The most common crystal growth methods for fluorides are reviewed and illustrated by examples of materials that have been the object of a lot of investigations in the past three decades. The attention is focused on the vibrational analysis of A^IM^IIF₃, A₂M^IIF₄, M^IIIF₃ and A^IM^IIIF₄ compounds whose structural arrangement are derived from the perovskite structure. The characteristics of the phonon spectra (measured in particular by inelastic neutron scattering when large single crystals are available) are described together with the parameters of the lattice dynamics models that makes it possible to calculate them. Such results are used to explain the mechanism of structural phase transitions in A^IM^IIF₃, A^IM^IIIF₄ compounds, and to investigate more complex structures such as KFeF₄, the piezoelectric compounds BaM^IIF₄, the laser matrix LiYF₄, mixed fluoride compounds and fluoride glasses. Applications to non destructive measurements of rare earth ions concentration in fluoride glasses and to solid state tunable lasers are also considered.

The overview of the research carried out during the past few years on the synthesis of sillenite structure photorefractive crystals, films and fibers by various techniques is presented. Comparison between different techniques of synthesis of sillenite structure materials is given. The main attention is concentrated on the features of crystallization of sillenite single-crystal fibers at steep temperature gradients by the LHPG method.

A way to interconnect optical fibers in a telecommunication network working between 1.3 and 1.55 micrometer is the use of two-wave mixing mirrors. These devices use the photorefractive effect which can be described as a modification of the refractive index under an electric field created by electric charges photo-induced and then trapped in the material. The index modulation reproduces then the image projected on the material. Due to its high electro-optic factor of merit, about three times higher than the one of III-V semiconductors, and its photosensitivity in the telecommunication wavelength range, CdTe doped with transition elements is very attractive. CdTe crystals dedicated to such devices have to obey severe criteria that are shown to guide their crystal growth. Several effects are discussed, such as solubility, segregation, precipitation, purity, not only related to the transition elements incorporated in CdTe, but also to zinc which is shown to present a specific behavior in photorefractive CdTe. The stoichiometry of the crystals is shown to be a significant parameter as well: from electrical measurements on CdZnTe crystals presenting various V doping levels, an effective segregation coefficient depending on stoichiometry and purity is introduced. The deviation from stoichiometry of CdTe is estimated from lattice parameter measurements. Finally the appropriateness, for the specific application of photorefractivity, of the different techniques of crystal growth classically used for CdTe is discussed.

In common opinion liquid encapsulated Czochralski (LEC) technique is not useful in obtaining of the crystalline ZnSe. In this paper we present the primary results of the ZnSe crystal growth by this technique. The influence of thermal conditions on the crystal growth process and the properties of the ingots were studied. The investigation of physical parameters (Hall measurements, photoluminescence, infrared transmission) showed the high purity level of the obtained material. It indicates that LEC technique can be used for obtaining crystalline ZnSe ingots of large size.

The paper reports on the growth of Cr³⁺:LiCaAlF₆ single crystals by the Czochralski method from a stoichiometric melt of LiF, CaF₂, and AlF₃. (Cr³⁺ doping was obtained by the replacement of about 3 Mol-% AlF₃ by the corresponding quantity CrF₃.) Only the peripheric region and the neck of the crystals have high optical quality, whereas scattering 'needles' of typically 5 multiplied by 5 multiplied by 35 micrometers cubed can be observed in the top region and very small particles very much less than 1 micrometer ('dust') can be observed in the bottom part of the crystals. By EDX element analysis performed after ion beam thinning of the samples the needles were determined to have an excess Ca content in comparison to the LiCaAlF₆ matrix. The binary compound LiAlF₄ has the highest vapor pressure in the ternary system LiF - CaF₂ - AlF₃. It can be concluded, that LiAlF₄ evaporates continuously during crystal growth, leaving in the melt CaF₂ in excess. The incongruently melting compound Ca₂AlF₇ is considered to be the most probable candidate for the observed scattering centers.

Single crystals of SrLaGa₃O₇ doped with 0.5 and 1 at.% praseodymium were grown by the Czochralski technique. A heating system with good thermal insulation and afterheater were applied in order to achieve appropriate radial and axial temperature gradients in the crystallization chamber. Low temperature gradients and flat crystal-melt interface could provide good optical quality crystals free of internal stresses. All single crystals were grown in [001] direction. The pulling rate was 1.5 - 3 mm/h and the rotation rate 50 rpm. The composition and dopant's distribution in crystals were checked by x-ray microprobe. The obtained crystals up to 25 mm in diameter and up to 80 mm in length were of good quality and the dopant's distribution was uniform. The doped crystals were investigated for their spectral an lasing properties. Absorption spectra in range of 180 - 8000 nm were measured, then laser rods were cut out and their generation properties were evaluated.

In this work, the conditions for preparation of raw material as well as the conditions for crystal growth of (gamma) - LiAlO₂ and (beta) -LiGaO₂ by Czochralski method were studied. As a result, single crystals of these compounds were obtained. The phases were checked by x-ray powder diffraction. High vapor pressure of the melt at the pulling temperature was identified as the main problem in the growing process. Preliminary high-resolution x-ray diffraction measurements were made, which indicated a high concentration of small defects in the LiGaO₂ crystals.

The Bridgman-Stockbarger method was used to grow single crystals of LiYF₄. Smaller LiYF₄ crystals can be grown in an induction furnace, whereas the resistance furnace is more useful for bigger crystals growth. The best parameters of crystal growth process were determined. The crystals were investigated by x-ray powder diffraction, the Laue x-ray reflection method and by using polarizing microscope after chemical etching. The best crystals were obtained from the resistance furnace using lowering rate 0.5 mm/h, the temperature gradient 60 degrees Celsius/cm and the c-axis oriented along the crucible.

Borate crystals posses excellent properties such as high damage threshold, high optical quality, high transparency far in the ultraviolet and good chemical stability. They find many applications as non-linear optical (NLO) materials in second harmonic generation (SHG), optical parametric oscillators (OPOs) and self-frequency doubling lasers. Borate anions exist in many structural types what allows to choose an appropriate material for specific applications. Crystal growth of borates by the Czochralski technique and top seeded solution growth (TSSG) has been discussed.

Single crystals of terbium scandium aluminum garnet (TSAG) have been grown for application in optical isolators by the Czochralski technique. The crystals were colorless and highly transparent but contained a strained core due to (211) growth faces. The Verdet constant and optical absorption were measured in the range of 500 - 1400 nm.

Optical grade single crystals of Pb_0.67Cd_0.33F₂ and Pb_1-xCa_xF₂ (x less than 0.05) were grown by the Bridgman technique in graphite crucibles under fluorinating atmosphere of teflon pyrolysis products. For determinations of concentration areas of solid solutions, suitable for crystal growth, the phase interactions in the systems PbF₂ with fluorides of alkaline-earth elements and Cd were studied by DTA and x-ray powder diffraction techniques. Phase diagrams were described by corresponding thermodynamic models. Transition from pure PbF₂ to two- component Pb_0.67Cd_0.33F₂ crystal is accompanied by some increase in radiation hardness of the latter and positive changes of mechanical characteristics (the Pb_0.67Cd_0.33F₂ composition microhardness is 147 plus or minus 5 kg/mm² that is 5 times that of a pure lead fluoride, 28 plus or minus 4 kg/mm²). These solid solutions have a cubic Fm3m fluorite-type lattice as a high-temperature modification of PbF₂.

The GaSb single crystals were grown under the flow of ionized hydrogen atmosphere using the Czochralski method without encapsulant. From the results it seems to be very likely that donors are passivated more than acceptors what was confirmed by the growth of low Te-doped GaSb. The crystals showed p-type conductivity in the whole volume and the free carriers concentration was almost homogeneous from the top to the bottom of the GaSb boule (1.8 - 2.3 multiplied by 10¹⁶ cm^-3). We suppose that an equilibrium between passivated donors and active donors has been established.

A novel, large scale, laboratory zone refiner for purification of organic materials is described. The device can operate in continuous mode and makes it easy to operate the temperature and the passing rate of the molten zones at wide-ranges. At the constant rate of molten zone it can be possible to purify of five different materials. High-purity naphthalene, acenaphthene and fluoranthene were obtained by using this zone refiner.

The results of the self-consistent phonon theory developed by Plakida and Siklos with the generalized form of the Lennard- Jones (n,m) model of interatomic interactions in the lattice of bcc ³He and ideally hcp ⁴He are given. Theoretical values for the pressure and temperature variations of the dynamic and thermodynamic function of strongly anharmonic crystals of helium are compared with experimental data.

The computer simulation method has been applied to study the structure of aqueous solutions of simple ionic salts in the region of very high concentrations. Most of the calculations were performed using different versions of the molecular dynamics method for sodium chloride, lithium chloride and sodium hydroxide solutions. The concentrations ranged from 0.5 M to saturated solutions, in some cases as much as 20 M. The structures of hydration shells of the ions were analyzed using such tools as radial distribution functions, Voronoi tessellations, O'Keeffe coordination numbers, etc. Particularly careful analysis was applied to the topological properties of the ionic structures in solution. Ruff's theory of ionic quasi-lattices in concentrated solutions was investigated for LiCl, NaCl, NaOH and MgCl₂ solutions. The distributions of the number of faces of the Voronoi polyhedra were calculated for the ionic substructures in the configurations produced by the molecular dynamics simulation. The increase of the salt concentration causes evolution of these distributions towards appearance of predominant geometries of the Voronoi polyhedra, what is reflected by the appearance of the peaks at certain numbers of faces of the polyhedra. This provides a proof for existence of the ordered structures of ions in the solution.

A new type apparatus for growth of organic single crystals from solutions by lowering temperature is described. Microcomputer system 'Crystal 01' our design was used to control the rate of temperature lowering and agitation of the crystal and growth solution. At the range of temperature 313 - 298 K practically linear cooling T equals minus 0.0008 t plus 313.02, R² equals 0.9998 with the rate 0.05 K/h was achieved.

We are describing ex situ observation of step bunching on the surfaces of solution grown potassium dihydrogen phosphate (KDP) and sodium chlorate monocrystals. The measurements have been done with the use of atomic force microscope. The use of this equipment allowed us to see directly the structure of macrosteps. Observation confirmed the existence of step pinning which is one of the proposed mechanisms of step bunching. Despite the very high resolution of AFM it was not possible to determine the nature of pinning point. The monatomic steps on KDP and sodium chlorate crystal surfaces are mainly one unit cell high what seems to be the result of the steps pairing. The origin of observed step pattern is discussed in frames of existing theories.

New experimental results concerning the influence of impurities on growth kinetics of KAP and KDP crystals are presented. The above crystals were chosen for these studies because apart from being useful technologically, they are very different one from another in structure and chemical nature. The organic impurities which were used in our experiments differ by chemical class causing different mechanisms of their influence on crystallization. In almost all experiments, however, the increase in crystal growth rate was observed for very low additives concentration, while an analogous decrease was observed for greater impurity concentrations. We call such an effect of increase in the growth rate: catalytic effect, and it was observed for 'tailor-made' additives too. The results are interpreted theoretically in terms of reduction in the edge free energy caused by additive adsorption at the step edge.

The time dependent BCF equation is analytically solved for transient growth conditions occurring just after placing crystal in supersaturated solution. Thus the time dependences of surface concentration and surface supersaturation are found. The obtained results show that the higher bulk supersaturation the sooner the steady state is reached. The characteristic time necessary to reach the steady state, may be shorter or greater than the relaxation time for leaving the surface adsorption layer.

The ultrasonic method for the measurement of the width of the metastable zone has been described. Application of this method for the naphthalene solution in 1,2-dichloroethane that is one of the most useful solvents for growth of single crystals of naphthalene has been discussed.

The rate constant of the diffusion-controlled recombination of ions in large ensembles of nonseparable ion pairs was calculated by means of computer simulation. The computer codes have been constructed to simulate diffusion-type transport and recombination of ions in model supersaturated solutions with different concentrations of ionic solutes and different dielectric constants of the solution. The simulations yielded the rate constant of the ion recombination as a function of the ion concentration. The calculated rates are compared with the theoretical Debye-Smoluchowski-type rate constant k_DS derived for isolated ion pairs and the Smoluchowski rate constant k_s for neutral reactants. It appears that the rate constant does not decrease with the increase of concentration, even in the range of 1 M solutions. The rate constants, for wide range of the dielectric permittivity, are slightly higher than the k_DS rate constant. A similar result has been obtained when the Jaffe model of the ion recombination in columns of ionization produced by a high energy particle was analyzed. The Jaffe kinetics agrees very well with the kinetics of recombination produced by the simulation codes only if the Jaffe rate k_J of ion recombination in multi-ion pair column, which is the free parameter of the Jaffe model, approaches the Debye- Smoluchowski rate constant k_DS.

The paper presents the investigations of gel inclusion formation in potassium dihydrogen phosphate (KDP) crystals grown in tetramethoxysilane (TMS) gel in relation to growth conditions i.e. KDP concentration in gel, gel density and cooling rate. The experiments show that increasing of KDP concentration in gels with the same density promotes formation of gel inclusions in KDP crystals. Increasing of gel density causes greater gel contamination in crystals even if KDP concentration in gels is maintained at the same level. Formation of gel inclusions in crystals may be suppressed if the temperature of gels is decreased very slowly. It was concluded that high supersaturation of solution in gel during nucleation and growth is responsible for the formation of gel inclusions.

A new modified Monte Carlo model of crystal growth is presented. The modification takes into account solvation and desolvation of growth units. The simulation results for growth on flat crystal surface are presented. The solvation effect changes the surface morphology as compared to the one simulated without solvation, but the growth rate seems to be practically unchanged.

The modification of Cabrera and Levine formula which describes step distance on crystal surface is proposed. Replacing of bulk supersaturation by theoretically calculated surface supersaturation makes the so modified Cabrera and Levine approximation usable for both low and high supersaturations. In the case of middle values of supersaturations which are most frequently used in crystal growth practice, the modified approximation gives better results than other approximations.

It is shown that there are some faces for which all possible ways of disappearance are probable in the same degree. This kind of faces may disappear by transformation to one of their edges or to a corner. On the other hand, there are faces which disappear in one way only, for example by transformation to one particular edge. Transforming to one of the other edges or transforming to a corner is impossible. It is shown that the way of disappearance of a given face may depend on geometrical conditions only.

This paper describes a theoretical and experimental investigation of the growth and especially the morphology of acenaphthene crystals for growth from solution in chloroform. Experimental data on acenaphthene morphology have been compared with theoretical models based on layer thickness d_hkl and on the attachment energy E_att. The attachment energy model calculated by HABIT reflects the general shape of the crystals better than Donnay-Harker model.

On the basis of the measured data of acenaphthene solubility in chloroform (CHL), tetrachloromethane (CCl₄), 1,2- dichloroethane (1,2-dCHLE), 1,1-dichloroethane (1,1-dCHLE), trichloroethylene (tri-CHLE) and tetrachloroethylene (tetra- CHLE), the experimental (gamma) s^WP) and predicted from regular solutions theory ((gamma) s^SH and (gamma) s^SHE) activity coefficients as well as some thermodynamical functions of mixing and their excesses have been evaluated. These values have been compared with the growth results of acenaphthene crystals obtained from particular above mentioned solvents and thermodynamical criterion of their selection for crystal growth, was proposed.

In situ STM studies of the Au(110) single crystal electrode have been carried out, in 0.1 M NaOH, under potential control. After sputter-annealing procedure, at sufficiently negative potential, in alkaline solution a (1 multiplied by 3) reconstructed Au(110) surface has been observed. Above the certain potential a (1 multiplied by 3) reconstruction vanishes and the surface forms a (1 multiplied by 1) structure.

This paper contains two main sections. In the first one, we illustrate the technological interest of crystals of the sillenite family and we present our powerful methods of investigation in some details. These are essentially optical absorption and magnetic circular dichroism at liquid helium temperatures, down to 4000 cm^-1. The latter is also used to detect electron paramagnetic resonance optically and to tag a given absorption component to a specific paramagnetic, intrinsic or extrinsic, defect. In the second part, we present a variety of experimental results and interpretations dealing with undoped crystals and with samples doped with transition ions of the iron (Mn, Cr, Fe, Co, Cu) group. Emphasis is put on the assignment of ligand field bands in the near infrared, since these are used to monitor the site, charge state, and amount of the dopants in a thermally bleached state or after various illuminations.

We present the first spectroscopic investigation concerning the role of four ions (Ru, Rh, Os, Re) of the platinum group on the photochromic behavior of the photorefractive crystal Bi₁₂SiO₂₀. Absorption and magnetic circular dichroism (MCD) spectra were taken in the thermally bleached state and after various illuminations so as to determine the coloration thresholds. Ruthenium and Osmium are demonstrated to enter the crystal, whereas the answer is not yet certain in the case of rhodium and rhenium. We believe that the doping occurs at the pseudo-octahedral Bi site.

The equilibrium and non-equilibrium thermal characteristics of the optical properties of photochromic materials are considered for the sillenites. For many years sillenites have been very well known as photochromic materials. The photoinduced coloration observed for them is connected with the charge transfer of some local centers. The kinetics of the photochromic absorption depends on temperature and light intensity. The photochromic saturation changes of the optical absorption are in a good relation to the hyperbolic tangent function of the temperature reverse. The fitting parameters describe the energy depth of the highest electron trap and the temperature range for stability of the effect. The new dynamic effect related to photochromism called the thermoabsorption is observed in the optical absorption during the enough quick temperature sweep. The magnitude of the effect is typically dependent on the rate of temperature's changes what is common for the non-equilibrium processes. The thermoabsorption effect is complementary to the thermoluminescence. The parameters describing the non-equilibrium optical absorption are connected with energy depth of electron and hole traps and they are in the reasonable agreement with the parameters for the equilibrium process.

Single crystals of scandium doped germanium sillenite (BGO:Sc) were obtained by the Czochralski method. The absorption and photochromic spectra were investigated as a function of temperature. For comparison the same spectra for nominally pure crystals were measured too. Scandium doping influences significantly on spectral dependences only at about 8000 cm^-1. But the presence of Sc ions modifies strongly the temperature dependences of spectra. The characteristic photochromic temperature T₀ for BGO:Sc is determined to be about 100 K. This value is higher than T₀ for pure material. The main part of the photochromic spectrum is divided into 4 absorption bands (at 8350, 11660, 18090, 21350 cm^-1). The fifth band is in the UV and it was not investigated in this paper. On the base of different temperature dependences the above four absorption bands are attributed to two centers.

For the first time the photochromic effect for cerium doped bismuth-germanium oxide Bi₁₂GeO₂₀ is presented. The results for coloring and optical decoloring at room temperature and at liquid nitrogen temperature are shown as function of illuminating light. The coloring of BGO:Ce crystals produces two different photochromic states dependent on the coloring temperature.

Influence of bismuth oxide purity and growth conditions on photorefractive properties of sillenite structure materials has been analyzed. Various impurities present in starting materials affect significantly on photoexcited charge carriers in sillenites. Small concentrations of chromium (approximately 10^-4 wt.%) in Bi₁₂TiO₂₀ crystals decreases the diffusion length L_d of photoinduced charge carriers. Cr- doped BTO crystals were found to be sensitive in near IR region due to 'tails' in their absorption spectrum. Sillenite structure crystals grown in an oxygen-free atmosphere contain lower concentration of acceptor centers and demonstrate higher photoconductivity.

Bismuth-germanium oxides (Bi₁₂GeO₂₀) and bismuth- silicon oxide (Bi₁₂SiO₂₀) single crystals doped with chromium or manganese are photochromic materials. The annealing of these materials in some atmospheres changes their optical properties. The results of experimental research are presented.

Diffusion and solubility of Fe in Bridgman grown CdTe crystals were studied by the radiotracer method (⁵⁵Fe+⁵⁹Fe) in the 800 - 1270 K temperature range at different Cd vapor pressures. Fe 'supersolubility' phenomenon was fixed at long annealing. Electrical and magnetic properties measurements on crystals with C_Fe approximately equals 10¹⁸ minus 10²⁰ at/cm³ were performed. High-temperature (850 - 1100 K) Hall-effect measurements didn't reveal increased electron concentrations in comparison with undoped CdTe. Thermal annealing of some samples under high P_Cd leads to high resistivity of inner parts of the sample ((rho) approximately equals 10¹⁰ (Omega) X cm) at 300 K. The measured magnetic susceptibility temperature dependencies and its anisotropy are discussed in the framework of different dopant states in the CdTe lattice.

High-temperature measurements at 973(673)K of electron (hole) concentration in Ge-doped CdTe crystals were performed under partial Cd and Te pressure. The results are compared with point-defect concentrations, calculated by use of approximated or full electroneutrality condition. The importance of the doped crystal thermal prehistory is evidenced. It determines the Ge in Cd sites to Ge in Te ones ratio, thus influences the electrical and optical properties of the crystal.

This paper deals with experimental study of structural and luminescent properties of Zn_1-xMg_xSe mixed crystals in the x range from 0.0 to 0.615. These crystals were grown by the high pressure Bridgman method. X-ray diffraction and high resolution electron transmission microscope measurements reveal that for magnesium concentration lower than about x equals 0.18 Zn_1-xMg_xSe crystallize in sphalerite structure but for higher -- in wurtzite one. The formation of 4H phase and some other polytypes has been found at the composition close to the phase transition. From investigations of luminescence and reflection spectra the dependence of the exciton transition energy on composition has been determined. In-Zn_0.9Mg_0.1Se-Au structure has been fabricated. Blue-violet, green and yellow electroluminescence was observed in the temperature range from 40 K to room temperature.

This paper presents results of investigation of photoluminescence (PL) and cathodoluminescence (CL) as well as Raman scattering in Zn_1-xMg_xSe mixed crystals grown by high pressure Bridgman method for 0 less than x less than 0.615. The crystals exhibit yellow-green and blue luminescence from 40 K up to room temperature. The intensity ratio of 'blue' band to the deep levels band increases with increasing magnesium content. Cathodoluminescence microscopy was used to examine the spatial distribution of luminescent centers in a sample. CL images of crystals surface at various wavelengths that correspond to different maxima in the CL spectra were obtained. Raman polarized spectra of Zn_1-xMg_xSe were measured at room temperature (RT). The dependence of phonon energies on composition can be quite well described by the modified random element isodisplacement model.

The photoacoustic spectroscopy with a piezoelectric transducer was employed to evaluate the band gaps of a series of Zn_{1- x}Mg_xSe mixed crystals of different composition. The measurements were performed at 300 K, 90 K and 6 K. The Jackson-Amer model of photoacoustic effect for thermally thin and optically thick samples was applied. For samples of x greater than 0.18 (wurtzite structure) subgap optical absorption was observed.

The values of the elasto-optic constants: p₁₁, p₁₂, and p₄₄ of n-type ZnSe single crystals with different free carrier concentrations were studied using Brillouin light scattering method. It has been shown that the value of the elasto-optic constants p_ij of ZnSe single crystals strongly depends on the free carrier concentration. Obtained results are also discussed in terms of the existence of twins, native defects, and uncontrolled dopants which may arise in the crystal during the growth process.

In this paper we present a single phenomenological magneto- elastic mechanism for the elastic properties of crystals with different free carrier concentration. Using this theory, the basic mechanism for the effect of free carrier concentration on the elastic properties of n-ZnSe crystals has been discussed.

Uniform stress effect on initial stages of oxygen precipitation in Cz-Si annealed at (870 - 1000) K under argon pressure, HP, up to 10⁹ Pa was investigated by FTIR, x- ray, selective etching and electrical methods. Cz-Si samples subjected to nucleation treatment were subsequently annealed at (1230 - 1400) K - 10⁵ Pa to check an effect of nucleation under HP on oxygen precipitation. Enhanced HP during nucleation influences kinetics of thermal donor creation, enlarges oxygen precipitation and concentration of oxygen-related defects. HP-induced phenomena are discussed in terms of decreased oxygen diffusion and of enhanced misfit at oxygen cluster/Si matrix boundary with activation of 'additional' nucleation centers for oxygen precipitation.

The influence of thermal annealing procedure on As- precipitates density and electrical properties was investigated. Undoped and Cr, V, O₂, and In doped GaAs single crystals grown by liquid encapsulated Czochralski method were analyzed. As-precipitates were investigated by optical microscope with Nomarski contrast after AB solution etching (AB-EPD), by laser scattering tomography (LST), by cathodoluminescence (CL) and transmission electron microscope (TEM). Annealing processes for ingots and wafers were carried out in closed quartz ampules at different temperature, time and arsenic partial pressure. The influence of thermal annealing on As-precipitates density was observed depending on starting materials properties and process parameters. The best results on reduction of As-precipitates density and homogenization of electrical properties of the material were obtained by multiannealing procedure.

The electrical properties and photoluminescence spectra of LEC gallium arsenide crystals after neutron transmutation doping (NTD) have been investigated as function of starting material properties, irradiation dose and thermal to fast neutron fluence ratio. The residual carbon acceptors interact with radiation induced defects (RD) in neutron irradiated GaAs crystals and form nonradiative recombination centers, which are stable up to 700 degrees Celsius.

Deep states in semi-insulating GaAs and InP are investigated by high resolution photo-induced transient spectroscopy (PITS). The results exemplify new potentialities of the improved PITS technique.

In the work we present results of studies of real structure and defects changes occurring in single crystalline samples of the (beta) ₁ phase of an CuZnAl alloy during cyclic martensitic transformation induced by tensile stress. Two groups of samples were studied -- these with a chaotic distribution of subgrain boundaries and those with subgrain boundaries parallel to the direction of elongation. Analysis of the x-ray topograms as well as results of the dislocation density measurements allowed us to establish the dependence of the sum of distortion angles of neighboring subgrains ((Sigma) _(alpha )) and dislocation density ((rho) ) in both groups of samples on the number of cycles (N) of the reversible martensitic transformation. It was shown that in case of samples with the directed distribution of subgrains after some number of cycles a local correlated increase of (Sigma) _(alpha )(N) and decrease of (rho) (N) was observed. This phenomena were not observed for specimens with the chaotic distribution of subgrain boundaries.

In this paper we report the study of temperature behavior of the hypersonic velocity in NH₄)₃H(SeO₄) single crystal using Brillouin scattering method. The measurements have been performed in the temperature range 230 - 317 K covering two phase transitions between IV - III and III - II (see Fig. 1). Obtained results are discussed in terms of the ordering of SeO₄ tetrahedra, also the existence of the different ferroelastic domain structure and its thermal evolution.

The vortex-induced strains in the flux lattice in high-T_c superconductors are studied. It is shown that the strain causes an extra intervortex interaction, which is long range and which is responsible for giant magnetostriction recently observed in high T_c single crystals and melt-textured superconductors.

The temperature and field dependences of reversible magnetization in Ba_1-xK_xBiO₃ single crystals (x equals 0.34 and 0.37) were studied. From the vortex fluctuation model the temperature dependence of the penetration depth is determined. The analysis of the experimental data suggests that for (BaK)BiO₃ family of superconductors the thermal fluctuation effects are very small and that an external magnetic field does not cause the reduction of the effective dimensionality of the system.

Cd_0.9Mn_0.1Se_0.3Te_0.7 photoluminescence and reflectivity were studied in magnetic field up to 5T in T equals 4.2 K. In luminescence spectra two lines were observed. Comparing results to previous studies in Cd_1-xMn_xTe and Cd_1-xMn_xSe they were identified as the free exciton X and exciton bound to neutral acceptor A⁰X. Influence of high alloy disorder on bound magnetic polaron effect was considered.

The low temperature phase transitions in the KDy(WO₄)₂ single crystal have been studied by ESR and specific heat C(T) methods. Both the broad maximum of C(T) with peak at T_c equals 6.38 K and (lambda) -shaped temperature dependence of the ESR line width (Delta) H(T) in the vicinity of the transition may be explained as being due to the structural phase transition. The analysis of C(T) and (Delta) H(T) dependences show that the second order structural phase transition observed at T_c equals 6.38 K is the transition of Jahn-Teller type and does not occur with a change of point symmetry. The phase transition observed at about 0.6 K for heat capacity is connected with magnetic order of dysprosium ions.

The influence of gamma and electron irradiation on optical and lasing properties of Y₃Al₅O₁₂, Gd₃Ga₅O₁₂, YAlO₃ and LiNbO₃ single crystals doped with rare-earth ions was studied. The laser output energy in the Nd-doped laser crystals and (gamma) -irradiation is decreased due to passive losses on the laser generation wavelength 1.06 micrometer (reabsorption of the laser radiation by color centers). The color centers in YAG-Er crystals may fulfill the sensibilizator function providing an increase of the pumping efficiency and output energy of the laser generation at 2.94 micrometer.

Gamma-induced transition of Ce⁴⁺ $ARLR Ce³⁺ was investigated for Ce,Nd:YAG samples cut off from the same crystal and differing one to another by a few tenth percent of Ce³⁺ ions concentration (starting concentration). Depending on the starting concentration changes of resulting concentration of Ce³⁺ ions were observed. The luminescence of Ce,Nd:YAG crystal at about 530 nm increased independently on Ce³⁺ starting concentration.

The polarized spectra of Raman scattering (RS) in the region 20 - 1000 cm^-1 and infrared absorption (IR) spectra at 5 K and 300 K were studied. The detail examination of polarized and low temperature absorption spectra in the region of Nd³⁺ transition from ground state ⁴I_9/2 to ²P_1/2 was performed in order to determine energy position of the ⁴I_9/2 Stark levels. An analysis and comparison of the RS and IR absorption spectra at room temperature allows us to assert that the NdGaO₃ structure at this temperature region belongs to the Pbnm space group.

A computer-controlled imaging conoscope has been used for investigation of optical homogeneity in large boules of doped and undoped uniaxial crystals. Two birefringence inhomogeneity maps acquired for two perpendicular directions in the crystal [z-optical axis, and perpendicular to it (x or y direction), respectively] are satisfactory to conclude whether the boule is (or not) suitable for optical applications. Such investigations are indispensable in factory check of crystalline boules grown by different techniques, and are also potential in scientific researches. An example for an undoped LiNbO₃ is presented for illustrating the method.

The results of spectroscopic investigations of YAP-Er (50 at %) single crystals at temperature T equals 50 K are presented in this work. The influence of (gamma) -irradiation and thermal annealing on optical properties of YAP-Er is studied.

Lithium niobate crystals doped with Pr³⁺ or Yb³⁺, as well as double doped with Yb³⁺ and Pr³⁺ ions were pulled by the Czochralski method. The doping concentration spread distributions were measured for each ion by the electron microprobe. The optical homogeneity of crystals was investigated using the conoscopic and polarimetric techniques. The absorption characteristics were also investigated. In the absorption spectra a careful attention has been paid to the peak associated with OH group, since from this one can conclude on the location of the doping ions in the crystal lattice.

Lithium niobate crystals doped with Dy³⁺ ions were grown by the Czochralski method. The doping concentrations were 0.3, 1, and 1.7 at.%, respectively. The dopant distribution was measured by the electron microprobe 'JOEL-JXA 50 A'-type device, and from these measurements the segregation coefficient has been found to be close to unity (k approximately equals 0.8). Optical homogeneity of crystals was investigated by the conoscopic and polarimetric methods. For the Z-optical axis direction it was found that the maximum residual birefringence (not exceeding 1.5 multiplied by 10^-4), involved by residual stresses, occurred at the perimeters of the crystals, and the remaining crystalline areas were almost entirely free from excessive stresses. The absorption characteristics in the wavelength range of 200 - 6000 nm were measured. The photoluminescence characteristics were also measured in the visible part of the spectrum. It has been found that an important feature associated with luminescence of the Dy³⁺ in LiNbO₃ is its high intensity and long decay time. From this it can be concluded that LiNbO₃:Dy³⁺ is particularly well suited for visible lasers.

The electron-spin resonance (ESR) was measured for trivalentium neodymium, dysporsium, erbium, and ytterbium in the single crystal samples of lithium niobiate. The measurements were made at x-band frequencies in the temperature range from 4 K to 50 K. Distinct hyperfine lines due to isotope ¹⁶⁷Er, and weak hyperfine lines due to isotopes ¹⁶¹Dy, ¹⁶³Dy, and ¹⁷¹Yb, ¹⁷³Yb were observed. The g factors and hyperfine parameters were obtained by use of the spin Hamiltonian and fitting to angular dependence of observed spectra. Moreover for LiNbO₃:Nd³⁺ g factors were verified for powder samples. According to these results some conclusions concerning sites in which rare earth ions are placed in the crystal lattice of LiNbO₃ can be drawn.