Search

Mid-infrared HgTe colloidal quantum dot electroluminescent devices are demonstrated. With emission at 4 μm, devices achieved an external quantum efficiency of ∼10

The magnetoresistance of HgTe quantum dot films, exhibiting a well-defined 1Se state charging and a relatively high mobility (1–10 cm2 V−1 s−1), is measured with controlled occupation of the first electronic state.

Fluorophores emitting in the NIR-IIb wavelength range (1.5 micron - 1.7 micron) show great potential for bioimaging due to their large tissue penetration. However, current fluorophores suffer from poor emission with quantum yields ~2% in aqueous solvents. In this work, we report the synthesis of HgSe/CdSe core/shell quantum dots emitting at 1.7 microns through the interband transition. Growth of a thick shell led to a drastic increase in the photoluminescence quantum yield, with a value of 55% in nonpolar solvents. The quantum yields of our QDs and other reported QDs are explained well by a model of Forster resonance energy transfer to ligands and solvent molecules. The model predicts a quantum yield >6% when these HgSe/CdSe QDs are solubilized in water. Our work demonstrates the importance of a thick type-I shell to obtain bright emission in the NIR-IIb region, Main text: 9 pages, 4 figures. Supplementary Information: 31 pages, 21 figures

A procedure is developed for the growth of thick, conformal CdS shells that preserve the optical properties of 5 nm HgSe cores. The n-doping of the HgSe/CdS core/shell particles is quantitatively tuned through a simple postsynthetic Cd treatment, while the doping is monitored via the intraband optical absorption at 5 μm wavelength. Photoluminescence lifetime and quantum yield measurements show that the CdS shell greatly increases the intraband emission intensity. This indicates that decoupling the excitation from the environment reduces the nonradiative recombination. We find that weakly n-type HgSe/CdS are the brightest solution-phase mid-infrared chromophores reported to date at room temperature, achieving intraband photoluminescence quantum yields of 2%. Such photoluminescence corresponds to intraband lifetimes in excess of 10 ns, raising important questions about the fundamental limits to achievable slow intraband relaxation in quantum dots.

In this work, we investigate the effect of size distribution on the mobility, the conductivity gap, and the intraband photoconduction of HgSe colloidal quantum dots (CQDs). Using electrochemistry, we measure the mobility for a series of ethandithiol cross-linked n-doped HgSe quantum dot films with different size distribution but a similar average size. The results show that mobility is exponentially dependent on size dispersion. This is interpreted as the size dispersion causing an increase in the average activation energy for hopping transport and the effect is reproduced by a model and a simulation. Comparing with the interband HgTe where the optical gap is between the valence and the conduction band, the conductivity gap in n-doped HgSe between the 1Se and 1Pe states is more strongly softened by the size distribution. This harms the intraband photoconductive properties and it implies that improved size distribution will be needed when using intraband photodetectors.

Integration of infrared detectors with current silicon-based imagers would not only extend their spectral sensing range but also enables numerous applications including thermal imaging, machine vis...

HgSe colloidal quantum dot films are made by using a hybrid ligand exchange (HgSe/hybrid) in polar inks and compared with the solid-state ligand exchange using ethanedithiol (HgSe/EDT). In both systems, the conductance shows a peak at one-electron filling of the 1Se state and a dip at 2 electrons before filling the 1Pe state. The HgSe/hybrid films show a ∼100-fold increased mobility, reaching up to ∼1 cm2/Vs for 7.5 nm diameter particles. While field effect transistor and Hall measurements give similar carrier density and mobility, the temperature dependence of the mobility is consistent with hopping transport.

Colloidal quantum wells are two-dimensional materials grown with atomically-precise thickness that dictates their electronic structure. Although intersubband absorption in epitaxial quantum wells is well-known, analogous observations in non-epitaxial two-dimensional materials are sparse. Here we show that CdSe nanoplatelet quantum wells have narrow (30–200 meV), polarized intersubband absorption features when photoexcited or under applied bias, which can be tuned by thickness across the near-infrared (NIR) spectral window (900–1600 nm) inclusive of important telecommunications wavelengths. By examination of the optical absorption and polarization-resolved measurements, the NIR absorptions are assigned to electron intersubband transitions. Under photoexcitation, the intersubband features display hot carrier and Auger recombination effects similar to excitonic absorptions. Sequenced two-color photoexcitation permits the sub-picosecond modulation of the carrier temperature in such colloidal quantum wells. This work suggests that colloidal quantum wells may be promising building blocks for NIR technologies., Multiple infrared lasing and detection technologies exploit intersubband transitions of epitaxial quantum wells, but such transitions are mainly limited to the mid-infrared. Here, the authors report narrow, polarized intersubband transitions up to telecom wavelengths in CdSe colloidal quantum wells.

Improved mid-infrared photoconductors based on colloidal HgTe quantum dots are realized using a hybrid ligand exchange and polar phase transfer. The doping can also be controlled n and p by adjusti...

Infrared multispectral imaging is attracting great interest with the increasing demand for sensitive, low-cost and scalable devices that can distinguish coincident spectral information. However, the widespread use of such detectors is still limited by the high cost of epitaxial semiconductors. In contrast, the solution processability and wide spectral tunability of colloidal quantum dots (CQDs) have inspired various inexpensive, high-performance optoelectronic devices. Here, we demonstrate a two-terminal CQD dual-band detector, which provides a bias-switchable spectral response in two distinct bands. A vertical stack of two rectifying junctions in a back-to-back diode configuration is created by engineering a strong and spatially stable doping process. By controlling the bias polarity and magnitude, the detector can be rapidly switched between short-wave infrared and mid-wave infrared at modulation frequencies up to 100 kHz with D* above 1010 jones at cryogenic temperature. The detector performance is illustrated by dual-band infrared imaging and remote temperature monitoring. Colloidal quantum dot detectors, switchable between short-wave infrared and mid-wave infrared, are demonstrated.

Multicarrier dynamics play an essential role in quantum dot photophysics and photochemistry, and they are primarily governed by nonradiative Auger processes. Auger recombination affects the performance of lasers, light-emitting diodes, and photodetectors, and it has been implicated in fluorescence intermittency phenomena which are relevant in microscopy and biological tagging. Auger cooling is an important mechanism of rapid electron thermalization. Inverse Auger recombination, known as impact ionization, results in carrier multiplication which can enhance the efficiencies of solar cells. This article first reviews the physical picture, theoretical framework and experimental data for Auger processes in bulk crystalline semiconductors. With this context these aspects are then reexamined for nanocrystal quantum dots, and we first consider fundamental features of Auger recombination in these systems. Methods for the chemical control of Auger recombination and Auger cooling are then discussed in the context of how they illuminate the underlying mechanisms, and we also examine the current understanding of carrier multiplication in quantum dots. Manifestations of Auger recombination in quantum dot devices are finally considered, and we conclude the article with a perspective on remaining unknowns in quantum dot multicarrier physics.

Spherical and tetrahedral HgTe colloidal quantum dots (CQDs) are synthesized, and their doping is tuned electrochemically. Compared to spherical dots of a similar volume, the tetrahedral CQDs show a decrease in confinement energy as well as a sharper band edge absorption. The intraband spectra of the tetrahedral CQDs also display a smaller splitting from spin-orbit coupling. The shape-controlled synthesis with an improved size distribution and sharper optical features could find applications in optoelectronic devices.

Mid-infrared core/shell quantum dots are synthesized starting with HgTe and HgSe cores which emit around 5 μm with interband and intraband transitions, respectively. HgTe/CdTe and HgSe/CdX (X = S, Se, and Te) are grown by colloidal atomic layer deposition at room temperature. HgSe/CdSe is also grown by hot-injection. For films of the core/shells, even a two-monolayer shell leads to a vastly improved stability against annealing, with no observable changes up to the alloying temperatures of ∼180 °C for HgTe/CdTe and ∼250 °C for HgSe/CdX. The improvement in the photoluminescence remains however small for all systems. In this study across interband and intraband emissions, the brightest emitter at 5 μm is the intraband transition of HgSe/CdSe with a quantum yield of ∼10–3.

Planar cylinder polystyrene–block-poly(2-vinylpyridine) (PS–P2VP) diblock copolymer thin films, with no corrugation and a uniform PS surface, undergo major restructuring upon sequential solvent swelling, yielding 10 nm P2VP ridges separated by PS troughs. Oven-annealed thin films were exposed to P2VP selective solvents, with or without an intermediate tetrahydrofuran vapor treatment, and the resulting surface morphologies were characterized. Experiments indicate that tetrahydrofuran enhances the permeability of the PS matrix to the P2VP selective solvents, with the ultimate swelling topography dictated by the hydrocarbon chain length and pKa of the selective solvent. We show that the film swelling occurs in stages, with P2VP punching to the surface as puckered pillars that eventually link into ridges separated by PS troughs. The chemical duality of the surfaces allows the selective deposition of negatively charged gold nanoparticles on the P2VP ridges.

Colloidal quantum dots (CQDs) with a band gap tunable in the mid-wave infrared (MWIR) region provide a cheap alternative to epitaxial commercial photodetectors such as HgCdTe (MCT) and InSb. Photoconductive HgTe CQD devices have demonstrated the potential of CQDs for MWIR photodetection but face limitations in speed and sensitivity. Recently, a proof-of-concept HgTe photovoltaic (PV) detector was realized, achieving background-limited infrared photodetection at cryogenic temperatures. Using a modified PV device architecture, we report up to 2 orders of magnitude improvement in the sensitivity of the HgTe CQD photodetectors. A solid-state cation exchange method was introduced during device fabrication to chemically modify the interface potential, leading to an order of magnitude improvement of external quantum efficiency at room temperature. At 230 K, the HgTe CQD photodetectors reported here achieve a sensitivity of 109 Jones with a cutoff wavelength between 4 and 5 μm, which is comparable to that of comm...

The biexciton lifetimes in HgTe colloidal quantum dots are measured as a function of particle size. Samples produced by two synthetic methods, leading to partially aggregated or well-dispersed particles, exhibit markedly different dynamics. The relaxation characteristics of partially aggregated HgTe inhibit reliable determinations of the Auger lifetime. In well-dispersed HgTe quantum dots, the biexciton lifetime increases approximately linearly with particle volume, confirming trends observed in other systems. The extracted Auger coefficient is three orders of magnitude smaller than that for bulk HgCdTe materials with similar energy gaps. We discuss these findings in the context of understanding Auger relaxation in quantum-confined systems and their relevance to mid-infrared optoelectronic devices based on HgTe colloidal quantum dots.

HgTe-based colloidal quantum dots (CQDs) fabricated between 10 nm and 20 nm in size readily lead to infrared cutoff wavelengths between 3 μm and 12 μm, due to their quantum confinement. In previous work, infrared photodetection using these films has been demonstrated to detect radiation out to a wavelength of 12 μm, and imaging in the mid-wave infrared region. In this work, a complete focal plane array and imager was fabricated and its performance measured for detecting radiation out to 12 μm. The photoconductive and optical properties of these HgTe CQD films are described, along with recent advancements in CQD detector technology. Anticipated improvements in the CQD synthesis and film deposition chemistries and techniques can raise the specific detectivity of these CQD films, bringing them closer to room-temperature operation.

Infrared multispectral imaging with curved focal plane array (FPA) is attracting great interest with increasing demand for sensitive, low-cost and scalable devices that can distinguish coincident spectral information and achieve wide field of view, low aberrations, and simple imaging optics at the same time. However, the widespread use of such detectors is still limited by the high cost of epitaxial semiconductors like HgCdTe, InSb, and InGaAs. In contrast, the solution-processability, mechanical flexibility and wide spectral tunability of colloidal quantum dots (CQDs) have inspired various inexpensive, high-performance optoelectronic devices covering important atmospheric windows from short-wave infrared (SWIR, 1.5 – 2.5 μm) to mid-wave infrared (MWIR 3 – 5 μm). Here, a potential route leading to infrared electronic eyes with multispectral imaging capability is demonstrated by exploring HgTe CQDs photovoltaic detectors. At room temperature, the HgTe CQDs detectors demonstrate detectivity D* up to 6 × 1010 Jones in SWIR and 6.5 × 108 Jones in MWIR. At cryogenic temperature, the MWIR D* becomes BLIP and increases to 1 × 1011 Jones. Besides high D* , the HgTe CQDs detector shows fast response with rise time below 300 ns. By stacking CQDs with different energy gaps or coupling CQDs with tunable optical filters, dual-band and multi-band infrared detection can be achieved in wide spectral ranges. Finally, infrared images are captured with flexible HgTe CQDs detectors at varying bending curvatures, showing a practical approach to sensitive infrared electronic eyes beyond the visible range.

Acoustic oscillations of metal nanoparticles can be used to study the properties of liquids at GHz frequencies and nanometer length scales. We use time-resolved spectroscopy to probe the dynamics of the metal nanoparticle oscillations utilizing a pump-probe technique. The incident pump laser pulse heats the nanoparticles leading to expansion and impulsive excitation of vibrations of the nanoparticles. The oscillations produce shifts in the plasmon resonance, which are monitored by measuring the change in absorption of a second weak broadband probe pulse. In our experiment, we immersed a sample of highly monodisperse gold bipyramids in water-glycerol mixtures from which we determined the damping resulting from the structure-liquid interactions. Performing these measurements over a range of temperatures provides a means to vary the fluid properties of a given water-glycerol mixture. Viscous damping could account for the measured results at low glycerol concentrations and sufficiently high temperatures but failed to describe the damping for high glycerol concentrations and sufficiently low temperatures. Accounting for the viscoelastic nature of the liquid mixtures mostly resolved the discrepancies, but consistently overestimated the degree of damping. Ultimately, allowing for a finite slip length produced good agreement with the measured damping rates. Our results show that standard assumptions in the fluid mechanics of simple liquids – a purely viscous response and the no-slip boundary condition – must be revisited at short length scales and fast time scales.

Devices based on small-gap mercury chalcogenide semiconductor nanocrystal inks have recently demonstrated increasingly high performance photodetection in the short and mid-wave infrared. These new colloidal inks are generating increasing interest because they could provide higher operating temperatures and vastly reduced costs compared to the current epitaxially-grown devices. However, in order to further increase detector operation temperatures and use these materials as infrared light sources, more detailed understandings of the carrier dynamics are required. Described here are picosecond mid-infrared absorption and emission studies of HgTe and HgSe colloidal quantum dots focusing on multicarrier nonradiative relaxation. Comparisons of the interband and intraband transitions in intrinsic and n-type systems reveal phenomena such as suppression of Auger relaxation in nanoparticles vs. bulk materials and slow or absent Auger relaxation in n-type quantum dots. Yet, the measured lifetimes are still limited by other nonradiative pathways that appear unique to small-gap nanomaterials. The deeper understanding of nonradiative relaxation in small-gap nanocrystals afforded by these experiments provides a path towards realizing high performance infrared photodetection near room temperature and robust mid-infrared light emission with colloidal quantum dots.

HgTe colloidal quantum dots (CQDs) are solution-processed, spectrally-tunable infrared materials for next-generation short- and mid-infrared photodetectors. Photodiodes with p-on-n and n-on-p architectures achieve room temperature specific detectivities >1010 Jones below 2.5 µm and up to 109 Jones at 4 µm with background-limited photodetection upon cooling.

HgS colloidal quantum dots (CQDs) are synthesized at room temperature using a dual-phase method. The HgS CQDs ranging from 3 to 15 nm exhibit air-stable n-doping and infrared intraband absorptions. For HgS CQDs of small sizes, the doping density is close to 2 electrons per dot, while for larger ones, their intraband absorption peaks shift to as far as 10 μm and exhibit Lorentzian line shapes. Under reducing potentials, these long-wavelength absorption peaks increase in strength and blue shift. This behavior can be explained through a classical model of the local field, showing how the degenerate single-electron transitions shift to a frequency that is the quadratic mean of the individual transition and a surface plasmon coming from a number of oscillators. This indicates that the intraband absorption of large, n-doped HgS CQDs is therefore becoming a surface plasmon. The same synthetic method works for HgS/CdS core/shells. Encapsulating HgS in a CdS shell removes the natural n-doping of the HgS cores, res...

Mid-infrared intraband photoluminescence is observed from CdSe and CdS colloidal quantum dots (CQDs) and core/shell systems when excited by a visible laser. The CQDs show more intraband photoluminescence with dodecanethiol than with other ligands. Core/shells show an increase of the intraband photoluminescence with increasing shell thickness. The detected emission is restricted to below 2900 cm(-1), bounded by the C-H vibrational modes of the organic ligands. Upon photoexcitation in air for all dodecanethiol ligands capped CQD systems studied, the intraband photoluminescence is quenched over time, and emission at lower frequency is observed, which is assigned to laser heating and thermal emission from oxides.

HgTe colloidal quantum dots are investigated as the active material in photodiodes for extended short-wave infrared up to 2.6 μm. The HgTe colloidal quantum dots photodiodes achieve external quantum efficiencies above 50% and specific detectivities of 1 × 1011 at 2.2 μm at room temperature with a microsecond response time and compete with commercial extended InGaAs photodiodes.

Three-dimensional (3D) subwavelength nanostructures have emerged and triggered tremendous excitement because of their advantages over the two-dimensional (2D) counterparts in fields of plasmonics, photonic crystals, and metamaterials. However, the fabrication and integration of 3D nanophotonic structures with colloidal quantum dots (CQDs) faces several technological obstacles, as conventional lithographic and etching techniques may affect the surface chemistry of colloidal nanomaterials. Here, the direct fabrication of functional quasi-3D nanophotonic structures into CQD films is demonstrated by one-step imprinting with well-controlled precision in both vertical and lateral directions. To showcase the potential of this technique, diffraction gratings, bilayer wire-grid polarizers, and resonant metal mesh long-pass filters are imprinted on CQD films without degrading the optical and electrical properties of CQD. Furthermore, a dual-diode CQD detector into an unprecedented mid-wave infrared two-channel polarization detector is functionalized by embedding an imprinted bilayer wire-grid polarizer within the CQDs. The results show that this approach offers a feasible pathway to combine quasi-3D nanostructures with colloidal materials-based optoelectronics and access a new level of light manipulation.

International audience; AbstractHgTe colloidal quantum dots (QDs) are of interest because quantum confinement of semimetallic bulk HgTe allows one to synthetically control the bandgap throughout the infrared. Here, we synthesize highly monodisperse HgTe QDs and tune their doping both chemically and electrochemically. The monodispersity of the QDs was evaluated using small-angle X-ray scattering (SAXS) and suggests a diameter distribution of similar to 10% across multiple batches of different sizes. Electron-doped HgTe QDs display an intraband absorbance and bleaching of the first two excitonic features. We see splitting of the intraband peaks corresponding to electronic transitions from the occupied 1Se state to a series of nondegenerate 1Pe states. Spectroelectrochemical studies reveal that the degree of splitting and relative intensity of the intraband features remain constant across doping levels up to two electrons per QD. Theoretical modeling suggests that the splitting of the 1Pe level arises from spin-orbit coupling and reduced QD symmetry. As a result, the fine structure of the intraband transitions is observed in the ensemble studies due to the size uniformity of the as-synthesized QDs and strong spin-orbit coupling inherent to HgTe.

The magnetoresistance of films of manganese-doped colloidal quantum dots of CdSe, ZnO, HgS, and ZnTe is investigated. At low concentration of manganese ions (1% or less), the hyperfine splitting of the Mn2+ electron spin resonance is resolved and similar to that of the bulk doped materials, indicating successful doping into the nanocrystals. At high Mn concentration (∼10%), the hyperfine splitting disappears because of interaction between the Mn2+ ions. Thin films of Mn:CdSe, Mn:ZnO, and Mn:HgS quantum dots are charged negative by applying an electrochemical potential, and the magnetoresistance is measured down to 2 K and up to 9 T. At low charging level, the magnetoresistance of thin films is positive, exhibits little effect of the manganese dopant, and is instead consistent with predictions from the variable range hopping model and the squeezing of the wave function of the quantum dots. At high charging level, the magnetoresistance becomes linear both for Mn:CdSe and Mn:ZnO, and this is not explained. A...

Colloidal quantum dots (CQD) attract much interest for optoelectronic applications, as potentially low-cost alternatives to epitaxial materials. In particular, in the mid-IR spectral range, CQD based on the zinc-blend mercury chalcogenides, Hg (S, Se, Te), lead efforts to create mid-IR technologies with solutions based materials. HgTe CQD with their tunable bandgap above 3 microns show promise as mid-IR detectors at a lower cost than existing HgCdTe (MCT) detectors. Progress towards the manufacture of mid-infrared cameras, improved sensitivity of PV devices, and new modalities, will be reviewed. HgS and HgSe CQDs also allow photodetection in the mid-IR because they are stably n-doped in ambient conditions, and they show an intense intraband transitions tunable in the mid-IR. Intraband CQDs is therefore another promising approach that broadens the types of materials considered. For both approaches, some of the challenges are similar, as one needs to develop tightly size-controlled colloidal quantum dots, and an interfacial chemistry that maximizes mobility and carrier lifetime, yet allows for controlling the doping.

II-VI colloidal quantum dots (CQDs) have made significant technological advances over the past several years, including the world’s first demonstration of MWIR imaging using CQD-based focal plane arrays. The ultra-low costs associated with synthesis and device fabrication, as well as compatibility with wafer-level focal plane array fabrication, make CQDs a very promising infrared sensing technology. In addition to the benefit of cost, CQD infrared imagers are photon detectors, capable of high performance and fast response at elevated operating temperatures. By adjusting the colloidal synthesis, II-VI CQD photodetectors have demonstrated photoresponse from SWIR through LWIR. We will discuss our recent progress in the development of low cost infrared focal plane arrays fabricated using II-VI CQDs.

Nonaggregating HgTe colloidal quantum dots are synthesized without thiols as stabilizing ligands. The dots are spherical with a size tunability from 4.8 to 11.5 nm. When the results from optical and electrochemical measurement are combined, air-stable n-doping is observed in large sizes of HgTe quantum dots, which is attributed to the Hg-rich surface.

The absolute positions of the energy levels of colloidal quantum dots of Hg(S, Se, Te), which are of interest as mid-infrared materials, are determined by electrochemistry. The bulk valence bands are at -5.85, -5.50, and -4.77 eV (±0.05 eV) for zinc-blend HgS, HgSe, HgTe, respectively, in the same order as the anions p-orbital energies. The conduction bands are conversely at -5.20, -5.50, and -4.77 eV. The stable ambient n-doping of Hg(S, Se) quantum dots compared to HgTe arises because the conduction band is sufficiently lower than the measured environment Fermi level of ∼ -4.7 eV to allow for n-doping for HgS and HgSe quantum dots even with significant electron confinement. The position of the Fermi level and the quantum dots states are reported for a specific surface treatment with ethanedithiol and electrolyte environment. The positions are however sensitive to different surface treatments, providing an avenue to control doping. Electrochemical gating is further used to determine the carrier mobility in the films of the three different systems as a function of CQD size. HgSe and HgS show increasing mobility with increasing particle sizes while HgTe shows a nonmonotonous behavior, which is attributed to some degree of aggregation of HgTe QDs.

Colloidal perovskite nanocrystals support bright, narrow PL tunable over the visible spectrum. However, bandgap tuning of these materials remains limited to laboratory-scale syntheses. In this work, we present a polar-solvent-free ligand-mediated transport synthesis of high-quality organic-inorganic perovskite nanocrystals under ambient conditions with photoluminescence quantum yields up to 97%. Our synthesis employs a ligand-mediated transport mechanism that circumvents the need for exquisite external control (e.g., temperature control, inert-gas protection, dropwise addition of reagents) required by other methods due to extremely fast reaction kinetics. In the ligand-mediated transport mechanism, multiple equilibria cooperatively dictate reaction rates and enable precise control over NC size. These small nanocrystals exhibit high photoluminescence quantum yields due to quantum confinement. Nanosecond transient absorption spectroscopy experiments reveal a fluence-independent PL decay originating from exciton recombination. Two-dimensional electronic spectroscopy resolves multiple spectral features reflecting the electronic structure of the nanocrystals. The resolved features exhibit size-dependent spectral positions, further indicating the synthesized nanocrystals are quantum-confined.

International audience; Over the past few years, colloidal nanoparticles have started to be investigated for their optical properties in the mid-infrared, past 3 microns. Research on detector application has led to background limited detection and fast video imaging at 5 microns. With further development, one could imagine that these new materials could vastly reduce the costs of infrared technology and this would lead to a trove of new applications for infrared imaging into our daily lives. This article reviews the progress regarding the optical, transport and photodetection properties of thin film based on these materials, and the three different ways by which infrared resonances have been realized with colloidal nanoparticles: interband absorption with small gap semiconductor quantum dots, intraband absorption in lightly doped quantum dots, and plasmonic resonances in heavily doped nanocrystals.

Photoconductivity is demonstrated with monodispersed HgSe colloidal quantum dots that are illuminated with radiation resonant with 1S(e)-1P(e) intraband electronic absorption, between 3 and 5 μm. A doping of two electrons per dot gives the lowest dark current, and a detectivity of 8.5 × 10(8) Jones is obtained at 80 K. Photoluminescence of the intraband transition is also observed. The detector properties are discussed in terms of the measured photoluminescence quantum yield, the electron mobility in the 1P(e) state, and the responsivity. The intraband photoresponse allows to fully harness the quantum confined states in colloidal nanostructures, extending the prior limited use of interband transition.

We present a facile methodology for the end-to-end assembly of gold nanorods of various aspect ratios on corrugated, horizontal, cylinder-forming diblock copolymer templates. Although the depth of corrugation is significantly smaller than the diameter of the nanorods, they exhibit excellent selectivity (>98%) and alignment for placement in the polymer grooves due to capillary forces and the substrate’s topography. Enhanced corrugation of the diblock template is achieved by chemical swelling prior to deposition of the metallic nanorods. Graphoepitaxy of the diblock copolymer in nanoconfining channels is employed to achieve essentially perfect long-range orientation of the substrate, while subsequent deposition of nanorod arrays whose alignment maps onto that of the diblock template with high fidelity provides novel organic–inorganic hybrid surfaces whose surface enhanced Raman spectroscopy (SERS) properties are characterized. These arrays of aligned gold nanorods exhibit polarization-dependent spectra for ...

An aqueous synthesis of gold bipyramid dimers is presented. The methodology, its selectivity, and the characterization of the resulting structures with optical dark-field and scanning electron microscopy are presented and discussed. In the bowtie orientation, the dimers exhibit a 20% red shift in their plasmon resonance as compared to the individual particles, with a weak dependence on the interparticle separation. From the analysis, it was found that the in situ absorption peaks that develop during the assembly can be assigned to specific dimer structures, which has not been shown previously. Last, the kinetics of the assembly are analyzed.

The photoluminescence quantum yield of HgTe colloidal quantum dots is measured from 1800 to 6500 cm–1. There is a steep drop to low energy reminiscent of the generic gap law. However, direct evidence of energy transfer to the C–H stretch and overtone vibrations is apparent when temperature tunes the PL wavelength of a given sample through the vibrational resonances. Calculations based on the radiative rate and resonant energy transfer to the ligand vibrations appear to account for much of the quantum yield drop. Power-dependent photoluminescence lifetime measurements on 3.7 nm particles show fast, ∼50 ps, biexciton lifetime similar to other colloidal quantum dot systems of similar sizes.

This perspective describes the advantages of infrared colloidal quantum dots (CQDs) for photodetection beyond silicon and provides a brief review of the development of CQD photodetection. The standard specifications for photodetectors are listed with particular emphasis on the detectivity. High gain improves the responsivity but does not improve the detectivity, while nonradiative losses do not prevent high responsivity but limit the detectivity. Performances of CQD detectors and HgTe CQDs, in particular, are compared with the maximum possible detectivity based on detailed balance from the device temperature and nonradiative losses.