination of phase and amplitude components related to photoinduced perturbations of the refractive index and absorption coefficient of the crystal. The formation of the grating is accompanied by a photoinduced decrease in the absorption coefficient of light by -0.07 cm-1. Photoinduced bleaching of the crystal occurs when the crystal is exposed to incoherent radiation at 600 nm (= -0.12 cm-1), while an increase in absorption is observed upon irradiation at 570 nm.

The absorption and circular dichroism spectra of Nd-doped Bi12SiO20crystals were measured in the range 10 000 to 20 000 cm–1. The spectra showed electronic transitions related to only one type of Nd-related center: Nd substituting for Bi in position with symmetry C1. The bands due to the transitions from the first Stark component of the ground state to Stark components of excites states (4I9/2→ 4G5/2, 4I9/2→ 2G7/2, and 4I9/2→ 4G7/2) were analyzed in detail. The dipole strength D0k, rotatory power R0k, and anisotropy factor G0kof these transitions were calculated. The intensities of transitions to Stark components were shown to vary by more than one order of magnitude within an excited-state multiplet. The anisotropy factors of the 4I9/2→ 2G7/2and 4I9/2→ 4G7/2transitions, allowed in the magnetic dipole approximation, are, on the average, larger than that of the 4I9/2→ 4G5/2transition, which points to a significant contribution of the magnetic moment (λ<μ>λ2) to the total intensity of the transition.

The results of investigations into the dynamics of the light-induced absorption and of its dark relaxation in a Bi12TiO20: Ca single crystal are presented. To illuminate the crystal and to measure the induced changes in the absorption, narrow-band radiation of an incoherent semiconductor light-emitting diode with the wavelength λ = 660 nm close to that of a helium-neon laser was used. The material parameters of the crystal are estimated based on a comparison of the experimental data with the results of calculations for a theoretical model that takes into consideration doubly ionized donor centers and shallow traps.

Abstract: Raman spectra of a Bi3B5O12 monocrystal are investigated for the first time and compared with the Raman spectra of crystals α-Bi2O3 and Bi12SiO20. The most intensive lines observed in the Raman spectrum of Bi3B5O12 are identified. Promising prospects of use of Bi3B5O12 crystals as SRS converters of radiation are shown.

The absorption and circular dichroism spectra of Bi12SiO20and Bi12TiO20crystals codoped with Mn or Cr and a penta- (P5+), tri- (Ga3+), or divalent (Cu2+) element were studied. The results demonstrate that the sillenite crystals contain Mn and Cr in two oxidation states, 5+ and 4+. The introduction of P5+increases the fractions of Mn4+and Cr4+, while Ga3+and Cu2+have the opposite effect. The bands observed in the spectra are assigned to electronic transitions of [MnO4]4–and [MnO4]3–.

It was earlier found from nuclear quadrupole resonance (NQR) measurements and computer modeling that α-Bi2O3, Bi3O4Br and mixed oxides Bi2O3· 2Al2O3, Bi2O3· 2Ga2O3, Bi2O3· 3GeO2, and 2Bi2O3· 3GeO2exhibit local ordered magnetic fields from 30 to 200 G. It thus follows that these compounds are not diamagnets in a conventional sence of the word. With the aim of revealing previously unknown magnetic properties in bismuth(III) oxide-based Main Group element compounds, the mixed bismuth–boron oxides 2Bi2O3· B2O3, 3Bi2O3· 5B2O3, and Bi2O3· 3B2O3were prepared and studied using 209Bi NQR. The quadrupole interactions of the 209Bi nuclei and their electronic environment were studied, the crystallochemical features of the compounds were discussed, and the conformity of the 209Bi results to the X-ray structure data was verified. The preliminary tests in the field of a permanent magnet showed that the resonance intensities increase in external magnetic fields, indicating that a magnetism of unknown nature develops in the titled compounds. It was found reasonable to continue studies of the magnetic properties of these compounds using single-crystal 209Bi NQR in external magnetic fields.

The experimental data of the past 10–15 years for the vibrational spectra of crystals with the structure of sillenite Bi12MxO20±δobtained by the methods of laser Raman scattering and infrared (IR) absorption are generalized. Correlations between the chemical composition and crystal structure of the compounds (variations of the cation M) and their vibrational spectra are established. It is shown that the main contribution to formation of the high‐frequency part of the spectrum of two‐, three‐, and four‐phonon absorption is given by phonons related to vibrations of the [MO4]n-complexes. On the basis of the analysis of Raman spectra, the effective use of crystals with the structure of sillenite in acousto‐optics is justified.

The optical, photochromic, and photorefractive properties of Ga-doped Bi_12TiO_20 (BTO:Ga) and Bi_12Gax Bi_1–xO_19.5 (BGaO) crystals have been compared. The dispersion of the refractive index of each crystal has been determined in the visible and the near-infrared regions. The static dielectric constant of BGaO is ∊r = 50.4. A photochromic effect that is stable at room temperature has been observed to increase with Ga concentration. Another photochromic effect that is unstable at room temperature has been observed in BTO:Ga and BGaO; the latter photochromic change is independent of the Ga concentration and has been associated with the presence of shallow traps. The photorefractive sensitivity and the photorefractive gain of the crystals decrease with increasing Ga concentration. A model assuming the presence of deep and shallow traps is used to describe qualitatively the writing and the erasure kinetics observed.

Cr-doped Bi12TiO20 (BTO) single crystals have been grown by the Czochralski technique. The optical absorption at 4.2 K of as-grown crystals is compared to that observed after vacuum annealing of the samples. This treatment modifies the visible and near infrared optical absorption. The absorption spectrum of Cr-doped BTO crystals before vacuum annealing is interpreted as the superposition of the crystal-field transition bands of (CrO4)4— and (CrO4)3— and charge transfer bands of (CrO4)3—. Annealing in vacuum leads to Cr5+ → Cr4+ conversion. Chromium reduction to lower oxidation states has not been observed. The optical absorption shows a vibrational character. The energy shifts of Cr4+ bands are as expected from the coupling with the T2(ν3) fundamental mode of (CrO4)4— clusters. On the other hand, it is proposed that the series of sharp lines observed in the 9500 to 11500 cm—1 range arises from the interaction with a vibration of about 300 cm—1, which seems to be the T2(ν4) fundamental mode of (CrO4)3— and with the lattice modes.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.