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Micro/nano patterns based on quantum dots (QDs) are of great interest for applications ranging from electronics to photonics to sensing devices for biomedical purposes. Several patterning methods have been developed, but all lack the precision and reproducibility required to fabricate precise, complex patterns of less than one micrometer in size, or require specialized crosslinking ligands, limiting their application. In this study, we present a novel approach to directly pattern QD nanopatterns by electron beam lithography using commercially available colloidal QDs without additional modifications. We have successfully generated reliable dot and line QD patterns with dimensions as small as 140 nm. In addition, we have shown that using a 10 nm SiO2 spacer layer on a 50 nm Au layer substrate can double the fluorescence intensity compared to QDs on the Au layer without SiO2. This method takes advantage of traditional nanolithography without the need for a resist layer.

InP@ZnS core-shell colloidal quantum dots (CQDs) were synthesized and characterized using the z-scan technique. The nonlinear refraction and nonlinear absorption coefficients (γ = −2 × 10−12 cm2 W−1, β = 4 × 10−8 cm W−1) of these CQDs were determined using 10 ns, 532 nm pulses. The saturable absorption (β = −1.4 × 10−9 cm W−1, Isat = 3.7 × 108 W cm−2) in the 3.5 nm CQDs dominated at small intensities of the probe pulses (I ≤ 7 × 107 W cm−2) followed by reverse saturable absorption at higher laser intensities. We report the optical limiting studies using these CQDs showing the suppression of propagated nanosecond radiation in the intensity range of 8 × 107–2 × 109 W cm−2. The role of nonlinear scattering is considered using off-axis z-scan scheme, which demonstrated the insignificant role of this process along the whole range of used intensities of 532 nm pulses. We discuss the thermal nature of the negative nonlinear refraction in the studied species.

Colloidal semiconductor quantum dots are attractive materials for the realization of solution-processable lasers. However, their applications as optical-gain media are complicated by a non-unity degeneracy of band-edge states, because of which multiexcitons are required to achieve the lasing regime. This increases the lasing thresholds and leads to very short optical gain lifetimes limited by nonradiative Auger recombination. Here, we show that these problems can be at least partially resolved by employing not neutral but negatively charged quantum dots. By applying photodoping to specially engineered quantum dots with impeded Auger decay, we demonstrate a considerable reduction of the optical gain threshold due to suppression of ground-state absorption by pre-existing carriers. Moreover, by injecting approximately one electron per dot on average, we achieve a more than twofold reduction in the amplified spontaneous emission threshold, bringing it to the sub-single-exciton level. These measurements indicate the feasibility of ‘zero-threshold’ gain achievable by completely blocking the band-edge state with two electrons. Blocking band-edge absorption of compositionally graded quantum dots with suppressed Auger recombination by pre-existing electrons allows for demonstrating near-zero-threshold optical gain and amplified spontaneous emission at sub-single-exciton pump levels.

A study is presented on improving the absorption of the PbS colloidal quantum dot (CQD) films using plasmonic scattering. Unlike previous methods that include high temperature annealing, an integrated circuits (IC) compatible method of introducing colloidal gold nanoparticles to PbS film during the spin deposition process is developed. The devices are composed of eight layers of PbS and gold nanoparticles are spin cast after the fourth layer that places them in the middle, sandwiched between PbS films in order to avoid electrical shorts between the fingers. Two different solutions of gold nanoparticles in citrate, 0.1% and 0.01%, are used to fabricate two different devices. Introducing 0.01% Au nanoparticles in PbS film increases the responsivity 2.6-fold, whereas introducing 0.1% Au nanoparticles results in a 6.5-fold increase in responsivity.

Lead sulfide (PbS) colloidal quantum dot (CQD) photodiodes integrated with silicon‐based readout integrated circuits (ROICs) offer a promising solution for the next‐generation short‐wave infrared (SWIR) imaging technology. Despite their potential, large‐size CQD photodiodes pose a challenge due to high dark currents resulting from surface states on non‐passivated (100) facets and trap states generated by CQD fusion. In this work, we present a novel approach to address this issue by introducing double‐ended ligands that supplementally passivate (100) facets of halide‐capped large‐size CQDs, leading to suppressed bandtail states and reduced defect concentration. Our results demonstrate that the dark current density is highly suppressed by about an order of magnitude to 9.6 nA cm−2 at −10 mV, which is among the lowest reported for PbS CQD photodiodes. Furthermore, the performance of the photodiodes is exemplary, yielding an external quantum efficiency of 50.8% (which corresponds to a responsivity of 0.532 A W−1) and a specific detectivity of 2.5 × 1012 Jones at 1300 nm. By integrating CQD photodiodes with CMOS ROICs, the CQD imager provides high‐resolution (640 × 512) SWIR imaging for infrared penetration and material discrimination. This work explores the potential of PbS colloidal quantum dots (CQDs) directly integrated with CMOS circuits for high‐resolution short‐wave infrared (SWIR) imaging. By using double‐ended ligands on (100) facets of CQDs, suppression of bandtails and defects is achieved. The prepared CQD photodiodes exhibit excellent performance with low dark current and high responsivity, providing a promising solution for SWIR imaging applications.

Luminescent solar concentrators (LSCs) have attracted significant attention as promising solar energy conversion devices for building integrated photovoltaic (PV) systems due to their simple architecture and cost‐effective fabrication. Conventional LSCs are generally comprised of an optical waveguide slab with embedded emissive species and coupled PV cells. Colloidal semiconductor quantum dots (QDs) have been demonstrated as efficient emissive species for high‐performance LSCs because of their outstanding optical properties including tunable absorption and emission spectra covering the ultraviolet/visible to near‐infrared region, high photoluminescence quantum yield, large absorption cross sections, and considerable photostability. However, current commonly used QDs for high‐performance LSCs consist of highly toxic heavy metals (i.e., cadmium and lead), which are fatal to human health and the environment. In this regard, it is highly desired that heavy metal‐free and environmentally friendly QD‐based LSCs are comprehensively studied. Here, notable advances and developments of LSCs based on unary, binary, and ternary eco‐friendly QDs are presented. The synthetic approaches, optical properties of these eco‐friendly QDs, and consequent device performance of QD‐based LSCs are discussed in detail. A brief outlook pointing out the existing challenges and prospective developments of eco‐friendly QD‐based LSCs is provided, offering guidelines for future device optimizations and commercialization. Luminescent solar concentrators (LSCs) based on unary, binary, and ternary eco‐friendly quantum dots (QDs) are reviewed. The synthetic methods, optical properties of these eco‐friendly QDs, and corresponding LSCs' device parameters (e.g., optical efficiencies) are discussed. A deep insight into eco‐friendly QD‐based LSCs paves the way for future low‐cost, environmentally friendly, and high‐efficiency solar energy conversion devices.

Lead sulfide colloidal quantum dots (PbS CQDs) are promising optoelectronic materials due to their unique properties, such as tunable band gap and strong absorption, which are of immense interest for application in photodetectors and solar cells. However, the tunable band gap of PbS CQDs would only cover visible short-wave infrared; the ability to detect longer wavelengths, such as mid- and long-wave infrared, is limited because they are restricted by the band gap of the bulk material. In this paper, a novel photodetector based on the synergistic effect of PbS CQDs and bismuth telluride (Bi2Te3) was developed for the detection of a mid-wave infrared band at room temperature. The device demonstrated good performance in the visible-near infrared band (i.e., between 660 and 850 nm) with detectivity of 1.6 × 1010 Jones at room temperature. It also exhibited photoelectric response in the mid-wave infrared band (i.e., between 4.6 and 5.1 μm). The facile fabrication process and excellent performance (with a response of up to 5.1 μm) of the hybrid Bi2Te3/PbS CQDS photodetector are highly attractive for many important applications that require high sensitivity and broadband light detection.

Colloidal II–VI nanoplatelets (NPLs) are solution-processable two-dimensional (2D) quantum dots that have vast potential in high-performance optoelectronic applications, including light-emitting diodes, sensors, and lasers. Superior properties, such as ultrapure emission, giant oscillator strength transition, and directional dipoles, have been demonstrated in these NPLs, which can improve the efficiency of light-emitting diodes and lower the threshold of lasers. In this review, we present an overview of the current progress and propose perspectives on the most well-studied II–VI NPLs that are suitable for the optoelectronic applications. We emphasize that the control of the symmetrical shell growth of NPLs is critical for the practical utilization of the advantages of NPLs in these devices.

We study nonclassical features of multiphoton light emitted by clusters of single-photon emitters. As signatures of nonclassicality, we use violation of inequalities for normalized correlation functions of different orders or the probabilities of multiphoton detection. In particular, for clusters of 2-14 colloidal CdSe/CdS dot-in-rods we observe antibunching and nonclassicality of up to the fourth-order. Surprisingly, violation of certain classical inequalities gets even more pronounced for larger clusters.

The surface chemistry of colloidal quantum dots (CQD) play a crucial role in fabricating highly efficient and stable solar cells. However, as‐synthesized PbS CQDs are significantly off‐stoichiometric and contain inhomogeneously distributed S and Pb atoms at the surface, which results in undercharged Pb atoms, dangling bonds of S atoms and uncapped sites, thus causing surface trap states. Moreover, conventional ligand exchange processes cannot efficiently eliminate these undesired atom configurations and defect sites. Here, potassium triiodide (KI3) additives are combined with conventional PbX2 matrix ligands to simultaneously eliminate the undercharged Pb species and dangling S sites via reacting with molecular I2 generated from the reversible reaction KI3 ⇌ I2 + KI. Meanwhile, high surface coverage shells on PbS CQDs are built via PbX2 and KI ligands. The implementation of KI3 additives remarkably suppresses the surface trap states and enhances the device stability due to the surface chemistry optimization. The resultant solar cells achieve the best power convention efficiency of 12.1% and retain 94% of its initial efficiency under 20 h continuous operation in air, while the control devices with KI additive deliver an efficiency of 11.0% and retains 87% of their initial efficiency under the same conditions. Ligand exchange is performed on PbS colloidal quantum dots using conventional PbX2 ligands and KI3 additives via a facile one‐step process, which simultaneously eliminate the undesirable sites and efficiently passivate the surface. The resulting solar cells achieve a power conversion efficiency of 12.1%.