Carrier Dynamics\nand Recombination Pathways in Ag–In–Zn–S\nQuantum Dots

Strong tolerance to off-stoichiometry of group I–III–VI\nsemiconductors in their nanocrystal form allows fabrication of multinary,\nalloyed structures of desired properties. In particular, alloyed Cu–In–Zn–S\nand Ag–In–Zn–S quantum dots (QDs) have recently\nemerged as efficient fluorophors, in which tailoring the composition\nallows tuning the optical properties, and achieving photoluminescence\n(PL) quantum yields approaching unity. However, poor understanding\nof the carrier recombination mechanism in these materials limits their\nfurther development. In this work, by studying transient absorption\nand temperature dependent PL on bare QDs and QDs conjugated with electron\nscavenger molecules, we obtain a detailed picture of carrier dynamics.\nOur results challenge the prevailing assumption that the PL is due\nto a donor–acceptor-pair transition. We show that the PL occurs\nas a result of a recombination of a delocalized electron with a localized\nhole.