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In spite of the interest in nonlinear optical (NLO) properties in glasses, the composite method has been successful only for the b-BaB2O4 polar crystal incorporated in the borosilicate glass matrix. In the present paper, transparent composites based on low melting borate and boron silicate glasses containing PbO or TeO2 and KNbSi2O7 ferroelectric crystal are obtained by a remelting technology. Depending on glass composition, NLO composites are subdivided in two types. The first are composites containing micron or submicron scaled crystals with a high second harmonic generation (SHG) activity, where refractive indexes of crystals and glass matrix are very similar. Such a type of transparent composites is expected to achieve SHG activity in the future comparable with that of single crystals. The second type are ‘nanocomposites’ where initial crystals are dissolved or transformed up to nanoscaled sizes. They are considered to be an analogue of nanostructured glasses exhibiting moderate second order optical nonlinearity.

The structure of glasses of the coinpositions xEr(2)O(3) - 2xTiO(2) - (100 - 3x)TeO2 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.