We report on the observation of similar temperature dependences of PL intensities of AgInGaS nanoparticles and AgInGaS  /  GaS_x core–shell nanoparticles. The intensity of band-edge emission in AgInGaS  /  GaS_x increases with temperature up to 200 K, and the intensity at room temperature is on the order of that at 5 K. Using a model that includes effects of thermal activation of carriers from trap states, we propose that a shallow trap state exists in the AgInGaS core, and the higher PL intensity of the band-edge emission at 200 K is due to the radiative recombination of carriers that have been thermally activated from the shallow state. Time-resolved PL measurements are employed to support this interpretation.