A5064738392- Quantum Dots Synthesis And Properties
- Chalcogenide Semiconductor Thin Films
- Nanocluster Synthesis and Applications
- Semiconductor Quantum Structures and Devices
- Gold and Silver Nanoparticles Synthesis and Applications
- Near-Field Optical Microscopy
- Perovskite Materials and Applications
- Advanced Fluorescence Microscopy Techniques
- Nanowire Synthesis and Applications
- Photonic Crystals and Applications
- Copper-based nanomaterials and applications
- Plasmonic and Surface Plasmon Research
- Carbon and Quantum Dots Applications
- Quantum Information and Cryptography
- Advanced biosensing and bioanalysis techniques
- Photonic and Optical Devices
- ZnO doping and properties
- Molecular Junctions and Nanostructures
- Nonlinear Optical Materials Studies
- Advanced Electron Microscopy Techniques and Applications
- Semiconductor materials and interfaces
- Laser-Ablation Synthesis of Nanoparticles
- Spectroscopy and Quantum Chemical Studies
- 2D Materials and Applications
- Pickering emulsions and particle stabilization
Center for Integrated Nanotechnologies
2016-2025
Los Alamos National Laboratory
2016-2025
Oak Ridge National Laboratory
2020
Vanderbilt University
2020
Los Alamos Medical Center
2007-2018
Material (Belgium)
2018
National High Magnetic Field Laboratory
2005-2011
Division of Chemistry
2010
Indian Institute of Science Bangalore
2006
Washington University in St. Louis
1997-2003
The development of optical gain in chemically synthesized semiconductor nanoparticles (nanocrystal quantum dots) has been intensely studied as the first step toward nanocrystal dot lasers. We examined competing dynamical processes involved amplification and lasing dots found that, despite a highly efficient intrinsic nonradiative Auger recombination, large can be developed at wavelength emitting transition for close-packed solids these dots. Narrowband stimulated emission with pronounced...
Semiconductor nanocrystal quantum dots (NQDs) comprise an important class of inorganic fluorophores for applications from optoelectronics to biology. Unfortunately, date, NQD optical properties (e.g., their efficient and particle-size-tunable photoluminescence) have been susceptible instabilities at the bulk single-particle levels. Specifically, ensemble yields (QYs) in emission are dependent upon surface chemistry chemical environment, while level, NQDs characterized by significant...
We report on the dynamics of resonant energy transfer in monodisperse, mixed-size, and energy-gradient (layered) assemblies CdSe nanocrystal quantum dots. Time-resolved spectrally resolved photoluminescence directly reveals energy-dependent rate excitons from smaller to larger dots via electrostatic coupling. The data show a rapid (0.7-1.9 ns) across large tens-of-meV gap (i.e., between disparate size), suggest that interdot can approach picosecond time scales structurally optimized systems.
Many potential applications of semiconductor nanocrystals are hindered by nonradiative Auger recombination wherein the electron−hole (exciton) energy is transferred to a third charge carrier. This process severely limits lifetime and bandwidth optical gain, leads large losses in light-emitting diodes photovoltaic cells, believed be responsible for intermittency ("blinking") emission from single nanocrystals. The development nanostructures which suppressed has recently been subject much...
Efficient mid-infrared sources are of considerable general interest for gas analysis, remote sensing, and atmospheric monitoring, but existing technologies limited. Here, we report the synthesis first colloidal QDs having photoluminescence (PL) in mid-infrared. We show particle-size-tunable emission large (10-17 nm), quantum-confined, PbSe QDs, with efficient, narrow-bandwidth PL at energies as low 0.30 eV (4.1 mum). Applying two new synthetic routes, have achieved fine control QD size...
Infrared-emitting nanocrystal quantum dots (NQDs) have enormous potential as an enabling technology for applications ranging from tunable infrared lasers to biological labels. Notably, lead chalcogenide NQDs, especially PbSe provide efficient emission over a large spectral range in the infrared, but their application has been limited by instability yield and peak position on exposure ambient conditions. Conventional methods improving NQD stability applying shell of more stable, wider band...
Nanocomposite materials provide the possibility for multifunctional properties in contrast with their more-limited single-component counterparts. Here, we report synthesis and characterization of first all-inorganic core/shell hybrid magnetic-optical nanoparticle, cobalt/cadmium selenide. The nanocrystals are prepared a facile one-pot reaction, microstructure is analyzed using low- high-resolution transmission electron microscopy. Using magnetic optical characterization, demonstrate...
We use a simple device architecture based on poly(3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-coated indium tin oxide anode and LiF/Al cathode to assess the effects of shell thickness properties light-emitting diodes (LEDs) comprising CdSe/CdS core/shell nanocrystal quantum dots (NQDs) as emitting layer. Specifically, we are interested in determining whether LEDs thick-shell nanocrystals, so-called "giant" NQDs, afford enhanced performance compared their counterparts...
We investigate the strongly temperature-dependent radiative lifetime of electron–hole excitations in colloidal CdSe nanocrystal quantum dots over nearly three orders magnitude temperature (300 K to 380 mK). These studies reveal an intrinsic, upper limit ∼1 μs for storage excitons below 2 K. At higher temperatures, exciton lifetimes are consistent with thermal activation from dark-exciton ground state, but two different thresholds.
A strong electron–hole exchange interaction (EI) in semiconductor nanocrystals (NCs) gives rise to a large (up tens of meV) splitting between optically active ('bright') and passive ('dark') excitons. This dark–bright has significant effect on the optical properties band-edge excitons leads pronounced temperature magnetic field dependence radiative decay. Here we demonstrate nanoengineering-based approach that provides control over EI while maintaining nearly constant emission energy. We...
Nanocrystal quantum dots are attractive materials for applications as nanoscale light sources. One impediment to these is fluctuations of single-dot emission intensity, known blinking. Recent progress in colloidal synthesis has produced nonblinking nanocrystals; however, the physics underlying blinking suppression remains unclear. Here we find that ultra-thick-shell CdSe/CdS nanocrystals can exhibit pronounced lifetimes (lifetime blinking), despite stable intensity. We demonstrate lifetime...
The growth of ultra-thick inorganic CdS shells over CdSe nanocrystal quantum dot (NQD) cores gives rise to a distinct class NQD called the "giant" (g-NQD). g-NQDs are characterized by unique photophysical properties compared their conventional core/shell counterparts, including suppressed fluorescence intermittency (blinking), photobleaching, and nonradiative Auger recombination. Here, we report new insights into numerous synthetic conditions that influence complex process thick-shell...
In van der Waals (vdW) heterostructures formed by stacking two monolayers of transition metal dichalcogenides, multiple exciton resonances with highly tunable properties are and subject to both vertical lateral confinement. We investigate how a unique control knob, the twist angle between monolayers, can be used dynamics. observe that interlayer lifetimes in MoSe2/WSe2 twisted bilayers (TBLs) change one order magnitude when is varied from 1° 3.5°. Using low-energy continuum model, we...
We study the effect of zero- to one-dimensional (1D) transformation on multiparticle Auger recombination using a series elongated semiconductor nanocrystals (quantum rods). observe transition from three- two-particle process as nanocrystal aspect ratio is increased. This indicates that in 1D confinement limit, decay dominated by Coulomb interactions between excitons recombine bimolecular fashion. One consequence this strongly reduced rates higher states lead increased optical-gain lifetimes...
We study different emission regimes in close-packed films of chemically synthesized CdSe nanoparticles [nanocrystal quantum dots (NQDs)]. observe that the NQD photoluminescence is dominated by excitons and biexcitons, respectively, before after threshold for stimulated emission. Furthermore, we demonstrate regime microring lasing into sharp, whispering-gallery modes using solids incorporated microcapillary tubes. This result indicates a feasibility miniature, solid-state laser devices based on NQDs.
We study the effect of thiols on emission efficiency aqueous CdSe/ZnS core/shell nanocrystal quantum dots (NQDs). observe that impact thiol addition yields (QYs) is time-, concentration-, and pH-dependent. Further, we use a combination time-resolved spectroscopic methods to determine mechanism by which can cause either increases or decreases in QYs. Specifically, through transient absorption measurements, show improve passivation electron traps, increasing QYs at low concentrations. using...
The use of ultrafast gating techniques allows us to resolve both spectrally and temporally the emission from short-lived neutral negatively charged biexcitons in ultrasmall (sub-10 nm) CdSe nanocrystals (nanocrystal quantum dots). Because forced overlap electronic wave functions reduced dielectric screening, these states are characterized by giant interaction energies tens (neutral biexcitons) hundreds (charged meV. Both types show extremely short lifetimes (from sub-100 picoseconds...
Biexciton photoluminescence (PL) quantum yields (Q(2X)) of individual CdSe/CdS core-shell nanocrystal dots with various shell thicknesses are derived from independent PL saturation and two-photon correlation measurements. We observe a near-unity Q(2X) for some nanocrystals an ultrathick 19-monolayer shell. High Q(2X)'s are, however, not universal vary widely among nominally identical indicating significant dependence upon subtle structural differences. Interestingly, our measurements...
The development of nanocrystal quantum dots (NQDs) with suppressed nonradiative Auger recombination has been an important goal in colloidal nanostructure research motivated by the needs prospective applications lasing devices, light-emitting diodes, and photovoltaic cells. Here, we conduct single-nanocrystal spectroscopic studies recently developed core−shell NQDs (so-called "giant" NQDs) that comprise a small CdSe core surrounded 16-monolayer-thick CdS shell. Using both continuous-wave...
The growing potential of quantum dots (QDs) in applications as diverse biomedicine and energy has provoked much dialogue about their conceivable impact on human health the environment at large. Consequently, there been an urgent need to understand interaction with biological systems. Parameters such size, composition, surface charge, functionalization can be modified ways either enhance biocompatibility or reduce deleterious effects. In current study, we simultaneously compared alone...
Nonblinking excitonic emission from near-infrared and type-II nanocrystal quantum dots (NQDs) is reported for the first time. To realize this unusual degree of stability at single-dot level, novel InP/CdS core/shell NQDs were synthesized a range shell thicknesses (~1-11 monolayers CdS). Ensemble spectroscopy measurements (photoluminescence peak position radiative lifetimes) electronic structure calculations established transition type-I to band alignment in these heterostructured NQDs. More...
Core/thick-shell giant quantum dots (gQDs) possessing type II electronic structures exhibit suppressed blinking and diminished nonradiative Auger recombination. We investigate CdSe/ZnSe ZnSe/CdS as potential new gQDs. show theoretically experimentally that both can partial or complete spatial separation of an excited-state electron-hole pair (i.e., behavior). However, we reveal thick-shell growth is challenged by competing processes: alloying cation exchange. demonstrate these be largely...
Tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) enantiomers’ spin filtering and chiroptical properties are studied. Spin-filtering assessed by recording spin-polarized I – V curves (mc-AFM) of TM-BEDT-TTF fibrils.