Core-shell nanostructures were grown in silica-based glasses. Copper-copper oxide and iron-iron oxide structures had diameters in the range 3-6 nm, with shell thicknesses similar to 1-2 nm. Silver-lithium niobate core-shell nanostructures had diameters in the range 4.2-46 nm and thicknesses varying from 2.2 to 22 nm. X-ray photoelectron spectroscopy studies were carried out on all these specimens. The analyses of these results show the presence of Cu+/Cu2+, Fe2+/Fe3+ and Nb4+/Nb5+, valence states in the above three systems. Electrical resistivity data were fitted satisfactorily to the small polaron hopping model in the case of copper and iron-containing specimens. The presence of ions in the lithium niobate shell provides direct evidence of the formation of localized states between which variable range hopping conduction can be effected. (c) 2007 Elsevier B.V. All rights reserved.