The change in the fluorescence spectra is consistent with the different optical appearances of the CdSe/CdS QDs before and after the injection of H2S as shownin Fig. 1. Similar to the UV–vis spectra, the fluorescence spectra do not change further after 15 s. The fast fluorescence quenching phenomenon associated with the CdSe/CdS QDs makes them suitable for the detection of H2S in the ppm range.