Luminescence and Absorption of Hybrid Xerogels Doped with PbS Nanoparticles Prepared by Gas Diffusion Method, J. T. Gonçalves, V. I. Boev, A. Solovyev, C. J. R. Silva, M. J. M. Gomes “Abstracts of the Materiais 2005 /Materials´2005-XII Portuguese Materials Society Meeting and III Materials Symposium SPM” – Universidade de Aveiro, 20-23 de Março de 2005, Aveiro, Portugal, pp.136-137.