Exciton Energy Transfer Research Articles

Efficient triplet exciton phosphorescence quenching from a rhenium monolayer on silicon

Using phosphorescence lifetime image microscopy (PLIM) measurements we report up to 95% efficient triplet exciton energy transfer from a rhenium(i) fac-tricarbonyl bipyridine complex deposited as a Langmuir–Blodgett monolayer to crystalline silicon.

Organic Bilayer Heterostructures with Built-In Exciton Conversion for 2D Photonic Encryption.

Organic multilayer heterostructures with accurate spatial organization demonstrate strong light-matter interaction from excitonic responses and efficient carrier transfer across heterojunction interfaces, which are considered as promising candidates toward advanced optoelectronics. However, the precise regulation of the heterojunction surface area for finely adjusting exciton conversion and energy transfer is still formidable. Herein, organic bilayer heterostructures (OBHs) with controlled face-to-face heterojunction via a stepwise seeded growth strategy, which is favorable for efficient exciton propagation and conversion of optical interconnects are designed and synthesized. Notably, the relative position and overlap length ratio of component microwires (LDSA /LBPEA = 0.39-1.15) in OBHs are accurately regulated by modulating the crystallization time of seeded crystals, resulting into a tailored heterojunction surface area (R = Loverlap /LBPEA = 37.6%-65.3%). These as-prepared OBHs present the excitation position-dependent waveguide behaviors for optical outcoupling characteristics with tunable emission colors and intensities, which are applied into two-dimensional (2D) photonic barcodes. This strategy opens a versatile avenue to purposely design OBHs with tailored heterojunctions for efficient energy transfer and exciton conversion, facilitating the application possibilities of advanced integrated optoelectronics.

Exciton energy transfer under low temperature in a lateral heteromonolayer of WSe2–MoSe2

We examined the exciton energy transfer process in a lateral heteromonolayer of WSe2–MoSe2 at low temperature. Position-dependent photoluminescence (PL) and PL excitation spectroscopy measurements revealed the occurrence of exciton energy transport from WSe2 to MoSe2 both at RT and 15 K. The effective energy transport distance in WSe2 was longer at 15 K than at RT, suggesting that the dark excitons with longer diffusion length than bright excitons preferentially contributed to the exciton energy transport across the heterojunction interface at 15 K. Additionally, we observed that no valley information was transported from WSe2 to MoSe2 via the energy transfer process. This study provides useful insights for the development of excitonic devices based on exciton transport in transition metal dichalcogenides.

Matrix-Assisted Processes in CH4-Doped Ar Ices Irradiated with an Electron Beam

The relaxation processes induced by exposure of the Ar matrices doped with CH4 (0.1–10%) to an electron beam were studied with a focus on the dynamics of radiolysis products—H atoms, H2 molecules, CH radicals, and energy transfer processes. Three channels of energy transfer to dopant and radiolysis products were discussed, including free charge carriers, free excitons and photons from the “intrinsic source” provided by the emission of the self-trapped excitons. Radiolysis products along with the total yield of desorbing particles were monitored in a correlated manner. Analysis of methane transformation reactions induced by free excitons showed that the CH radical can be considered a marker of the CH3 species. The competition between exciton self-trapping and energy transfer to the dopant and radiolysis products has been demonstrated. A nonlinear concentration behavior of the H atoms in doped Ar matrices has been established. Real-time correlated monitoring of optical emissions (H atom and CH3 radicals), particle ejection, and temperature revealed a nonmonotonic behavior of optical yields with a strong luminescence flash after almost an hour of exposure, which correlated with the explosive pulse of particle ejection and temperature. The connection of this phenomenon with the processes of energy transfer and recombination reactions has been established. It is shown that the delayed explosive ejection of particles is driven by both the recombination of H atoms and CH3 radicals. This occurs after their accumulation to a critical concentration in matrices at a CH4 content C ≥ 1%.

Optical Non‐Reciprocity in Coupled Resonators by Detailed Balance

AbstractInspired by the photosynthetic energy transfer process, a method to realize non‐reciprocal optical transmission in an array of coupled resonators is theoretically proposed. The optical non‐reciprocity of the coupled resonators arises from the frequency gradient between adjacent cavities and the interaction with the environment, which is similar to photosynthetic energy transfer. An increase in the frequency gradient or the number of the cavities can lead to better non‐reciprocity. However, although a higher environment temperature will increase the total photon number in the coupled cavities, non‐reciprocity will be weakened. All these findings can be well described by the detailed balance. The similarity between the noise‐induced optical non‐reciprocity and exciton energy transfer in natural photosynthesis is revealed by the discovery.

(Invited) Quantifying Long-Range Exciton Energy Transfer in Carbon Nanotube Polariton Microcavities

In Ref. 1 and at the Spring 2022 ECS B03 Symposium on Carbon Nanotubes, we reported on the long-range energy transfer of excitons from (6,5) to (7,5) carbon nanotubes across an insulating barrier in an optical microcavity, mediated by moderate and strong exciton-photon polariton coupling and measured via two-dimensional, white-light spectroscopy. This talk will present on the alternative use of nanotube-C60 photovoltaic devices embedded in microcavities to quantify the efficiency of this long-range energy transfer and the factors that affect it.[1] Energy cascades in donor-acceptor exciton-polaritons observed by ultrafast two-dimensional white-light spectroscopy, M. Son, Z.T. Armstrong, R.T Allen, A. Dhavamani, M.S. Arnold, M.T. Zanni, Nature Communications 13, 7305 (2022). DOI: 10.1038/s41467-022-35046-2

High-Performance Hot-Exciton OLEDs via Fully Harvesting Triplet Excited States from Both the Exciplex Co-Host and the TBRb Emitter.

The high-level reverse intersystem crossing (HL-RISC, T2 → S1 ) process from triplet to singlet exciton, namely the "hot exciton" channel, has recently been demonstrated in the traditional fluorescent emitter of TBRb. Although it is a potential pathway to improve the utilization of non-radiative triplet exciton energy, highly efficient fluorescent organic light emitting diodes (FOLEDs) based on this "hot exciton" channel have not been developed. Herein, high-efficiency and low-efficiency roll-off FOLEDs are achieved through doping TBRb molecules into an energy-level matched exciplex co-host. Combining the low-level RISC (LL-RISC, EX3 → EX1 ) process in the exciplex co-host with the HL-RISC process of hot excitons in TBRb to fully harvest the triplet energy, a record-high external quantum efficiency (EQE) of 20.4% is obtained via a proper Dexter energy transfer of triplet excitons, realizing the efficiency breakthrough from fully fluorescent material-based OLEDs with TBRb as an end emitter. Furthermore, the fingerprint Magneto-electroluminescence (MEL) as a sensitive measuring tool is employed to visualize the "hot exciton" channel in TBRb, which also directly verifies the effective energy confinement and the full utilization of hot excitons. Obviously, this work paves a promising way for further fabricating high-efficiency TBRb-based FOLEDs for lighting and flat-panel display applications.

Study on the exciton dynamic processes of exciplex host–guest system by transient magnetic field effects

Utilizing exciplex as the host and fluorescence emitter with dopant materials has been proved successfully to fabricate highly-efficient organic light-emitting diodes. Exciton evolution and energy transfer in this exciplex host–guest system are complex. Gaining insight into the electroluminescence (EL) mechanisms in exciplex-based devices is key for further optimizing device configuration. Here, we have investigated exciton dynamics in devices with exciplex as host and 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) as red fluorescence emitter. Two exciplexes, 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPY) doped 2,4,6-tris[3-(triphenylphosphine)phenyl]-1,3,5-triazine (POT2T), and 4,4′,4″-tris[3-methylphenyl(phenyl)amino]-triphenylamine (m-MTDATA) doped tris(8-hydroxyquinoline)aluminum(III) (Alq3), with different band energy are utilized as host materials. Combining the measurements of transient EL, transient photoluminescence and magnetic field effect (MFE), it is concluded that Dexter energy transfer, together with Förster resonance energy transfer, are confirmed in the pure fluorescence doped system. Meanwhile, it is found that DCJTB works with the hot excitons mechanism but not a traditional red fluorescence emitter as recognized previously. This work presents that the transient MFE is powerful for detecting excitonic dynamic processes in excipelx based host–guest EL systems.

Three-photon luminescence assisted by excitonic energy transfer in gold nanoparticle-WS2 monolayers

2D transition metal dichalcogenides coupled to semiconductor quantum dots or metallic nanoparticles give rise to novel energy transfer pathways and intricate nonlinear optical properties. In this article, by using multiphoton microscopy, we observe photoluminescence signals in the green or blue light spectrum (higher than 2 eV) emitting from the gold nanoparticles that are coupled to tungsten disulfide (WS2) monolayers, even when the excitation energy is as low as 1 eV. The pump power dependence indicates that these photoluminescence signals involve the absorption of three photons not by the gold nanoparticles or WS2 alone but through a one-photon intraband excitation in the gold nanoparticle and a two-photon excitation in WS2 that, via the excitonic resonance energy transfer, delivers the energy to the gold nanoparticle by inducing an interband excitation. We suggest ways to improve the light emission efficiency of this hybrid structure for a potential room temperature upconversion emitter.

Efficient Ultrathin Self‐Powered Organic Photodetector with Reduced Exciton Binding Energy and Auxiliary Föster Resonance Energy Transfer Processes

AbstractRecent advances in organic photodetectors (OPDs) have enabled high detectivity, high quantum efficiency, and fast response, due to their broad spectral response, easy processing, compatibility with flexible devices, and cooling‐free operations. The advantages of combining ultrathin and self‐powered OPDs are rarely explored, as technological limitations and lack of knowledge on the underlying mechanisms may lead to low light absorption efficiency and carrier recombination issues. Here, a modification layer‐assisted approach is developed to construct ultrathin self‐powered OPDs with enhanced sensitivity and ultrafast response time performance due to efficient exciton dissociation, energy transfer, and charge extraction processes. Specifically, this strategy enables a reduced exciton binding energy (42.4 meV) for efficient dissociation, as well as an increased dielectric constant of the photosensitive layer that shields undesirable lattice binding effects of photogenerated excitons. As a result, a remarkable device responsivity (0.45 A W−1), improved response detectivity (1.25 × 1012 Jones), and enhanced energy transfer efficiency (78.7%) are observed in the modified ultrathin organic photodetector. These findings illustrate a clear correlation between the exciton dissociation process, photogenerated exciton yields, and energy transfer channels, providing essential insight into the design of efficient ultrathin organic photodetectors.

Roles of Molecular Spatial Arrangement in Exciton Energy Transfer in Organic Light-Emitting Diodes: A Theoretical Study

Revealing the mechanism of exciton energy transfer (EET) in the emitting layer (EML) of organic light-emitting devices is significant for improving the device performance. In this paper, we explore how the host-TADF combinations influence EET in the amorphous film, especially for the Dexter energy transfer (DET) process. With the help of density functional theory calculations and molecular dynamics simulations, we study the Förster resonance energy transfer and the DET of two thin films (2,6-2CzBN:4tCzBN and 3,5-2CzBN:4tCzBN) to determine how the intermolecular interaction influences the energy transfer. We find that the exciton coupling value is the decisive factor that leads to the external quantum efficiency difference between the two amorphous films by analyzing the variable in Marcus theory. The molecular spatial arrangement in 3,5-2CzBN is beneficial to enhance exciton coupling. The more space around benzonitriles helps to strengthen fragment interaction between benzonitriles, which plays a vital role in exciton coupling and spatial distribution. This work reveals how the molecular spatial arrangement and interaction influence energy transfer.

An experimental approach to ensure energy quenching and fluorescence resonance energy transfer of excitons from P3HT to CuInSe2

This letter reports the paramount fluorescence resonance energy transfer mechanism for photo induced charge transfer from P3HT to solvothermally derived CuInSe2. The HOMO (-4.85 eV) and LUMO (-3.38 eV) energy states of CuInSe2 (electrical conductivity = 1.1x 10-7 Scm−1) are determined from cyclic voltammetry and optical study. This HOMO-LUMO position agrees to select P3HT polymer as possible donor of excitons. Steady-state luminescence study of composite (P3HT:CuInSe2) demonstrates possibility of successful charge transfer. Stern–Volmer analysis of absorption and emission spectroscopy ensures static energy quenching phenomena. The Förster distance (R0) of critical energy transfer is estimated as 3.61 nm. The average distance between donor–acceptor (ravg = 4.71 nm) is<8 nm and within the range 0.5R0 < r < 1.5R0 (1.81 nm < r < 5.42 nm), which ensures energy transfer from P3HT to CuInSe2.

Arrays of size-dispersed ZnSe quantum dots as artificial antennas: Role of quasi-coherent regime and in-gap states of excitons for enhanced light harvesting and energy transfer

Densely packed thin films of semiconductor quantum dots (QDs) shows specific the optoelectronic properties originate from the QDs coupling that may pave the way for new controllable building blocks for quantum technologies and light-harvesting complexes in natural photosynthetic systems and photovoltaic cells. In this work we were compared the optical properties and an excitonic energy transfer (EET) process in an aqueous solutions and dense packed films of ZnSe QDs with a narrow size distribution. An unexpectedly large nonlinear increase in the photoluminescence (PL) intensity was detected in QDs films with the decrease of an excitation energy that can be explained by resonantly transferred of EET through the quantum states. We found that with decreasing of the excitation energy form of quasi-coherent regime of excitons and the quantum and surface PL emission increases by a factor ∼10 and ∼6, respectively, due to increasing the EET rate.

Pursuing excitonic energy transfer with programmable DNA-based optical breadboards.

DNA nanotechnology has now enabled the self-assembly of almost any prescribed 3-dimensional nanoscale structure in large numbers and with high fidelity. These structures are also amenable to site-specific modification with a variety of small molecules ranging from drugs to reporter dyes. Beyond obvious application in biotechnology, such DNA structures are being pursued as programmable nanoscale optical breadboards where multiple different/identical fluorophores can be positioned with sub-nanometer resolution in a manner designed to allow them to engage in multistep excitonic energy-transfer (ET) via Förster resonance energy transfer (FRET) or other related processes. Not only is the ability to create such complex optical structures unique, more importantly, the ability to rapidly redesign and prototype almost all structural and optical analogues in a massively parallel format allows for deep insight into the underlying photophysical processes. Dynamic DNA structures further provide the unparalleled capability to reconfigure a DNA scaffold on the fly in situ and thus switch between ET pathways within a given assembly, actively change its properties, and even repeatedly toggle between two states such as on/off. Here, we review progress in developing these composite materials for potential applications that include artificial light harvesting, smart sensors, nanoactuators, optical barcoding, bioprobes, cryptography, computing, charge conversion, and theranostics to even new forms of optical data storage. Along with an introduction into the DNA scaffolding itself, the diverse fluorophores utilized in these structures, their incorporation chemistry, and the photophysical processes they are designed to exploit, we highlight the evolution of DNA architectures implemented in the pursuit of increased transfer efficiency and the key lessons about ET learned from each iteration. We also focus on recent and growing efforts to exploit DNA as a scaffold for assembling molecular dye aggregates that host delocalized excitons as a test bed for creating excitonic circuits and accessing other quantum-like optical phenomena. We conclude with an outlook on what is still required to transition these materials from a research pursuit to application specific prototypes and beyond.

Optical response and multi-exciton effects in 2D PTCDA aggregates with local excitation.

3,4,9,10-Perylenetetracarboxylic-dianhydride (PTCDA) aggregates have unique optical properties and are model materials for studying exciton energy transfer (EET) in planar stacked molecular aggregates. In the framework of density matrix theory, a hierarchy of molecular transition operator expectation values could be constructed to derive the equations of motion of multi-exciton states. Realistic parameters for PTCDA molecules are used to study EET and the optical response of two-dimensional aggregates upon local excitation. Our simulations show that information about the dark state can be obtained with local field excitation and the inter-chain coupling results in a red-shift of the lowest excitonic energy level. Configuration effects, inter-chain detuning and multi-exciton states are discussed. The calculated lowest excitonic energy level of a 2D PTCDA aggregate is qualitatively consistent with the lowest experimental absorption peak of a PTCDA film. The obtained results are valuable for the study of aggregates in optical nanocavities and for the design of photoelectric devices.

A Comprehensive Approach to Exciton Delocalization and Energy Transfer.

Electrostatic intermolecular interactions lie at the heart of both the Förster model for resonance energy transfer (RET) and the exciton model for energy delocalization. In the Förster theory of RET, the excitation energy incoherently flows from the energy donor to a weakly coupled energy acceptor. The exciton model describes instead the energy delocalization in aggregates of identical (or nearly so) molecules. Here, we introduce a model that brings together molecular aggregates and RET. We will consider a couple of molecules, each described in terms of two diabatic electronic states, coupled to an effective molecular vibration. Electrostatic intermolecular interactions drive energy fluxes between the molecules, that, depending on model parameters, can be described as RET or energy delocalization. At variance with the standard Förster model for RET and of the exciton model for aggregates, our approach applies both in the weak and in the strong coupling regimes and fully accounts for the quantum nature of molecular vibrations in a nonadiabatic approach. Coupling the system to a thermal bath, we follow RET and energy delocalization in real time and simulate time-resolved emission spectra.

Detection of rabies virus via exciton energy transfer between CdTe quantum dots and Au nanoparticles.

Rabies is a fatal encephalitis caused by the rabies virus. The diagnosis of the disease depends in large part on the exposure history of the victim and clinical manifestations of the disease. Rapid rabies diagnosis is an important step in its prevention and control. Therefore, for accurate and timely diagnosis and prevention of rabies, we developed nanomaterials for a novel photoelectrochemical biosensing approach (PBA) for the rapid and reliable diagnosis of rabies virus. This approach uses high-efficiency exciton energy transfer between cadmium telluride quantum dots and Au nanoparticles and is low cost, and easy to miniaturize. By constructing PBA, rabies virus can be detected quickly and with a high degree of sensitivity and specificity; the minimum detection concentration limit for rabies virus is approximately 2.16 ffu/mL of rabies virus particles, or 2.53 × 101 fg/mL of rabies virus RNA. PBA could also detect rabies virus in the brain and lung tissue from rabid dogs and mice with better sensitivity than RT-PCR.

Blue Light Hazard Optimization for White Light‐Emitting Diode of Mn2+‐Activated 0D Cs3Cu2Br5 Perovskite Materials

AbstractThe zero‐dimensional perovskite‐like derivative Cs3Cu2X5 (X = Cl, Br, I) with self‐trapped excitons (STEs) photoluminescence (PL) has attracted tremendous interest in the field of optoelectronics. Nonetheless, it is challenging for Cs3Cu2Br5 material to attain full visible spectrum emission and prevent light‐induced photochemical damage to the retina (blue light hazard) in applications. Herein, Mn2+ is chosen as the dopant to alloy into Cs3Cu2X5 via a one‐step solid state synthesis method. Significantly, the series of Mn2+‐doped show the emission peak of 460 nm STEs and the emission peak of 550 nm Mn2+. More importantly, the high energy absorption of Mn2+ facilitates the transfer of exciton energy, contributing to a reduction in blue emission peak at 460 nm. Simultaneously, ≈17.5% of Mn2+ is alloyed into the Cs3Cu2X5lattice to induce the energy transfer channels from the Cs3Cu2X5 host to the Mn2+ guest to lead to the emission of Mn2+, which broadens emission spectrum (400–620 nm) and realizes 80% reduction of the blue emission peak at 460 nm. Additionally, a white light‐emitting diodes can decrease the blue emission band via 71.45% and an ultrahigh color rendering index (CRI) of 94.5 is produced using the 17.5% Mn2+: Cs3Cu2X5 perovskite‐like derivative powder material.

Non-radical degradation of organic pharmaceuticals by g-C3N4 under visible light irradiation: The overlooked role of excitonic energy transfer

In this work, an excitonic energy transfer (EET) based non-radical mechanism was proposed for the degradation of organic pharmaceuticals by graphitic carbon nitride (g-C3N4) under visible light irradiation. Using diclofenac (DCF) as a model molecule, the competition between single electron transfer (SET) and EET was studied through modulating the exciton binding energy of g-C3N4. The different mechanisms of SET and EET for DCF degradation were predicted by DFT calculation, and further confirmed by their different degradation pathways. When EET played an important role, the rationality of some very popular radical scavengers, such as p-BQ, TEMPOL and furfuryl alcohol must be reconsidered. In addition, humic acid (HA) had a distinct effect on EET and SET. Specifically, HA enhanced the EET process through photosensitization, but suppressed SET through radical quenching effect. The effect of HA on DCF degradation depended on the contribution ratio of SET and ET.

Strain-Modulated Interlayer Charge and Energy Transfers in MoS2/WS2 Heterobilayer.

Excitonic properties in 2D heterobilayers are closely governed by charge transfer (CT) and excitonic energy transfer (ET) at van der Waals interfaces. Various means have been employed to modulate the interlayer CT and ET, including electrical gating and modifying interlayer spacing, but with limited extent in their controllability. Here, we report a novel method to modulate these transfers in the MoS2/WS2 heterobilayer by applying compressive strain under hydrostatic pressure. Raman and photoluminescence measurements, combined with density functional theory calculations, show pressure-enhanced interlayer interaction of the heterobilayer. Heterobilayer-to-monolayer photoluminescence intensity ratio (η) of WS2 decreases by five times up to ≈4 GPa, suggesting enhanced ET, whereas it increases by an order of magnitude at higher pressures and reaches almost unity. Theoretical calculations show that orbital switching and charge transfers in the heterobilayer's hybridized conduction band are responsible for the non-monotonic modulation of the transfers. Our findings provide a compelling approach toward effective mechanical control of CT and ET in 2D excitonic devices.