Luminescence properties of chalcopyrite AgInS2 nanocrystals: Their origin and related electronic states

We report on the photoluminescence (PL) mechanisms of the chalcopyrite AgInS2 nanocrystals with dodecanethiol surfactants. The nanocrystals present broad PL spectra (full width at half maximum of 0.4 eV) with large Stokes-shifts (0.8-1.0 eV). Time-resolved PL measurements revealed that the PL decay time depends strongly on the emission energies corresponding to the temporal redshift of the PL bands. The PL bands also exhibit the blueshift with increasing excitation intensity. These characteristic behaviors observed in the PL spectra indicate that the luminescence of the AgInS2 nanocrystals originates from the electron-hole pair emission via donor-acceptor pair-like recombination mechanisms. The quantum yield (QY) of PL is up to > 40%, which is at least 4-fold larger compared with QYs reported for other chalcopyrite nanocrystals without ZnS shell ( < 10%), indicating that surface passivation of AgInS2 nanocrystals by dodecanethiol molecules efficiently eliminates surface defects act as non-radiative recombination centers. We conclude that the donor and acceptor states associated with the PL of AgInS2 nanocrystals originate from the lattice defects formed in the interior of nanocrystals, not on surfaces. (c) 2011 Elsevier B.V. All rights reserved.