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Transparent glass composites containing nonlinear optical (NLO) and luminescent crystals are of significant interest for the optical materials science in spite of a lot of difficulties to synthesize high-quality NLO composites: refractive index and density matching of glass matrix and crystal, controlled chemical interaction between them, absence of crystal aggregation, cords, bubbles, etc. Low density and refractive index, high second harmonic generation (SHG) activity, rather a high melting point allow to refer KNbSi 2 O 7 ferroelectric to a promising candidate for using in the NLO glass composite technology.Manifestation of NLO properties of crystals in glass composites is established to depend drastically on glass matrix composition. During re-melting lead containing glasses react chemically with KNbSi 2 O 7 forming pyrochlore Pb 2 Nb 2 O 7 which is dissolved gradually up to nano-scaled state exhibiting moderate SHG efficiency by analogy with nanostructured glasses because of space modulation of polarizability originated from nano-sized inhomogeneities enriched with Pb and Nb. Using of TeO 2 -based glasses permits to match refractive indexes of glass matrix and crystal, reduce glass melting temperature and fabricate transparent composites containing micron and sub-micron crystals with high second harmonic generation activity.

The structure of glasses of the compositions xEr 2 O 3 -2xTiO 2 -(100 -3x )TeO 2 was investigated and the glass formation region, situated in the range of 2 < x < 7 was established. The possibility of increasing the glass transition temperature and consequently the thermal stability of erbium tellurite glass by doping with titanium (IV) oxide was demonstrated.The number of publications on development and investigation of active media based on tellurite glasses has increased significantly in recent years. This is because TeO 2 glass has high refractive indexes (n > 2.0), high transparency, including in the near IR region of the spectrum (0.35 -6.00 mm) [1], the possibility of varying the compositions of the glass within wide limits, and higher solubility of the cations of rare-earth elements in comparison to quartz glass. The last two circumstances allow obtaining a much broader luminescence band of Er 3+ (about 80 nm) in fibers made of tellurite glass than with quartz fibers (about 35 nm) [1, 2], which is necessary for simultaneously enhancing some signals in current WDM (wavelength-division multiplexing) networks. For this reason, broad-band fiber amplifiers based on tellurite glass with Er 3+ dopants are now being actively developed [1 -3]. The main drawback of tellurite glass, which is related to the low glass transition temperature (about 290°C) and prevents it from being used in conditions of intensive radiation, can be partially eliminated by complicating the composition of the glass and doping with high-melting oxides, for example, WO 3 , Nb 2 O 5 , etc. [1 -3].For this reason, the system Er 2 O 3 -TiO 2 -TeO 2 (ETT) is of special interest. The high-melting oxides (Er 2 O 3 and TiO 2 ) in it makes the possibility of developing new laser glasses that have high thermal stability and chemical resistance in comparison to the investigated analogs of laser tellurite glasses very attractive. In addition, the possibility of separating active Er 2 Ti 2 O 7 crystals with the structure of pyrochlore and the fluorite-like phase Er 2 Te 5 O 13 , which has been studied very little, in the glasses of this system offers new prospects for developing glass ceramic materials with a high Er 3+ content (> 5´10 20 cm -3 ) and improved luminescence characteristics. Such materials are of great interest as the active elements of tunable and fiber lasers, laser microchips, and broadband signal amplifiers.However, almost nothing is known of glass formation in the ETT system. There is thus no information on the structure and crystallization of erbium-titanium-tellurite glasses and its effect on the luminescence-spectral properties.We synthesized and investigated glasses in which Er 2 O 3 : TiO 2 = 2, and the composition can be expressed by the general formula xEr 2 O 3 -2xTiO 2 -(100 -3x )TeO 2 . This ratio was selected for the purpose of subsequently fabricating glass ceramic materials containing Er 2 Ti 2 O 7 with the same Er 2 O 3 : TiO 2 ratio from these glasses.We found that transparent glasses in the xEr 2 O 3 -2xTiO 2 -(100 -3...