A. A. Onushchenko

Radiative properties of Nd-doped transparent glass-ceramics in the lithium aluminosilicate system

Abstract We have studied the optical (absorption, luminescence) properties of Nd3+-doped transparent glass-ceramics obtained in the lithium aluminosilicate system. Phase composition of the glass-ceramics has been determined to affect their luminescent characteristics. We have found out that concentration quenching of neodymium fluorescence decreases upon recrystallization of β-eucryptite solid solutions (SS) into β-spodumene ones. The effect is due to partitioning of the rare-earth ions into the crystalline phase. For glass-ceramics nucleated with titania we have shown using the Judd–Ofelt theory that introduction of P2O5 in the glass-ceramic composition has a favorable effect on radiative parameters increasing noticeably the stimulated emission cross-section for the transition 4 F 3/2 → 4 I 11/2 . The influence of crystalline phase value fraction on quantum efficiency estimated from fluorescence decay measurements has been elucidated as well. It has been shown that reasonable values of the fluorescence quantum yield can be obtained provided that thermal shock resistance of materials remains sufficiently high. We have also carried out laser operation testing in a setup with flash lamp pumping. The observed spread in values of lasing characteristics can be attributed to insufficient optical quality of materials due to phase separation effects.

Size effects in phase transitions of semiconductor nanoparticles embedded in glass

Phase transitions of copper halide particles have been investigated by optical means. A decrease of particle melting temperature with decrease of size has been found. It is shown that the observed size dependencies of crystallization and melting temperatures can be described with practically the same value of surface tension in the framework of homogeneous nucleation theory and particle melting model in which the idea about thermally activated formation of a liquid layer on the particle surface is used. It has been found that the lowest temperature at which high temperature modification of CuBr (β-phase) can be stabilized due to extra annealing of samples depends weakly on particle size. Decrease of melting temperature prevents stabilization of β-phase for particles having radii less than 5 nm.

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.

Vector Soliton Bunching in Thulium-Holmium Fiber Laser Mode-Locked With PbS Quantum-Dot-Doped Glass Absorber

Saturable absorber based on PbS quantum-dot-doped glasses exhibiting bi-temporal recovery dynamics provides effective means for control of vector soliton bunching in 2-μm spectral range. The slow response of absorption creates an attractive force between pulses, and a bunch of tightly bounded vector solitons propagates in a cavity as an entity. Subjected to the joint action of attractive and repulsive forces, the solitons tend to oscillate within the bunch.

Nanostructured glass-crystal materials with lead sulfide for passive Q switching of IR lasers

New results are obtained from an investigation of the formation processes of nanostructured material accompanying the heat treatment of silicate glasses containing lead sulfide dissolved during synthesis. Important morphological features of the material have been detected—close-to-monodisperse distribution of PbS nanocrystals (NCs) over size and partial spatial ordering of the NCs. The heat-treatment regimes developed for the initial glasses make it possible to obtain high-quality samples that demonstrate narrow absorption lines of the PbS NCs for the 2-2.5-µm spectral region. The fundamental physical limitation of the subsequent broadening (λ>2.5 µm) of the working range of passive Q switches using such materials is the impossibility of implementing the regime of strong size quantization of electron-hole pairs when the radius of the NCs is comparable with the Bohr radii of electrons and holes.

Influence of heat treatment conditions on the precipitation and dissolution of lead sulfide nanocrystals in sodium zinc silicate glasses

The influence of the temperature of the primary heat treatment in the case of two-stage heat treatment of glasses on the kinetics of precipitation of PbS nanocrystals and the structure of the glass-ceramic materials prepared has been investigated. The main structural parameters of the glass-ceramic material, such as the radius of lead sulfide nanocrystals, relative volume of the crystalline phase, concentration of nanocrystals, and dispersion of nanocrystal sizes, have been determined under different heat treatment conditions. It has been demonstrated that a variation in the temperature of the primary heat treatment in the range below the glass transition temperature of the glass matrix makes it possible to control the nanocrystal sizes and to obtain close-to-monodisperse size distributions of nanocrystals.

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.

Ho:KLu(WO 4 ) 2 Microchip Laser Q-Switched by a PbS Quantum-Dot-Doped Glass

We report on passive Q-switching of a Ho:KLu(WO4)2 (Ho:KLuW) microchip laser in-band-pumped by a Tm:KLuW laser at ~1.96 μm. As a saturable absorber, PbS-quantum-dot-doped glass was used which exhibits a saturation intensity of ~3 MW/cm2 near 2 μm. Maximum average output power of 84 mW was achieved from the Ho laser at 2.061 μm with a slope efficiency of 42% (with respect to the absorbed pump power). The shortest pulse duration was 30 ns. In the continuous-wave mode, the maximum output power of the Ho laser reached 530 mW at 2.08 μm with a slope efficiency of 88%.

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.

The kinetics of the formation of CdSe nanocrystals in sodium-zinc-silica glass

The kinetics of precipitation of CdSe nanocrystals in sodium-zinc-silica glass subjected to a two-stage heat treatment at different temperatures of the primary and secondary heat treatments has been studied by small-angle X-ray scattering (SAXS). The primary low-temperature heat treatment is accompanied by the nucleation of crystallization centers, i.e., supercritical nucleation centers. During the secondary heat treatment, crystals largely grow on the formed centers. In this case, the crystals are distributed in the bulk of the glass in a certain order, which apparently results from the regular pattern of distribution of the crystallization centers formed during the primary heat treatment. It has been found that the precipitated nanocrystals have a narrow size distribution at all stages of heat treatment. After the completion of precipitation of the crystalline phase, a stable structure is formed. The crystal sizes and the volume fraction of the phase do not change within the measurement accuracy (±1–2%) for the heating times that are at least an order of magnitude longer than the duration of the precipitation stage.