Abstract
We investigate multi-color spontaneous emission from quantum-dot- quantum-well heteronanocrystals made of onion-like (CdSe)ZnS/CdSe/ZnS (core)shell/shell/shell structures, with our theoretical results explaining experimental measurements for the first time. In such multi-layered heteronanocrystals, we discover that the carrier localization is tuned from type-1-like to type-2-like localization by controlling CdSe and ZnS shell thicknesses, and that 3-monolayer ZnS barriers are not necessarily sufficient for carrier localization, unlike in conventional (CdSe)ZnS (core)shell structures. We demonstrate that exciton localization in distinct layers of (CdSe)ZnS/CdSe/ZnS heteronanocrystals with high transition probability (for n=1 states in CdSe core and n=2 states in CdSe shell) is key to their multi-color emission.
Highlights
Quantum structures are of fundamental interest to study the modification of light-material interactions through quantum confinement
We further identify the conditions of multi-color spontaneous emission from a single multi-layered heteronanocrystal in CdSe-ZnS material system, with our theoretical results explaining experimental measurements for the first time
We showed that the carrier localization at the first excited state is tuned from type-1-like to type-2-like localization and from type-2-like to type-1-like localization back again, by varying the first shell (ZnS) and the second shell (CdSe) thicknesses
Summary
Quantum structures are of fundamental interest to study the modification of light-material interactions through quantum confinement. Recently multi-color emission in the visible has been accomplished in CdSe-ZnS based QDQW systems to generate white light [23,24] In these structures, around a core made of CdSe, a ZnS shell barrier is synthesized, and subsequently CdSe shell quantum well is added surrounding this ZnS barrier. To date the conditions of multi-color spontaneous emission from a single type of such heteronanocrystals have not been completely understood These multi-layered heteronanocrystal systems (including the multi-color emitting (CdSe-core)ZnS-shell/CdSe-shell heteronanocrystals) have not been theoretically investigated till date. To seek answers for these fundamental questions, we investigate multi-color spontaneous emission from quantum-dot-quantum-well heteronanocrystals in CdSe-ZnS material system In spite of the well-known fact that a 3-monolayer ZnS shell barrier is sufficient for full carrier confinement in conventional (CdSe)ZnS (core)shell structures, we discover that the carriers in the CdSe core and CdSe shell in a multi-layered heteronanocrystal might be still coupled despite the use of 3-monolayer ZnS shells as the barrier
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