The enhancement of the Er3+ ions’ photoluminescence (PL) emission at 1.54 um in a Si and Er coimplanted aluminosilicate glass is investigated in detail. A postimplantation thermal treatment has been performed to recover the damage induced by the implantation process and to promote Si aggregation. It will be shown that 1 h treatment in N2 atmosphere is not sufficient to induce Si precipitation for temperatures up to 500 °C. Nevertheless, the most intense Er3+ PL emission at 1.54 um is achieved after a thermal treatment at 400 °C. Such emission has been investigated by pumping in and out of resonance, showing a very efficient energy transfer process in the whole excitation wavelength range (360–515 nm). These results suggest that good energy transfer mediators could be small Si aggregates and not only crystalline clusters. For the best performing sample, the effective Er excitation cross section has been measured to be higher than 10−17 cm2 at 379 and 390 nm and about 2x10^−16 cm^2 at 476 nm, that is, several orders of magnitude higher than the Er direct absorption cross section (of the order of 10−21 cm2 in this glass). Moreover the coefficient of cooperative upconversion has been evaluated to be 2.7x10^−18 cm^3 s^−1. The structural and optical properties of this material are discussed and compared to those found for Si and Er codoped silica.