Real-Time Observation of Exciton-Phonon Coupling Dynamics in Self-Assembled Hybrid Perovskite Quantum Wells

Self-assembled hybrid perovskite quantum wells have attracted attention due to their tunable emission properties, ease of fabrication and device integration. However, the dynamics of excitons in these materials, especially how they couple to phonons remains an open question. Here, we investigate two widely used materials, namely butylammonium lead iodide (CH3(CH2)3NH3)2PbI4 and hexylammonium lead iodide (CH3(CH2)5NH3)2PbI4, both of which exhibit broad photoluminescence tails at room temperature. We performed femtosecond vibrational spectroscopy to obtain a real-time picture of the exciton phonon interaction and directly identified the vibrational modes that couple to excitons. We show that the choice of the organic cation controls which vibrational modes the exciton couples to. In butylammonium lead iodide, excitons dominantly couple to a 100 cm-1 phonon mode, whereas in hexylammonium lead iodide, excitons interact with phonons with frequencies of 88 cm-1 and 137 cm-1. Using the determined optical phonon energies, we analyzed PL broadening mechanisms. At low temperatures (<100 K), the broadening is due to acoustic phonon scattering, whereas at high temperatures, LO phonon-exciton coupling is the dominant mechanism. Our results help explain the broad photoluminescence lineshapes observed in hybrid perovskite quantum wells and provide insights into the mechanism of exciton-phonon coupling in these materials

Research data supporting "Real-Time Observation of Exciton-Phonon Coupling Dynamics in Self-Assembled Hybrid Perovskite Quantum Wells"

Zip folder containing data related to the figures of the manuscript, which include absorption, photoluminescence, photothermal deflection spectroscopy , transient absorption and fast Fourier transformed data. See the readme file and main manuscript for more details

Real-Time Observation of Exciton-Phonon Coupling Dynamics in Self-Assembled Hybrid Perovskite Quantum Wells

Self-assembled hybrid perovskite quantum wells have attracted attention due to their tunable emission properties, ease of fabrication and device integration. However, the dynamics of excitons in these materials, especially how they couple to phonons remains an open question. Here, we investigate two widely used materials, namely butylammonium lead iodide (CH3(CH2)3NH3)2PbI4 and hexylammonium lead iodide (CH3(CH2)5NH3)2PbI4, both of which exhibit broad photoluminescence tails at room temperature. We performed femtosecond vibrational spectroscopy to obtain a real-time picture of the exciton phonon interaction and directly identified the vibrational modes that couple to excitons. We show that the choice of the organic cation controls which vibrational modes the exciton couples to. In butylammonium lead iodide, excitons dominantly couple to a 100 cm-1 phonon mode, whereas in hexylammonium lead iodide, excitons interact with phonons with frequencies of 88 cm-1 and 137 cm-1. Using the determined optical phonon energies, we analyzed PL broadening mechanisms. At low temperatures (<100 K), the broadening is due to acoustic phonon scattering, whereas at high temperatures, LO phonon-exciton coupling is the dominant mechanism. Our results help explain the broad photoluminescence lineshapes observed in hybrid perovskite quantum wells and provide insights into the mechanism of exciton-phonon coupling in these materials

Optical Projection and Spatial Separation of Spin-Entangled Triplet Pairs from the S<inf>1</inf> (2¹ A<inf>g</inf>^–) State of Pi-Conjugated Systems

The S1 (21Ag-) state is an optically dark state of natural and synthetic pi-conjugated materials that can play a critical role in optoelectronic processes such as, energy harvesting, photoprotection and singlet fission. Despite this widespread importance, direct experimental characterisations of the electronic structure of the S1 (21Ag-) wavefunction have remained scarce and uncertain, although advanced theory predicts it to have a rich multi-excitonic character. Here, studying an archetypal polymer, polydiacetylene, and carotenoids, we experimentally demonstrate that S1 (21Ag-) is a superposition state with strong contributions from spin-entangled pairs of triplet excitons (1(TT)). We further show that optical manipulation of the S1 (21Ag-) wavefunction using triplet absorption transitions allows selective projection of the 1(TT) component into a manifold of spatially separated triplet-pairs with lifetimes enhanced by up to one order of magnitude and whose yield is strongly dependent on the level of inter-chromophore coupling. Our results provide a unified picture of 21Ag-states in pi-conjugated materials and open new routes to exploit their dynamics in singlet fission, photobiology and for the generation of entangled (spin-1) particles for molecular quantum technologies

Partial acute transverse myelitis is a predictor of multiple sclerosis in children

International audienceBackground: Acute transverse myelitis (ATM) in children is a rare and often severe disease for which there are few known prognostic factors, particularly the subsequent risk of multiple sclerosis (MS) diagnosis.Objectives: To determine the clinical course and prognostic factors after a first episode of ATM in children.Methods: Thirty children below 16 years of age diagnosed with a first neurological episode of ATM were included retrospectively. Clinical evaluation, treatment, laboratory, and MRI data were collected.Results: Median age at onset was 11 years (range 3-15 years). Follow-up data were available for a median of 4 years (range 0.5-16.7 years). Five patients subsequently had a diagnosis of MS (17%), which was associated with acute partial transverse myelitis (odds ratio 5; 95% confidence interval 2.3-11), with a 60% probability of having a relapse at five years (p < 0.01). The 2011 Verhey criteria correctly identified MS in children with the highest specificity (96%) and sensitivity (80%).Conclusion: Acute partial transverse myelitis and brain MRI abnormalities at initial presentation are significantly predictive of a subsequent diagnosis of MS in children with ATM. These findings suggest that closer brain MRI monitoring after acute partial transverse myelitis might make the earlier introduction of disease-modifying therapies possible

Research data supporting "Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission"

This data corresponds to the data presented in the Journal Article, " Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission" conducted in the Cavendish between years 2013-2016 by Stern and co-workers.The authors thank the Winton Programme for the Physics of Sustainability and the Engineering and Physical Sciences Research Council for funding. R.H.F. thanks the Miller Institute for Basic Research and the Heising–Simons Foundation at the University of California Berkeley for support. The authors thank T. Arnold (Diamond Light Source), J. Novak, D. Harkin and J. Rozboril for support during the beamtime at beamline I07 and the Diamond Light Source for financial support. The computational work was supported by the Scientific Discovery through Advanced Computing program funded by the US Department of Energy, Office of Science, Advanced Scientific Computing Research, Basic Energy Sciences