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High fidelity single photon sources are required for the implementation of quantum information processing and communications protocols. Although colloidal quantum dots (CQDs) are single photon sources, their efficacy is limited by their tendency to show finite multiphoton emission at higher excitation powers. Here, we show that wave function engineering of CQDs enables the realization of emitters with significantly improved single photon emission performance. We study the ZnS/CdSe/CdS system. It is shown that this system offers significantly improved probabilities of single photon emission. While conventional CQDs such as CdSe/CdS exhibit a g2(0) > 0.5 ± 0.02 at ⟨N⟩ = 2.17, ZnS/CdSe/CdS show a greatly improved g2(0) ≈ 0.04 ± 0.01. Improved single photon emission performance encourages the use of colloidal materials as quantum light sources in emerging quantum devices. [ABSTRACT FROM AUTHOR]

Inherent disorder in perovskite films has been suggested as a factor that improves exciton separation. At the same time, the disorder can potentially disrupt electron flow, deteriorating device performance. In this paper, we study the role of disorder in electron transport in perovskite films using kinetic Monte Carlo simulations. The effect of temperature on the conductivity of the system is studied. We find that at room temperature, where most solar cells operate, the effect of disorder on the conductivity is minimal. At lower temperatures, current flows along specific paths in the film. In contrast, the ability of carriers to sample all sites in the film at room temperature allows realisation of higher device efficiencies. We find that conductivity obeys Mott's expression for variable range hopping σ(T) ∝ T−1e−(To/T)1/3. The value of the universal proportionality constant α2 associated with the characteristic temperature has been computed. The effect of electric field on transport has also been studied. The average hopping distance is found to increase with the increase in the electric field at low temperatures, although this dependence is not observed at room temperature. Likewise, the conductivity is also a function of applied field F, and is found to be obey σ(F) ∝ F−1/3e−(Fo/F)1/3 at low temperatures while being field-independent at room temperature. [ABSTRACT FROM AUTHOR]

Microbolometers have emerged as a cost‐effective alternative to cooled infrared photon detectors, albeit with certain trade‐offs in terms of responsivity (Rλ$R_{\lambda}$), detectivity (D*$D_{\*}$), and response time (tr$t_{\text{r}}$). The research in this field is driven by the potential applications in night vision devices, military surveillance, and autonomous vehicles, leading to a growing interest in exploring new materials to bridge the performance gap between cooled photon detectors and uncooled bolometers. This study focuses on the optoelectronic and bolometric characteristics of CuFeSe2$\left(\text{CuFeSe}\right)_{2}$ nanocrystals (NCs) in a colloidal solution. These NCs exhibit a significant change in resistivity (ρ) when subjected to temperature variations ranging from 170 to 400 K. Specifically, the temperature coefficient of resistance (TCR), α, is 1.9% per Kelvin for a room temperature resistivity of 505 Ω cm. Furthermore, the responsivity of CuFeSe2$\left(\text{CuFeSe}\right)_{2}$ NCs is reported to be 0.101 A W−1, and the Hall mobility of the colloidal solution is determined as 0.1 cm2 V s−1$0 \text{.1} \textrm{ } \left(\text{cm}\right)^{2} \textrm{ } \text{V} \textrm{ } \left(\text{s}\right)^{- 1}$. Finally, a comprehensive comparison is conducted between the performance metrics of established bolometer materials, such as VOx and a‐Si, and those of colloidal CuFeSe2$\left(\text{CuFeSe}\right)_{2}$ NCs. Based on the results, colloidal CuFeSe2$\left(\text{CuFeSe}\right)_{2}$ NCs are a promising option for future bolometer technology. [ABSTRACT FROM AUTHOR]

Photonic devices stand to benefit from the development of chromophores with tunable, precisely controlled spontaneous emission lifetimes. Here, we demonstrate a method to continuously tune the radiative emission lifetimes of a class of chromophores by varying the density of electronic states involved in the emission process. In particular, we examined the peculiar composition-dependent electronic structure of copper doped CdZnSe quantum dots. It is shown that the nature and density of electronic states involved with the emission process is a function of copper inclusion level, providing a very direct handle for controlling the spontaneous lifetimes. The spontaneous emission lifetimes are estimated by examining the ratios of emission lifetimes to absolute quantum yields and also measured directly by ultrafast luminescence upconversion experiments. We find excellent agreement between these classes of experiments. This scheme enables us to tune spontaneous emission lifetimes by three orders of magnitude from ∼15 ns to over ∼7 µs, which is unprecedented in existing lumophores. [ABSTRACT FROM AUTHOR]

Core/shell growth in nanosystems is usually accomplished either through deposition of the shell material or else through the conversion of a part of the core into the shell through ion exchange. Here we describe the interplay of both deposition processes in the case of CuFeSe2/CdS nanocrystals. Specifically, we synthesize eskebornite CuFeSe2 nanoparticles. Films of the nanocrystals exhibit an optical absorbance onset of 0.11 eV. Core/shell structures prepared from CuFeSe2 show a unique dependence on the growth steps followed. In particular, we find that the addition of the cationic precursor before the anionic precursor leads to the formation of CdSe at the interface of the core and the shell. This is found to limit the tunability of the emission to 820 nm. In contrast, reversing the order of precursor addition prevents the formation of such a layer and leads to structures with a significantly greater emission tunability (900 nm to 1200 nm). Our observations are suggestive of the interplay of both processes in current syntheses for I‐III‐VI2 based core/shell structures. [ABSTRACT FROM AUTHOR]

I‐III‐VI2 semiconductor nanocrystals have been explored in countless optoelectronics and green energy applications. While indium‐based compounds are arguably the best‐known variants of these semiconductors and have been widely studied for their photophysical properties, other I‐III‐VI2 semiconductors are emerging as serious competitors. This review focuses on the current state of the art and recent progress made in the research and technology of one of the most promising competitors to indium‐based I‐III‐VI2 semiconductor nanocrystals, CuFeS2 nanocrystals. CuFeS2 is a promising alternative to indium‐based systems, mostly because many properties are competitive and because iron is much more abundant than indium. Replacing In(III) with Fe(III) would thus significantly alleviate the issue of raw material availability. The article highlights new synthesis approaches and summarizes and discusses advanced optical properties including surface plasmon resonance and luminescence properties. Moreover, potential applications in thermoelectric, photodetection, photothermal, and photovoltaics are illustrated and discussed. Finally, future perspectives for materials development, upscaling, and application in new processes and devices, such as self‐assembly, patterning, or plasmonic catalysis, are presented as well. [ABSTRACT FROM AUTHOR]

Auâ€"Ag nanostructures comprising of ∼1 nm Ag nanoparticles embedded into an Au matrix show several unconventional optical, electric and magnetic properties. Here, we review progress made towards the preparation of these materials as well as analysis of their structure. Further, electrical and magnetic transitions in these materials are discussed. Finally, we review the properties of these materials as revealed from optical and electron microscopic probes. [ABSTRACT FROM AUTHOR]

CuAlS2/ZnS Quantum dots (QDs) are known to directly convert aqueous solutions of bicarbonate ions to oxygen and organic molecules such as formate with a remarkable efficiency even under sunlight. In cases, fairly complicated organic reaction products such as acetate and methanol have been observed when reactions are allowed to continue for longer periods of time. Here, we investigate the electron dynamics that occurs within CuAlS2/ZnS QDs and show that it is essentially dominated by ultrafast electron transfer (560 fs for 0.4 excitons per dot) to the surface. The electron dwell time in the conduction band increases exponentially (for example 872 fs for 1.4 excitons per dot) with the excitation fluence. This is reverse of the auger limited response of conventional QDs and is hypothesized to exhibit strong charge separation that lies at the root of the remarkable photocatalytic activity. We further investigate this system through multi‐pump experiments. We find that the system response to prior excitation changes over the period of nanoseconds, consistent with the charge reorganization in the system, well after the initial electron transfer. The results of these experiments are summarized in terms of a coulomb‐well interpretation. [ABSTRACT FROM AUTHOR]

This study describes the optoelectronic characteristics of CuFeS2/Si nanocrystal/bulk heterojunctions. These heterojunctions show a strong photocurrent response under ambient conditions upon excitation from a wide optical spectrum, from 460 to 2200 nm. The devices comprise of a heterojunction formed between heavily doped n‐type silicon (1–100 Ω cm) and copper iron sulfide (CuFeS2) nanocrystal films. Over the spectral range 460–2200 nm the device shows a fast response (20 µs at NIR wavelengths), along with responsivity and detectivity of 4.68 mA W−1 and 5.29 × 109 Jones at 1900 nm wavelength. The photocurrent is further observed to be a nonlinear function of power. These properties of the devices are discussed in terms of a defect filling mechanism. Besides their regular photoresponse described above, the devices also exhibit a slower photothermal response, allowing these to also sense hot objects (450 K; excess 6 mW incident onto the device) within the focal plane, thereby extending the useful sensing range of the devices deeper into the infrared. [ABSTRACT FROM AUTHOR]

The rates of multicarrier recombination are measured in colloidal quantum dots with and without hole surface trapping and with hole extraction in type II core/shell systems. We report that hole trapping or the physical separation of electronic and hole wavefunctions into different semiconductor domains of a type II system have an insignificant effect on the multicarrier recombination dynamics. These observations are inconsistent with the accepted Auger transition mechanism. [ABSTRACT FROM AUTHOR]

The interband and intraband spectra of colloidal II-VI CdS and CdSe quantum dot cores and CdS/ZnSe, CdS/CdSe, CdSe/CdS, and CdSe/ZnSe core/shell systems are reported. Infrared absorption peaks between 0.5 and 0.2 eV are observed. The slope of the intraband energy versus the first interband absorption feature is characteristic of the relative band alignments of the materials constituting the core and the shell and it is analyzed within an effective mass model. The analysis provides a new estimate of the band gap of zinc blende CdSe as well as the band offsets in zinc blende and wurtzite CdSe, CdS, and ZnSe. [ABSTRACT FROM AUTHOR]

The reduction potential of plastocyanin was determined by using the quantum mechanics/molecular mechanics (QM/MM) method. The main objective was to determine the rate of electron transfers from cytochromef to plastocyanin and from plastocyanin to p700+.

Li5AlO4, a well-known material for solid state electrolyte application, has never been considered hitherto as a gate dielectric of metal oxide thin film transistors (TFTs). Here we demonstrate the salient features of Li5AlO4 as a gate dielectric outperforming the conventional inorganic dielectrics used in TFTs. The high dielectric constant (k) of this insulator has been achieved by utilizing the improved capacitance contributed by mobile lithium ions (Li+) within the dielectric film. We have synthesized this dielectric via a cost-effective sol–gel method followed by a low-temperature annealing process yielding three phases such as amorphous-Li5AlO4 (a-Li5AlO4), α-Li5AlO4, and β-Li5AlO4 under different annealing conditions. Optimized TFTs fabricated with all of these three phases of Li5AlO4 on top of a highly doped silicon (p++-Si) wafer and a solution processed semiconducting layer of indium zinc oxide (IZO) exhibit an excellent TFT performance at different operating voltages. Among these three different types of TFTs, the device with an α-Li5AlO4 gate dielectric annealed at 500 °C shows the best device performance with an on/off ratio of 5 × 104 and an electron mobility of 21.4 ± 2.16 cm2 V−1 s−1. In addition, this device requires the least drain voltage (＜2 V) to reach the saturation drain current due to the higher Li+ mobility of the α-Li5AlO4 gate dielectric. This TFT performance on the p++-Si substrate is superior to that of a previously reported device with a sodium beta-alumina (SBA) gate dielectric, where the percentage of mobile ions within the dielectric material was comparatively much lower. Moreover, this dielectric requires ∼300 °C lower annealing temperature compared to the SBA dielectric. A metal oxide/quantum dot heterojunction phototransistor was fabricated by coating an IZO TFT with colloidal lead sulphide (PbS) quantum dots that shows a responsivity and a response time of 4.5 × 10−4 A W−1 and 2.2 s respectively. [ABSTRACT FROM AUTHOR]

The introduction of dopants into II-VI semiconductor quantum dots (QDs) allows for the realization of materials with novel electro-optical properties. Motivated by its vast potential applications, Manganese doping into II-VI semiconductor QDs has been studied by several groups. Studies have focused on applications of manganese doped QDs as phosphors, diluted magnetic semiconductors as well as more recently their potential in light harvesting. Herein we review recent advances in understanding the emissive properties and electronic structure of Mn doped QDs. We survey synthetic approaches that have been proposed as well as advantages and disadvantages of conventional approaches to Mn doping. In particular, we discuss the advantages of reduced self-absorption, as well as the problem of emission tunability. Effects of pressure on manganese emission are discussed. We then summarize recent efforts to tune Mn emission by generating pressure and strain in nanostructured QDs. [ABSTRACT FROM AUTHOR]

We report the synthesis of copper iron sulfide (CuFeS2) quantum dots (QDs). These materials exhibit a tunable band gap that spans the range 0.5-2 eV (600-2500 nm). Although the as-prepared material is nonemissive, CuFeS2/CdS core/shell structures are shown to exhibit quantum yields that exceed 80%. Like other members of the I-III-VI2 family QDs, CuFeS2 based nanoparticles exhibit a long-lived emission that is significantly red-shifted compared to the band gap. CuFeS2 QDs are unique in terms of their composition. In particular, these QDs are the only band-gap-tunable infrared chromophore composed entirely of elements with atomic numbers less than 30. [ABSTRACT FROM AUTHOR]

In most template directed preparative methods, while the template decides the nanostructure morphology, the structure of the template itself is a non-general outcome of its peculiar chemistry. Here we demonstrate a template mediated synthesis that overcomes this deficiency. This synthesis involves overgrowth of silica template onto a sacrificial nanocrystal. Such templates are used to copy the morphologies of gold nanorods. After template overgrowth, gold is removed and silver is regrown in the template cavity to produce a single crystal silver nanorod. This technique allows for duplicating existing nanocrystals, while also providing a quantifiable breakdown of the structure – shape interdependence. [ABSTRACT FROM AUTHOR]

We investigate the processes involved in the nucleation of colloidal lead selenide nanoparticles. Our studies show that an unusual pathway – an anion exchange reaction, causes the nucleation of lead selenide nanocrystals. In this process, one quantum dot is transformed into another due to a substitution of its constituent anions. The existence of this pathway was never anticipated perhaps due to its unusually rapid kinetics. The nucleation and growth kinetics of colloidal lead selenide quantum dots are found to fit well to a two-step process. The rate constant associated with the anion exchange process is found to be four orders of magnitude greater than that of the nanocrystal growth. The complete consumption of the initial oxide nanoparticle thus provides a sharp, temporally well-defined nucleation event. [ABSTRACT FROM AUTHOR]

Despite significant improvements in their properties as emitters, colloidal quantum dots have not had much success in emerging as suitable materials for laser applications. Gain in most colloidal systems is short lived, and needs to compete with biexcitonic decay. This has necessitated the use of short pulsed lasers to pump quantum dots to thresholds needed for amplified spontaneous emission or lasing. Continuous wave pumping of gain that is possible in some inorganic phosphors has therefore remained a very distant possibility for quantum dots. Here, we demonstrate that trilayer heterostructures could provide optimal conditions for demonstration of continuous wave lasing in colloidal materials. The design considerations for these materials are discussed in terms of a kinetic model. The electronic structure of the proposed dot architectures is modeled within effective mass theory. [ABSTRACT FROM AUTHOR]

We report an efficient synthesis of copper indium sulfide nanocrystals with strong photoluminescence in the visible to near-infrared. This method can produce gram quantities of material with a chemical yield in excess of 90% with minimal solvent waste. The overgrowth of as-prepared nanocrystals with a few monolayers of CdS or ZnS increases the photoluminescence quantum efficiency to> 80%. On the basis of time-resolved spectroscopic studies of core/shell particles, we conclude that the emission is due to an optical transition that couples a quantized electron state to a localized hole state, which is most likely associated with an internal defect. [ABSTRACT FROM AUTHOR]

My aim through this article is to propagate that Pinter has shown the neurotic anxiety, aloneness, identity and about envy in the play The Caretaker. In this play he has tried to show the inner Psyche of a character Davies. Harold Pinter lies in the exploration of the inner world of human psyche and sensibility. He explores the psychological recesses of an individual's quest for life itself, trying, thus to draw the meaning and reason behind the thinking prototype of an individual. He has perfectly treated the complex tracts of human psyche in his play The Caretaker. This play is an instruction in the psyche of people who lose their ability for rational consideration on being subjected to traumatic experiences. The Caretaker is one of Mr. Pinter's most satisfying psychological plays, with the careful combustion of its language and moments of almost deranged humor. [ABSTRACT FROM AUTHOR]

We describe optical switching in solutions of semiconductor nanocrystals illuminated by a 404 nm continuous wave laser source, driven by the formation of a micro-bubble of solvent vapor in the solution. Low boiling solvents such as hexane show an oscillatory modulation of transmitted light intensity (period ∼4 s) while solvents with intermediate boiling points such as toluene give a stable switching response. An on/off ratio of 83% is observed in the transmitted pump beam. Using this, a pump beam (404 nm, 80 mW continuous wave) was shown to reversibly switch the state of a probe laser (630 nm, 5 mW continuous wave). This switch thus serves as an optical analog of an electronic transistor and demonstrates the potential for all optical switching of low power light beams. Further, all optical universal logic gates, NAND and NOR, were also demonstrated using the micro-bubble switch.

We observe and study the anomalous Stokes shift of CuAlS 2 /CdS quantum dots. While all known I-III-VI 2 semiconductor core/shell quantum dots show Stokes shifts in excess of 100 meV, the shift associated with CuAlS 2 /CdS quantum dots is uniquely large, even exceeding 1.4 eV in some cases. CuAlS 2 /CdS quantum dots are thus associated with cross sections less than 10 -17 cm 2 under the emission maximum. We investigate this anomaly using spectroscopic techniques and ascribe it to the existence of a strong type-II offset between CuAlS 2 and CdS layers. Besides their strong Stokes shift, CuAlS 2 /CdS quantum dots also exhibit high quantum yields (63%) as well as long emission lifetimes (∼1500 ns). Because of the combined existence of these properties, CuAlS 2 /CdS quantum dots can act as tunable, transparent emitters over the entire visible spectrum. As a demonstration of their potential, we describe the construction of a wide area transparent lighting device with waveguided optical excitation and a clear aperture of 7.5 cm 2 .

While several potential applications of CuFeS 2 quantum dots have already been reported, doubts regarding their optical and physical properties persist. In particular, it is unclear if the quantum dot material is metallic, a degenerately doped semiconductor, or else an intrinsic semiconductor material. Here we examine the physical properties of CuFeS 2 quantum dots in order to address this issue. Specifically, we study the bump that is observed in the optical spectra of these quantum dots at ∼500 nm. Using a combination of structural and optical characterization methods, ultrafast spectroscopy, as well as electronic structure calculations, we ascertain that the unusual purple color of CuFeS 2 quantum dots as well the golden luster of CuFeS 2 films arise from the existence of a plasmon resonance in these materials. While the presence of free carriers causes this material to resemble gold, surface treatments are also described to suppress the plasmon resonance altogether.

We study the optical properties of copper containing II-VI alloy quantum dots (Cu x Zn y Cd 1-x-y Se). Copper mole fractions within the host are varied from 0.001 to 0.35. No impurity phases are observed over this composition range, and the formation of secondary phases of copper selenide are observed only at x Cu > 0.45. The optical absorption and emission spectra of these materials are observed to be a strong function of x Cu , and provide information regarding composition induced impurity-impurity interactions. In particular, the integrated cross section of optical absorption per copper atom changes sharply (from 1 × 10 -2 nm 3 to 4 × 10 -2 nm 3 ) at x Cu = 0.12, suggesting a composition induced change in local electronic structure. These materials may serve as model systems to understand the electronic structure of I-III-VI 2 semiconductor compounds.

Two initially neutral semiconductor quantum dots with appropriate band offsets can participate in a ground state charge transfer process. The charge transfer manifests itself in the form of bleaching of optical transitions and also causes the quantum dots to precipitate from solution, giving rise to assemblies with unusual properties. As this represents a postsynthetic modification of the electronic structure of quantum dots, it holds tremendous potential for improving the characteristics of quantum dot devices. Here, we study the dependencies of the properties of these assemblies on the structure of the participating quantum dots. In particular, we find that for assemblies formed out of Cu:CdS and ZnTe/CdS quantum dots, the composition of the assembly varies from 1:1.26 to 1:0.23 ZnTe/CdS to Cu:CdS as the shell thickness of CdS in ZnTe/CdS is increased. In contrast, the composition changes from 1:1.1 to 1:15 for PbSe/CdSe and Cu:CdS quantum dots, as the size of the PbSe core is increased. These observations are explained on the basis of a phenomenological thermodynamic model. The applicability of thermodynamics to this example of self-assembly is verified empirically., Competing Interests: The authors declare no competing financial interest.

Dielectric constants of MAPbX 3 (X = Br, I) in the 1 kHz-1 MHz range show strong temperature dependence near room temperature, in contrast to the nearly temperature-independent dielectric constant of CsPbBr 3 . This strong temperature dependence for MAPbX 3 in the tetragonal phase is attributed to the MA + dipoles rotating freely within the probing time scale. This interpretation is supported by ab initio molecular dynamics simulations on MAPbI 3 that establish these dipoles as randomly oriented with a rotational relaxation time scale of ∼7 ps at 300 K. Further, we probe the intriguing possibility of transient polarization of these dipoles following a photoexcitation process with important consequences on the photovoltaic efficiency, using a photoexcitation pump and second harmonic generation efficiency as a probe with delay times spanning 100 fs-1.8 ns. The absence of a second harmonic signal at any delay time rules out the possibility of any transient ferroelectric state under photoexcitation.

We report the synthesis of copper iron sulfide (CuFeS2) quantum dots (QDs). These materials exhibit a tunable band gap that spans the range 0.5-2 eV (600-2500 nm). Although the as-prepared material is nonemissive, CuFeS2/CdS core/shell structures are shown to exhibit quantum yields that exceed 80%. Like other members of the I-III-VI2 family QDs, CuFeS2 based nanoparticles exhibit a long-lived emission that is significantly red-shifted compared to the band gap. CuFeS2 QDs are unique in terms of their composition. In particular, these QDs are the only band-gap-tunable infrared chromophore composed entirely of elements with atomic numbers less than 30.

In view of the continued controversy concerning the polar/nonpolar nature of the hybrid perovskite system, CH3NH3PbI3, we report the first investigation of a time-resolved pump-probe measurement of the second harmonic generation efficiency as well as using its more traditional form as a sensitive probe of the absence/presence of the center of inversion in the system both in its excited and ground states, respectively. Our results clearly show that SHG efficiency, if nonzero, is below the limit of detection, strongly indicative of a nonpolar or centrosymmetric structure. Our results on the same samples, based on temperature dependent single crystal X-ray diffraction and P-E loop measurements, are entirely consistent with the above conclusion of a centrosymmetric structure for this compound in all three phases, namely the high temperature cubic phase, the intermediate temperature tetragonal phase and the low temperature orthorhombic phase. It is important to note that all our experimental probes are volume averaging and performed on bulk materials, suggesting that basic material properties of CH3NH3PbI3 are consistent with a centrosymmetric, nonpolar structure.

Semiconductor quantum dots have replaced conventional inorganic phosphors in numerous applications. Despite their overall successes as emitters, their impact as laser materials has been severely limited. Eliciting stimulated emission from quantum dots requires excitation by intense short pulses of light typically generated using other lasers. In this Letter, we develop a new class of quantum dots that exhibit gain under conditions of extremely low levels of continuous wave illumination. We observe thresholds as low as 74 mW/cm(2) in lasers made from these materials. Due to their strong optical absorption as well as low lasing threshold, these materials could possibly convert light from diffuse, polychromatic sources into a laser beam.

Although semiconductor quantum dots are promising materials for displays and lighting due to their tunable emissions, these materials also suffer from the serious disadvantage of self-absorption of emitted light. The reabsorption of emitted light is a serious loss mechanism in practical situations because most phosphors exhibit subunity quantum yields. Manganese-based phosphors that also exhibit high stability and quantum efficiency do not suffer from this problem but in turn lack emission tunability, seriously affecting their practical utility. Here, we present a class of manganese-doped quantum dot materials, where strain is used to tune the wavelength of the dopant emission, extending the otherwise limited emission tunability over the yellow-orange range for manganese ions to almost the entire visible spectrum covering all colors from blue to red. These new materials thus combine the advantages of both quantum dots and conventional doped phosphors, thereby opening new possibilities for a wide range of applications in the future.

Semiconductor nanocrystals of different formulations have been extensively studied for use in thin-film photovoltaics. Materials used in such devices need to satisfy the stringent requirement of having large absorption cross sections. Hence, type-II semiconductor nanocrystals that are generally considered to be poor light absorbers have largely been ignored. In this article, we show that type-II semiconductor nanocrystals can be tailored to match the light-absorption abilities of other types of nanostructures as well as bulk semiconductors. We synthesize type-II ZnTe/CdS core/shell nanocrystals. This material is found to exhibit a tunable band gap as well as absorption cross sections that are comparable to CdTe. This result has significant implications for thin-film photovoltaics, where the use of type-II nanocrystals instead of pure semiconductors can improve charge separation while also providing a much needed handle to regulate device composition.

Hybrid superstructures allow a convenient route to the development of materials with multiple functionalities (e.g., sensor, marker, conductor) out of monofunctional (e.g., excitonic, plasmonic) building blocks. This work describes a general synthetic route to the preparation of metal|dielectric|quantum dot hybrid superstructures that have excitonic and plasmonic resonances independently tunable from the ultraviolet to the mid-infrared spectral region. We demonstrate that structural tuning can be used to control intercomponent coupling leading to the emergence of unique optical properties. We illustrate this capability by demonstrating single- and multicolor emission from coupled systems, and a significant enhancement of two-photon absorption cross sections of quantum dots. Such properties in a robust yet dispersible particle can be useful in a number of applications including bioimaging and microscopy, and in optoelectronic devices, as well as serve as a platform for fundamental studies of metal-semiconductor interactions.