Subpicosecond time-resolved photoluminescence of thioglycerol-capped CdS nanoparticles in water

Subpicosecond time-resolved photoluminescence (STRPL) of aqueous colloidal solutions of thioglycerol-capped CdS nanoparticles (TG-CdS) was successfully measured by fluorescence up-conversion techniques. In their STRPL obtained within the time range of 30 ps after the excitation, the intensity of photoluminescence (PL) around 500 nm at which their static PL is not noticeable is considerably outstanding compared with that at a longer wavelength region at which PL is attributed to deep trap sites in CdS nanoparticles. From the analysis of the PL decay profile at the wavelength region of 490–550 nm at which PL is mainly attributed to near band edge emission, we observed two fast PL decay components of ca. 1 ps and ca. 10 ps, similar to those already reported for the band edge emission of CdS nanoparticles in a glass matrix. In the present study, former decay component was related to trapping rate of photogenerated holes, following the case already reported for CdS nanoparticles embeded in a glass matrix. However, the origin of the latter PL decay component is not clear at present. It is necessary to study in further detail to elucidate it.