SiO2 glass incorporated with Tb3+ ions was synthesized by the sol-gel process, with and without codoping Al-3. Glass with Tb3+ ions shows high fluorescence (FL) intensity at 545 nm, which results from the transition of D-5(4) to F-7(5). The FL intensity of the samples increased with codoping Al3+ up to the molar ratio Al/Tb = 20, at which the FL intensity was more than 10 times higher than that without codoping with Al3+. Codoping with Al3+ beyond that molar ratio (>20) resulted in insignificant FL intensity increase. All the samples in this study were annealed in air at different temperatures ranging from 473 to 1273 K. The FL intensity at 545 nm increased with increasing annealing temperature. There was a more significant increase in FL intensity for the annealed Al3+-codoped samples when the treatment temperature was higher than 773 K. These results are explained in terms of the removal of Tb3+ ion clusters and OH groups and the change in structure surrounding the Tb3+ ions.