Influence of Zn on the photoluminescence of colloidal (AgIn)xZn2(1-x) S2 nanocrystals

We study the effect of Zn on the photophysical properties of a family of group I-III-VI nanocrystals (NCs), namely in solid solutions of (AgIn)(x)Zn2(1-x)S2 (ZAIS). We focus on the comparison of the photo-luminescence (PL) properties of ZAIS NCs of comparable sizes and different amounts of Zn. This approach helps us to decouple the effects of size and varying chemical composition of the NCs which both influence the PL properties. We show that in the presence of Zn new radiative centers are generated which improve the NC quality in terms of PL quantum yield. However, an amount of Zn beyond a particular limit places the radiative recombination centers close to each other, leading to undesired interactions among charge carriers and non-radiative transitions. Proximity between the energy levels of these radiative centers and the conduction band leads to non-radiative localized-delocalized transitions, as evidenced from temperature dependent absorption, PL and lifetime measurements.