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We have studied the temperature dependence of the thermal conductivity of a series of experimentally obtained aluminum-silicon alloys with different silicon addition and additional iron content of 1 % by weight. The article shows how the change in the silicon content affects the thermal properties of the experimentally obtained alloys at room temperature. Also, the article describes the character of the change in thermal conductivity when the samples are heated up to 150 °C. Based on the obtained data, we con clude that the alloy containing 4 % silicon by weight is the most prospective for usage as a material for solving heat transfer problems.

Ni:MgAl2O4 spinel shows a reversible random Ni2+ site redistribution with increasing temperature. With the aim of determining the influence of the structure evolution induced by heat-treatment on the nature of luminescence centers in NiO-doped spinel-based magnesium aluminosilicate glass-ceramics nucleated by a mixture of TiO2 and ZrO2, the detailed spectroscopic study of the initial glass during its heat-treatments at increasing and decreasing temperatures has been performed and accompanied by an XRD analysis and Raman spectroscopy. The initial glass was X-ray amorphous. Its optical spectrum is mainly formed by absorption of [5]Ni2+ sites with a small amount of [4]Ni2+ ones. Crystals of the nucleating catalyst, ZrTiO4, about 4 nm in size, appear during heat-treatment at 800 °C, while the absorption spectrum of Ni2+ ions remains near unchanged. At 850 °C, spinel crystals with size of about 6 nm precipitate, which is accompanied by a broadband luminescence in the near-IR centered at 1330 nm with a bandwidth of 380 nm. At 950 °C, there is a slight reduction in intensity of absorption bands attributed to [6]Ni2+, which can be explained by a tendency toward random Ni2+ site redistribution with increasing temperature. A decrease in the amount of the [6]Ni2+ luminescent centers is not accompanied by a decrease in the luminescence intensity because of the increased size of spinel crystals. Additional low-temperature heat-treatment does not lead to a redistribution between [6]Ni2+ and [4]Ni2+ sites in spinel crystals in favor of [6]Ni2+ ones. An increase of the luminescence intensity after low-temperature heat-treatment is associated with additional spinel crystallization.

Differential scanning calorimetry, X-ray diffraction analysis, transmission electron microscopy, high- and low-frequency Raman and optical spectroscopy were applied to the study of structural transformations in glass of the K2O – ZnO – Al2O3 – SiO2 system codoped with Er2O3 and Yb2O3 and subjected to heat-treatments at 680–1300 °C. Transparent glass-ceramics based on ZnO nanocrystals are prepared by heat-treatments at 680–800 °C, while at 860–900 °C, β-Zn2SiO4 (β-willemite) nanocrystals precipitate in addition to ZnO; α-Zn2SiO4 nanocrystals appear additionally at 950 °C, and the material loses transparency. Opaque glass-ceramic prepared by heat-treatments at 1000 °C contains only crystals of ZnO and α-Zn2SiO4, while crystallization of potassium aluminosilicates, KAlSi2O6 (from the surface) and KAlSiO4 (from the bulk) in addition to ZnO and α-Zn2SiO4, is observed at above 1000 °C. Optical absorption and luminescence of the initial glass and GCs are reported. A shift of the UV absorption edge and the near-IR losses due to the free charge carrier scattering are indications of the ZnO crystallization. Multiple visible emissions from the glass and GCs are determined by the Er3+ ions, nanocrystals of α-Zn2SiO4 and defects of the ZnO nanocrystals. The color of the latter emission can be tuned by varying the heat-treatment temperature. The rare-earth ions (RE3+) do not enter into the Zn-containing nanocrystals and remain in the residual glassy phase until ~ 1200 °C, when the RE silicates (RE2Si2O7) are formed resulting in structured intense Er3+ emission.

We report on a comparative study of a transparent Fe:MgAl2O4 (spinel) ceramics and a transparent nanophase Fe:MgAl2O4-based glass-ceramics. The 0.1 mol% Fe:MgAl2O4 ceramics was synthesized by hot pressing (at 1500 °C/50 MPa) of powders obtained by the sol-gel method using LiF as a sintering aid. The Fe:MgAl2O4 ceramic is a single-phase material (cubic structure, sp. gr. Fd3‾m, a = 8.083 A) with a mean grain size of ~50 μm. The ceramic exhibits a broadband transparency of 0.2–6.0 μm and a high in-line transmission at ~1 μm of 74.4%. The iron ions are presented in the ceramics in the single state of Fe2+ species in tetrahedral (Td) sites. A broad absorption band spanning from ~1.2 to 3.7 μm assigned to the 5E → 5T2 (5D) transition of Fe2+ ions in Td sites is observed, corresponding to a ground-state absorption cross section of 0.28 × 10−18 cm2 at 1.90 μm. The glass-ceramics were prepared by secondary two-stage heat-treatments of the magnesium aluminosilicate glass nucleated by titanium oxide and doped with 0.1 mol% FeO. Transparent Fe:MgAl2O4-based glass-ceramics obtained at the temperature of the second stage of 800–1000 °C were multi-phase materials containing two crystalline nanophases, i.e., spinel (mean size: 3.7–7.4 nm) and magnesium aluminotitanate solid solution (mean size: 6.4–20.6 nm), as well as residual silica-rich glass. Glass-ceramics obtained at the temperature of the second stage of 1050 °C were transparent and based on Fe-doped sapphirine. For glass-ceramics, absorption has a much more complex character as it is caused by interplay of iron and titanium ions in different valence states, coordination sites and locations. The iron ions enter the spinel nanocrystals but unlike the ceramic, in the form of both VIFe2+ and IVFe2+ species. The developed ceramics and glass-ceramics are promising for saturable absorbers of mid-infrared (2–3 μm) lasers.

Transparent polycrystalline ZnAl2O4 (gahnite) ceramic doped with 0.1 at.% Co2+ is synthesized by hot pressing of powders (1600 °C, 50 MPa) using the sintering additive, ZnF2. Structure, Raman spectra, linear and nonlinear spectroscopic properties of this material are characterized and compared to those of nanophase Co:ZnAl2O4-based transparent glass-ceramics (GCs). Co2+ ions in ZnAl2O4 ceramic exhibit absorption saturation at ∼1.54 μm (the 4A2(4F) → 4T1(4F) transition); the corresponding saturation fluence FS is 0.46 ± 0.07 J/cm2 and the saturation contrast γ = 0.15 ± 0.05. As compared to the transparent GCs, the main drawback of Co:ZnAl2O4 transparent ceramic is a low laser-induced damage threshold, which is attributed to the imperfect microstructure (the presence of pores and non-uniform grain size distribution). Providing optimization of the sintering process, the Co:ZnAl2O4 transparent ceramic looks promising for saturable absorbers of erbium lasers.

Transparent glass-ceramics (GCs) based on Co2+-doped γ-GaxAl2−xO3 spinel nanocrystals were developed in the lithium aluminogallosilicate glass system with TiO2 as a nucleating agent. The initial glass contains spinel nanocrystals with sizes less than 3 nm. Secondary heat-treatments in the temperature range of 680–800 °C result in fabrication of transparent GCs based on γ-GaxAl2−xO3 crystals enriched in aluminum with cubic spinel structure (sp. gr. Fd3m) and a mean size up to 5.5 nm. At higher temperatures, GCs become translucent and then opaque due to additional crystallization of lithium aluminosilicate solid solutions (ss) with β-quartz structure and lithium aluminogallium silicate ss with β-spodumene (keatite) structure. The introduction of gallium oxide improves the temperature stability of spinel crystals that are not decomposed at high heat-treatment temperatures when aluminosilicate crystals evolve. The Co2+ ions in GCs enter the spinel crystals predominantly in tetrahedral sites. Transparent GCs feature broadband absorption (1.15–1.7 μm) owing to the 4A2(4F) → 4T1(4F) transition of IVCo2+ species in spinel nanocrystals. They exhibit saturable absorption and high ground-state absorption (GSA) cross-section σGSA of 3.1 ± 0.4 × 10−19 cm2 at 1.54 μm. Glass-ceramic based on γ-GaxAl2−xO3 crystals is employed as a saturable absorber of an eye-safe diode-side-pumped Er3+,Yb3+:glass laser delivering 1.1 mJ/42 ns pulses at 1535 nm.

Transparent glass-ceramic materials based on glasses of the MgO–Al2O3–SiO2–TiO2 system doped with CoO and Ga2O3 are synthesized. The secondary heat treatment of the initial glasses at temperatures of 800–950°C leads to precipitation of nanosized (6–7 nm) crystals of magnesium aluminogallium spinel doped with cobalt ions and magnesium aluminotitanate solid solutions. The optical absorption spectra of the initial glass and glass-ceramic materials are studied. It is shown that the absorption band caused by the 4 A 2(4F)→ 4 T 1(4 F) transitions of tetrahedrally coordinated Co2+ ions in glass-ceramics with nanosized Co:Mg(Al,Ga)2O4 crystals is shifted to longer wavelengths (up to ~1.67 µm) compared to the position of this band in materials with Co:MgAl2O4 crystals. The synthesized glass-ceramics are characterized by a relatively low saturation fluence FS ~ 0.5 ± 0.1 J/cm2 at a wavelength of 1.54 µm, as well as by a high radiation resistance to nanosecond laser pulses, which is no lower than ~15 ± 2 J/cm2. This explains their attractiveness as materials for saturable absorbers for erbium lasers emitting in the spectral range 1.5–1.7 µm.

Three glasses in the Li2O–Al2O3–SiO2 (LAS), MgO–Al2O3–SiO2 (MAS) and ZnO–Al2O3–SiO2 (ZAS) systems were investigated to obtain spinel-based transparent glass-ceramics doped with TiO2 to induce internal nucleation and with NiO to provide optically active ion. The sequence of phase transformations of initial glasses during heat-treatments was studied by in situ X-ray absorption spectroscopy, X-ray diffraction and room temperature optical spectroscopy. For all glasses, there is a change of Ni2 + coordination with the increase of the heat-treatment temperature. The [5]Ni2+ sites in the parent glass disappear and new distorted [6]Ni2+ sites are formed within aluminotitanate and (Ni, or Ni,Mg, or Ni,Zn) aluminate amorphous regions. The local environment around Ni2+ then evolves from distorted octahedra to regular octahedra due to the nickel-doped spinel crystallization. In LAS glass-ceramics only, Ni2+ incorporates at elevated temperature octahedral and tetrahedral sites in crystals of β-quartz solid solution, whose content increases with time and temperature of heat treatment accompanied by a continuous decomposition or dissolution of spinel. In MAS and ZAS glass-ceramics, Ni-doped spinel exist in the whole temperature range of applied heat-treatments.

The evolution of Ni 2+ environment has been systematically investigated using optical and in situ X-ray absorption spectroscopy (XAS) to determine the influence of nucleating agents (TiO 2 and/or ZrO 2 ) during the formation of spinel in magnesium aluminosilicate glass–ceramics. The results were complemented by in situ X-ray diffraction data. According to XAS and optical spectroscopy, the nature of nucleating agents does not modify significantly the Ni environment in initial glasses. However, it has a relatively strong influence in the observed crystallization sequence. Ni 2+ ions do not enter the Zr-containing crystalline phase of ZrO 2 or ZrTiO 4 but a Ni 2+ coordination change from the fivefold coordinated sites, with a small amount of tetrahedral sites in parent glasses, to [6] Ni 2+ and [4] Ni 2+ sites in spinel (in glasses nucleated by ZrO 2 and/or TiO 2 ) or in β-quartz solid solutions (in glasses nucleated by ZrO 2 ) has been found.

Transparent spinel-based glass-ceramics are synthesized on the basis of the magnesium aluminosilicate glass with the addition of nucleating agents (a mixture of TiO 2 and ZrO 2 ) and dopants, Er 2 O 3 and Yb 2 O 3 , by a secondary heat-treatment at 800–1050 °C. The precipitation of rare-earth titanate–zirconate (Er,Yb) 2 (Ti,Zr) 2 O 7 nanosized (5–17 nm) crystals is observed, as well as their transformation from the defect-fluorite to the disordered pyrochlore structure. Optical absorption and upconversion luminescence spectra are studied for various Er/Yb ratios, as well as for single Er-doped glasses and glass-ceramics. A substantial enhancement (10-times) of the red emission (~ 650 nm) with the heat-treatment is observed and explained with the analysis of the results of lifetime measurements of the 2 H 11/2 , the 4 S 3/2 , the 4 F 9/2 and the 4 I 11/2 excited states of Er 3 + ions. The mechanisms of upconversion in (Er,Yb) 2 (Ti,Zr) 2 O 7 nanocrystals are discussed.

We demonstrate a pulse-bursting phenomenon in Yb:Er glass laser operating at 1.54 μm. Glass-ceramic material with a low value of saturation threshold based on Co2+:β-ZnSiO4 nanocrystals was used as a passive gate for pulse-burst operation. The bursts of pulses were 1.5 ms long, each burst consisted of 40-55 pulses with 9-30 μJ energy per pulse and 0.2-3 μs pulse width. Bursting outputs arise via a coupling between slow switching arising via a slow pump modulation and fast pulsations resulting from Q-switch mechanism. We show that absorption cross-section strongly affects the mode of laser operation ranging from relaxation oscillations corresponding to low cross-section values to bursting and conventional Q-switch operation in the case of their higher values.

We report on the passive Q-switching of a compact diode-side-pumped Er,Yb:glass laser by a novel saturable absorber (SA) based on transparent glass-ceramics (GC) containing Co2+Mg(Al,Ga)2O4 nanocrystals. To prepare the GC, an initial magnesium aluminosilicate glass doped with Ga2O3 containing 0.1 mol% CoO was synthesized by a conventional melt-quenching technique and heat-treated at 850–950 °C. The X-ray diffraction analysis of the GC confirmed the precipitation of Co2+Mg(Al,Ga)2O4 crystals with spinel structure (6-7 nm in size). Depending on the heat-treatment temperature, the saturation intensity for the GC measured at 1540 nm was in the 0.5...0.7 J/cm2 range and the recovery time was in the 240...335 ns range. Using the SA based on GC prepared by the heat-treatment at 950 °C with an initial transmission of 84.7%, we generated stable Q-switched pulses 1.14 mJ in energy and 7.2 ns in duration. The peak power reached 160 kW, the repetition rate was 1 Hz and the laser wavelength was 1535 nm. The developed GCs are promising for Q-switching of erbium lasers emitting at 1.5-1.7 μm.

We demonstrated the efficiency of the Raman spectroscopy method in the study of the process of the formation of the amorphous zinc aluminotitanate (ZAT) phase during the phase decomposition of the titanium-containing zinc aluminosilicate glasses doped with cobalt oxide. The quantitative dependences of the variation of the intensity of the Raman bands characteristic for amorphous and crystalline phases on the temperature of the thermal treatment and the cobalt oxide concentration have been obtained. The speed of phase decomposition with the separation of the nanosize crystals of zinc aluminate spinel (gahnite) and ZAT phase increases at low-temperature thermal treatments with increasing cobalt oxide concentration. The addition of cobalt oxide increases the amount of the amorphous ZAT phase separated during phase decomposition and increases its thermal stability during high-temperature treatments. It has been shown that the Co2+ ions enter the zinc aluminate spinel (gahnite) crystals precipitated during phase decomposition. It has been supposed that the composition of the residual glass is close to that of the quartz glass and it contains a very small amount of titanium-oxygen tetrahedra.

Transparent glass-ceramics of the lithium gallium aluminosilicate system based on cobalt-doped Li(Al, Ga) 5 O 8 spinel nanosized crystals were developed. Their structure and optical properties were evaluated. Passive Q-switching of an Er, Yb:glass laser with 1 mJ/45 ns pulses at ∼1.54 μm is realized.

Transparent glass-ceramics based on Co2+:ZnO nanocrystals are synthesized in cobalt-doped glasses of the K 2 O-ZnO-Al 2 O 3 -SiO 2 system. Passive Q-switching of an Er, Yb:glass laser with 0.37 mJ/100 ns pulses at ∼1.54 μm is realized.

Transparent lithium alumosilicate glass-ceramics containing nanosized (8–15 nm) crystals of rare-earth orthoniobates, Yb, Tm:YNbO 4 , and β-quartz solid solutions are synthesized. Under the near-IR excitation by an InGaAs diode, they demonstrate intense near-IR upconversion luminescence at ∼800 nm. The efficiency of Yb3+ →Tm3+ energy transfer is ∼90%.

The evolution of structure, phase composition and spectroscopic properties of CoO-doped (up to 5 mol%) titania-containing zinc aluminosilicate glasses with their heat-treatment has been studied using Raman scattering, small angle X-ray scattering, X-ray diffraction analysis and optical absorption spectra. Addition of cobalt oxide was observed to facilitate amorphous phase separation of the parent glass and gahnite, ZnAl2O4, crystallization. Cobalt oxide entered phases formed during low-temperature heat-treatments (720 °C), i.e., amorphous phase, enriched in ZnO, Al2O3 and TiO2 and crystalline phase of gahnite. The absorption of these glass-ceramics was defined mainly by tetrahedral Co2+ ions located in gahnite nanocrystals. As the temperature was increased further, traces of anosovite solid solution appeared and then decomposed. Even after high-temperature heat-treatments, a certain portion of Co2+ ions remained in amorphous zinc aluminotitanate phase and in octahedral sites of inversed gahnite spinel. In glass-ceramics, the residual high silica amorphous phase contained a small quantity of [TiO4] centers, which content was smaller in Co:ZAS samples as compared with non-doped glass-ceramics.

Glass-ceramics are usually formed through passing several stages of phase transformations (nucleation, crystallization of metastable and stable crystalline phases). The properties of glass-ceramics depend on at what stage the process was stopped. The phase assemblage of glass-ceramics is controlled by the composition of the initial glass and heat-treatment conditions. Raman and optical spectroscopy, in combination with X-ray diffraction and small angle X-ray scattering techniques are used to study the behavior of the nucleation and crystallization of lithium, magnesium and zinc aluminosilicate glasses. Specific heat-treatments has given the opportunity to achieve a desired phase assemblage ensuring unique properties of glass-ceramics by interrupting the process at a certain stage. Examples of such glass-ceramic developments include thermal shock resistant color filters, passive Q-switchers for eye-safe Er:glass lasers, as well as transparent materials based on rare-earth titanates with pyrochlore structure with luminescence in the range of 1.5 μm. The approach to developing the dual active–passive media for the eye-safe spectral region is demonstrated for the first time.

A resonantly pumped passively Q-switched Er:YAG laser operating at 1.617 and 1.645 µm is reported with γ-Ga2O3:Co2+-based glass-ceramics (GCs) as a saturable absorber. The maximum average output power achieved from this laser was 273 mW; the highest pulse energy was 5.9 µJ, corresponding to a pulse duration of 3.0 µs at a repetition frequency of 31 kHz. To the best of our knowledge, this is the first time to use the γ-Ga2O3:Co2+-based GC as a passive Q-switcher for Er:YAG lasers and this is also the first time to obtain 1.617 µm and 1.645 µm pulses with a GC-based saturable absorber.

Formation processes and morphology of nanostructured glass ceramic materials containing finely dispersed lead sulfide crystalline phase has been studied by X-ray technique. The spatial ordering of PbS nanocrystals has been revealed which manifests itself by interference effects in X-ray scattering. We have ascertained that important morphology feature of the system is nearly monodisperse size distribution of nanocrystals.

An evolution of the structure of three glasses of Na2O-Nb2O5-SiO2 system in the course of isothermal heat treatments at 660–700°C and the extinction coefficient of the material were studied. Spinodal phase separation was found to be a primary process followed by precipitation of nano-sized NaNbO3 crystalline phase. It was found that the spectral dependence of the extinction coefficient in the wavelength range λ= 400–800 nm corresponds to light scattering by spinodal structure at the phase separation stage and by independent Rayleigh scatterers (NaNbO3 nanocrystals) at the early stage of crystallization. The extinction coefficient increases at the first half of the crystallization stage and then decreases. At the late stage of crystallization and for the final glass-ceramics, the extinction coefficient α is 10–20 times smaller than that calculated for independently scattering nanocrystals and is characterized by anomalous wavelength dependence (α ∝ λ−6). The model for calculation of extinction coefficient is proposed, in which the interference effects in light scattering by nanocrystals are taken into account. On this basis, the variation of extinction coefficient in the course of crystallization and its wavelength dependence are explained.

We report on the development of a compact diode-end-pumped eye-safe (similar to 1.54 mu m) passively-cooled Er, Yb:glass laser. The design of this laser is facilitated by the use of a double-pass pumping scheme and a special ZrO2 diffuse reflector for a uniform pump distribution. In the free-running mode, this laser generates 8.2 mJ/3 ms pulses with a slope efficiency of 15%. Passive Q-switching is provided by saturable absorbers made of transparent glass-ceramics containing Co2+:gamma-Ga2O3 or Co2+:MgAl2O4 nanocrystals with a spinel structure. In the latter case, 0.7 mJ/10.5 ns pulses are generated corresponding to >60 kW peak power and good beam quality (M-2 = 1.4). The designed laser is suitable for portable range-finders.

Pump–probe spectroscopy studies on cobalt-doped spinel-based aluminosilicate glass–ceramics of various compositions have been made in the visible part of the spectrum. Stimulated emission from the 4 T 1 ( 4 P) state to the 4 A 2 one of tetrahedral Co 2+ ion has been observed for all glass–ceramic materials. The peak values of effective stimulated emission cross-sections for Co 2+ ions are estimated to be 4–5 × 10 −19 cm 2 depending on glass–ceramics composition and are found to be higher than in spinel single crystals.

We have studied the radiation output parameters for an erbium glass laser, lasing at a wavelength of 1.54 µm, with passive Q-switching by means of a cobalt-containing magnesium aluminosilicate sitall compared with a saturable absorber based on a magnesium aluminum spinel crystal with cobalt ions. We have shown that the output characteristics of the laser emission when using sitall are not inferior to the analogous characteristics of a laser based on a spinel crystal, and are practically independent of the temperature of the saturable absorber in the range 0°C–80°C. The duration (energy) of the output pulses was 70 nsec (∼4 mJ), the energy dispersion of the radiation pulse relative to the average value was no greater than 3%, the beam divergence was 2.8 mrad, the laser beam quality factor was M2 = 1.2.

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 Co 2 +:MgAl 2 O 4 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.

The influence of small additions of CoO (0.05–2.0 mol%) on phase decomposition and further crystallization in glasses of the Li 2 O–Al 2 O 3 –SiO 2 –TiO 2 system were studied by comparison of variations in corresponding Raman scattering spectra, optical absorption spectra and X-ray diffraction patterns. It is found out that at early stages of phase decomposition at heat-treatment temperatures of 660–700 °C, cobalt oxide enters the alurninotitanate phase, increases temperature range of its existence and influences the kinetics of formation of crystalline phases with anatase and anosovite structure precipitated in this phase upon heat-treatment. Upon heat-treatments at higher temperatures (720–750 °C), crystallization of aluminocobalt spinel and of small amounts of cobalt titanate is revealed. Addition of CoO facilitates crystallization of β-eucryptite solid solution with β-quartz structure, which takes place at the same temperatures. With increasing heat-treatment temperature, anosovite, spinel, and cobalt titanate are decomposed. At 950 °C, a part of TiO 2 precipitates in the form of aluminum titanate, tialite, which leads to slowing down the crystallization of anatase.

The evolution of structure and phase composition of NiO-doped titania-containing magnesium aluminosilicate glasses has been studied using small angle X-ray scattering and X-ray diffraction analysis. After initial heat-treatments, three-phase immiscibility develops resulting in precipitation of two amorphous phases. One of them is enriched in MgO, Al 2 O 3 and TiO 2 , the other in MgO and Al 2 O 3 . Nickel oxide enters both phases, which impedes to crystallization of the magnesium aluminotitanates phase; nickel-containing aluminomagnesium regions become centers of further crystallization of aluminomagnesium spinel. The spinel crystallization temperature, as well as mean sizes decreases with increasing the NiO content in the initial glass.

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.

The changes observed in the structure and phase composition of titanium-containing glasses in the magnesium aluminosilicate system at the equimolar ratio of MgO and Al2O3 during their heat treatment are investigated using the small-angle X-ray scattering (SAXS) technique and X-ray powder diffraction analysis. Nickel oxide additives (from 0.5 to 5.0 mol %) are introduced into the glasses. It is shown that heat treatment of the studied glasses is accompanied by three-phase separation. As a result, two amorphous phases precipitate in the high-silica matrix. One phase (magnesium aluminotitanate) is enriched with magnesium, aluminum, and titanium oxides, whereas the other phase (magnesium aluminate) is enriched with aluminum and magnesium oxides. Nickel oxide is incorporated into both phases. Moreover, nickel oxide reduces the crystallization ability of the magnesium aluminotitanate phase and magnesium aluminotitanates do not crystallize in glasses containing 5 mol % NiO. During Subscriptsequent heat treatments, regions of the nickel magnesium aluminate phase serve as precipitation centers of the magnesium aluminate phase, and, consequently, nickel oxide affects the microinhomogeneous structure of glasses at the final stages of heat treatment. This leads in particular to a decrease in the size of spinel microcrystals. The temperature of the onset of crystallization in regions of existence of the nickel magnesium aluminate phase (spinel precipitation) is lower than that in glasses free from nickel oxide. It is assumed that spinel microcrystals are solid solutions of nickel aluminum and magnesium aluminum spinels.

Optical properties of cobalt-doped zinc aluminosilicate transparent glass ceramics in the visible – near-infrared (IR) spectral range have been studied. It was shown that the absorption and luminescence properties of these glass ceramics are defined mainly by tetrahedrally coordinated Co2+ ions located in ZnAl2O4 gahnite nanocrystals formed in the glass ceramic matrix. The luminescence in the visible and near IR was assigned to the transitions from the 4T1(4P) to the 4A2 and 4T2 energy levels of tetrahedrally coordinated Co2+ ion. Absorption saturation and bleaching relaxation under excitation of the 4A2→4T1(4F) transition were studied. Luminescence decay and bleaching relaxation times lie in the ranges 25–200 and 500–800 ns, respectively, depending on the Co concentration. The value of the ground-state absorption cross section of tetrahedrally coordinated Co2+ ions in zinc aluminosilicate transparent glass ceramics was estimated to be 2.0×10−19 cm2 at the wavelength of 1.54 μm.

Electronic absorption and luminescence spectra and nonlinear optical properties of magnesium aluminosilicate glass-ceramics doped with divalent cobalt ions are studied in relation to their synthesis conditions. The lifetimes of the 4 T 1(4 P) and 4 T 1(4 F) excited levels of tetracoordinate Co2+ ions in these glass-ceramics are found to depend on the cobalt concentration and lie within the ranges from 25 to 40 and from 120 to 450 ns, respectively. Using the absorption saturation curves, the ground state absorption cross section for the wave-length of 1.54 μm is estimated to be σGSA=3.3×10−19cm2. The induced emission of the tetrahedrally coordinated Co2+ ion, which dominates over the absorption from the excited state in the spectral range from 640 to 690 nm (4 T 1(4 P)→4 A 2 transition), is found.

Absorption, luminescence and saturation of absorption for cobalt-doped glass-ceramics were studied. Characteristic times of 44 4 21 luminescence decay of T ( P)→ A transition for tetrahedrally coordinated Co ions in lithium-, zinc-, magnesium- and magnesium- 12 44 4 gallium-aluminosilicate glass-ceramics were evaluated to be in tens of ns time scale. Kinetics of bleaching relaxation of A → T(F ) 21 21 transition for tetrahedrally coordinated Co ions in magnesium-aluminosilicate glass-ceramics was found to be 4506150 and 120640 21 ns for 0.1 and 0.3 wt% cobalt concentration, respectively. Ground-state absorption cross-section for Co ions at 1.54 mm was estimated 219 2 to be |3310 cm . Passively Q-switched pulses from Er:glass laser of 6 mJ in energy and 80 ns in duration using the Co-doped magnesium-aluminosilicate glass-ceramics sample as saturable absorber were demonstrated.  2002 Elsevier Science B.V. All rights reserved.

The evolution of the Raman spectra of the 20MgO · 20Al2O3 · 60SiO2 glass with 10 mol % TiO2 and glasses doped with 0.5 wt % NiO or 2.5 and 5.0 mol % Ga2O3 is investigated in the course of heat treatment resulting in phase separation and crystallization. The composition and structure of the amorphous and crystalline phases (precipitating in the course of phase separation) and the residual glass are analyzed on the basis of Raman scattering, small-angle X-ray scattering (SAXS), and X-ray powder diffraction data. The size of nanoparticles of the precipitated phases is determined by low-frequency Raman spectroscopy, and the results obtained are compared with the nanoparticle size derived from the SAXS data.

The evolution of low-frequency ( −1 ) Raman scattering of titania-containing magnesium aluminosilicate (20MgO:20Al 2 O 3 :60SiO 2 with 10 mol% TiO 2 ) glasses with heat-treatment has been studied. It was found that in spectra of heat-treated glasses the intensity of the boson peak is rapidly diminished. Under certain conditions of heat-treatment schedules the boson peak disappears while the sample remains amorphous. It implies that sometimes the boson peak is missing from spectra of amorphous materials. In Raman spectra of heat-treated glasses that show the disappearance of the boson peak a new narrow highly polarized low-frequency band appears and increases in intensity. This band has been associated with a spheroidal mode of elastic vibrations in nanometer sized particles of aluminomagnesium phase formed upon phase decomposition of the glass. Its frequency changes with heat-treatment in the temperature range 750–950°C, from 50 to 17 cm −1 reflecting an increase in the sizes of corresponding nanometer particles. The composition and structure of amorphous and crystalline phases formed upon heat-treatment and also of residual glass as well were analyzed using the Raman scattering data, small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) analysis.

A complex approach to the development of electrooptic glasses is proposed. The approach is based on the use of the traditional methods of structural-physical investigations in combination with the Rayleigh and Mandelstam-Brillouin scattering spectroscopic techniques. The structural features of niobate glasses and their properties are considered. It is shown that niobium selectively enters into the fluctuation microinhomogeneities in the alkali borosilicate vitreous matrix. The conditions for the precipitation of sodium niobate microcrystals are determined, and their influence on the increase in the Kerr constant for glass-ceramic materials is analyzed.

The crystallization processes of glass of the MgO–Al2O3–SiO2–TiO2–ZrO2–Y2O3 system, which is close in composition to cordierite, have been studied after heat treatment in the range 800–1300°C. X-ray phase analysis is used to detect a new yttrium-containing crystalline phase, x-ray microanalysis is used to determine its composition, and a model sample is synthesized. Indices are assigned to the diffractogram of the model sample, and the space group of the crystal symmetry is determined, along with the parameters and volume of its unit cell.

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.

PbS quantum-dot-doped glasses are demonstrated as saturable absorber Q-switches for 2 microm holmium lasers. Q-switched pulses from Ho3+:Y3Sc2Al3O12 and Ho3+:Y3Al5O12 lasers of 50 and 70 ns in duration, respectively, have been obtained demonstrating up to 13% of energy conversion efficiency from free-running to Q-switched output.

Glass ceramic materials containing tetrahedral divalent cobalt ions have been recently introduced as laser saturable absorbers. Here we present study of stimulated emission from co-doped zinc-aluminosilicate glass ceramics (Co:ZAS).

Saturable absorbers on the base of lead sulfide QDs for mode-locking and Q-switching of lasers emitting at 1, 1.3, 1.5, 2 microns are introduced and characterized.

Nonlinear optical properties of Co(2+)-doped magnesium aluminosilicate glass ceramics prepared under normal and reducing conditions are studied in the range of the 4A2 --> 4T1(4F) transition of tetrahedral Co2+ ions. The results of passive Q switching of a 1.54-microm Er3+:glass laser with saturable absorbers made of Co(2+)-doped glass ceramics prepared at different conditions are presented. Q-switched pulses of 60 ns in duration and of 4.6 mJ in energy, corresponding to approximately 20% of the Q-switching conversion efficiency, are achieved.

Q switching of a diode-pumped Nd3+:KGd(WO4)2 laser at 1.35 microm by use of cobalt-doped magnesium- and zinc-aluminosilicate glass ceramics as saturable absorbers is demonstrated. Q-switching efficiency up to 40% has been obtained. Ground-state absorption cross sections for Co2+ ions at the wavelengths of 1.35 and 1.54 microm are estimated to be (3.5-4.0) x 10(-19) cm2. Bleaching relaxation times under the excitation of the 4A2 --> 4T1(4F) transition of tetrahedrally coordinated Co2+ ions are of 280 +/- 50 ns and 700 +/- 80 ns for magnesium- and zinc-aluminosilicate glass ceramics, respectively.

Absorption saturation as well as bleaching relaxation of 4A2 yields 4T1(4F) transition of tetrahedrally coordinates Co2+ ion in magnesium-aluminum and magnesium-gallium-aluminum glass ceramics prepared under different conditions were studied. Ground state absorption cross sections at the wavelength of 1.54 mm were estimated. The level of unsaturable losses was observed to be proportional to the cobalt concentration in the raw materials. The difference spectrum of stimulated emission and excited state absorption under excitation in the 4A2 yields 4T1 (4P) transition of the tetrahedral Co ion was derived and analyzed.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Intensity dependent transmission and excited state relaxation measurements of PbS and PbSe quantum dots in silicate and phosphate glasses and their applications for mode-locking of Nd:YAG laser at 1.064 micrometers as well as for Q-switching of Nd:KGW at 1.067 micrometers and 1.35 micrometers and Er:glass at 1.54 micrometers lasers with diode and flash-lamp pumping are presented.

It is experimentally shown that low nickel oxide doping (0.01–0.15 mol. %) can quantitatively and qualitatively alter the light-scattering properties of glass–ceramics that have zinc spinel as the base crystalline phase. Based on experimental data concerning the structure of the glass–ceramics studied here, it is concluded that the observed character of the light scattering cannot be explained on the basis of the independent-scatterer model and that interference effects need to be taken into account in the scattering. It is shown that interference effects can play a defining role in the case of a system of particles that strongly differ in their scattering properties. It is illustrated that the properties of glass–ceramics can be significantly altered by introducing small amounts of dopants.

New saturable absorber Q-switch for 1.54 %mum Er: glass laser is present. The saturable absorber is transparent glass ceramic containing magnesium-aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co2+ ions. Q-switched pulses of up to 5.5 mJ in energy and 80 ns in duration at 1.54 micrometers were achieved. Relaxation time of the 4A2 to 4T1(4F) transition bleaching was measured to be (450+/- 150)ns. Ground-state absorption cross-sections at 1.54 micrometers wavelength were estimated to be (3.2+/- 0.4)*10-19 cm2 and (5.0+/- 0.6)X10-20 cm2, respectively. Results of study absorption and luminescence spectra of different glass ceramics on the base of magnesium-aluminum, zinc-aluminum, lithium-aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co2+ ions are also analyzed.