I. P. Alekseeva

Kinetic regularities of the precipitation of PbS nanocrystals in sodium zinc silicate glasses

The kinetics of formation of nanostructured glass-ceramic materials based on silicate glass doped with lead sulfide PbS is investigated using small-angle X-ray scattering and X-ray powder diffraction. The influence of two-stage heat treatment on the properties of the material is studied. It is established that, in the initial stages of the precipitation during secondary heat treatment, the volume of the lead sulfide phase increases proportionally with the cube of the nanocrystal size; i.e., the number of growing particles is constant and does not depend on the temperature of the secondary heat treatment. At high temperatures of the secondary heat treatment, an increase in the heat treatment time leads to a decrease in the volume of the crystalline phase. The inference is made that this effect is possibly caused by the reaction PbS + Na2O = PbO + Na2S, which should bring about a decrease in the lead sulfide concentration in the matrix and the dissolution of precipitated nanocrystals. The observed kinetics of crystal growth has defied description in terms of the known mechanisms. This is explained by the occurrence of a competing process of dissolution of the crystalline phase that is responsible for the absence of the Ostwald ripening stage, which is governed by the universal kinetics of diffusion phase decomposition at the late stages in supersaturated solid solutions.

Spectroscopic and X-ray Diffraction Investigations into the Specific Features of Crystallization of Potassium Niobium Silicate Glasses

The Raman spectra and X-ray diffraction patterns of initial and crystallized glasses of the composition 25K2O · 27.5Nb2O5 · 47.5SiO2 (mol %) are investigated. It is demonstrated that, upon heat treatment at temperatures in the range 740–900°C, nanocrystals similar in composition to the initial glass precipitate in the glass. The sizes of nanocrystals are estimated with the use of both methods.

Glass-ceramics with γ-Ga2O3:Co2+ nanocrystals: saturable absorber for 1.5–1.7 μm Er lasers

Transparent glass-ceramics containing ?-Ga2O3:Co2+ nanosized (7?12?nm) crystals are synthesized in a lithium gallium silicate system. Their spectroscopic and nonlinear properties are studied. The absorption band related to the 4A2g(4F)???4T1g(4F) transition of Co2+ ions in tetrahedral sites for these glass-ceramics is red-shifted up to ~1.8??m. The absorption saturation fluence is determined to be ~0.8?J?cm?2. The developed glass-ceramics are used for passive Q-switching of diode-pumped Er,Yb:glass laser delivering 1.75?mJ 25?ns-long pulses at 1540?nm.

Morphology of silicate glasses with lead sulfide nanocrystals

The specific features in the structure of nanostructured glass-ceramic materials based on sodium zinc silicate glasses doped with lead sulfide are investigated using small-angle X-ray scattering and X-ray powder diffraction. It is established that a close-to-monodisperse size distribution of PbS nanocrystals is an important structural feature of the system under investigation. An analysis of the X-ray powder diffraction data demonstrates that the shape of the lead sulfide nanocrystals precipitated depends on the heat treatment conditions and can differ from a spherical shape.

Effect of yttrium oxide on the crystallization of glasses of the MgO–Al 2 O 3 –SiO 2 system, nucleated by a mix of titanium and zirconium dioxides, and the transparency of glass--crystalline materials in the superhigh-frequency spectral region

Glass–crystalline materials of the MgO–Al2O3–SiO2 system are used for the production of items with low dielectric losses in the superhigh-frequency spectral region, high mechanical strength, and thermal stability of the dielectric properties. Some glass–crystalline materials of this system are also transparent in the visible region. This paper discusses the phase transformations that accompany the crystallization of glasses of the MgO–Al2O3–SiO2 system with an additive of yttrium oxide, nucleated by a mix of titanium and zirconium dioxides. Segregation of nanosize crystalline phases not previously recorded in this system is detected. A mechanism is proposed for the effect of yttrium oxide on the phase-separation processes. The permittivity and the tangent of the dielectric-loss angle at a frequency of 1010  Hz of the glass–crystalline materials with a mixed crystallization nucleator are compared with the phase composition of the samples.

Synthesis and spectroluminescence properties of lithium aluminosilicate glass–ceramics containing Er x Y b 2?x Ti 2 O 7 nanocrystals

Transparent glass–ceramics in the lithium aluminosilicate system with nanosize crystals of erbium and ytterbium titanates having defect-fluorite and pyrochlore structures have been synthesized for the first time, and the structural transformations that accompany their formation have been investigated. The absorption and the luminescence spectra and kinetics in the near IR region of the erbium and ytterbium ions have been investigated, along with the up-conversion luminescence of erbium ions in glasses and glass–ceramics obtained at various heat-treatment temperatures.

Transparent glass–ceramics based on ZnO and ZnO:Co 2+ nanocrystals

Glasses of the potassium zinc aluminum silicate system, undoped and doped with cobalt oxide, have been synthesized. Differential-thermal analysis and x-ray phase-diffraction analysis were used to study the crystallization physics and the nature of the phases precipitated when the starting glasses were heat treated in the temperature interval 680°C–950°C, as well as the effect of adding cobalt oxide on the phase-transformation processes. Transparent glass–ceramic materials based on only nanocrystals of zinc oxide were obtained, along with zinc oxide and β-willemite. It is found that, when the cobalt-bearing glasses are heat-treated, cobalt ions from the starting glass initially enter into the resulting zinc oxide nanocrystals and, as the temperature is increased, into the β-willemite nanocrystals.

Structural transformations and spectroluminescence properties of magnesium aluminosilicate glass–ceramics containing Er x Y b 2-x (Ti,Zr) 2 O 7 nanocrystals

Transparent glass–ceramics with nanosize crystals of the titanate–zirconates of erbium and ytterbium that have the defect-fluorite and disordered-pyrochlore structures have been synthesized in the magnesium aluminosilicate sitall-forming system, and the structural transformations that accompany their formation have been studied. This paper discusses the absorption and the luminescence spectra and kinetics of erbium and ytterbium ions in the near-IR region and the up-conversion luminescence of erbium ions in glasses and glass–ceramics obtained at various heat-treatment temperatures. A comparison is made of the structures of crystals with the defect-fluorite and pyrochlore structures formed in magnesium- and lithium aluminosilicate glasses when they are heat-treated, as well as the spectroluminescence properties of the resulting magnesium- and lithium aluminosilicate glass–ceramics.

Phase transformations in sodium zinc silicate glasses containing PbS nanocrystals

The phase composition and the kinetics of formation of the lead sulfide crystalline phase at the late stages of heat treatments of sodium zinc silicate glasses have been investigated using small-angle X-ray scattering and X-ray powder diffraction. It has been established that, after the completion of the precipitation of the PbS crystalline phase, the reaction PbS + ZnO = PbO + ZnS begins to proceed on the surface of nanocrystals. This reaction results in a decrease in the volume of the PbS phase and the precipitation of ZnS nanocrystals. The size effect has been revealed: PbS nanocrystals with a radius larger than approximately Å are stable, whereas nanocrystals with smaller sizes initiate the reaction PbS + ZnO = PbO + ZnS.

1 mJ single-rod fiber Er:glass laser for rangefinding

We demonstrate a compact Er:glass single-rod fiber laser for rangefinding with 1 mJ energy Q-switched at 1.54μm. Double-pass pumping with 16 W power and 5 ms pulse duration was used. Active medium was enveloped with diffuse reflector. Thus efficient output power operation achieved. Free-running mode output pulse energy was 12 mJ with a slope efficiency of 16%. Transparent glass-ceramics containing Co2+:MgAl2O4 nanocrystals were selected as the optimal passive gate to ensure Q-switching in a temperature range and transverse mode selection. The Q-switch mode had steady operation at 1 Hz repetition rate with thermal effects playing no visible role.