Size effect on carrier dynamics in CdS nanoparticles studied by photoluminescence and picosecond time-resolved photoluminescence measurements

Effect of size on carrier dynamics in CdS nanoparticles (NPs), synthesized by chemical evacuation with thiophenol as organic stabilizer, have been studied using steady state Photoluminescence (PL) and Picosecond Time-resolved Photoluminescence (TRPL) measurements. An enhancement of the NPs PL intensity when increasing temperature up to100 K, together with a distinctive thermal red-shift of the CdS-related PL peak emission have been demonstrated. These behaviors indicate the thermally activated carriers' redistribution between CdS NPs with different size. The low temperature PL decay curves of CdS NPs recorded at different emission wavelengths show that two recombination paths of the excitons with significantly different decay rates exist at high emission wavelength corresponding to the large NPs size (LNPs). However, as decreasing the NPs size, the dynamic of carrier becomes mono-exponential indicating a strong competition between the transfer and radiative recombination for the carriers inside the small NPs (SNPs). These results can provide useful information for fabrication and investigation of CdS NPs for implementing solar cells applications. (paper)