The main ZnO physical properties are reviewed and some of them compared to those of GaN. As a result of these attractive properties, the various applications it could be thought of for ZnO are summarized. A critical review is then proposed of the different techniques used for the growth of bulk ZnO crystals and of ZnO epitaxial films. The result are discussed from the assessment of their structural and electrical properties. The key issue of p-type doping is finally discussed in the light of the most recent results.

A review is presented of the author's rece4nt work on the influence of mechanical stress on the growth rate of materials. On the basis of the results, it is proposed that growth rate dispersion of secondary nuclei arises asa result of competition between stress reduction and dislocation enhancement of growth rates in the developing particles, with the former being the major influence at low particle sizes. The results are shown to account for the particle size and material dependence of the dispersion. Mechanistic studies suggest that the principal mechanism of stress reduction in growth rate is the influence of the applied stress on the surface free energy of the crystal. This effects both nucleation at the growth center and the migration of growth steps across the crystal surface.

High quality fluoride and oxide single crystals for optical, piezoelectric and other applications have been grown by advanced crystal growth techniques. Corquitiite- and Perovskite-type fluoride single crystals - LiCaAlF₆, LiSrAlF₆, KmgF₃ and BaLiF₃ - have been grown for solid state UV laser applications, and as window materials for next generation optical lithography. La₃Nb_0.5Ga_5.5O₁₄ and La₃Ta_0.5Ga_5.5O₁₄ piezoelectric single crystal of size and quality comparable to La₃Ga₅SiO₁₄, have been produced. The piezoelectric and deice properties of the crystal were investigated. A search for new langasite-type materials was also performed. Promising new structural materials. Undoped and doped eutectic fibers, have been grown by the micro- pulling-down technique. Undoped and doped(beta) -Ga₂O₃ single crystals have been grown by the floating zone technique as promising transparent conductive oxides.

The main methods of crystal growth from the melt the Czochralski and floating zone will be discussed and compared. Advantages, disadvantages and limitations of both methods as well as ways of solving some of the problems existing during growth of different types of multioxides crystals will be discussed. The chemical composition of crystals grown by the Czochralski method very often differs from the stoichiometric composition. Such deviations were found and well documented in a few groups of materials for example in garnets. Since the deviation is not known for most of the crystal, a simple way to determine the optimum starting composition of the melt will be presented. In order to determine the composition of the melt one should take into account evaporation of a volatile component that dissociates at high temperatures during crystal growth. Some problems related to the dopant distribution along the crystal growth direction in correlation with segregation coefficient for both methods will be discussed. To grow solid solution single crystal by the Czochralski method with a desired concentration of the admixture one has to know segregation coefficients of the components. A few examples of the dopant solubility limit in different crystal matrices will be presented.

Large Dy-123 single-domains have been grown y the top- seeding melt-textured growth technique on yttrium oxide substrates. The main obstacles in fabricating such 'single grain' 123 superconducting samples are discussed, i.e. (I) the dissolution of the seed during the melting and the peritectic cooling stages, (ii) the nucleation of subsidiary 123 grains at the compact/substrate interface. Such secondary nucleation process prevents the single grain from going further. Solutions are suggested as for example by considering the use of a modified coating. BaZrO₃ displays a strong inertia in barium cuprate fluxes which suggests to use it as a very promising candidate for buffer layer in between the 123 compact and the furnace 'environment'. In order to provide such 'high quality' sufficiently dense BaZrO₃ coatings, soft solution routes have been investigated. Advantages of these are a low calcination temperature and the production of very homogeneous and fine monodisperse powders. The influence of the synthesis conditions on the properties of BaZrO₃ and on the sintering process is thus reported.

A review of some of the most important applications of the wide-gap II-VI semiconductors is presented, the key parameters of the crystals for specific applications are emphasized, and the necessity of growing crystals of very high quality is substantiated. Modern methods of growth of high-quality wide-gap II-VI semiconductor crystals are shortly descried. The results of the physical vapor transport method, chosen by the authors for ZnTe and CdZnTe crystals are shown.

GaSb undoped wafer were annealed in flowing ionized hydrogen atmosphere at temperature range between 100-350 degrees C for 1-50 hours. The free carrier concentration and resistivity were measured. It was found out that the wafers being treated at a temperature of 150 degrees C for 24 hours reached the resistivity of about 10²-10³ (Omega) cm and the free carrier concentration was lower than 1 by 10¹⁵ cm^-3. However, the thickness of the passivated layer was only 0.4-0.6 micrometers .

A series of La_1-xSr_xGaO₃ solid solution single crystal with x equals 0, 0.04 and 0.12 were grown by the Czochralski method and with x equals 0.01, 0.06 and 0.1 by the floating zone method. The segregation coefficient of Sr in LaGaO₃ has been found to be k_eff (Sr) equals 1.25. The crystals were grown from the melt with stoichiometric Ga₂O₃ amount at a growth rate ranging from 2.5 mm/h for pure LaGaO₃ to 1.2 mm/h for La_0.88Sr_0.12GaO₃. The structure of these crystals was investigated by x- ray powder diffraction technique using CuK_(alpha ) radiation. The diffraction patterns were analyzed by Rietveld refinement method. Crystals with strontium concentrations from x equals 0 to 0.1 crystallizes adopting Pbnm structure. It was found that deviation from the ideal perovskite structure decreases with rising strontium concentration, finally reaching centrosymmetric Ibmm structure at x equals 0.12. Orthorombic unit cell parameters c and b decreases whereas a increases with x. Thermal analysis proved that the temperature of the first order phase transition observed in pure LaGaO₃ at 150 degrees falls to 126 degrees at x equals 0.01 and remains almost constant at higher x.

An Al-Cu-Co alloy was obtained by the inclined front of crystallization method. During crystallization the alloy delaminated into three layers, two of which were single decagonal quasicrystals of different orientations and the third one was a mixture of two phase. The first quasi crystalline layer was formed in a peritectic reaction of an earlier crated single crystalline layer of an approximant, the second-grew directly from liquid. With the use of X-ray topography it was found that the planes of both quasicrystals are rotated of about 1 degree against each other.

In this paper both the diffusion of Cu ions in ZnSe monocrystals of M_1-yX type as well as its influence on the concentration of cation vacancy have been investigated. For the purpose of the investigation the phenomenon of luminescence was used since the diffused impurity by acting on the native defects of the crystal was found to have caused the formation of complexes e.g. centers of luminescence. Thus we can have a few diffusion mechanisms.

The influence of reducing and oxidizing annealing on optical absorption spectra of the yttrium aluminium garnet (YAG) single crystal co-doped with Mg and Cr is investigated using step-by-step isothermal and isochronous thermal treatment in H₂ or air flow. The changes in the spectral were analyzed using decomposition on elementary absorption bands of Gaussian shape. The separated absorption bands attributed to the Cr⁴⁺ ions occupying octahedral and tetrahedral sites in garnet lattice demonstrate different behavior. The analysis allows to distinguish the electronic recharging process Cr⁴⁺ $ARLR Cr³⁺ taking place in the octahedral sites of garnet lattice and having lower activation energy from the chromium migration process Cr⁴⁺ $ARLR Cr⁴⁺ happening at higher temperatures or longer exposure. Estimations show that approximately 0. 2 percent of total number of chromium ions occupied tetrahedral sites forming phototropic centers in the YAG: Mg, Cr crystal.

Single crystals of double tungstates find applications as laser materials having very good parameters. One of the intensively investigated material sis KGD(WO₄)₂ doped with rare earth elements. Single crystal of KGd(WO₄)₂ were grown with the use of Top Seeded Solution Growth technique from K₂W₂O₇ solvent. The crystals have low absorption loses and show high lasing efficiency. Optical investigations of as grown KGW:Nd single crystal confirmed their good optical quality and high absorption coefficient near 810 nm, what in connection with strong luminescence near 1067 nm allows fabrication of diode pumped microchip lasers working both in CW and giant pulse regime. Absorption and luminescence spectra of Nd³⁺ doped KGW single crystals are presented. Laser action was obtained in form of 128.5 kHz train of 100 ns giant pluses due to YAG:Cr⁴⁺ passive Q-switch.

This paper describes efforts taken in Institute of Applied Physics and Institute of Electronic Materials Technology to obtain several single crystals from borate family, namely, CsLiB₆)₁₀, Ca₄GdO(BO₃)₃, Li₂B₄O₇, (beta) -BaB₂O₄, and Yal₃(BO₃)₄, pure and doped with several ions. The main goal of this investigation was to develop technology of these new nonlinear optical materials to create possibility of their applications in higher harmonics generators and self- frequency doubling lasers. Depending on such properties of crystallized borate materials as incongruent melting or high temperature phase transitions, Czochralski technique or high temperature solution growth technique were used. The main aspects of crystallization of these materials as well as their optical properties are discussed.

Oxygen agglomeration processes leading to the formation of thermal donors in Czochralski grown silicon subjected to heat treatment at T equals 450 degrees C at atmospheric pressure and a high hydrostatic pressure of P equals 1 are studied. The samples investigated were doped with isoelectronic impurities of carbon and germanium. Both impurities are known to suppress the formation processes of thermal donors under normal conditions of heat treatment. It has been shown that the stress applied during heat treatment to Cz-Si with high concentrations of these impurities results in an enhanced formation of thermal donors. This effect is thought to be associated with increasing oxygen diffusivity under stress.

Effect of intentionally created oxygen-related structural defects on generation of thermal donors, TDs in Cz-Si treated at 720K under enhanced hydrostatic pressure of gas ambient, HP, up to 1.5 GPa was investigated. The as-grown Cz-Si samples with initial interstitial oxygen content up to 1.2 X 10¹⁸ cm^-3 as well as that pre-annealed at 720-1020 K - 10⁵ Pa for up to 170 h, indicate strongly HP - dependent increase of electron concentration in the conduction band after the HT-HP treatment at 720 K for 2-20 h. This confirms the stress-stimulated creation of TDs. HP-induced creation of TDs was much weaker after pre- annealing at 920-1020 K while not detected for the samples containing extended defects. Qualitative explanation of observed phenomena was proposed.

Czochralski-grown silicon crystals of the same initial oxygen content were subjected to various high temperature- high pressure (HTHP) treatments for different time durations. Subsequently, the crystals were irradiated by fast neutrons at approximately 50 degrees C. One of the main defects form is VO pair usually identified in the IR spectra by the 830 cm^-1 localized vibrational model (LVM) band. Upon annealing, this defect is converted to the VO₂ defect responsible for a LVM band at 887 cm^-1. The purpose of this work is to study the effect of various combinations of HTHP treatment prior to irradiation on the annealing behavior of the VO defect and particularly on its conversion to the VO₂ defect. We have concluded that the conversion of VO to VO₂ depend on the forms of oxygen impurity and on other defects created in the sample after the HTHP treatment, as for example dislocations and stacking faults.

2D mathematical model of the intrinsic point defects recombination during Cz growth of dislocation-free silicon single crystals is developed. The result of its verification are compared with the data of the 1D model supposing the 'fast' vacancies and interstitial recombination near the liquid-solid interface. For various growth conditions and with use of the calculated 2D temperature fields in Cz silicon crystals the resulting distributions of these intrinsic point defects in a crystal are analyzed.

For the last ten years or so, the gasketed diamond anvil cell (DAC) has become the standard tool for the generation of high pressures. Compared with the classical hydraulic piston-cylinder devices, a DAC is three to four orders of magnitude less massive, and will generate static pressures one to two orders of magnitude higher than previous devices. In this paper, we attempt to give an understanding of the gasket behavior which will be helpful to the worker requiring routine and reliable use of a DAC in the submegabar pressure range.

Extensive experiment studies of the IV elements have been made in recent years. Motivations have included the rich variety of phase and structural transitions.

Two Czochralski (CZ) silicon ingots, named NCZ and ACZ silicon, were grown under the same procedure in nitrogen and an argon atmosphere respectively. The experiments reveal that nitrogen was doped into the silicon ingot and N-O complexes were generated during the crystal growth, while it was grown in a nitrogen atmosphere. The nitrogen concentration profile in the NCZ silicon ingot indicates that the nitrogen concentration in the wafer edges was less than that in the center. It is also found that the as-grown oxygen-thermal donors were almost the same. Furthermore, it is discovered that the profile of phosphorus concentration in NCZ silicon was also the same as that in ACZ silicon. It is considered that compared with argon atmosphere, nitrogen atmosphere ha no influence on the evaporation rates of phosphorus from melting silicon.

Transformation of defects in hydrogen implanted silicon and silicon-on-insulator structures caused by external pressure of argon ambient at the stage of defect removal in implanted material and high temperature annealing SOI structures is reported. The results are compared to these for crystals annealed at argon atmosphere of ambient pressure. Formation of the new phase crystallites was found in SOI structures annealed at high temperature in conditions of high pressure. Small insulations were also observed in hydrogen implanted silicon, which can be patterns of the new phase. Two reasons can cause phase transformation in the top silicon layer of as-bonded SOI structures: high hydrogen concentration and high local strain.

The computer simulation methods have been applied to study the structure of aqueous solutions of simple ionic salts in the region of very high concentrations. The calculations of ionic structures in solutions were performed for NaOH, NaCl, LiCl and MgCl₂ solutions. The concentrations ranged from 0.2M to saturated solutions, in some case as much as 19M.

The diffusion and recombination process in an ensemble of isolated single pairs of opposite charges is usually described by the Debye-Smoluchowski equation. The present work is an overview of a series of computer simulations of diffusion and recombination of ions in solution performed with the aim to determine the limits of validity of the Debye-Smoluchowski equation.

Cellular Automation modeling the repeated application of simple rules can result in very complex behavior and is being increasingly used to simulate physical process. This paper outlines the technique with special emphasis on ordered states and order/disorder transitions.

In our earlier papers, we solved the time-dependent equation of Burton, Cabrera and Frank for transient state conditions occurring immediately after submersion of a crystal surface in supersaturated solution. As a result, the expression for the transient surface supersaturation was found and discussed. In this paper we present an approximation of that expression. The approximation enables a simple estimation of the time required to attain the steady-state value of the surface supersaturation.

Using the thermodynamical studies it seems proved that ionized hydrogen acts as amphoteric dopant of GaSb. It is splitting to H+ and H- and between these two kinds certain equilibrium is created depending on the concentration of acceptor's and donor's impurities in the GaSb material. There is an inclination of such a crystal to maintain the GaSb structure to be iso electric. This behavior has been studied on undoped and slightly Te-doped GaSb single crystal grown by use of the Czochralski method without encapsulant under a flow of ionized hydrogen. For comparison the studies were repeated under a flow of molecular hydrogen.

Formally one can distinguish between the thermodynamic stability conditions and the dynamical ones. These last consists are easily formulated in the self-consistent phonon theory (SCPT) base don the thermodynamic double-time Green's function method. According to it the dynamic instability temperature T_s for a simple Bravais lattice defines the temperature at which the bound crystalline state of atoms vanishes that really means that the phonon frequencies become complex at sufficiently high temperatures T<EQT_s. Using the reduced second order approximation of the SCPT the dynamics of crystal lattice and the thermodynamical properties of the quantum crystal in the vicinity of the instability point are investigated. The results of calculations of the pressure dependence of the instability temperature, melting criterion, internal and free energy, free Gibbs energy gas well as selected dynamic properties obtained with the help of the generalized form of the Buckingham, the Lennard-Jones and the Morse self-consistent potentials are given and compared with experimental data of solid hcp ⁴He and fcc ²⁰Ne. Comparison of the theoretical and experimental results allows us to state that the limiting temperature of the dynamical stability obtained for the above-mentioned models pair potentials always appear to be the upper estimations of the real melting temperature.

Hyper-Raman scattering by the zone-center optical phonons in some alkali halides is investigated. In our calculations we relate the electrooptic part of the hyper-Raman tensor to the third-order optical susceptibility and the electric field associated with the LO phonons. The result obtained for those alkali halides for which the third-order optical susceptibility has not been measured yet, show that the electrooptic and lattice contributions to the hyper-Raman scattering are comparable. In all crystals considered, we found the cubic anisotropy of the electrooptic part of the hyper-Raman tensor to be not strongly exhibited.

The evaluated Gd³⁺-Yb³⁺ exchange interactions over the nearest and the next-nearest neighbors in LiYb_xY_1-1F₄ are found to increase in parabolic manner with x, the concentration of Yb³⁺ ions. The Gd³⁺-Yb³⁺ exchange interactions are sensitive to x in the range x equals 0.6-1.0, while they are almost constant in the range x- equals 0.1-0.5. The estimated Gd³⁺-Yb³⁺ exchange interaction constants are in the range 0.5-2.8 Ghz for x from 0.1 to 1, respectively. These exchange interaction constants are increased with lowering temperature. The results are comparable to those of estimated using the molecular-field model. The average Gd³⁺-Yb³⁺ pari exchange interaction constant is determined to be 0.33 Ghz in paramagnetically diluted LiYb_xY_1-xF₄ crystals.

A valence force field model with an added ionic interaction is applied to an explanation of phonon dispersion curves in 6H-SiC. The phonon dispersion curves in 3C-, 2H-, and 4H-SiC are calculated within the same model. Our results are compared with the published result of ab initio calculations. One can suppose that the present model may be applied for other polytypes of SiC. A phonon contribution to Helmholtz energy is determined for the simplest four polytypes. The results indicate a stability of hexagonal polytypes in relation to the cubic one at high temperatures.

The aim of this paper is better understanding of the process of carrier flow generation on the boundary of electrode-dye layer in a photoelectrochemical cell for application in solar energy conversion. Such a boundary of two semispaces is a theoretical 2D model of a photoelectrochemical cell which consists of electrodes and a layer of organic dye molecules in which electron transport process can take place. The semispaces are described in their own micorcanonical distributions. We will consider the process of carrier flow generation on the boundary of electrode-dye layer by means of formalism of thermodynamical quantum statistics. We have obtained the statistical average value of the function of electromagnetic field at the given temperature and in approximation of the low temperature.

Besides the well-known 3D surface topography, scanning probe methods give access to a whole world of local physical information on solid surfaces. Here, we demonstrate opportunities given by scanning tunneling spectroscopy (STS) and scanning electrical force microscopy/spectroscopy. In this paper, we compare the wide-spread UHV-STM/STS technique with ambient SEFM/SEFS. After short description of the methods, some applications to semiconductor surfaces are discussed. Possibly SEFS has a great potential for local electronic spectroscopy in near future.

The rare earth double tungstates are of special interest because of manifestation of cooperative Jahn-Teller effect (CJTE) for low-dimensional and low-symmetry crystallographic structure. The structural phase transition (SPT) as a result of the CJTE is unique one among large number of various SPT in solids. In the alkali-dysprosium double tungstates ADy(WO₄)₂ in spite of monoclinic symmetry the SPT of CJTE types are realized because the presence of Dy³⁺ ions with closely spaced energy levels. In alkali-dysprosium double tungstates the magnetically ordered structures possessing a number of features connected with low- dimensional interactions of Dy³⁺ ions were observed. Studies of specific heat in magnetic field and of magnetic susceptibility led to conclusion that the magnetic phase transitions (MPT) from paramagnetic to antiferromagnetic state take place at subkelvin temperature region. Both MPT and SPT are very sensitive to magnetic field. In case of SPT this confirms its CJTE nature and allows to determine the type of the elastic ordering. The external magnetic field induced the transitions from antiferro- to ferromagnetic states. The alkali-dysprosium double tungstates belong to the more general class of magneto-elastics with interrelation between magnetic and elastic ordering.

An interesting phenomenon of thermal annealing in gamma irradiated undoped, and photorefractive Cu- and Fe-doped, Z- oriented LiNbO₃ crystal has been observed. Prior and after each gamma irradiation the crystals were thermally annealed in the air at 800 degrees C for a couple of hours. Optical homogeneity was investigated on the entire area of LiNbO₃ wafers by measuring distributions of birefringence, the principal azimuth, transmission, and parameters associated with birefringence dispersion, and also by measurements of additional absorption in a few wafers' points. It has been rather unexpectedly observed that the classical thermal annealing can lead to a decease in optical homogeneity in the majority of cases. It is attributed to generation of an internal electric field by the pyroelectric effect, and to the electrooptic effect involved thereafter. On the other hand, the secondary electrons generated by gamma irradiation are believed to increase the optical homogeneity by increasing the crystal's conductivity and dissipating this field. A uniform temperature heating across the wafer generated by this irradiation is also a helpful factor in this gamma- annealing. It has been found that this effect at room temperature by this irradiation is also a helpful factor in this gamma-annealing. It has been found that this effect at room temperature is small for gamma irradiation of 10⁵ Gy, while increasing the doses to 10⁶ Gy and 10⁷ Gy can profile in a considerable reduction of the optical inhomogeneity. A certain influence of Cu-doping on this effect has also been observed.

Electrical characteristics of metal-semiconductor structure based on monocrystals Ag₃SbS₃ are reported. Studies carried out at the room temperature were shown space-charge limited current caused by the peculiarities of Ag₃SbS₃ crystallographic structure: velocity saturation mode and ballistic regime were observed. Results of the numerical modeling of experimental data are also presented.

In this contribution we demonstrate the influence of shallow charge traps on emissions kinetics of LuAlO₃:Ce³⁺ scintillator. Shallow traps through their interference with the recombination process not only introduce into the emission time profiles long components but also can change the rising and decaying parts of time profiles. The lifetime of excited Ce³⁺ ion in LuAP crystal is approximately 18 ns, while the excitation at 78 nm leads to the emission described by 21.5 and 1.22 ns decay and rise time constants, respectively. Furthermore, temperature dependence of time profile phase is observed. The analysis of emissions kinetics measured against temperature shows that observed features can be explained in terms of a trap described by the following parameters: E equals 0.142 eV and S equals 6.087 X 10¹⁰ s^-1.

In this paper, we present initial result of studies on energy transfer processes in Ce-activated Lu, Y and Gd aluminum perovskite crystals that contribute to production of scintillation light in these new scintillator materials. In particular we report and analyze emission spectra, excitation spectra, and emission time profiles under pulsed synchrotron excitation in the wavelength range of 50-300 nm.

The thermal decay of holographic gratings recorded using the conventional two-wave mixing technique has been studied in congruent and nearly stoichiometric LiNbO₃ crystal doped with Mn. The activation energies of this process have been determined in the 70-130 degrees C range for congruent and 20-80 degrees C range for nearly stoichiometric crystals, the obtained values being 1.06 +/- 0.03 and 1.10 +/- 0.03 eV, respectively. The kinetics of the OH absorption spectrum has also been studied in undoped nearly stoichiometric LiNbO₃ between 40-120 degrees C. The time dependence of the band intensities can be characterized by exponential time constants obeying the Arrhenius-law. The average activation energy, E_a equals 1.1 +/- 0.1 eV is in good agreement with those obtained from the thermal decay indicating that the hologram fixing process in nearly stoichiometric LiNbO₃ is governed by proton migration.

The reduced second-order approximation of the self- consistent phonon theory was applied some years ago for cubic metallic crystals those interatomic were approximated by the Morse and Lennard-Jones pair potentials were generally obtained with the help of semi-classical method basin on the classical static relationships between ground- state properties of a crystal and its interatomic potential, and the zero-point vibrations were taken into account only by certain corrections to the experimental data. Moreover, the further self-consistent calculations were being carried out semi-analytically which required some simplifications. In this paper we can reject them because all essential calculations are being carried out numerically. In the studies at high-temperature properties of selected fcc metallic crystal we take as a model of interatomic interactions the Buckingham, Lennard-Jones and Morse pair potentials with the parameters determined self-consistently with the help of the experimental data for the zero-point lattice constant, cohesive energy and isothermal compressibility. Our new theoretical result for pressure variations of the limiting temperatures of dynamical and thermodynamical stability and for the stability criteria are collected and compared with available experimental data.

The excitation and emission spectra obtained for Pr³⁺:YAlO₃, Pr³⁺:LiYF₄ and K₅PrLi₂F₁₀ crystals by means of high-energetic excitation with synchrotron radiation are presented. In the emission spectra broad, overlapping bands in UV range are present. Their positions, bandwidths as well as the short emission decay times suggest, that emission from levels of 4f5d configuration dominate in all of the crystal investigated.

The mixed La_xRE_1-xF₃ single crystal doped with Gd³⁺ were grown by a modified Bridgmann- Stockbarger method. The crystal field was investigated using electron paramagnetic resonance technique. The angular dependencies of Gd³⁺ line positions with magnetic field oriented in plane were measured in the temperature range 4.2-295 K. The surroundings of Gd³⁺ ions were investigated analyzing spin-Hamiltonian parameters in the light of the superposition model. The small distortion of the D⁴_3D trigonal symmetry has been observed in LaF₃, La_0.9Ce_0.1F₃ and La_0.9Nd_0.1F₃ below 150K. The local structure deformation of the site symmetry of Dg³⁺ ions induced by temperature starts at about 150K becoming larger at 4.2K. In PrF₃ the distortion was not observed in the temperature range 4.2- 295K. The results were compared with those of Gd³⁺- doped LiYF₄ crystals.

The mixed La_xRE_1-xF₃ single crystals doped with Gd³⁺ were grown by a modified Bridgmann- Stockbarger method. The PIXE method was used to the determination of a composition x of this material. The value of x for these samples does not differ more than 2.5 percent and 7.5 percent in La_xCe_1-xF₃ and La_xNd_1-xF₃ respectively, from the assumed one. In addition, concentrations of the doped rare earth atoms were controlled by XRF method. The abundance of other than Gd³⁺ rare earth impurities was estimated to be below 0.058 at percent. The magnetic susceptibility of the single crystals was measured in the temperature range 4-300 K, in a magnetic field B equals 0.2 T applied in the crystallographic plane perpendicular to the c-axis using the Faraday method. The magnetic susceptibility measurements confirm the lack of Ce³⁺ and Nd³⁺ clusters in the diluted crystals. The effective spins of hosts Ce³⁺ and Nd³⁺ are equal to ½ in the temperature range 4-300 K.

Non-linear I-V behavior and electrical switching exhibited by chalcogenide glassy semiconductors, find applications in variety of areas including information storage and power control. In this work, semiconducting chalcogenide As₄₀Te_60-xIn_x glasses have been prepared by melt quenching technique. The current-voltage and electrical switching behavior of these glasses have been studied using a custom-built PC based system. The results obtained clearly indicate that all the glasses studied exhibit current controlled negative resistance behavior, which leads to the low resistance state. The switching to the low resistance estate is found to be reversible and the samples revert back to the high resistance state on reducing the current. Threshold switching over such a wide range of compositions has been observed only in very few systems so far. The most interesting outcome of the present studies is the variation of the switching voltage with composition. It is observed that there is an increase in the switching voltage V_t with the increase in indium concentration in the composition range 7.5 <EQ x <EQ 12.5. Further, the composition dependence of switching field is found to exhibit a distinct change in slope at x equals 12.5 and V_t continues to increase with x until x equals 13.5. Around x equals 13.5, the trend is reversed and V_t starts decreasing with x. A minimum in V_t is seen around the composition x equals 14.3, which corresponds to the chemical threshold of the As-Te-In system. Beyond x equals 14.3, switching voltage is found to increase with composition again. The present result are consistent with earlier observations, which indicate the composition dependence of switching voltages of chalcogenide glasses are influenced by chemical ordering and rigidity percolation.

The results of the magnetization measurements of single crystal of Yba₂Cu₃O_y with Tc equals 91K are adduced. The temperature, field and time dependencies of the remnant magnetization M_r(T, B, t) were obtained using VSM method for the temperature range from 4.2 K to 75 K for Hc configuration. The single crystal has been irradiated by the fast electrons with fluences up to 2 X 10¹⁸ cm^-2. The relaxation of M_r(t) obeys to the logarithmic law for the time interval t equals 1 h for whole temperature range except the approximately 30-50 K interval for starting and irradiated states. After irradiation the J_c decease despite the flux creep reduction. The irradiation become less effective at high temperatures. The results are discussed in frame of conventional flux creep theory and of the interaction model of radiation defects with the background ones.

We performed dc-magnetization measurements in low magnetic fields on single crystals of Ba_1-xK_xBiO_y with the different potassium content. The single crystal reveal the superconducting transition at 29-31K. It is shown that the lower critical fields H_Cl in crystals amount to 104 Oe, 126 and 112 Oe. The values of the penetration depth (lambda) are equal to 2530 A, 2430 A and 2670 A for x equals 0.34, 0.37 and 0.4 respectively.

The phonon and electron subsystems were studied in quaternary solid solutions of Zn_xCd_yHg_1-x-yTe by means of Raman scattering and Magnetophonon Resonance. The Raman spectra of several compositions confirm the three-mode behavior of phonon spectra. The cluster mode has also been observed. Four kinds of LO-phonons participate in the electron-phonon interaction. Four types of one-phonon Magnetophonon Resonances and two types of Magnetophonon Resonances on the difference of phonon frequencies have been observed.

Magnetic ordering of Dy³⁺ ion in low-dimensional magnet CsDy(WO₄)₂ has been first studied by means of measurements of the low temperature specific heat over a temperature range of 0.5-23K. The ordering temperature of the Dy³⁺ sublattice was established to be 1.34K. The experimental data indicate on the antiferromagnetic character of Dy³⁺ ions interactions. The magnetic behavior above and below T_n is discussed in the framework of different theoretical models.

In this work, we present the studies of manganites with superfluous manganese content performed by the magnetic resonance spectroscopy methods. The ferromagnetic resonance (FMR) has been measured on the films. The symmetrical FMR line in paramagnetic phase has the Dysonian-like shape below T_c. The FMR linewidth increases abruptly near the transition temperature. By comparing resonance fields oriented parallel and perpendicular to the film plane, the easy axis of magnetization was determined to be perpendicular to the film plane. In the perpendicular magnetic field, the spin-wave resonance (SWR) spectrum consisting of seventeenth of spin-wave modes has been observed in the (formula available in paper) film. Two of them observed on the high-field side of SWR spectrum are connected to a surface modes. The others are the bulk nonuniform spin-wave modes. Based on a study of temperature and angular dependencies of SWR and FMR spectra, the spin- wave stiffness, g-factor and exchange constant were established. An analysis of the (formula available in paper)has shown that a wide asymmetrical line can be uniquely expanded into four components with different resonance frequencies. There are manganese ions, which ionization states are close to (3+) and (4+) as well as the Mn ions with intermediate valence resulted from the high-frequency electron exchange.

We report on the pressure, field and temperature dependencies of magnetization and resistance in manganites of (La_1-xCa_x)_1-yMn_1+y O₃ type. The M(T) dependencies is established to exhibit the following peculiarities: the first is connected with the paramagnet (PM)-ferromagnet (FM) transition at 267 K; the peak of M(T) dependence eat 263K is presumable due to an existence of AFM clusters; an anomaly in magnetization is connected with the FM-canted phase transition at 42K and the large irreversibility in the field-cooled and zero field- cooled magnetization. As field is increased above 200 Oe, the sign of the M(T) anomaly changes, namely, the M(T) magnetization increases with increasing field at 42K. The character of M(T) dependencies does not change under pressure. However, both the Curie temperature, Tc, and the resistance peak corresponding to metal-insulator transition shift in the direction of high temperatures with increasing pressure. A pressure stabilizes the ferromagnetic metallic phase. The temperature of the FM-canting phase transition does not change under pressure. The magneto resistance effect increase by 15 percent under pressure of 12.6 kbar.

Results of spectroscopic investigations of crystalline potassium-erbium double tungstate Ker(WO₄)₂ are reported. The single crystal of Ker(WO₄)₂ were grown by Top Seeded Solution Growth technique. They belong to the chain-layered group of materials crystallizing in monoclinic syngony. The investigations were carried out in the broad spectral and temperature range. It was found that the potassium erbium double tungstate belong to the class of the diaxial crystals and it is a pleochroic. The main optical absorption spectra are determined.

A new borate material, BiB₃O₆ (BiBO) has been reported to have extremely high nonlinear optical (NLO) coefficient. In our investigations we obtained both glass and single crystal of BiBO. Owing to its composition, the material is very viscous when molten. This factor cause serious problems both during synthesis and crystallization of BiBO. In this paper only properties of BiBO glass are reported. We found that for the increase of the long-range ordering the photoinduced optical second harmonic generation (SHG) shows a maximum, which is shifted towards the lower photo inducing power with the increase of the temperature. Maximal value of SHG was about 0.081 pm/V at 1.06 micrometers radiation from YAG:Nd laser.

Study of the optic and elastic properties of SrLaAlO₄ and SrLaGaO₄ crystals are presented. The investigated crystals were grown by Czochralski method. The elastic constants of SrLaAlO₄ and SrLaGaO₄ crystals at room temperature have been determined by Brillouin scattering method. Refractive indices have been measured independently by ellipsometry technique. The results are discussed in terms of the oxygen point defects, which can be crated in the lattices of SrLaAlO₄ and SrLaGaO₄ crystals during the growth process.

Recently, wide gap II-VI mixed crystals are studied for their application in technology of blue-green laser diodes. The mixed crystals were growth using the modified pressure Bridgman method. The temperature, absorption and excitation study of Zn_1-xA_xSe mixed crystals using Raman scattering method is reported. Measurements have been performed for crystal with x equals 0.07 for A equals Mg content and x equals 0.09 for A equals Be content. From the Raman spectra the longitudinal optical (LO) and transverse optical (TO) modes which correspond to ZnSe-, MgSe- and BeSe-like single crystals were distinguished. For all used excitation wavelengths and different temperatures the integrated intensities of LO and TO modes using a curve-fitting method have been calculated.

It is shown that the thermal ionization energy of Mg acceptors in GaN, as determined by temperature dependent Hall effect measurements, exhibits the usual dependence on the concentration of ionized impurities, as seen in many other semiconductors. The observed difference in the thermal and optical ionization energies of Mg acceptors can be quantitatively understood based on a simple electrostatic interaction model.

In this paper we report experimental results concerning the elastic and elastooptic properties of Zn_1-xBe_xSe mixed crystals grown by high pressure Bridgman technique. Using Brillouin scattering method some of the elastic and elastooptic constants of Zn_1-xBe_xSe crystals with different Be content have been determined at room temperature. It has been revealed that the elastic and elastooptic properties strongly depend on the content of Be.

This paper presents work over correlation between parameters of domain structure and pyroelectric current in IR sensors based on TGS. In the frames of realized works new single- crystal of TGS doped with amino acid-serine was grown. Computer measuring system making possible registration of domain structure images of non-linear dielectrics was designed and executed. We worked out measuring and analysis algorithms of domain images. Software making possible calculations and analysis of parameters of observed structures was created and static measurements of domain structure within different growth pyramids were performed. Correlation between parameters of domain structure, quantity of admixture and temperature characteristics of pyroelectric coefficient was found.

We present excited state absorption (ESA) measurements of the Cr:Li₂B₄O₇ glass along with preliminary interpretation. The most distinct feature in the ESA characteristics is connected with the presence of chromium in its hexe-valence states. The Cr⁶⁺ ions appear to contribute in the deexcitation processes and their evidence can be seen in the ESA spectra under excitation wavelength at 308 nm. We interpret the ESA spectra detected with UV excitation in terms of transitions in the framework of Cr⁵⁺O^- center which forms aster charge- transfer-type absorption in (CrO₄)^2- group. We assume the presence of the double-electron state of the 3d²2p⁴ electronic configuration together with crystal field-split states of the 3d¹2p⁵ configuration, both allow to reproduce the obtained ESA spectra.

The main issue which is yet to be resolved in further developing the Surface Channel MOSFETs is understanding and eliminating deterioration of the carrier mobility at the insulator-semiconductor interface. The main factor causing this deterioration is hole and electron trapping-detrapping. One of the ways recently suggested of minimizing hole and electron trapping-detrapping at the Si-SiO₂ interface involves replacing the SiO₂ by silicon oxynitride. However, degradation of MOSFETs, which have oxynitrides as gate dielectric, caused by trapping of hot electrons from the channel, is still found.

This paper deals with the possibilities offered by the wavelet transform used in the analysis of the transient response of MIS circuits. This approach has certain advantages over the classical finite element or finite difference-based algorithms when applied to drift-diffusion model.

The SAW devices are widely used as filters, delay lines, resonators and gas sensors. It is possible to use it as mechanical force. The paper describes sensitivity of acceleration sensor based on SAW using the Rayleigh wave propagation. Since characteristic of acceleration SAW sensors are largely determined by piezoelectric materials, it is very important to select substrate with required characteristics. Researches and numerical modeling based on simply sensor model include piezoelectric beam with unilateral free end. An aggregated mass is connected to the one. The dimension and aggregated mass are various. In this case a buckling stress and sensitivity are changed. Sensitivity in main and perpendicular axis are compare for three sensor based on SiO₂, LiNbO₃, Li₂B₄O₇. Influences of phase velocity, electro-mechanical coupling constant and density on sensitivity are investigated. Some mechanical parameters of the substrates in dynamic work mode are researched using sensor model and Rayleigh model of vibrations without vibration damping. The model is useful because it simply determines dependencies between sensor parameters and substrate parameters. Differences between measured and evaluated quantities are less than 5 percent. Researches based on sensor modes, which fulfilled mechanical specifications similarly to aircraft navigation.

The two photon absorption coefficient and third order nonlinear optical susceptibility of ZnSe crystals were investigated using the transmission and degenerate four wave mixing methods. The experimental results show that imaginary part of third order nonlinear optical susceptibility decrease with increase of free carriers and the absolute value of third order nonlinear optical susceptibility increase with increase of free electron concentration.

Bulk single crystals up to 20 mm in diameter and 40 mm long for LiInS₂ and up to 10 mm, 20mm, respectively, for LiInSe₂ have been grown. Their color changed from colorless to rose for the first one and from yellow to dark red for the other. All crystals have wurtzite-type lattice, lattice parameters were determined. A band gap was found to be 3.72 and 3.57 eV for LiInS₂ and 3.02, 2.86 eV for LiInSe₂ at 80 and 300K respectively. Color variations are due to point defects, first of all to interstitial sulfur, resulting in additional wide absorption bands in the shortwave part of transparency range. For LiInS₂ the SHG phase matching conditions were found to be similar for samples of different color and some difference from Boyd's predictions of 1973 was shown.

In this communication we report initial results of studies on x-ray and VUV excited luminescence of YAP and YAG crystals activated with Pr³⁺ and YAP activated with Ce³⁺. Excitation and luminescence spectra of Pr³⁺ and Ce³⁺ d-f and Pr³⁺ f-f emissions and luminescence time profiles under pulsed synchrotron excitation are presented and analyzed in order to identify and characterize various host-to-ion energy transfer channels. The results support the notion that direct and trap mediated capture and recombination of holes and electrons via Pr³⁺ or Ce³⁺ ions provide the dominant mechanism of radio luminescence production in both YAP and YAG crystals.

Cobalt doped SrLaGa₃O₇ single crystals have been grown by the Czochralski method in a nitrogen atmosphere and by a floating zone method with optical heating in air. Starting concentrations of Co in the melt were: 0.15, 0.3, 2 and 3 mol percent with respect to Ga by the Czochralski method whereas 2 and 4 mol percent by the floating zone method. We have presented absorption spectra as well as EPR spectra related to octahedrally coordinated Co²⁺ ion in SrLaGa₃O₇.

In this paper changes in active and lattice ions valence were investigated in some laser materials such as: Cr:Y₃Al₅O₁₂, Cr:LiNbO₃ and Cr:Li₂B₄O₇ glass, Ti:Al₂O₃ and Ti:LaGaO₃, Co:SrLaGa₃O₇ and Co:Li₂B_{4$?O(subscript 7} glass, Eu, Dy:Li₂B₄O₇ glass, Ho:LiTaO₃, Nd:YVO₄ , Nd:SrLaGa₃O₇ and Pr:SrLaGa₃O₇ after annealing in oxidization and reducing atmospheres, ionizing with gamma, electrons and protons. After (gamma) -irradiation 446 nm emission is observed for Ti:LaGaO₃ single crystal due to ²E yields ²T₂ transition of Ti³⁺.

Single crystals of Ca₄GdO(BO₃)₃ have ben grown from a melt by the Czochralski puling method making use seed orientation. Defects, like dislocation were investigated. Chemical methods were developed on various planes of crystals, in order to reveal the nature and the distribution of these defects. Dielectric measurements in frequency range 20Hz-13MHz in three main crystallographic directions were carried out. The values of elastic and piezoelectric coefficients were calculated for the first mode of piezoelectric vibration in each direction.

Rare-earth doped SrLaGa₃O₇ single crystal are promising laser materials. Also crystal doped with Ho³⁺ ions could be used as efficient laser in visible and near IR regions. Laser materials, generating in visible and IR regions, can be used for optical data recording in micro photolithography and in medicine. SrLaGa₃O₇ single crystal doped with 0.3, 1.5 and 2 at percent of Ho³⁺, respectively were grown by the Czochralski method with use of iridium crucible and after heater. According to EPMA measurements distribution coefficient of Ho³⁺ in SrLaGa₃O₇ was estimated to be k approximately equals 0.22. Optical absorption spectra in visible and IR regions were measured at 300K and 12K respectively. Optical quality of single crystals was checked by the use of computerized imaging spectropolarimeter and polariscopic measurements. Temperature dependence of capacitance and conductivity for different dopant concentrations were also measured.

Crystals of Er:YVO₄ were grown by Czochralski method. Uniformly doped and good quality crystals have been obtained. The lifetimes of the ⁴S_3/2, and the luminescence dynamics were studied as a function of temperature in the region 5-500K. The green luminescence around 550 nm has been observed in excitation by the Ti:sapphire laser into ⁴I_11/2 level. The excitation spectrum recorded for ⁴S_3/2 has been compared with absorption cross section spectrum and calculated ESA spectrum for ⁴I_11/2-⁴F_7/2 transition. The contribution of ESA process in upconversion phenomenon under excitation into ⁴I_11/2 has been assessed. The emission cross-section and the gain coefficient for ⁴I_13/2-⁴I_15/2 transition of Er³⁺ in YVO₄ have been calculated.

This paper deals with the excitation and decay of excited state of holmium in LiTaO₃ single crystals. Particular attention is paid to processes governing a population build up on the ⁵S₂ and ⁵I₇ metastable states whose quantum efficiencies are sufficiently high to be considered as initial levels for a laser transition. We observed for the first time, to our knowledge, an efficient conversion of the 647.1 nm light of a krypton ion laser into green luminescence in the material studied. Based upon analysis of excited state relaxation dynamics it is concluded that the mechanism involved is the excited state absorption from the long lived ⁵I₇ level. Efficient single wavelength excitation is due to coincidence of transition energies of the ground state absorption and excited state absorption.

Absorption and emission spectra of Cr, Eu and Dy ions in Li₂B₄O₇ glasses melted in oxygen and hydrogen were measured for valency states and excited states analysis. It was stated that the presence of Cr⁶⁺ ion is limited by composition of the starting mixture and atmosphere of the melting and that this ions arises as Cr⁶⁺O₄ complex.

Yttrium aluminium garnet thin films doped with neodymium have been prepared by Pulsed Laser Deposition method on (111)-oriented Si substrates. The substrate was heated up to temperature in the range between 200 and 600 degrees C. Obtained films were then characterized both by x-ray diffraction method using Siemens D5000 diffracto-meter and radioluminescence spectroscopy.

In this work we report on numerical investigations of the effect of the light beam divergence or imperfect crystal alignment on the response of electrooptic modulators. Resulting non linearities are discussed both in terms of nonlinear distortion of modulators and as related to errors in measurements of quadratic electrooptic coefficients. Our calculations based on the Jones calculus have been performed for uniaxial crystals including KDP, and its isomorphs, and LiNbO₃. The results obtained confirm that either the response of the modulators or results of electrooptic measurements can be significantly affected by the light divergence or imperfections in the crystals alignment.

The results of examinations of spectroscopic properties and generation parameters of new active media, i.e., Er³⁺ and Yb³⁺ doped YAG crystals are given. Erbium and ytterbium doped YAG single crystals were obtained by the Czochralski method. The spectral properties and laser characteristics were investigated. Absorption spectra of Er³⁺ and Yb³⁺-doped active media were measured in the spectral range 190 divided by 5000 nm at room temperature. Excitation and luminescence spectra were also recorded at room temperature with a JOBIN-YVON spectrofluorimeter using a diode laser as an excitation source. The measurements of the lifetime of the Er³⁺ ions in the upper laser level of the samples were made by the direct method with pulse excitation. We present also the result of investigations on spectroscopic properties and non-linear absorption effect in YAG:Co²⁺ crystal-new absorber used for the systems generating giant-pulse radiation at 1.5 micrometers .