8 research outputs found
Organic Photodiodes with an Extended Responsivity using Ultrastrong Light-Matter Coupling
In organic photodiodes (OPDs) light is absorbed by excitons, which dissociate
to generate photocurrent. Here, we demonstrate a novel type of OPD in which
light is absorbed by polaritons, hybrid light-matter states. We demonstrate
polariton OPDs operating in the ultra-strong coupling regime at visible and
infrared wavelengths. These devices can be engineered to show narrow
responsivity with a very weak angle-dependence. More importantly, they can be
tuned to operate in a spectral range outside that of the bare exciton
absorption. Remarkably, we show that the responsivity of a polariton OPD can be
pushed to near infrared wavelengths, where few organic absorbers are available,
with external quantum efficiencies exceeding those of a control OPD
Inverting Singlet and Triplet Excited States using Strong Light-Matter Coupling
In organic microcavities, hybrid light-matter states can form with energies
that differ from the bare molecular excitation energies by nearly 1 eV. A
timely question, given recent advances in the development of thermally
activated delayed fluorescence materials, is whether strong light-matter
coupling can be used to invert the ordering of singlet and triplet states and,
in addition, enhance reverse intersystem crossing (RISC) rates. Here, we
demonstrate a complete inversion of the singlet lower polariton and triplet
excited states. We also unambiguously measure the RISC rate in strongly-coupled
organic microcavities and find that, regardless of the large energy level
shifts, it is unchanged compared to films of the bare molecules. This
observation is a consequence of slow RISC to the lower polariton due to the
delocalized nature of the state across many molecules and an inability to
compete with RISC to the dark exciton reservoir, which occurs at a rate
comparable to that in bare molecules
Triplet harvesting in the polaritonic regime: a variational polaron approach
We explore the electroluminescence efficiency for a quantum mechanical model
of a large number of molecular emitters embedded in an optical microcavity. We
characterize the circumstances under which a microcavity enhances harvesting of
triplet excitons via reverse intersystem-crossing (R-ISC) into singlet
populations that can emit light. For that end, we develop a time-local master
equation in a variationally optimized frame which allows for the exploration of
the population dynamics of chemically relevant species in different regimes of
emitter coupling to the condensed phase vibrational bath and to the microcavity
photonic mode. For a vibrational bath that equilibrates faster than R-ISC (in
emitters with weak singlet-triplet mixing), our results reveal that significant
improvements in efficiencies with respect to the cavity-free counterpart can be
obtained for strong coupling of the singlet exciton to a photonic mode, as long
as the singlet to triplet exciton transition is within the inverted Marcus
regime; under these circumstances, we show the possibility to overcome the
detrimental delocalization of the polariton states across a macroscopic number
of molecules. On the other hand, for a vibrational bath that equilibrates
slower than R-ISC (i.e., emitters with strong singlet-triplet mixing), we find
that while enhancemnents in photoluminiscence can be obtained via vibrational
relaxation into polaritons, this only occurs for small number of emitters
coupled to the photon mode, with delocalization of the polaritons across many
emitters eventually being detrimental to electroluminescence efficiency. These
findings provide insight on the tunability of optoelectronic processes in
molecular materials due to weak and strong light-matter coupling
Aluminum Nanoantenna Complexes for Strong Coupling between Excitons and Localized Surface Plasmons
We study the optical dynamics in
complexes of aluminum nanoantennas coated with molecular J-aggregates
and find that they provide an excellent platform for the formation
of hybrid exciton-localized surface plasmons. Giant Rabi splitting
of 0.4 eV, which corresponds to âŒ10 fs energy transfer cycle,
is observed in spectral transmittance. We show that the nanoantennas
can be used to manipulate the polarization of hybrid states and to
confine their mode volumes. In addition, we observe enhancement of
the photoluminescence due to enhanced absorption and increase in the
local density of states at the exciton-localized surface plasmon energies.
With recent emerging technological applications based on strongly
coupled lightâmatter states, this study opens new possibilities
to explore and utilize the unique properties of hybrid states over
all of the visible region down to ultraviolet frequencies in nanoscale,
technologically compatible, integrated platforms based on aluminum
Temporal Dynamics of Localized ExcitonâPolaritons in Composite OrganicâPlasmonic Metasurfaces
We
use femtosecond transient absorption spectroscopy to study the
temporal dynamics of strongly coupled excitonâplasmon polaritons
in metasurfaces of aluminum nanoantennas coated with J-aggregate molecules.
Compared with the thermal nonlinearities of aluminum nanoantennas,
the excitonâplasmon hybridization introduces strong ultrafast
nonlinearities in the composite metasurfaces. Within femtoseconds
after the pump excitation, the plasmonic resonance is broadened and
shifted, showcasing its high sensitivity to excited-state modification
of the molecular surroundings. In addition, we observe temporal oscillations
due to the deep subangstrom acoustic breathing modes of the nanoantennas
in both bare and hybrid metasurfaces. Finally, unlike the dynamics
of hybrid states in optical microcavities, here, ground-state bleaching
is observed with a significantly longer relaxation time at the upper
polariton band
Measurement of apoptosis by SCAN©, a system for counting and analysis of fluorescently labelled nuclei
Apoptosis-like programmed cell death (A-PCD) is a universal process common to all types of eukaryotic organisms. Because A-PCD-associated processes are conserved, it is possible to define A-PCD by a standard set of markers. Many of the popular methods to measure A-PCD make use of fluorescent ligands that change in intensity or cellular localization during A-PCD. In single cell organisms, it is possible to quantify levels of A-PCD by scoring the number of apoptotic cells using flow cytometry instruments. In a multicellular organism, quantification of A-PCD is more problematic due to the complex nature of the tissue. The situation is further complicated in filamentous fungi, in which nuclei are divided between compartments, each containing a number of nuclei, which can also migrate between the compartments. We developed SCAN©, a System for Counting and Analysis of Nuclei, and used it to measure A-PCD according to two markers â chromatin condensation and DNA strand breaks. The package includes three modules designed for counting the number of nuclei in multi-nucleated domains, scoring the relative number of nuclei with condensed chromatin, and calculating the relative number of nuclei with DNA strand breaks. The method provides equal or better results compared with manual counting, the analysis is fast and can be applied on large data sets. While we demonstrated the utility of the software for measurement of A-PCD in fungi, the method is readily adopted for measurement of A-PCD in other types of multicellular specimens
Spectral Responsivity and Photoconductive Gain in Thin Film Black Phosphorus Photodetectors
We have fabricated black phosphorus photodetectors and characterized their
full spectral responsivity. These devices, which are effectively in the bulk
thin film limit, show broadband responsivity ranging from <400 nm to the ~3.8
m bandgap. In the visible, an intrinsic responsivity >7 A/W can be
obtained due to internal gain mechanisms. By examining the full spectral
response, we identify a sharp contrast between the visible and infrared
behavior. In particular, the visible responsivity shows a large photoconductive
gain and gate-voltge dependence, while the infrared responsivity is nearly
independent of gate voltage and incident light intensity under most conditions.
This is attributed to a contribution from the surface oxide. In addition, we
find that the polarization anisotropy in responsivity along armchair and zigzag
directions can be as large as 103 and extends from the band edge to 500 nm. The
devices were fabricated in an inert atmosphere and encapsulated by AlO
providing stable operation for more than 6 months
Organic Photodiodes with an Extended Responsivity Using Ultrastrong LightâMatter Coupling
In organic photodiodes
(OPDs), light is absorbed by excitons that
dissociate to generate photocurrent. Here, we demonstrate a novel
type of OPD in which light is absorbed by polaritons, hybrid lightâmatter
states. We demonstrate polariton OPDs operating in the ultrastrong
coupling regime at visible and infrared wavelengths. These devices
can be engineered to show narrow responsivity with a very weak angle-dependence.
More importantly, they can be tuned to operate in a spectral range
outside that of the bare exciton absorption. Remarkably, we show that
the responsivity of a polariton OPD can be pushed to near-infrared
wavelengths, where few organic absorbers are available, with external
quantum efficiencies exceeding those of our control OPD