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The formation and crystal structure of a novel rare-earth compound series, R₃ Co₂₉ M₄ B₁₀ , have been investigated by electron microscopy, x-ray diffraction and Rietveld refinement. R₃ Co₂₉ M₄ B₁₀can form for R = La, Ce, Pr, Nd, Sm, Gd, Ho, Tb, Er, Tm, Dy, Lu and M = Si, Al, Ge, and are isostructral with Nd₃ Ni₂₉ Si₄ B₁₀ .

We report on the use of a low-temperature scanning probe microscope to investigate non-equilibrium electronic transport through a one-dimensional ballistic constriction. Transconductance images of electrons backscattered in the adjoining two-dimensional reservoirs show a weak acceptance cone consistent with semiclassical collimation. The images also show a strong highly collimated beam of quasi-particles injected into each reservoir with a divergence consistent with quantum mechanical diffraction. In the lower-chemical-potential reservoir these quasi-particles are interpreted as hot electrons while in the higher-chemical-potential reservoir they are interpreted as conduction-band holes.

A tunnel junction based on the half-metallic oxide CrO₂uses a native oxide barrier layer and a cobalt top electrode. The I :Vcharacteristic is fitted to the Simmons model with = 0.76 eV and t= 2.0 nm. The magnetoresistance is positive with R /R= 1.0% at 77 K.

⁵⁷ Fe Mössbauer spectra of RNiBC (R = Gd, Tb, Dy, Ho, and Er) compounds doped with ⁵⁷ Fe (0.5 at.%) taken above their magnetic ordering temperatures reveal a quadrupole doublet with a splitting |E_Q| which decreases on going from Gd to Er. The values of |E_Q| depend linearly on the parameter c ´/a , with c ´ being the distance apart of the R-C layers between which the Ni₂ -B₂layer is sandwiched and abeing the lattice parameter in the basal plane. The |E_Q| versus c ´/arelation is identical with that previously found for RNi₂ B₂ C compounds.

Boron-doped diamond-like carbon (DLC) was prepared using an inductive radio-frequency Ar + C₂ H₂+ B₂ H₆plasma-immersion ion-processing (PIIP) technique. The novel results show that B incorporation reduces the stress and that low-energy Ar-ion impingement suppresses the increase of the amount of hydrogen in the B-doped DLC film. An optimal combination of higher hardness, 24.6 - 28 GPa, and reduced stress was reached in DLC film doped with 4 to 10 at.% B. An increase in the sp³carbon and sp³CH bonding in the DLC films was found with B doping and was correlated with the enhancement of the properties.

The properties of a molecularly thin film of spherically symmetric molecules confined to a chemically heterogeneous slit-pore were investigated by Monte Carlo simulations in a grand mixed stress-strain ensemble. The slit-pore comprises two identical plane-parallel solid substrates, each of which consists of alternating strips of solid of two types: strongly adsorbing (width d_s ) and weakly adsorbing. Under favourable thermodynamic conditions the confined film consists of fluid bridges - that is, a high(er)-density fluid over the strongly attractive strip surrounded by a low(er)-density fluid supported by the (outer) weakly attractive strips. By misaligning the opposite substrates, bridge phases can be exposed to a shear strain s_x(0 ½, s_xthe side length of the simulation cell) and the associated shear stress T_zxof (fluidic) bridge phases can be calculated from molecular expressions. The stress curve T_zx (s_x ) is qualitatively similar to the one characteristic of solidlike films confined between atomically structured substrates in that the initial response to small shear strains is Hookean, and this is followed by an increasingly nonlinear regime up to the yield point where T_zx (s_x ) assumes its maximum. We also investigated the influence of chemical corrugation c_r : = d_s /s_xon T_zx (s_x ). With increasing c_r , yield strain and stress increase at first up to a maximum and decline thereafter. By employing the theory of corresponding states, T_zx (s_x ) is renormalized by yield stress and strain such that the results can be represented uniquely by a master curve independent of any system-dependent parameters.

In this paper we investigate the phase behaviour of a `simple' fluid confined to a slit of nanoscopic width s<sub>z</sub>by chemically decorated, plane-parallel substrates consisting of slabs of weakly and strongly adsorbing solid which alternate in the x -direction with period s<sub>x</sub> . In the y -direction the substrates, occupying the half-spaces - z - s<sub>z</sub> /2 and s<sub>z</sub> /2 z , are translationally invariant. On account of the interplay between confinement (i.e., s<sub>z</sub> ) and chemical decoration, three fluid phases are thermodynamically permissible, namely (inhomogeneous) gaslike and liquidlike phases and `bridge phases' consisting of high(er)-density fluid over the `strong' part which alternates in the x -direction with low(er)-density fluid over the `weak' part of the substrate. In the x -yplane the two are separated by an interface. Because of their lateral inhomogeneity, bridge phases can be exposed to a shear strain s_x(0 ½) by misaligning the substrates in the x -direction. Depending on the thermodynamic state of the confined fluid and details of the chemical decoration, shear-induced first-order phase transitions are feasible during which a bridge phase may be transformed into either a gaslike (evaporation) or a liquidlike phase (condensation). These phase transitions are studied by computing phase diagrams as functions of s_xfor a mean-field lattice-gas model. The lattice-gas calculations are amended by grand canonical ensemble Monte Carlo simulations of a fluid confined between chemically decorated substrate surfaces. The combination of the two sets of data reveals that the lattice-gas model captures correctly key characteristics of shear-induced first-order phase transitions in this rather complex system despite its mean-field character.

A microscopic approach to the investigation of the behaviour of a symmetrical binary fluid mixture in the vicinity of the vapour-liquid critical point is proposed. It is shown that the problem can be reduced to the calculation of the partition function of a three-dimensional Ising model in an external field. For a square-well symmetrical binary mixture we calculate the parameters of the critical point (critical temperature and critical density) as functions of the microscopic parameters: the parameter rmeasuring the relative strength of interactions between the particles of dissimilar and similar species and the parameter measuring the width of the potential well. The results obtained agree well with the ones from computer simulations.

A neutron scattering study of the dynamics of CH₄molecules in the restricted geometry of porous TiO₂with an average pore diameter of 110 Å is presented. Two different coverages were studied: (1) completely filled pores; (2) walls covered by a monomolecular film. Rotational tunnelling spectra of the methane rotors at T= 5 K show the coexistence of the low-temperature phase of bulk methane (phase II) with a disordered phase (phase I´) in a layer close to the wall. In the melting region of the condensate, the neutron spectra yield information about translational and rotational motion of the methane molecules. The fraction x (T ) of molecules that are in the liquid phase increases over a rather wide temperature range from x ~0 at T= 83 K up to x ~1 at T= 95 K.

Order-Ntight-binding molecular dynamics has been implemented with a Fermi operator expansion and applied to a low-density liquid carbon at a temperature above the melting point of graphite. For various sets of the parameters introduced in the order-Napproximation, the radial distribution function and the mean square displacement are calculated. The conservation of energy during a constant-energy simulation is studied.

We present a model of the glass transition viewed as the agglomeration and growth of clusters forming a covalent network. The creation of new layers of atoms on the rims of the clusters is treated in a probabilistic way as a linear transformation (encoded in what is called a stochastic matrix ) of a vector whose components represent the probability distribution of various sites found on the rim. The asymptotic limit of the statistics of sites in the network is given by the matrix eigenvector with eigenvalue equal to one. The model reproduces the modified Gibbs-DiMarzio equation with a system parameter that is comparable to the one observed experimentally for many chalcogenide glasses. Some other features of the glass transition process, like the form of the specific heat, are also obtained.

In this paper, we investigate the behaviour of electrons in the -helix polypeptide chain and show that an electron can be bound in the compression area of the proton sublattice and become an electrosoliton state described by a bell-shaped electronic wave function. Due to the coupling between the three hydrogen-bonded chains, symmetric and asymmetric electrosoliton-soliton pairs are obtained.

The present study reports several novel results pertinent to the wetting transition in Ga-Bi. These results show that complete wetting depends crucially on the boundary conditions between the liquid sample and the container. If liquid Ga does not wet the container wall a thick Bi film of about 50 µ spreads over the Ga surface at nearly room temperature due to the Marangoni effect. If Ga wets the wall the wetting transition occurs near to the monotectic temperature of this system. The interfacial tension inferred from the surface light scattering data displays non-monotonic behaviour on heating.

In order to combine the advantages of tight-binding integral equation methods with basis sets not restricted to the lowest two orbital quantum numbers we extend the molecular fluid approach for the sp³model of Lomba et alto arbitrarily high orbital quantum numbers. As an example, we present a single-superchain/effective-medium calculation of the electronic density of states for liquid silicon within a tight-binding approximation that includes, besides the 3s and 3p orbitals, also the 3d orbitals. Comparison with results from the sp³model and different molecular dynamics results shows that within this sp³ d⁵model very good agreement with plane-wave calculations is found whereas the sp³model leads to unsatisfactory results.

Results are presented of studies of linear and nonlinear dielectric measurements in the isotropic, smectic E phase in 4,4-alkyl-4´-isothicyanatobiphenyls (4BT). The mean-field behaviour was valid up to the smectic E phase transition. In the smectic E phase the Vogel-Fulcher law describes temperature and pressure dependences of the relaxation time. An analysis of the higher temperature relaxation time data led to predictions of the mode coupling theory with the power law universal function = A (T- T_C ) , where = -3.3, T_C= 288 ± 15 K. Increase of pressure brings the ´´ curve closer to the Debye shape.

Samples with nominal compositions La_1.2 (Sr_1-x Ca_x )_1.8 Mn₂ O₇(x= 0.00, 0.25, 0.50, 0.65, 0.80 and 1.00) have been prepared and characterized by x-ray diffraction (XRD) and ac susceptibility techniques. Drastic changes in the XRD pattern and in the ac susceptibility versus temperature behaviour at x= 0.65 indicate that single phase compounds with layered Sr₃ Ti₂ O₇structure are formed only up to x= 0.50. Rietveld refinement of the XRD patterns of x= 1.00 composition suggests that the compositions with x 0.65 form multiphase mixtures comprising hole doped perovskite manganates as majority phases and CaO as the minority phase. These results are at variance with the literature reports that the compound La_1.2 Ca_1.8 Mn₂ O₇forms with layered Sr₃ Ti₂ O₇structure.

We report the first observation of structural phase transitions in Cs₆ In_0.5 W_10.5 O₃₆crystallizing with a structure intermediary between the hexagonal tungsten bronze and pyrochlore structure. The recorded Raman spectra indicate the onset of three phase transitions at about 256, 505 and above 800 K. The crystal structure above the highest temperature transition point seems to be trigonal and the Raman study suggests that below the transition point the unit cell volume is multiplied. This transition is observed also as a marked dielectric anomaly at 867 K. The character of this anomaly suggests that this transition may be ferroelectric and diffuse or order-disorder type. The heat capacity, dielectric and Raman studies show that the transition at 505 K is second order or nearly so. It is of displacive type and is induced by a soft mode, which is most likely due to a tilt of WO₆octahedra. The low-temperature transition at 256 K has been observed in Raman experiment only. However, the observed changes in Raman spectra, which may indicate the onset of a phase transition at 256 K, are slight and therefore the confirmation of this transition needs further studies.

The structural phase transformations of ZnSe under high pressure are studied by using a first-principles pseudopotential method and the local density approximation for the exchange-correlation potential. A new phase, which is simple cubic with a 16-atom basis (SC16), is predicted to be thermodynamically stable between 9.2 and 16.4 GPa, which is below the stability pressure range of the rock-salt structure. The cinnabar structure of ZnSe is found to be unstable, contrary to the findings of a previous theoretical investigation. The structural properties of the zinc-blende, rock-salt, cinnabar and SC16 phases are presented.

The commensurate-incommensurate phase transition of a Rb₂ ZnCl₄crystal was studied using a conduction calorimeter. By identifying the contribution of the specific heat to the transition enthalpy it was possible to show, for the first time for a compound of this type, transition latent heat. This was estimated to be Q= 2.3 J mol^-1 . The result was compared with theoretical predictions for a domain wall model having repulsive-attractive interaction; satisfactory results were obtained for the first time. The same analysis was applied to the normal-incommensurate phase transition and no latent heat was observed, as expected.

Equilibrium properties for the -phase of Pu have been calculated. Taking into account strong electron correlations in the 5f shell, we show how the equilibrium volume and the bulk modulus are improved in comparison to previous results using the local density approximation (LDA) or the generalized gradient approximation (GGA). In addition, an augmentation of the orbital moment is observed following Hund's rules, reducing the total magnetic moment. The stability of the -phase is explored and for the first time a positive value for the tetragonal shear constant is found.

We present the results of self-consistent LMTO-ASA band structure calculations for SrNbO_3.4based on the LDA. Eight bands per spin cut the Fermi surface. In accordance with experiment, we obtain a low density of states at the Fermi level, rising steeply with increasing energy. This explains qualitatively the low susceptibility found in this material. Similar to the simple perovskite structure SrNbO₃ , the conduction band complex is separated from the 5.6 eV wide valence band region by a gap of 1.7 eV. The spatial charge distribution shows that the bonding between the niobium and the oxygen atoms within the two-dimensional octahedral network is of primarily ionic character. A band complex of width 3.45 eV found at 17 eV below E_Fis due to the O 2s states. The reasonable agreement between our calculated XAS cross sections for different light polarizations with recent experimental results suggest that an LDA treatment of this class of substances is appropriate, whereas Coulomb correlations play a minor role.

We have investigated momentum dependent excitations in conjugated organic oligomer materials. Theoretical simulations based on the intermediate neglect of differential overlap (INDO) approach coupled to a single configuration interaction (SCI) technique considering the proper transition matrix elements for inelastic electron scattering are compared to experimental electron energy-loss spectroscopy (EELS) investigations. In this work we concentrate on sexiphenyl (6P), sexithienyl (6T) and beta-carotene. 6P and 6T are widely used in a number of electronic and optoelectronic devices and together with beta-carotene they can be regarded as model substances for the three big classes of conjugated polymer materials, namely phenylenes, thiophenes and acetylenes. Both experimental and theoretical results underline the validity of the so called quasi-band-structure model for the description of periodic molecules with only a finite number of repeat units. We also highlight the influence of chain orientation on EELS spectra and discuss the reasons for certain deviations between molecule-based simulations and the excitation processes occurring in the actual molecular crystals upon inelastic electron scattering.

We report electronic, magnetic and transport properties of (Fe_1-x V_x )₃ Al alloys with x= 0 - 0.38 and analyse the results on the basis of the measured electronic specific-heat coefficient, the Debye temperature and the magnetic stiffness constant. As the V composition increases, the electrical resistivity increases rapidly at low temperatures and the magnetization decreases significantly in parallel with a sharp reduction in the Curie temperature. In particular, the Heusler-type Fe₂ VAl compound (x= 0.33) is found to be in a marginally magnetic state and to exhibit a semiconductor-like behaviour with the resistivity reaching 3000 µ cm at 2 K. Low-temperature specific heat studies demonstrate a substantial decrease in carrier concentration with the V substitution, being consistent with recent band calculations, which predict that Fe₂ VAl is a nonmagnetic semimetal with a sharp pseudogap at the Fermi level. A large mass enhancement deduced from the electronic specific-heat measurements suggests that Fe₂ VAl is a possible candidate for a 3d heavy-fermion system. The unusual electron transport is mainly attributed to the effect of strong spin fluctuations, in addition to the existence of very low carrier concentrations.

We investigate theoretically the possibility of finding a charge-density-wave (CDW) instability in a zero-temperature double-electron-quantum-wire structure. Intrawire and interwire correlations are treated on the same footing within the self-consistent-field approximation of Singwi and co-workers. To check for the CDW instability, the static density susceptibility is calculated over a wide range of wire parameters (electron number density, wire size, and wire spacing). We find that the double-quantum-wire structure may become unstable against a long-wavelength CDW instability for sufficiently low electron density and narrow wire size, in the close proximity of two wires.

The out-of-plane static magnetoconductivity is calculated as a function of temperature for a single quantum well and a double quantum well in the presence of a parallel magnetic field. The effects of the extended states above the top of the potential barrier are included in the calculations of the temperature dependence. The electron tunnelling between wells is shown to enhance as the temperature is increased. At low temperatures (T <<T_F), the variation of with temperature is determined by the electron density.

A quantum theory of the dependence on bias voltage of the tunnel magnetoresistance in a triple barrier system of the form MOMOMOM is presented. The Ms represent magnetic metallic layers and the Os are thin tunnel barriers. The two inner layers form spin-dependent quantum wells. The relative orientation of the magnetization in the successive magnetic layers can be changed from parallel to antiparallel. For a particular thickness of the inner metallic layers, a very large change of resistance occurs between the parallel and antiparallel magnetic configurations due to the spin dependence of the resonant tunnelling in these layers. It is shown that oscillations in the voltage dependence of the magnetoresistance amplitude take place associated with oscillations between resonant and antiresonant tunnelling as a function of the electrons' energy.

We present results for the measured low temperature magnetoresistance of nanostructured Ag produced by inert gas phase condensation. The Ag particles are typically between 2 and 100 nm in diameter and the material is in the form a network of chains of particles. The magnetoresistance is negative and consistent with the presence of quantum interference effects similar to that seen in disordered metals. From the field dependence of the resistance we can infer characteristic length scales associated with the network of connected Ag particles.

The magnetoresistances of two-dimensional electron systems in strained silicon on a relaxed silicon-germanium buffer have been measured at low temperatures (50 mK). Samples, with Hall mobilities up to 3.61 × 10⁵cm²V^-1s^-1 , have shown a marked asymmetry between adjacent Shubnikov-de Haas peaks and a prominent overshoot on the low-field side of the odd-filling-factor quantum Hall plateaux. This effect persisted to unusually small magnetic fields. It is argued that both of these phenomena can be explained by a strong back-scattering of multiple edge modes which is suppressed at integer filling factors.

The nonlinear susceptibilities of the random-exchange Pd₅ Co₅₀ Al₄₅and Pd₈ Co₅₀ Al₄₂alloys are derived from dc magnetic measurements. They are investigated in the critical region and spin-glass exponents characterizing these materials are obtained. A progressive development of a canonical spin-glass phase is traced from Pd₅ Co₅₀ Al₄₅to Pd₈ Co₅₀ Al₄₂ . The conventional spin-glass phase in Pd₈ Co₅₀ Al₄₂is characterized with the exponents = 3.25 and = 6.4 and a phase transition temperature T_g= 25.3 K.

The magnetization distributions in a series of ternary intermetallic compounds based on the composition Co₂ YZ where Y is Ti, Mn or Fe and Z a subgroup-B element have been determined from polarized neutron diffraction measurements. Comparison of the magnetic structure factors with model calculations shows that the magnetization is associated principally with those atoms which in their elemental state are themselves magnetic. The observed deviations of the magnetic moment distributions from spherical symmetry have been used to deduce which of the 3d sub-bands are active at the Fermi energy. A small moment close to the limits of resolution is observed at some of the Z sites, together with a small delocalized moment which in most cases is negative. The results have been compared with the predictions of band models, which indicate that the Fermi level falls in a broad minimum in the minority-spin density of d states. Although the identity of the bands active at the Fermi surface is in broad agreement with predictions of band-structure calculations (Ishida S, Akazawa S, Kubo Y and Ishida J 1982 J. Phys. F: Met. Phys.121111), the results suggest that there is a finite density of states in the minority-spin d band of manganese. Hence the compounds cannot be classified as half-metallic ferromagnets.

The ground-state energy of spin polarons is investigated by means of squeezed states. The analytical theory developed by Barentzen for the intermediate-coupling region in the t- Jmodel is improved by a procedure of diagonalization of quadratic terms in the effective Hamiltonian through a squeezing transformation.

Powder diffraction patterns were measured on a high quality sample of manganese thiophosphate, MnPS₃ , at temperatures between 2 and 120 K and magnetic fields between 0 and 60 kOe. In zero field, the magnetic moments in MnPS₃are collinear and normal to the abplanes. On applying a sufficiently large magnetic field along the normal to the abplane, it was found that the moments flop towards the baxis, in agreement with a dipole-dipole interaction model for the anisotropy. The width of this transition was found to be greater than 20 kOe. No evidence for critical fluctuations was seen during the spin flop phase transition.

Temperature cw-EPR and pulsed EPR electron spin echo experiments were performed for a low concentration of Cu²⁺ions in cubic SrF₂crystals. The well resolved EPR spectrum at low temperatures (below 30 K) with parameters g= 2.493, g= 2.083, A= 121, A= 8.7, A (¹⁹ F) = 135, A (¹⁹ F) = 33.0 (A -values in 10^-4cm^-1 ) is transformed continuously into a single broad line above 225 K on heating, due to the g -factor shift and EPR line broadening. These data along with the angular variation EPR data are described in terms of a pseudo-Jahn-Teller effect of (T_2g +A_2u ) (a_1g +e_g +t_1u ) type producing six off-centre positions of the Cu²⁺ion in the fluorine cube. Above 30 K a two-step averaging g -factor process occurs and is governed by vibronic dynamics between potential wells of the off-centre positions. This dynamics governs the electron spin relaxation in the whole temperature range. The electron spin-lattice relaxation rate 1/T₁grows rapidly by six orders of magnitude in the temperature range 30-100 K and is determined by the Orbach-type process with excitations to two excited vibronic levels of energy 83 and 174 cm^-1 . For higher temperatures the relaxation is dominated by overbarrier jumps leading to the isotropic EPR spectrum above 225 K. The phase memory time T_Mhas the rigid lattice value 3.5 µs determined by nuclear spectral diffusion and its temperature variation is governed by the vibronic dynamics indicating that the excitations between vibronic levels produce a dephasing of the electron spin precessional motion.

The experimental investigation of the polarization-dependent photoinduced changes of the magnetic state in the haematite crystals doped with ytterbium and gallium ions is presented. The method of antiferromagnetic resonance was used. A detailed study of the kinetics and temperature changes of the photoinduced shift of the magnetic resonance field is made.

Rubber materials for high-voltage outdoor applications have been studied. They were prepared as mixtures of silicone polymer with different concentrations of powdered aluminium trihydrate as a filler. The dielectric properties, *( ) = ´-i ´´, were measured at different temperatures using a low-frequency dielectric spectroscopy technique. Without any filler a classical interfacial relaxation was pronounced with dominating direct-current (dc) conduction in the losses, ´´. On increasing the concentration of filler, a low-frequency dispersion mechanism started to dominate the relaxation behaviour. On adding the filler, the dc conduction first decreased and then increased again after a certain concentration level was passed. This behaviour showed that the filler particles acted like scattering centres or traps for conduction when the concentration was low. As the concentration increased, the conductivity of the filler particles and of the interface (between the filler particles and the polymer matrix) started to dominate the conduction. Master curve shifts of the data showed an Arrhenius type of activation. The data were modelled by superposition of three different processes, Havriliak-Negami dipolar relaxation, dc conduction and low-frequency dispersion (hopping conduction) contributions, using a nonlinear least-squares fitting method.

On the basis of our studies on a method of constructing a class of one-dimensional Fibonacci-class quasilattice ferroelectric domain systems and the properties of the electric field of the second-harmonic-generation light, we obtained the output power per unit area of the second-harmonic-generation light and the efficiency of the output power versus input power. By means of the formula for the output second-harmonic-generation light, we have also obtained the analytical rules governing the absence effect for output ordinary-light spectral lines and that of extraordinary light.

In this paper, a quantum cascade laser has been treated as a three-level system, and the calculation of the spontaneous emission and gain spectra has been given. In the calculation, the conduction band nonparabolicity and the injection and exit of electrons have been considered. Results have shown that with increasing injection current, the spontaneous emission peak blue shifts, and the peak intensity increases near linearly with current. With increasing temperatures, the broadening of the spontaneous emission spectra has been attributed to the electron-optical phonon interactions. The peak gain of the stimulated emission has been shown to be determined mainly by the subband lifespans. We have pointed out that it is essential to obtain a long lifespan for the second excited state and short lifespan for the first excited state in order to obtain efficient population inversion and high peak gain for quantum cascade lasers.

Raman spectroscopy of radiation-damaged natural zircon samples shows increased line broadening and shifts of phonon frequencies with increasing radiation dose. Stretching and bending frequencies of SiO₄tetrahedra soften dramatically with increasing radiation damage. The frequency shifts can be used to determine the degree of radiation damage. Broad spectral bands related to Si-O stretching vibrations between 900 and 1000 cm^-1were observed in metamict/amorphous zircon. The radiation-dose-independent spectral profiles and the coexistence of this broad background and relative sharp Raman modes in partially damaged samples indicate that these bands are correlated with amorphous domains in zircon. The spectral profiles of metamict zircon suggest that in comparison with silica, the SiO₄tetrahedra are less polymerized in metamict zircon. This study also shows that ZrO₂and SiO₂are not the principal products of metamictization in zircon. No indication of bulk chemical unmixing of zircon into ZrO₂and SiO₂was found in 26 samples with a large variation of radiation damage (maximum dose: 23.5 × 10¹⁸ -eventsg^-1 ). Only one sample showed clearly, in all measured sample areas, extra sharp lines at 146, 260, 312, 460 and 642 cm^-1characteristic of tetragonal ZrO₂ . The geological (and possibly artificial heating) history of this sample is not known. It is concluded that radiation damage without subsequent high temperature annealing does not cause unmixing of zircon into constituent oxides.

This paper describes the growth of single crystals of Cr⁴⁺ -doped Y₃ Ga₅ O₁₂(YGG) and Y₃ Al₅ O₁₂(YAG). Control of melt composition and post-growth annealing yields material that contains optimal concentrations of Cr⁴⁺ions in distorted tetrahedral sites normally occupied by Ga³⁺ions in YGG and Al³⁺ions in YAG. Both Cr⁴⁺ -doped garnets exhibit strong visible and near-infrared absorption bands with peak cross sections of order 10^-18 -10^-19cm²and emit into vibronically broadened but weakly allowed ³ B₂(³ T₂ )³ B₁(³ A₂ ) transitions. Nonradiative decay is more efficient in YGG than in YAG as a consequence of the slightly reduced energy gap against radiative decay in the Ga-based garnet.

Thin films were grown by vacuum co-evaporation of CsI and PbI₂compounds from two independent crucibles. X-ray diffraction spectroscopy revealed formation of CsPbI₃and Cs₄ PbI₆nanoaggregates in the thin film samples and gave an estimate of their volume percentage as well. It provided also the grain size estimates, which were compared with direct observation of a thin film surface by atomic force microscopy. The absorption, luminescence and decay kinetics characteristics of thin films grown were measured. The optical characteristics of the mentioned ternary nanoaggregates were determined and compared with those of CsPbX₃and Cs₄ PbX₆(X = Cl, Br) bulk structures.

We have measured the emission spectra and decay kinetics of Ce-doped YAG under both optical and gamma excitation, at temperatures ranging from 60 to 600 K. The decay traces under gamma excitation display an unusual pattern of temperature dependence. Beginning with the lowest temperatures, the characteristic time constant of the decay coincides with the intrinsic (radiative) decay time up to about 180 K, at which point it suddenly jumps by more than 30%. The decay time remains longer than radiative until well above room temperature, then gradually reverts to the intrinsic value. This behaviour can be explained in terms of an array of shallow traps, whose existence is confirmed by the presence of thermoluminescent glow peaks. Depending on temperature, one or more of these traps acts as a temporary way-station for the free carriers that carry the excitation to the Ce ion, delaying its emission beyond what would be required by radiative decay alone.