M. Ya. Tsenter

A Raman Spectroscopic Study of Phase Transformations in Titanium-Containing Magnesium Aluminosilicate Glasses

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.

Low-frequency Raman scattering of magnesium aluminosilicate glasses and glass-ceramics

Abstract 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.

Structure and nonlinear optical properties of novel transparent glass-ceramics based on Co2+:ZnO nanocrystals

Transparent glass-ceramics (GCs) based on Co2+:ZnO nanocrystals (mean diameter, 11?nm) are synthesized on the basis of cobalt-doped glasses of the K2O?ZnO?Al2O3?SiO2 system. For these GCs, the absorption band related to the 4A2(4F)?????4T1(4F) transition of Co2+ ions in tetrahedral sites spans until ~1.73 ?m. Saturation of the absorption is demonstrated at 1.54 ?m, with a saturation fluence F s??=??0.8?????0.1 Jcm?2 (? GSA??=??1.7?????0.2??×??10?19 cm2) and a recovery time of 890?????10 ns. Passive Q-switching of an Er,Yb:glass laser is realized with the synthesized GCs. This laser generated 0.37 mJ/100 ns pulses at 1.54 ?m. The developed GCs are promising as saturable absorbers for 1.6?1.7 ?m crystalline erbium lasers.

Saturable absorber: transparent glass-ceramics based on a mixture of Co:β-Zn 2 SiO 4 and Co:ZnO nanocrystals.

We report on the development of novel saturable absorbers for erbium lasers based on transparent glass-ceramics (GCs) containing a mixture of cobalt-doped β-willemite, Co²⁺:β-Zn₂SiO₄, and zinc oxide, Co²⁺:ZnO, nanosized (10-14 nm) crystals. The structure of the parent glass and GCs is studied by x-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and Raman spectroscopy. Variations of absorption spectra with heat-treatment reveal that Co²⁺ ions from the parent glass enter the crystals of ZnO and β-willemite. GCs are characterized by a broad absorption band due to the A₂4(F4)→T₁4(F4) transition of Co²⁺ ions in tetrahedral sites spanning up to ∼1.74u2009u2009μm, relatively low saturation fluence, F_S=0.75u2009u2009J/cm² at 1.54 μm, short recovery time, τ=830u2009u2009ns, and high laser damage threshold, ∼14u2009u2009J/cm². By using the developed GCs in a diode-side-pumped Er, Yb:glass laser, 0.77 mJ/45 ns pulses are generated.

Low-frequency Raman scattering and small-angle X-ray scattering of glasses inclined to phase decomposition

Abstract Low-frequency ( −1 ) Raman scattering of lithium aluminosilicate (12Li 2 Oxa0:xa015Al 2 O 3 xa0:xa073SiO 2 with 4 mol% TiO2) glasses with addition of titanium dioxide has been studied. With a heat treatment at temperatures 660°C, 700°C, 720°C and 820°C and for various times and sequences of temperature, our samples decompose into nanometer sized dispersed aluminotitanate particles. In Raman spectra of these glasses an evolution of a boson peak was observed. The width of the relatively broad boson band decreases as does the frequency of the band. From small-angle X-ray scattering data we conclude that the boson peak is connected with elastic vibrations of amorphous or crystalline regions of inhomogeneity with a dimension of ∼1.7 nm in initial glasses or larger depending on the heat treatment sequences.

Features of the phase transformations in titanium-containing zinc aluminosilicate glasses doped with cobalt oxide

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.

Synthesis, structure and Q-switching behaviour of transparent glass-ceramics based on a mixture of Co:β-Zn 2 SiO 4 and Co:ZnO nanocrystals

We report on synthesis, structure, optical spectroscopy, nonlinear properties and passive Q-switching performance of novel transparent potassium zinc aluminosilicate glass-ceramics containing a mixture of cobalt-doped β-willemite, Co:Zn2SiO4 and zinc oxide, Co:ZnO.

Glass-ceramics with Yb, Tm:YNbO 4 nanocrystals: Novel NIR-to-NIR upconversion phosphor

Transparent lithium alumosilicate glass-ceramics containing nanosized (8-15 nm) crystals of rare-earth orthoniobates, Yb, Tm:YNbO₄, 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%.

Novel transparent glass-ceramics based on Co:Li(Al, Ga) 5 O 8 nanocrystals for passive Q-switching of Er lasers

Transparent glass-ceramics of the lithium gallium aluminosilicate system based on cobalt-doped Li(Al, Ga)5O8 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.

Glass-ceramics with Co 2+ :ZnO nanocrystals: Novel saturatable absorber for Er lasers

Transparent glass-ceramics based on Co²⁺:ZnO nanocrystals are synthesized in cobalt-doped glasses of the K₂O-ZnO-Al₂O₃-SiO₂ system. Passive Q-switching of an Er, Yb:glass laser with 0.37 mJ/100 ns pulses at ~1.54 μm is realized.