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Silicon nanoclusters formed in triethoxysilane during annealing at temperatures above 900°C are used for increasing the excitation cross section of Er atoms. A stronger sensitization of the Er luminescence is observed, for a given Er concentration, when the Er3+ ions are introduced in the matrix by ion implantation than when adding a salt to the precursor solution, because of a better dispersion of the implanted atoms. The logarithmic increase of the emission yield with the Er concentration up to 1 at% which is found in the case of implanted samples is ascribed to the quenching processes by interaction between neighbour Er3+ ions.