Photoluminescence Properties and Its Origin of AgInS₂ Quantum Dots with Chalcopyrite Structure

We report on the photoluminescence (PL) mechanisms and the nature of the related electronic states of AgInS2 quantum dots (QDs) synthesized via a metathesis reaction of metal complexes. A broad PL band with a large Stokes shift is apparent in the PL spectra of AgInS2 QDs whose average diameter is 2.6 nm. The characteristic decay behavior of the PL spectra and the peak shift of the PL band depending on the excitation intensity indicate that the PL is attributed to the donor−acceptor (DA) pair recombination. The binding energies of the donor and acceptor are estimated to be 100 and 220 meV. These values are derived from the temperature dependence of the PL intensity and an analysis of the spectral profile of the PL spectrum considering the DA pair recombination processes. Furthermore, we show that the phonon sidebands constitute the dominant contribution to the PL spectra because of the strong electron−phonon interaction of carriers trapped by these donors or acceptors.