EP02.14.05 : One-Dimensional Carrier Confinement in Excitonic Nanoshells

9:15 AM–9:30 AM Apr 6, 2018

PCC North, 200 Level, Room 222 BC

Luis Royo Romero1 Mikhail Zamkov1

1, Bowling Green State University, Bowling Green, Ohio, United States

We report on the synthesis and spectroscopy of energy-gradient nanostructures that support the formation of two-dimensional excitons in the shell domain. The developed geometry places a wide-gap semiconductor (CdS) at the core of the composite nanoparticle in order to funnel the photoinduced energy into the low-gap CdSe surface layer. As a result, the quantum confinement is achieved in nanoparticles which total size exceeds the exciton Bohr radius. The formation of excitons in the CdSe shell layer was manifested through a size-tunable emission and the characteristic step-like absorption profile. Transient absorption measurements further elucidate the dynamics of the photoinduced energy relaxation in CdS/CdSe nanoshells providing evidence that excitations of the bulk-like core domain result in a rapid, ~ 2-ps recovery of the CdS bleach attributed to electron cooling. The subsequent decay of excitons in the shell proceeds at a lower rate with a markedly multi-exponential temporal character. The charge transport characteristics of nanoshell assemblies were evaluated through a side-by-side comparison with CdSe quantum dot solids. According to photocurrent measurements, nanoshell solids showed an enhanced photoconductivity relative to similarly processed films of spherical CdSe nanocrystals. We expect that the developed nanoshell architecture could potentially be extended to a broader range of semiconductors (e.g. CdS/PbS, ZnS/CdS) facilitating the development of quantum confined solids offering improved charge transport characteristics.