Hole scavenging and aging effect on the photoluminescence of CdS quantum dots

On photoexcitation the excited state of colloidal quantum dots usually exhibit multi-exponential decay with long lifetime due to mixing of a number of excitonic and surface states. However, during present investigation the luminescence decay from CdS quantum dots stabilized by sodium dodecyl sulphate (SDS) follows single exponential decay function. Photoluminescence from these (particle size ∼ 3.0 nm) quantum dots originate from the trap-state (λmax - 516 nm) and exhibit mono-exponential decay with a time constant of 1.7 ns. The hole scavenging characteristics of SDS seems to be instrumental in controlling the decay kinetics of these nanoparticles. On aging band-edge emission peak appears in the lower wavelength region at ∼410 nm and the time-resolved photoluminescence fits to a bi-exponential decay function. The photoluminescence excitation and 3D-luminescence spectroscopic analysis suggests that both band-edge and trap-state emissions from aged samples are associated with the same species. Change in the emission spectra on aging occurs due to self-surface passivation of defects by sulphide ions.