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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Auger Recombination Lifetime Scaling for Type I and Quasi-Type II Core/Shell Quantum Dots

Having already achieved near-unity quantum yields, with promising properties for light-emitting diode, lasing, and charge separation applications, colloidal core/shell quantum dots have great technological potential. The shell thickness and band alignment of the shell and core materials are known to influence the efficiency of these devices. In many such applications, improving the efficiency requires a deep understanding of multiexcitonic states. In this paper, we elucidate the shell thickness and band alignment dependencies of the biexciton Auger recombination lifetime for quasi-type II CdSe/CdS and type I CdSe/ZnS core/shell quantum dots. We find that the biexciton Auger recombination lifetime increases with the total nanocrystal volume for quasi-type II CdSe/CdS core/shell quantum dots and is independent of the shell thickness for type I CdSe/ZnS core/shell quantum dots. To perform these calculations and compute Auger recombination lifetimes, we developed a low-scaling approach based on the stochastic resolution of identity. The numerical approach provided a framework for studying the scaling of the biexciton Auger recombination lifetimes in terms of the shell thickness dependencies of the exciton radii, Coulomb couplings, and density of final states in quasi-type II CdSe/CdS and type I CdSe/ZnS core/shell quantum dots.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Excitonic Spin-Coherence Lifetimes in CdSe Nanoplatelets Increase Significantly with Core/Shell Morphology

Here, we report spin-polarized transient absorption for colloidal CdSe nanoplatelets as functions of thickness (2–6 monolayer thickness) and core/shell motif. Using electro-optical modulation of co- and cross-polarization pump–probe combinations, we sensitively observe spin-polarized transitions. Core-only nanoplatelets exhibit few-picosecond spin lifetimes that weakly increase with layer thickness. The spectral content of differenced spin-polarized signals indicate biexciton binding energies that decrease with increasing thickness and smaller values than previously reported. Shell growth of CdS with controlled thicknesses, which partially delocalize the electron from the hole, significantly increases the spin lifetime to ~49 ps at room temperature. Implementation of ZnS shells, which do not alter delocalization but do alter surface termination, increased spin lifetimes up to ~100 ps, bolstering the interpretation that surface termination heavily influences spin coherence, likely due to passivation of dangling bonds. Spin precession in magnetic fields both confirms long coherence lifetime at room temperature and yields the excitonic g factor.

2D semiconductor↗
DOE OSTI2015

Radiative lifetimes of zincblende CdSe/CdS quantum dots

Recent synthetic advances have made available very monodisperse zincblende CdSe/CdS quantum dots having near-unity photoluminescence quantum yields. Because of the absence of nonradiative decay pathways, accurate values of the radiative lifetimes can be obtained from time-resolved PL measurements. Radiative lifetimes can also be obtained from the Einstein relations, using the static absorption spectra and the relative thermal populations in the angular momentum sublevels. We found that one of the inputs into these calculations is the shell thickness, and it is useful to be able to determine shell thickness from spectroscopic measurements. We use an empirically corrected effective mass model to produce a “map” of exciton wavelength as a function of core size and shell thickness. These calculations use an elastic continuum model and the known lattice and elastic constants to include the effect of lattice strain on the band gap energy. The map is in agreement with the known CdSe sizing curve and with the shell thicknesses of zincblende core/shell particles obtained from TEM images. Furthermore, if selenium–sulfur diffusion is included and lattice strain is omitted from the calculation then the resulting map is appropriate for wurtzite CdSe/CdS quantum dots synthesized at high temperatures, and this map is very similar to one previously reported (J. Am. Chem. Soc. 2009, 131, 14299). Radiative lifetimes determined from time-resolved measurements are compared to values obtained from the Einstein relations, and found to be in excellent agreement. For a specific core size (2.64 nm diameter, in the present case), radiative lifetimes are found to decrease with increasing shell thickness. Thus, this is similar to the size dependence of one-component CdSe quantum dots and in contrast to the size dependence in type-II quantum dots.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Substantial lifetime enhancement for Si-based photoanodes enabled by amorphous TiO2 coating with improved stoichiometry

Abstract Amorphous titanium dioxide (TiO 2 ) film coating by atomic layer deposition (ALD) is a promising strategy to extend the photoelectrode lifetime to meet the industrial standard for solar fuel generation. To realize this promise, the essential structure-property relationship that dictates the protection lifetime needs to be uncovered. In this work, we reveal that in addition to the imbedded crystalline phase, the presence of residual chlorine (Cl) ligands is detrimental to the silicon (Si) photoanode lifetime. We further demonstrate that post-ALD in-situ water treatment can effectively decouple the ALD reaction completeness from crystallization. The as-processed TiO 2 film has a much lower residual Cl concentration and thus an improved film stoichiometry, while its uniform amorphous phase is well preserved. As a result, the protected Si photoanode exhibits a substantially improved lifetime to ~600 h at a photocurrent density of more than 30 mA/cm 2 . This study demonstrates a significant advancement toward sustainable hydrogen generation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Coupling a recurrent neural network to SPAD TCSPC systems for real-time fluorescence lifetime imaging

Fluorescence lifetime imaging (FLI) has been receiving increased attention in recent years as a powerful diagnostic technique in biological and medical research. However, existing FLI systems often suffer from a tradeoff between processing speed, accuracy, and robustness. Inspired by the concept of Edge Artificial Intelligence (Edge AI), we propose a robust approach that enables fast FLI with no degradation of accuracy. This approach couples a recurrent neural network (RNN), which is trained to estimate the fluorescence lifetime directly from raw timestamps without building histograms, to SPAD TCSPC systems, thereby drastically reducing transfer data volumes and hardware resource utilization, and enabling real-time FLI acquisition. We train two variants of the RNN on a synthetic dataset and compare the results to those obtained using center-of-mass method (CMM) and least squares fitting (LS fitting). Results demonstrate that two RNN variants, gated recurrent unit (GRU) and long short-term memory (LSTM), are comparable to CMM and LS fitting in terms of accuracy, while outperforming them in the presence of background noise by a large margin. To explore the ultimate limits of the approach, we derive the Cramer-Rao lower bound of the measurement, showing that RNN yields lifetime estimations with near-optimal precision. To demonstrate real-time operation, we build a FLI microscope based on an existing SPAD TCSPC system comprising a 32 x 32 SPAD sensor named Piccolo. Four quantized GRU cores, capable of processing up to 4 million photons per second, are deployed on the Xilinx Kintex-7 FPGA that controls the Piccolo. Powered by the GRU, the FLI setup can retrieve real-time fluorescence lifetime images at up to 10 frames per second. The proposed FLI system is promising and ideally suited for biomedical applications, including biological imaging, biomedical diagnostics, and fluorescence-assisted surgery, etc.

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

Phosphorescence lifetimes of organic light-emitting diodes from two-component time-dependent density functional theory

“Spin-forbidden” transitions are calculated for an eight-membered set of iridium-containing candidate molecules for organic light-emitting diodes (OLEDs) using two-component time-dependent density functional theory. Phosphorescence lifetimes (obtained from averaging over relevant excitations) are compared to experimental data. Assessment of parameters like non-distorted and distorted geometric structures, density functionals, relativistic Hamiltonians, and basis sets was done by a thorough study for Ir(ppy){sub 3} focussing not only on averaged phosphorescence lifetimes, but also on the agreement of the triplet substate structure with experimental data. The most favorable methods were applied to an eight-membered test set of OLED candidate molecules; Boltzmann-averaged phosphorescence lifetimes were investigated concerning the convergence with the number of excited states and the changes when including solvent effects. Finally, a simple model for sorting out molecules with long averaged phosphorescence lifetimes is developed by visual inspection of computationally easily achievable one-component frontier orbitals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Lineshape theory of pigment-protein complexes: How the finite relaxation time of nuclei influences the exciton relaxation-induced lifetime broadening

In pigment-protein complexes, often the excited states are partially delocalized and the exciton-vibrational coupling in the basis of delocalized states contains large diagonal and small off-diagonal elements. This inequality may be used to introduce potential energy surfaces (PESs) of exciton states and to treat the inter-PES coupling in Markov and secular approximations. The resulting lineshape function consists of a Lorentzian peak that is broadened by the finite lifetime of the exciton states caused by the inter-PES coupling and a vibrational sideband that results from the mutual displacement of the excitonic PESs with respect to that of the ground state. So far analytical expressions have been derived that relate the exciton relaxation-induced lifetime broadening to the Redfield [T. Renger and R. A. Marcus, J. Chem. Phys. 116, 9997 (2002)] or modified Redfield [M. Schröder, U. Kleinekathöfer, and M. Schreiber, J. Chem. Phys. 124, 084903 (2006)] rate constants of exciton relaxation, assuming that intra-PES nuclear relaxation is fast compared to inter-PES transfer. Here, we go beyond this approximation and provide an analytical expression, termed Non-equilibrium Modified Redfield (NeMoR) theory, for the lifetime broadening that takes into account the finite nuclear relaxation time. In an application of the theory to molecular dimers, we find that, for a widely used experimental spectral density of the exciton-vibrational coupling of pigment-protein complexes, the NeMoR spectrum at low-temperatures (T < 150 K) is better approximated by Redfield than by modified Redfield theory. At room temperature, the lifetime broadening obtained with Redfield theory underestimates the NeMoR broadening, whereas modified Redfield theory overestimates it by a similar amount. A fortuitous error compensation in Redfield theory is found to explain the good performance of this theory at low temperatures. Since steady state spectra of PPCs are often measured at low temperatures, Redfield theory still provides a numerically efficient alternative to NeMoR theory. At higher temperatures, we suggest to use NeMoR theory, because it has the same numerical costs as modified Redfield theory, but is more accurate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Lifetime and universal distribution of seed runaway electrons

The lifetime of pre-existing runaway electrons determines how likely the runaways will undergo avalanche multiplication. We estimate the lifetime of runaway electrons via kinetic analysis. We show that the rate of runaway decay depends on the combination of parameters α≡(Z+1)/$\sqrt{{\bar{τ}}_{rad}}$ (where $τ_{rad}$ is the synchrotron timescale normalized to the collisional timescale and Z is the ion charge) compared to the electric field. We identify two cases where the decay rate is slow enough to enable a quasi-steady shape of the runaway distribution function. This distribution and its lifetime represent the eigenfunction and the lowest eigenvalue of the kinetic equation. In one case, α$\ll$1: the field required to sustain the pre-existing runaways is barely larger than the Connor-Hastie critical value. In the same manner as by Aleynikov and Breizman [Phys. Rev. Lett. 114, 155001 (2015)], we solve the kinetic equation perturbatively but extend the work to demonstrate that the lifetime grows exponentially with the field at a rate that depends on α. Finally, in the second case, α$\gg$1: the sustainment field is much greater than the Connor-Hastie value, and the largeness of the field in this case enables us to universalize the kinetic equation via the re-scaling procedure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 degrees C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 degrees C, we measure VOC that is ~50 mV higher for the GaAs solar cell and ~60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-type GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 degrees C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 degrees C to 400 degrees C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4x reduction in the effective lifetime and ~40x increase in the surface recombination velocity as the temperature is increased from 25 degrees C to 400 degrees C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 degrees C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.

14 SOLAR ENERGY↗
DOE OSTI2019

Measurement of wave-particle interaction and metastable lifetime using laser-induced fluorescence

Extensive information, such as ion temperature and wave-particle interactions, can be obtained by the direct measurement of ion distribution functions using laser-induced fluorescence (LIF). This nonintrusive plasma diagnostics provides an important window into the ion motions in phase-space. Previous simulation results suggest that LIF measurements, which are performed on metastable ions produced directly from neutral gas particles and also from ions in other electronic states, place restrictions on the metastable lifetime. In the case where metastable population is produced from direct ionization of neutral atoms, the velocity distribution measured using LIF will only faithfully represent processes which act on the ion dynamics in a time shorter than the metastable lifetime. In this paper, the metastable lifetime effects are explored experimentally for the first time using wave-particle interaction in an Argon multidipole plasma. Here, we demonstrate that this systematic effect can be corrected using the theory addressed in this paper based on the metastable lifetime and relative fraction of metastables produced from pre-existing ions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Probing autoionization decay lifetimes of the 4d−16ℓ core-excited states in xenon using attosecond noncollinear four-wave-mixing spectroscopy

The decay of core-excited states is a sensitive probe of autoionization dynamics and correlation effects in many-electron systems, occurring on ultrafast timescales. Xenon, with its dense manifold of autoionizing resonances that can be coupled with near-infrared light, provides a platform to investigate these processes. In this work, the autoionization decay lifetimes of 4d-16ℓ (ℓ = s, p, d, …) core-excited states in xenon atoms are probed with extreme ultraviolet (XUV) attosecond noncollinear four-wave-mixing (FWM) spectroscopy. The 4d{5/2,3/2}-16p XUV-bright states (optically dipole-allowed) exhibit decay lifetimes of ∼6 fs, which is consistent with spectator-type decay. In contrast, the 4d{5/2,3/2}-16s and 4d{5/2,3/2}-16d XUV-dark states (optically dipole forbidden) show longer decay lifetimes of ∼20 fs. Photoionization calculations confirm that all core-hole states with 4d character should decay via spectator channels in ≤6 fs, suggesting that the apparently longer dark-state decay times arise from an alternative mechanism. A few-level simulation of the FWM process shows that the inclusion of a nearby, longer-lived dark state can mimic the experimental FWM signal, suggesting population cycling with a second electronic state with non-4d character. Ab initio calculations support the presence of such multielectron excited states in the 60-70 eV range. These results demonstrate that FWM signals can encode coupled-state dynamics when probing complex systems, highlighting the importance of combining theoretical and experimental approaches to disentangle accurate core-level decay pathways and lifetimes.

Puskar, Nicolette G↗
DOE OSTI2024

The lifetime risk and impact of vitiligo across sociodemographic groups: a UK population-based cohort study

Abstract Background Vitiligo is an autoimmune skin disorder characterized by depigmented patches of skin, which can have significant psychological impacts. Objectives To estimate the lifetime incidence of vitiligo, overall, by ethnicity and across other sociodemographic subgroups, and to investigate the impacts of vitiligo on mental health, work and healthcare utilization. Methods Incident cases of vitiligo were identified in the Optimum Patient Care Database of primary care records in the UK between 1 January 2004 and 31 December 2020. The lifetime incidence of vitiligo was estimated at age 80 years using modified time-to-event models with age as the timescale, overall and stratified by ethnicity, sex and deprivation. Depression, anxiety, sleep disturbance, healthcare utilization and work-related outcomes were assessed in the 2 years after vitiligo diagnosis and compared with matched controls without vitiligo. The study protocol for this retrospective observational study was registered with ClinicalTrials.gov (NCT06097494). Results In total, 9460 adults and children were newly diagnosed with vitiligo during the study period. The overall cumulative lifetime incidence was 0.92% at 80 years of age [95% confidence interval (CI) 0.90–0.94]. Cumulative incidence was similar in female (0.94%, 95% CI 0.92–0.97) and male patients (0.89%, 95% CI 0.86–0.92). There were substantial differences in lifetime incidence across ethnic groups, listed by Office for National Statistics criteria [Asian 3.58% (95% CI 3.38–3.78); Black 2.18% (95% CI 1.85–2.50); Mixed/multiple 2.03% (95% CI 1.58–2.47); Other 1.05% (95% CI 0.94–1.17); and White 0.73% (95% CI 0.71–0.76)]. Compared with matched controls, people with vitiligo had an increased risk of depression [adjusted odds ratio (aOR) 1.08, 95% CI 1.01–1.15]; anxiety (aOR 1.19, 95% CI 1.09–1.30); depression or anxiety (aOR 1.10, 95% CI 1.03–1.17); and sleep disturbance [adjusted hazard ratio (aHR) 1.15, 95% CI 1.02–1.31]. People with vitiligo also had a greater number of primary care encounters (adjusted incidence rate ratio 1.29, 95% CI 1.26–1.32) and a greater risk of time off work (aHR 1.15, 95% CI 1.06–1.24). There was little evidence of disparities in vitiligo-related impacts across ethnic subgroups. Conclusions Clinicians should be aware of the markedly increased incidence of vitiligo in people belonging to Asian, Black, Mixed/multiple and Other groups. The negative impact of vitiligo on mental health, work and healthcare utilization highlights the importance of monitoring people with vitiligo to identify those who need additional support.

Eleftheriadou, Viktoria↗
DOE OSTI2023

Measuring autoionization decay lifetimes of optically forbidden inner valence excited states in neon atoms with attosecond noncollinear four-wave-mixing spectroscopy

Attosecond noncollinear four-wave-mixing spectroscopy with one attosecond extreme ultraviolet (XUV) pulse and two few-cycle near-infrared (NIR) pulses was used to measure the autoionization decay lifetimes of inner valence electronic excitations in neon atoms. After a 43-48-eV XUV photon excites a 2s electron into the 2s2p 6 (np) Rydberg series, broadband NIR pulses couple the 2s2p 6 3p XUV-bright state to neighboring 2s2p 6 3s and 2s2p 6 3d XUV-dark states. Controllable delays of one or both NIR pulses with respect to the attosecond XUV pulse reveal the temporal evolution of either the dark or bright states, respectively. Experimental lifetimes for the 3s, 3p, and 3d states are measured to be 7±2, 48±8, and 427±40 fs, respectively, with 95% confidence. Accompanying calculations with two independent ab initio theoretical methods, newstock and astra, verify the findings. The results support the expected trend that the autoionization lifetime should be longer for states that have a smaller penetration in the radial region of the 2s core hole, which in this case is for the higher angular momentum Rydberg orbitals. In conclusion, the underlying theory thus links the lifetime results to electron correlation and provides an assessment of the direct and exchange terms in the autoionization process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Radiative lifetime of the A Π 1 / 2 2 state in RaF with relevance to laser cooling

The radiative lifetime of the A Π 1 / 2 2 ( v = 0 ) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Γ = 2.86 ( 8 ) × 10 7 s − 1 are of relevance to the laser cooling of RaF via the optically closed A Π 1 / 2 2 ← X Σ 1 / 2 2 transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Owing to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just three cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8 P 3 / 2 state in Fr to be 83(3) ns, in agreement with literature. Published by the American Physical Society 2024

Optics↗
DOE OSTI2015

New lifetime measurements in Pd 109 and the onset of deformation at N = 60

We measured several new subnanosecond lifetimes in 109 Pd using the fast-timing βγ γ (t ) method. Fission fragments of the A = 109 mass chain were produced by bombarding natural uranium with 30 MeV protons at the Jyväskylä Ion Guide Isotope Separator On-Line (IGISOL) facility. We obtained lifetimes for excited states in 109 Pd populated following β decay of 109 Rh. The new lifetimes provide some insight into the evolution of nuclear structure in this mass region. In particular, the distinct structure of the two low-lying 7/2+ states occurring systematically across the Pd isotopic chain is supported by the new lifetime measurements. Finally, the available nuclear data indicate a sudden increase in deformation at N = 60 which is related to the strong p-n interaction between πg 9/2 and νg 7/2 valence nucleons expected in this region.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Measurement of the Λ hyperon lifetime

A new, more precise measurement of the Λ hyperon lifetime is performed using a large data sample of Pb-Pb collisions at $\sqrt{s_{NN}}$=5.02 TeV with ALICE. The Λ and $\bar{Λ}$ hyperons are reconstructed at midrapidity using their two-body weak decay channel Λ→p+π - and $\bar{Λ}$→$\bar{p}$+π + . The measured value of the Λ lifetime is τ Λ =[261.07±0.37(stat.)±0.72(syst.)] ps. The relative difference between the lifetime of Λ and $\bar{Λ}$, which represents an important test of CPT invariance in the strangeness sector, is also measured. The obtained value (τ Λ -τ $\bar{Λ}$ )/τ Λ =0.0013±0.0028(stat.)±0.0021(syst.) is consistent with zero within the uncertainties. Both measurements of the Λ hyperon lifetime and of the relative difference between τ Λ and τ $\bar{Λ}$ are in agreement with the corresponding world averages of the Particle Data Group and about a factor of three more precise.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Precision measurement of the Ξ b − baryon lifetime

A sample of p p collision data, corresponding to an integrated luminosity of 5.5 fb − 1 and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the Ξ b − baryon to that of the Λ b 0 baryon, r τ ≡ τ Ξ b − / τ Λ b 0 . The value r τ = 1.076 ± 0.013 ± 0.006 is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain r τ Run 1 , 2 = 1.078 ± 0.012 ± 0.007 . Multiplying by the world-average value of the Λ b 0 lifetime yields τ Ξ b − Run 1 , 2 = 1.578 ± 0.018 ± 0.010 ± 0.011 ps , where the uncertainties are statistical, systematic, and due to the limited knowledge of the Λ b 0 lifetime. This measurement improves the precision of the current world average of the Ξ b − lifetime by about a factor of 2, and is in good agreement with the most recent theoretical predictions. © 2024 CERN, for the LHCb Collaboration 2024 CERN

Aaij, R. (ORCID:0000000305331952)↗
DOE OSTI2021

Twist Angle-Dependent Interlayer Exciton Lifetimes in van der Waals Heterostructures

In van der Waals (vdW) heterostructures formed by stacking two monolayers of transition metal dichalcogenides, multiple exciton resonances with highly tunable properties are formed and subject to both vertical and lateral confinement. We investigate how a unique control knob, the twist angle between the two monolayers, can be used to control the exciton dynamics. We observe that the interlayer exciton lifetimes in MoSe 2 /WSe 2 twisted bilayers (TBLs) change by one order of magnitude when the twist angle is varied from 1° to 3.5°. Additionally, using a low-energy continuum model, we theoretically separate two leading mechanisms that influence interlayer exciton radiative lifetimes. The shift to indirect transitions in the momentum space with an increasing twist angle and the energy modulation from the moiré potential both have a significant impact on interlayer exciton lifetimes. We further predict distinct temperature dependence of interlayer exciton lifetimes in TBLs with different twist angles, which is partially validated by experiments. While many recent studies have highlighted how the twist angle in a vdW TBL can be used to engineer the ground states and quantum phases due to many-body interaction, our studies explore its role in controlling the dynamics of optically excited states, thus, expanding the conceptual applications of “twistronics”.

36 MATERIALS SCIENCE↗