Semiconductor nanocrystals (NCs) are interesting nanoscale systems that have been extensively explored due to the possibility to control their optical and electronic properties by tuning their size and shape through controlled chemical processes and for the wide range of applications including light emitting diodes, solar cells, photodetectors. In this context heterostructured core/shell “giant” NCs (i.e. NCs with a thick shell) are very interesting due to their possible ability to simultaneously emit light of different color by means of radiative recombination in the core and in the shell^[1]. Great efforts have been devoted to the understanding of their optoelectronic properties to give a rationale explanation of  the phenomena responsible of dual or single (from the core) emission, which is still lacking for “giant” PbS/CdS NCs. To gain a picture of the physical processes and conditions causing single or double emission in “giant” PbS/CdS, we studied two NCs differing only for the shell crystalline structure and volume. We performed transient transmission measurements with 100fs time resolution and tunable pump photon energies and we recorded fluence dependent photoluminescence. A combined analysis of the results shows that, although both systems share the same confinement regime, the different morphology and volume of the CdS shell play a key role in the exciton dynamics. In particular, an interfacial zincblende CdS layer and larger shell volume allow a decoupling of the core and shell excitons. This decoupling together with a reduction of the Auger recombination rate, due to the large shell volume, lead to the simultaneous emission from the strongly quantum confined PbS core (at 690nm, close to the NIR region) and from the CdS shell (at 480nm) with similar intensities, otherwise PbS emission is largely favored. We obtained further demonstration of core and shell excitons decoupling from amplified spontaneous emission (ASE) measurements on drop-casted films of both NCs, using 150fs pulsed excitation. As a matter of fact photoluminescence from CdS appeared in both films but a sharp peak of ASE from CdS occurred only in the sample with the interfacial zincblende CdS and large shell volume. This study highlights the important role of the shell in the double emitting NCs and pave the way for the effective exploitation of dual emission in PbS/CdS NCs^[2]. References: [1] H. Zhao, G.Sirigu, A. Parisini, A. Camellini, G. Nicotra, F. Rosei, V. Morandi, M. Zavelani-Rossi, A. Vomiero, Nanoscale 8, 4217-4226 (2016); [2] H. Zhao, A. Vomiero, F. Rosei, small 2015, DOI: 10.1002/smll.201502249.