Resonant ablation rules of femtosecond laser on Pr–Nd doped silicate glass

Resonant effect is found in femtosecond laser ablating Pr–Nd glass. When processed with resonant wavelength of807 nm, resonant ablation efficiency(RAE) with a single pulse can be improved by 45.22%. Furthermore, RAE closely relates to laser intensity. For resonant ablation, RAE is increased significantly when laser intensity0.556 × 1014 W∕cm2 at which multiphoton ionization dominates, while it fades away when laser intensity0.556 × 1014 W∕cm2 at which tunnel ionization dominates. Besides, it is also found that the ablation depth increases along with the wavelength rise when multiphoton ionization dominates, while the change rule is inversed when tunnel ionization dominates.     

Inorganic phosphors in lead–silicate glass for white LEDs

Using spectrophotometry and stationary and kinetic fluorimetry, we have shown that xanthene dye fluorescein forms complexes with polycationic derivative of fullerene in aqueous solutions mainly due to electrostatic interactions. It is found that efficient quenching of singlet excited states of dye occurs in the structure of these complexes due to the transfer of excitation or electron from dye to fullerene. As a result, the photodynamic activity of the newly formed complex is much higher than that of fluorescein and fullerene derivative. This effect makes it possible to predict the formation of new-generation hybrid photodynamic preparations using dyes excited only into a singlet state; as a result, directed searches for these dyes are significantly facilitated.     

Does the standard model of low-temperature glass dynamics describe a real glass?

We present the first experimental single-molecule (SM) spectroscopy study of the local dynamics in molecular glasses (frozen toluene and deuterated toluene weakly doped with a substituted terrylene) at T=2-30 K. Surprisingly, the dynamics does not follow the standard model of low-temperature glasses. An extra contribution to the dynamics was detected causing drifts and irreproducible jumps of the SM spectra. The isotope effects in the SM linewidth distribution and the density of states (boson peak) show that the fast dynamics at T=2 K is due to excitations of tunneling nature, whereas at T>7 K it is related to vibrations; H/D atoms are directly involved in both types of excitations.     

Green and red up-conversion emissions and thermometric application of Er^3＋-doped silicate glass

The green and red up-conversion emissions centred at about 534, 549 and 663 nm of wavelength, corresponding respectively to the ^2H11/2 → ^4I15/2, ^4S3/2 → ^4I15/2 and ^4F9/2 → ^4I15/2 transitions of Er^3＋ ions, have been observed for the Er^3＋-doped silicate glass excited by a 978 nm semiconductor laser beam. Excitation power dependent behaviour of the up-conversion emission intensity indicates that a two-photon absorption up-conversion process is responsible for the green and red up-conversion emissions. The temperature dependence of the green up-conversion emissions is also studied in a temperature range of 296-673 K, which shows that Er^3＋-doped silicate glass can be used as a sensor in high-temperature measurement.     

Electrical and thermal properties of chalcogenide glass system Se75Ge25−x Sb x

The dc and thermal conductivities of five different compositions of the chalcogenide glass system Se₇₅Ge_25–x Sb _x have been studied in a temperature range below T _g. The dc conductivity results indicate that each composition has a single activation energy in the considered temperature range. The coefficient of thermal conductivity increased linearly with temperature below T _g for the compositions investigated. The increase of Sb content in the chalcogenide glass system leads to an increased coefficient of electrical conductivity , an increased coefficient of thermal conductivity , and to a decreased activation energy E and pre-exponential factor ₀. The observed compositional dependencies of and E have been correlated with the increase of weak bond density and the decrease of covalent bond density in the structure of the compositions investigated with increasing Sb content at the expense of Ge content. The decrease in ₀ and the increase in has been, respectively, correlated with the decrease in mobility and the increase in phonon velocity.     

Quantum confinement effect in the vibrational spectrum of CdSxSe1−x quantum dots in a fluorophosphate glass matrix

The vibrational spectra of mixed cadmium sulfoselenide nanocrystals in a fluorophosphate glass matrix are investigated by Raman spectroscopy. The asymmetry of the lines of the fundamental modes of nanocrystals is experimentally observed in the region of lattice vibrations, which is interpreted as a quantum confinement effect. In the framework of the model of confined phonons, the contribution of the band states to the Raman scattering spectrum is calculated and the size of nanocrystalline regions is estimated. The results obtained are in good agreement with the data on the low-frequency Raman scattering in these objects.     

Quantum confinement in CdSxSe1−x spherical nanocrystals in a fluorophosphate glass matrix

Differential (wavelength-modulated) absorption of sulfoselenide solid-solution nanocrystals has been studied in a glassy fluorophosphate matrix near the fundamental absorption edge at 360–620 nm. The observed oscillations in the absorption are attributed to size quantization of electrons and holes under strong quantum-confinement conditions. The sulfur content in the mixed semiconductor has been refined from Raman scattering spectra in CdS_xSe_1?x samples with x=0.30, and the nanocrystal size (R?30 Å) has been derived from low-frequency Raman scattering spectra. These data were used to calculate the energies of electron-hole transitions in nanocrystals of mixed composition, and their subsequent comparison with experiment. The calculations were found to be in a good agreement with the observed experimental absorption spectrum for nanocrystals about 45 Å in size. The applicability of band-structure simulation for a nonspherical nanocrystal grown in a fluorophosphate glass matrix is discussed.     

Mössbauer studies of ZnCr2xGa2−2x O4 spinel solid solutions: A cluster spin glass for 0.6 ≲x ≲ 0.85

Mössbauer studies of topologically frustrated ZnCr_2xGa_2–2xO₄ system (0.6 x 1) are performed. Almost all the spectra consist of a superposition of a paramagnetic doublet and an enlarged magnetic hyperfine pattern. Two models are used to fit the spectra, a static hyperfine field distribution method and a superparamagnetic type relaxation simulation method. In the composition range 0.6 x 0.85, for which spin glass behavlour has been evidenced, only the second model gives coherent results rather in agreement to a dynamic non equilibrium process with a progressive freezing of cluster moment.     

Investigations on ultrafast welding of glass–glass and glass–silicon

Using ultrafast laser radiation glass substrates are welded with glass and silicon plates. The pump beam is focused by a microscope objective with large NA=0.4 (beam diameter 4 μm) into the glass. After partial absorption of the optical energy, the glass is heated and melted. Procedures for high-quality welding of glass–glass and glass–silicon substrates with high-repetition ultra-fast laser radiation have been derived at the repetition rate 700 kHz. The dependencies of the dimension and geometry of the welding seam on scan velocity, repetition rate and pulse energy have been investigated defining a process window. Adding a noninterferometric technique for quantitative phase detection with the welding setup, the interaction zone of the welding seam for the welding partners glass–glass is detected. A change in refractive index is induced by heating and compression of the glass and has been detected by phase detection up to 2 μs after irradiation with 100 fs time resolution.     

Preparation and luminescence characteristics of Eu^2＋ activated silicate phosphor

This paper synthesizes the Sr2SiO4：Eu^2＋ phosphor by high temperature solid-state reaction. The emission spectrum of Sr2SiO4 ： Eu^2＋ shows two bands centred at 480 and 547 nm, which agree well with the calculation values of emission spectrum, and the location of yellow emission of Sr2SiO4 ： Eu^2＋ is influenced by the Eu^2＋ concentration. The excitation spectrum for 547 nm emission has two bands at 363 and 402 nm. The emission spectrum of white light emitting diodes （w-LEDs） based on Sr2SiO4 ： Eu^2＋ phosphor ＋ InGaN LED was investigated.     

Modeling of a structural phase transition in La2−x SrxCuO4

The structural, vibrational, and elastic properties of La₂CuO₄ are calculated using a model for calculating the energy of the crystal based on interionic potentials with the multiparticle Jahn-Teller contribution included explicitly. The microscopic reasons for the structural instability of the La₂CuO₄ lattice relative to rotations of the oxygen octahedra are investigated. A structural phase transition from the orthorhombic phase (space group D _2h ¹⁸ ) into the tetragonal phase (space group D _4h ¹⁷ ) under hydrostatic compression of an La_2−x Sr_xCuO₄ crystal is modeled. The (P,x) structural phase diagram for La_2−x Sr_xCuO₄ is constructed. Fiz. Tverd. Tela (St. Petersburg) 41, 1096–1102 (June 1999)     

Writing of internal gratings in optical glass with a femtosecond laser

The writing of an internal diffraction grating in optical glass plate is demonstrated using low-density plasma formation excited by a high-intensity femtosecond Ti:sapphire laser. The same diffraction efficiency at ±1,±2, and 0 order is achieved by multiple layers writing. The dependences of diffractive efficiency on the irradiated energy, the speed of writing, the numerical aperture (NA) of the focusing objective, and materials are investigated in detail. The grating is birefringent. It is attributed to residual stress interaction between glass and femtosecond laser pulse.     

Characterisation of Ba2In2 − x Sn x O5 + x/2 oxide ion conductors

The Ba₂In_2 − x Sn _x O_5 + x/2 solid solution was confirmed up to x = 1 by solid-state reaction. X-ray diffraction at room and at elevated temperatures, Raman scattering and impedance spectroscopy were used to characterise the samples. The structure refinement of the composition x = 0.1 from neutron diffraction data reveals that tin is preferentially located in the tetrahedral layers of the brownmillerite. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007     

Crystallization kinetics of the TeO2–BaO glass system

Tellurite glasses of the system (100–x)TeO₂–xBaO, with x = 05, 10, 15 and 20 wt%, have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under non-isothermal conditions, applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC, using continuous-heating techniques. In addition, from the dependence of the glass-transition temperature (T _g) on heating rate, the activation energy for the glass transition was derived. Similarly, the activation energy of the crystallization process was determined and the crystallization mechanism characterized. The thermal stability of these glasses are considered in terms of the characteristic temperatures, T _g and T _in (the onset temperature of crystallization), via ΔT = T _in?T _g and a kinetic parameter K(T _g). The results confirm that thermal stability decreases with increasing BaO content. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of α-TeO₂, γ-TeO₂ and BaTeO₃ in the remaining amorphous matrix.     

Magneto-optical properties of terbium glass

Dispersion of the Verdet Constant of Tb-glass is investigated.The cause of thisdispersion is dicussed by a comparison with the dispersion of refractive index.Relationship be-tween the Verdet constant and Tb~(3 ) concentration is summaried and can be used to estimatethe Verdet constant of Tb~(3 )-materials.     

Ferri-spin glass nature of spinel ferrites Gax Fe1−x Ni Cr O4

Mössbauer measurements in mixed spinel ferrite Ga_x Fe_1–x Ni Cr O₄ (0x0.8), carried out between 4.2 and 298°K, show the presence of entropic spins in this system. Recent Monte Carlo calculations /4/ have predicted the presence of such spins in a frustrated spin glass lattice.     

Specific features of plastic relaxation of a metastable Ge x Si1 − x layer buried between a silicon substrate and a relaxed germanium layer

Heterostructures Ge/Ge _x Si_{1 ? x} /Si(001) grown by molecular beam epitaxy have been investigated using atomic scale high-resolution electron microscopy. A germanium film (with a thickness of 0.5–1.0 μm) grown at a temperature of 500°C is completely relaxed. An intermediate Ge_0.5Si_0.5 layer remains in a strained metastable state, even though its thickness is 2–4 times larger than the critical value for the introduction of 60° misfit dislocations. It is assumed that the Ge/GeSi interface is a barrier for the penetration of dislocations from a relaxed Ge layer into the GeSi layer. This barrier is overcome during annealing of the heterostructures for 30 min at a temperature of 700°C, after which dislocation networks having different degrees of ordering and consisting predominantly of edge misfit dislocations are observed in the Ge/GeSi and GeSi/Si(001) heteroboundaries.     

Thermal conductivity of single crystals of the Ca1 − x Y x F2 + x solid solution

The thermal conductivity of single crystals of the solid solution of yttrium fluoride in calcium fluoride Ca_{1 ? x} Y _x F_{2 + x} with the fluorite structure (x ≤ 0.20) and the Ca_0.27Y_0.73F_2.73 phase with the tisonite structure has been studied by the absolute steady-state longitudinal heat flow method in the temperature range 50–300 K. It has been established that the thermal conductivity drops sharply with increasing yttrium trifluoride concentration, especially in the low-temperature region.