I. Földvári

Spectroscopic and electrical conductivity investigation of Mg doped LiNbO3 single crystals

Abstract Series of Mg doped congruent LiNbO3 crystals were investigated by UV a nd IR spectrophotometry and AC conductivity. The position of the UV absorption edge, the shape of the absorption band of the OH- vibration and the value of the electrical conductivity at 400°C changed monotonously up to a critical concentration of Mg ions. Above the concentration of about 4.5×10-2 mol/mol Mg in the crystal anomalous behaviour was observed. We conclude that the mechanism of the incorporation of Mg ions changes at this concentration.

Growth and properties of Bi2TeO5 single crystals

The authors report the successful growth of Bi2TeO5 single crystals by the Czochralski method. This crystal is a new prospective piezoelectric material. Boules as large as 25 mm diameter and 50 mm length were grown, providing pale yellow, optically transparent specimens suitable for indepth physical investigations.

Investigation of the photorefractive effect in Bi2TeO5

Single crystals of Bi2TeO5, both undoped and doped with transition‐metal‐ion dopants, were grown with high optical quality. Continuous‐wave four‐wave‐mixing experiments on these crystals show a strong photorefractive signal with a multicomponent decay. The photorefractive efficiency was studied as a function of the wavelength, intensity, polarization direction, and crossing angle of the laser write beams, and the sample orientation. Both absorption and phase gratings were observed with their relative strengths dependent on the laser wavelength and sample dopants. The signal evolves in time from a defect population grating, to trapped charge gratings involving two different types of traps, to fixed gratings produced by oxygen ion displacements. The photorefractive effect in this material is found to be of the photoconductive type and it produces a larger diffraction efficiency than that observed in sillenite materials under the same experimental conditions. A mechanism is proposed for the various physical ...

Improvement of the quality of ZnWO4 single crystals for scintillation applications

Abstract ZnWO 4 is a prospective high-Z number scintillator material whose application is limited by its colour and mechanical properties. Single crystals were grown by the Czochralski technique from raw materials with various impurity and dopant contents. The origin of the crystal colour is discussed. Correlation between the crystal colour and the scintillation output is shown. Methods are suggested to eliminate crystal defects and coloration.

The role of impurities in the quality of paratellurite single crystals

Abstract Paratellurite crystals grown by the Czochralski technique often contain Pt inclusions unless extrapure source material is used. Using analytical data obtained on comparable uniform paratellurite crystal samples we have shown that there is a joint incorporation of Pt and the added Fe. In the absence of Fe in the melt no incorporation of Pt occurs. The undesirable interactions of Pt inclusions with dislocations are pointed out.

The low-temperature photochromic response of bismuth germanium oxide

Exposing the photorefractive bismuth germanium oxide (BGO) at low temperatures to 2.5–3.3 eV light produces photochromic absorption bands. In both undoped and Fe‐doped material the absorption consists of overlapping bands at 1.5, 2.2, 2.7, and 3.1 eV. The 1.5‐ and 2.2‐eV components are relatively weaker in Fe‐doped BGO. In undoped BGO the photochromic bands anneal together above 200 K. Doping with iron adds an anneal stage in the 110–200 K range that matches the recovery of Fe3+. Optical bleaching with 1.5‐eV light was much less efficient than with visible band light. Thus, the 1.5‐eV photochromic band may be an internal transition of the center responsible for the 2.2‐eV band. In BGO:Al the aluminum electronically compensates the deep donor center responsible for the yellow coloration observed in undoped crystals. Photoexcitation at 9 K produces overlapping absorption bands at 1, 1.38, and 2.45 eV. All three bands have major anneal stage in the 80–100 K range. They also bleach out together when the sampl...

Spectroscopic properties of ZnWO4:Fe single crystals

Abstract The incorporation and charge of iron in ZnWO4:Fecrystals were investigated by absorption spectrometry. The UV bands at 350 nm and the visible band at 460 nm have been found to be related to Fe3+ and Fe2+ ions respectively. Both ions are mainly in substitutional Zn positions. The infrared absorption at 3445 cm−1 is related to Fe3+ OH complexes. The OH− ions compensating the excess charge of Fe3+ are probably situated in interstitial positions.

Spectroscopic investigation and crystal field modelling of Dy3+ and Er3+ energy levels in yttrium aluminium borate (YAB) single crystals

High resolution (0.04 cm−1) absorption spectra of Dy3+-doped YAl3(BO3)4 (YAB) single crystals were measured by Fourier transform spectroscopy in the spectral (2000–23 000 cm−1) and temperature (9–300 K) ranges. Samples with nominal 1 and 4% Dy/Y molar ratios were studied. Dy3+ transitions from the 6H15/2 ground state to the 6H13/2, 6H11/2, 6H9/2+ 6F11/2, 6H7/2+ 6F9/2, 6H5/2, 6F7/2, 6F5/2, 6F3/2, and 4F9/2 excited states were analysed. A small (~3.3 cm−1) splitting between the first two sublevels of the 6H15/2 ground manifold was detected. The experimentally determined energy levels were fitted with a single-ion Hamiltonian and the crystal-field parameters were obtained. The same procedure was applied to analyse the previously published high resolution spectra of YAB:Er3+, leading to a reliable unified picture for the two dopants.

Photorefractive effects in Bi2TeO5 single crystals

Bismuth tellurium oxide (Bi2TeO5) is a new material expected to exhibit nonlinear properties because of its noncentrosymmetric crystal structure. A conventional crossed cw laser beam technique has been used to write photorefractive gratings in this material. Typical dark decay times of the gratings are 10 seconds. In addition to the usual build-up and decay of these gratings transient effects and oscillation of the photorefractive efficiency were also observed.

Crystal growth and stoichiometry of LiNbO3 prepared by the flux method

The high temperature top seeded solution growth technique (HTTSSG) is the leading candidate to grow stoichiometric lithium niobate single crystals. The effect of the growth conditions on the crystal perfection prepared by the HTTSSG from potassium containing flux was investigated. Various flux compositions were tested to assign the limits of the preparation of stoichiometric crystals. It was shown that the key parameter is the crystallization temperatures and that it should be below 1160 °C to obtain stoichiometric crystals with homogeneous composition.