title: Giant nanocrystal quantum dots: stable down-conversion phosphors that exploit a large stokes shift and efficient shell-to-core energy relaxation.
abstract: A new class of nanocrystal quantum dot (NQD), the "giant" NQD (g-NQD), was investigated for its potential to address outstanding issues associated with the use of NQDs as down-conversion phosphors in light-emitting devices, namely, insufficient chemical/photostability and extensive self-reabsorption when packed in high densities or in thick films. Here, we demonstrate that g-NQDs afford significantly enhanced operational stability compared to their conventional NQD counterparts and minimal self-reabsorption losses. The latter results from a characteristic large Stokes shift (>100 nm; >0.39 eV), which itself is a manifestation of the internal structure of these uniquely thick-shelled NQDs. In carefully prepared g-NQDs, light absorption occurs predominantly in the shell but emission occurs exclusively from the core. We directly compare for the first time the processes of shell→core energy relaxation and core→core energy transfer by evaluating CdS→CdSe down-conversion of blue→red light in g-NQDs and in a comparable mixed-NQD (CdSe and CdS) thin film, revealing that the internal energy relaxation process affords a more efficient and color-pure conversion of blue to red light compared to energy transfer. Lastly, we demonstrate the facile fabrication of white-light devices with correlated color temperature tuned from ∼3200 to 5800 K.
authors.affiliation: Materials Physics and Applications Division, Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
authors.forename: Janardan
authors.initials: J
authors.lastname: Kundu
authors.forename: Yagnaseni
authors.initials: Y
authors.lastname: Ghosh
authors.forename: Allison M
authors.initials: AM
authors.lastname: Dennis
authors.forename: Han
authors.initials: H
authors.lastname: Htoon
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Hollingsworth
mesh_terms: D004735:Energy Transfer; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D045663:Quantum Dots