We study the effects of low-temperature capping (200-450°C) on the optical properties of GaAs/AlGaAs quantum wells. Photoluminescence measurements clearly show the formation of abundant nonradiative recombination centers in an AlGaAs capping layer grown at 200°C, while there is a slight degradation of the optical quality in AlGaAs capping layers grown at temperatures above 350°C compared to that of a high-temperature capping layer. In addition, the optical quality can be restored by post-growth annealing without any structural change, except for the 200°C-capped sample.