Origin and Dynamics of Highly Efficient Broadband Photoluminescence of Aqueous Glutathione-Capped Size-Selected Ag-In-S Quantum Dots

The 2-3 nm size-selected glutathione-capped Ag In S (AIS) and core/shell AIS/ZnS quantum dots (QDs) were produced by precipitation/redissolution from an aqueous colloidal ensemble. The QDs reveal broadband photoluminescence (PL) with a quantum yield of up to 60% for the most populated fraction of the core/shell AIS/ZnS QDs. The PL band shape can be described by a self-trapped exciton model implying the PL band being a sequence of phonon replica of a zero-phonon line resulting from strong electron phonon interaction and a partial conversion of the electron excitation energy into lattice vibrations. It can be concluded that the position and shape of the PL bands of MS QDs originate not from energy factors (depth and distribution of trap states) but rather from the dynamics of the electron phonon interaction and the vibrational relaxation in the QDs. The rate of vibrational relaxation of the electron excitation energy in MS QDs is found to be size-dependent, increasing almost twice from the largest to the smallest QDs.