title: Influence of the core size on biexciton quantum yield of giant CdSe/CdS nanocrystals.
abstract: We present a systematic study of photoluminescence (PL) emission intensity and biexciton (BX) quantum yields (QYBX) in individual "giant" CdSe/CdS nanocrystals (g-NCs) as a function of g-NC core size and shell thickness. We show that g-NC core size significantly affects QYBX and can be utilized as an effective tuning parameter towards higher QYBX while keeping the total volume of the g-NC constant. Specifically, we observe that small-core (2.2 nm diameter) CdSe/CdS NCs with a volume of ∼200 nm(3) (shell comprises 4 CdS monolayers) show very low average and maximum QYBX's of ∼3 and 7%, respectively. In contrast, same-volume medium-core (3 nm diameter) NCs afford higher average values of ∼10%, while QYBX's of ∼30% are achieved for same-volume large-core (5.5 nm diameter) CdSe/CdS NCs, with some approaching ∼80%. These observations underline the influence of the g-NC core size on the evolution of PL emissive states in multi-shell NCs. Moreover, our study also reveals that the use of long anneal times in the growth of CdS shells plays a critical role in achieving high QYBX.
authors.affiliation: Materials Physics and Applications Division, Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. htoon@lanl.gov.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Mangum
authors.forename: Siddharth
authors.initials: S
authors.lastname: Sampat
authors.forename: Yagnaseni
authors.initials: Y
authors.lastname: Ghosh
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Hollingsworth
authors.forename: Han
authors.initials: H
authors.lastname: Htoon
authors.forename: Anton V
authors.initials: AV
authors.lastname: Malko