4 research outputs found
Plasmon-Enhanced Energy Transfer in Photosensitive Nanocrystal Device
Förster
resonance energy transfer (FRET) interacted with
localized surface plasmon (LSP) gives us the ability to overcome inadequate
transfer of energy between donor and acceptor nanocrystals (NCs).
In this paper, we show LSP-enhanced FRET in colloidal photosensors
of NCs in operation, resulting in substantially enhanced photosensitivity.
The proposed photosensitive device is a layered self-assembled colloidal
platform consisting of separated monolayers of the donor and the acceptor
colloidal NCs with an intermediate metal nanoparticle (MNP) layer
made of gold interspaced by polyelectrolyte layers. Using LBL assembly,
we fabricated and comparatively studied seven types of such NC-monolayer
devices (containing only donor, only acceptor, Au MNP–donor,
Au MNP–acceptor, donor–acceptor bilayer, donor–Au
MNP–acceptor trilayer, and acceptor–Au MNP–donor
reverse trilayer). In these structures, we revealed the effect of
LSP-enhanced FRET and exciton interactions from the donor NCs layer
to the acceptor NCs layer. Compared to a single acceptor NC device,
we observed a significant extension in operating wavelength range
and a substantial photosensitivity enhancement (2.91-fold) around
the LSP resonance peak of Au MNPs in the LSP-enhanced FRET trilayer
structure. Moreover, we present a theoretical model for the intercoupled
donor–Au MNP–acceptor structure subject to the plasmon-mediated
nonradiative energy transfer. The obtained numerical results are in
excellent agreement with the systematic experimental studies done
in our work. The potential to modify the energy transfer through mastering
the exciton–plasmon interactions and its implication in devices
make them attractive for applications in nanophotonic devices and
sensors
Phonon-Assisted Exciton Transfer into Silicon Using Nanoemitters: The Role of Phonons and Temperature Effects in Förster Resonance Energy Transfer
We study phonon-assisted Förster resonance energy transfer (FRET) into an indirect band-gap semiconductor using nanoemitters. The unusual temperature dependence of this energy transfer, which is measured using the donor nanoemitters of quantum dot (QD) layers integrated on the acceptor monocrystalline bulk silicon as a model system, is predicted by a phonon-assisted exciton transfer model proposed here. The model includes the phonon-mediated optical properties of silicon, while considering the contribution from the multimonolayer-equivalent QD film to the nonradiative energy transfer, which is derived with a <i>d</i><sup>–3</sup> distance dependence. The FRET efficiencies are experimentally observed to decrease at cryogenic temperatures, which are well explained by the model considering the phonon depopulation in the indirect band-gap acceptor together with the changes in the quantum yield of the donor. These understandings will be crucial for designing FRET-enabled sensitization of silicon based high-efficiency excitonic systems using nanoemitters
Macrocrystals of Colloidal Quantum Dots in Anthracene: Exciton Transfer and Polarized Emission
In this work, centimeter-scale macrocrystals
of nonpolar colloidal
quantum dots (QDs) incorporated into anthracene were grown for the
first time. The exciton transfer from the anthracene host to acceptor
QDs was systematically investigated, and anisotropic emission from
the isotropic QDs in the anthracene macrocrystals was discovered.
Results showed a decreasing photoluminescence lifetime of the donor
anthracene, indicating a strengthening energy transfer with increasing
QD concentration in the macrocrystals. With the anisotropy study,
QDs inside the anthracene host acquired a polarization ratio of ∼1.5
at 0° collection angle, and this increases to ∼2.5 at
the collection angle of 60°. A proof-of-concept application of
these excitonic macrocrystals as tunable color converters on light-emitting
diodes was also demonstrated
Large-Area (over 50 cm × 50 cm) Freestanding Films of Colloidal InP/ZnS Quantum Dots
We propose and demonstrate the fabrication of flexible,
freestanding
films of InP/ZnS quantum dots (QDs) using fatty acid ligands across
very large areas (greater than 50 cm × 50 cm), which have been
developed for remote phosphor applications in solid-state lighting.
Embedded in a polyÂ(methyl methacrylate) matrix, although the formation
of stand–alone films using other QDs commonly capped with trioctylphosphine
oxide (TOPO) and oleic acid is not efficient, employing myristic acid
as ligand in the synthesis of these QDs, which imparts a strongly
hydrophobic character to the thin film, enables film formation and
ease of removal even on surprisingly large areas, thereby avoiding
the need for ligand exchange. When pumped by a blue LED, these Cd-free
QD films allow for high color rendering, warm white light generation
with a color rendering index of 89.30 and a correlated color temperature
of 2298 K. In the composite film, the temperature-dependent emission
kinetics and energy transfer dynamics among different-sized InP/ZnS
QDs are investigated and a model is proposed. High levels of energy
transfer efficiency (up to 80%) and strong donor lifetime modification
(from 18 to 4 ns) are achieved. The suppression of the nonradiative
channels is observed when the hybrid film is cooled to cryogenic temperatures.
The lifetime changes of the donor and acceptor InP/ZnS QDs in the
film as a result of the energy transfer are explained well by our
theoretical model based on the exciton–exciton interactions
among the dots and are in excellent agreement with the experimental
results. The understanding of these excitonic interactions is essential
to facilitate improvements in the fabrication of photometrically high
quality nanophosphors. The ability to make such large-area, flexible,
freestanding Cd-free QD films pave the way for environmentally friendly
phosphor applications including flexible, surface-emitting light engines