Apurba De1,Jayanta Dana1,Adar Levy1,Efrat Lifshitz2,Uri Banin1,Sandy Ruhman1
The Hebrew University of Jerusalem1,Technion Israel Institute of Technology2
Apurba De1,Jayanta Dana1,Adar Levy1,Efrat Lifshitz2,Uri Banin1,Sandy Ruhman1
The Hebrew University of Jerusalem1,Technion Israel Institute of Technology2
The relaxation dynamics of hot multiexcitons can be influenced by the presence of another charge carrier in the band edge level (cold carrier). This phenomenon can be understood by considering Pauli spin blockade where the same spin orientation of both the hot and the cold carrier can inhibit the relaxation of the former. This we first demonstrated in CdSe/CdS nanocrystals (NCs) in one of our earlier studies (<i>J. Phys. Chem. Lett</i>. <b>2019</b>, 10, 2341-2348). The idea of ‘spin blockade’ of the hot multiexciton in semiconductor materials is of great interest since it can open up multiple opportunities like in hot-carrier solar cells, photo catalysis etc. To test the generality of such behavior in II-VI quantum dots family members, we extend our study to CdTe. Experimentally this is performed by adopting a unique approach, ‘spectator exciton’ approach where the multiexciton relaxation dynamics is compared with and without a singly deposited cold exciton (we call it ‘spectator exciton’). This spectator exciton actually impose the spin conflict for the cooling of hot multiexcitons. A major observation is that the bleach associated to the state filling of 1s<sup>e</sup>-1h<sup>e </sup>level becomes half in amplitude in presence of spectator exciton. The comparison of carrier cooling time in the absence and presence of spectator reveal a prolonged time scale in case of later which is indicative of effective spin blockade. While in case of CdSe/CdS, there is clear separation between the cooling (~ 2 ps) and spin flip time (~25 ps), which made it easy for the determination of spin flipping time, for CdTe situation become a little complex. Mixed-up situation of the time scales in CdTe further influence the Auger process afterward. In this situation, the Auger process appeared to be slower than expected. We thus suggest that hot multiexciton dynamics should be investigated with extra caution since spin blockade can influence the decay dynamics of such. Further we validate this generality with varying sizes of CdS shell thickness for CdSe/CdS NCs. Overall, our findings prove the generic behavior of spin blockade and provides a unique visualization to the multiexciton dynamics of this II-VI family.