A5075377046- Quantum Dots Synthesis And Properties
- Perovskite Materials and Applications
- Chalcogenide Semiconductor Thin Films
- Luminescence and Fluorescent Materials
- Luminescence Properties of Advanced Materials
- Advanced Chemical Physics Studies
- Astrophysics and Star Formation Studies
- Nanocluster Synthesis and Applications
- Solid-state spectroscopy and crystallography
- Organic Electronics and Photovoltaics
- Advanced Photocatalysis Techniques
- Organic Light-Emitting Diodes Research
- Conducting polymers and applications
- Polyoxometalates: Synthesis and Applications
- Optical properties and cooling technologies in crystalline materials
- Atomic and Molecular Physics
- Photochromic and Fluorescence Chemistry
- Semiconductor materials and interfaces
- Advanced Nanomaterials in Catalysis
- Conferences and Exhibitions Management
- Molecular Spectroscopy and Structure
- Mesoporous Materials and Catalysis
- Chemical Synthesis and Reactions
- Inorganic Chemistry and Materials
- Porphyrin and Phthalocyanine Chemistry
University of Colorado Boulder
2020-2025
University of Colorado System
2021-2025
Brandeis University
2023-2024
Massachusetts Institute of Technology
2017-2022
Wellesley College
2014-2019
Perovskite quantum emitters The development of many optical technologies is dependent on the availability solid-state single with near-perfect coherence. Light-emitting defects in diamond and dots grown by molecular beam epitaxy have demonstrated transform-limited emission linewidths. However, they are limited terms production scalability reproducibility between individual emitters. Utzat et al. now show that perovskite can overcome these limitations provide unprecedented versatility for...
Lead halide-based perovskite thin films have attracted great attention due to the rapid increase in solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials cells are also beneficial other light-harvesting applications and them prime candidates as triplet sensitizers upconversion via triplet–triplet annihilation rubrene. In this contribution, we take advantage of long carrier lifetimes diffusion lengths films, their high absorption...
A key debate involving mixed-cation lead mixed-halide perovskite thin-films relates to the effects of process conditions on film morphology and local performance solar cells. In this contribution, we investigate influence precursor concentration thickness, grain size, orientation these polycrystalline thin-films. We vary molar containing Rb, Cs, MA, FA, Pb, I, Br from 0.4 1.2 M. use optical electrical probes measure properties correlate effect crystallographic inter- intragrain...
Cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals (PNCs) have recently become a promising material for optoelectronic applications due to their high emission quantum yields and facile band gap tunability via both composition size. The spectroscopy of single PNCs enhances our understanding the effect confinement on excitations in absence obfuscating ensemble averaging can also inform synthetic efforts. However, PNC studies been hampered by poor photostability under confocal...
We characterize exciton–exciton interactions in weakly confined CsPbBr3 nanocrystals by combining fluence-dependent transient absorption spectroscopy with a robust spectral deconvolution method. This data-driven approach allows for the extraction of overlapping spectra exciton and biexciton states while making no assumptions about line shape. The ensemble spectrum state is found to be broader blue-shifted from state, both effects becoming more prominent as nanocrystal size decreases....
In the interstellar medium, UV photolysis of condensed methanol (CH<sub>3</sub>OH), contained in ice mantles surrounding dust grains, is thought to be mechanism that drives formation “complex” molecules, such as methyl formate (HCOOCH<sub>3</sub>), dimethyl ether (CH<sub>3</sub>OCH<sub>3</sub>), acetic acid (CH<sub>3</sub>COOH), and glycolaldehyde (HOCH<sub>2</sub>CHO). The source this reaction-initiating light assumed local because externally sourced radiation cannot penetrate...
The generation of reduced semiconductor nanocrystals is interest for a variety optoelectronic applications. In comparison to other nanocrystalline materials, little work has been reported on reduction CdS nanocrystals, which are particularly interesting solar photochemistry Most nanocrystal strategies require electron donors that reduce ground state or photoexcited nanocrystals. this work, we report the discovery photocharging under continuous wave illumination with no added reductants....
Perovskite-sensitized upconversion (UC) has resulted in near-infrared-to-visible UC at solar-relevant fluxes. However, the successful implementation of devices into operating solar cells will result exposure to similar environmental stressors as for commercial photovoltaics (PVs), mainly elevated temperatures, and continuous irradiation. In this article, we investigated effects these two stressors, heat light, on triplet generation process perovskite/rubrene interface. Following both local...
The capture of photoexcited hot electrons in semiconductors before they lose their excess energy to cooling is a long-standing goal photon conversion. Semiconductor nanocrystals have large electron spacings that are expected slow down relaxation by phonon emission, but nanocrystals, nevertheless, cool rapidly transfer holes. This makes the intrinsic phonon-bottleneck-limited lifetime elusive. We used combination theory and experiments probe hot-electron dynamics negatively charged cadmium...
The mobility of atoms, molecules, and radicals in icy grain mantles regulates ice restructuring, desorption, chemistry astrophysical environments. Interstellar ices are dominated by H2O, diffusion on external internal (pore) surfaces H2O-rich is therefore a key process to constrain. This study aims quantify the kinetics barrier abundant constituent CO into H2O-dominated at low temperatures (15–23 K), measuring mixing rate initially layered H2O(:CO2)/CO ices. mixed fraction as function time...
We report the first infrared study of low-energy (<20 eV) electron-induced reactions condensed methanol. Our goal is to simulate processes which occur when high-energy cosmic rays interact with interstellar and cometary ices, where methanol, a precursor several prebiotic species, relatively abundant. The interactions radiation, such as (Emax ∼ 1020 eV), matter produce large numbers secondary electrons, are known initiate radiolysis in phase. Using temperature programmed desorption (TPD)...
Transient absorption (TA) spectroscopy of semiconductor nanocrystals (NCs) is often used for excited state population analysis, but recent results suggest that TA bleach signals associated with multiexcitons in NCs do not scale linearly exciton multiplicity. In this manuscript, we probe the factors determine intensities and spectral positions biexciton components spectra CdSe quantum dots (QDs) five diameters. We find that, all cases, peak intensity spectrum less than 1.5 times single...
Multiexcitons in emerging semiconducting nanomaterials play a critical role potential optoelectronic and quantum computational devices. We describe photon resolved single molecule methods to directly probe the dynamics of biexcitons triexcitons colloidal CdSe dots. confirm that emit from spin-correlated state, consistent with statistical scaling. Contrary current understanding, we find triexciton emission is dominated by band-edge 1Se1S3/2 recombination rather than higher energy 1Pe1P3/2...
Abstract Low carrier mobility and lifetime in semiconductor polymers are some of the main challenges facing field organic photovoltaics (OPV) quest for efficient devices with high current density. Finding novel strategies such as device structure engineering is a key pathway toward addressing this issue. In work, light absorption collection OPV improved by employment ZnO nanowire (NW) arrays an optimum NW length (50 nm) antireflection (AR) film nanocone structure. The optical...
Cesium lead halide perovskite nanocrystals are promising emissive materials for a variety of optoelectronic applications. To fully realize the potential these materials, we must understand energetics and dynamics multiexciton states which populated under device relevant excitation conditions. We utilized time-resolved spectrally-resolved photoluminescence studies to investigate biexciton binding energy as well red-shifted emission feature previously reported high-flux determine that this can...
As luminescence applications of colloidal semiconductor nanocrystals push toward higher excitation flux conditions, there is an increased need to both understand and potentially control emission from multiexciton states. We develop a spectrally resolved correlation method study the triply excited state that enables direct measurements recombination pathway for triexciton, rather than relying on indirect extraction rates. demonstrate that, core–shell CdSe–CdS nanocrystals, triexciton arises...
We elucidate mechanisms of electron-induced radiolysis in cosmic (interstellar, planetary, and cometary) ice analogs ammonia (NH3), likely the most abundant nitrogen-containing compound interstellar medium (ISM). Astrochemical processes were simulated under ultrahigh vacuum conditions by high-energy (1 keV) low-energy (7 eV) electron-irradiation nanoscale thin films deposited on cryogenically cooled metal substrates. Irradiated analyzed temperature-programmed desorption (TPD). Experiments...
Combining the remarkable catalytic properties of redox enzymes with highly tunable light absorbing semiconductor nanocrystals enables light-driven catalysis complex, multielectron reactions. This Article focuses on systems that combine CdS nanorods (NRs) MoFe protein nitrogenase to drive photochemical N2 reduction. We used transient absorption spectroscopy (TAS) examine kinetics electron transfer (ET) from NRs protein. For dimensions similar those previously for reduction, rate constant ET...
The capture of photoexcited hot electrons in semiconductors before they lose their excess energy to cooling is a long-standing goal photon conversion. Semiconductor nanocrystals have large electron spacings that are expected slow down relaxation by phonon emission, but nevertheless cool rapidly transfer holes. This makes the intrinsic phonon-bottleneck limited lifetime elusive. We used combination theory and experiments probe dynamics negatively charged Cadmium Sulfide (CdS) colloidal...
Interactions between excitons and molecular vibrational modes limit the extent of exciton delocalization rate energy transport in organic aggregates, diminishing their performance many optical device applications. This coupling leads to self-trapping subsequently changes emission behavior. Certain amphiphilic cyanine dyes form nanotubular aggregates that demonstrate high rates show no such modes. However, under sustained illumination these undergo photobrightening (PB) can a doubling quantum...
This Perspective discusses the phenomenon of trapped-hole diffusion in colloidal semiconductor nanocrystals. Surface charge-carrier traps are ubiquitous nanocrystals and often dictate fate photoexcited carriers. New measurements calculations unveiling nature nanocrystal surface, but many challenges to understanding dynamics trapped carriers remain. In contrast view that holes stationary, we have put forward a series reports demonstrating on surfaces CdS CdSe mobile move between sequence...
The lack of viable solid-state annihilators is the greatest hurdle in perovskite-sensitized triplet-triplet annihilation upconversion (UC). Unfavorable singlet and triplet energy surfaces solid state have limited successful implementation many conventional solution-based annihilators. To date, rubrene still best performing annihilator; however, this comes at cost a small apparent anti-Stokes shift. point, anthracene derivatives are promising candidates to increase well-known green glowstick...