Distribution Of Quantum Dots Research Articles

Mitochondrial dynamics and mitophagy involved in MPA-capped CdTe quantum dots-induced toxicity in the human liver carcinoma (HepG2) cell line.

Quantum dots (QDs) are nanoparticles of inorganic semiconductors and have great promise in various applications. Many studies have indicated that mitochondria are the main organelles for the distribution and toxic effects of QDs. However, the underlying mechanism of QDs interacting with mitochondria and affecting their function is unknown. Here, we report the mechanism of toxic effects of 3-mercaptopropionic acid (MPA)-capped CdTe QDs on mitochondria. Human liver carcinoma (HepG2) cells were exposed to 25, 50 and 100μmol/L of MPA-capped CdTe QDs. The results indicated that MPA-capped CdTe QDs inhibited HepG2 cell proliferation and increased the extracellular release of LDH in a concentration-dependent manner. Furthermore, MPA-capped CdTe QDs caused reactive oxygen species (ROS) generation and cell damage through intrinsic apoptotic pathway. MPA-capped CdTe QDs can also lead to the destruction of mitochondrial cristae, elevation of intracellular Ca2+ levels, decreased mitochondrial transmembrane potential and ATP production. Finally, we showed that MPA-capped CdTe QDs inhibited mitochondrial fission, mitochondrial inner membrane fusion and mitophagy. Taken together, MPA-capped CdTe QDs induced significant mitochondrial dysfunction, which may be caused by imbalanced mitochondrial fission/fusion and mitophagy inhibition. These findings provide insights into the regulatory mechanisms involved in MPA-capped CdTe QDs-induced mitochondrial dysfunction.

Embedding PbS Quantum Dots (QDs) in Pb-Halide Perovskite Matrices: QD Surface Chemistry and Antisolvent Effects on QD Dispersion and Confinement Properties

Hybrid materials of metal chalcogenide colloidal quantum dots (QDs) embedded in metal halide perovskites (MHPs) have led to composites with synergistic properties. Here, we investigate how QD size, surface chemistry, and MHP film formation methods affect the resulting optoelectronic properties of QD/MHP “dot-in-matrix” systems. We monitor the QD absorption and photoluminescence throughout synthesis, ligand exchange, and transfer into the MHP ink, and we characterize the final QD/MHP films via electron microscopy and transient absorption. In addition, we are the first to globally map how PbS QDs are distributed on the micrometer scale within these dot-in-matrix systems, using three-dimensional (3D) tomography time-of-flight secondary ion mass spectrometry. The surface chemistry imparted during synthesis directly affects the optical properties of the dot-in-matrix composites. Pb-halide passivation leads to QD/MHP dot-in-matrix samples with optical properties that are well-described by a theoretical model, based on a Type I finite-barrier heterostructure between the PbS QD and the MHP matrix. Samples without Pb-halide passivation show complicated size-dependent behavior, indicating a transition from a Type I heterostructure between the PbS QD wells and MHP barriers for small-sized QDs to PbS QDs that are electronically decoupled from the MHP matrix for larger QDs. Furthermore, the choice in perovskite antisolvent crystallization method leads to a difference in the spatial QD distribution within the perovskite matrix, differences in carrier lifetime, and photoluminescence shifts of up to 180 meV for PbS in methylammonium lead iodide. This work establishes an understanding of such emerging synergistic systems relevant for technologies such as photovoltaics, infrared emitters and detectors, and other unexplored technological applications.

Realizing Reduced Imperfections via Quantum Dots Interdiffusion in High Efficiency Perovskite Solar Cells

Realization of reduced ionic (cationic and anionic) defects at the surface and grain boundaries (GBs) of perovskite films is vital to boost the power conversion efficiency of organic-inorganic halide perovskite (OIHP) solar cells. Although numerous strategies have been developed, effective passivation still remains a great challenge due to the complexity and diversity of these defects. Herein, a solid-state interdiffusion process using multi-cation hybrid halide perovskite quantum dots (QDs) is introduced as a strategy to heal the ionic defects at the surface and GBs. It is found that the solid-state interdiffusion process leads to a reduction in OIHP shallow defects. In addition, Cs+ distribution in QDs greatly influences the effectiveness of ionic defect passivation with significant enhancement to all photovoltaic performance characteristics observed on treating the solar cells with Cs0.05 (MA0.17 FA0.83 )0.95 PbBr3 (abbreviated as QDs-Cs5). This enables power conversion efficiency (PCE) exceeding 21% to be achieved with more than 90% of its initial PCE retained on exposure to continuous illumination of more than 550 h.

GaAs/InGaAs heterostructure strain effects on self-assembly of InAs quantum dots

Abstract In this study, the quantum dots (QDs) self-assembly properties were affected by strain modulation. The strain of the GaAs (100) surface was modulated prior to the growth of InAs with the aim to tailor the size and distribution of self-assembled QDs. Changes in the strain fields were achieved with the buried GaAs/InGaAs heterostructure by varying the GaAs layer thickness Σ, which significantly influences several parameters collectively involved in the QDs self-assembly process. In situ characterization of the heterostructure shows that the InAs/GaAs critical thickness and the surface diffusion parameter, the latter of which is an indicative of the QDs density, decreased with Σ. High-resolution X-ray diffraction measurements confirmed that depending on Σ, the InGaAs layer can be partially relaxed, presumably through the introduction of dislocations that are advanced by the QDs strain. Numerical simulations of the heterostructures were performed, with the sample's geometry and other properties obtained from its experimental characterization as input data. The results confirmed variations in strain resulting from changes in the GaAs/InGaAs heterostructure. These findings contribute to the understanding of strain distribution and can thus lead to improvements in the self-assembly properties of InAs QDs.

Growth kinetics and optical properties of PbSe quantum dots in dual-phase lithium-aluminum-silicate glass ceramic

Lead selenide quantum dots (QDs) were precipitated in lithium-aluminum-silicate glass-ceramics. Their optical properties and the crystallization behavior of both glass host and PbSe QDs were investigated. When the glasses heat-treated at 480–520 °C for 10 h, the absorption bands from PbSe QDs were tuned from 1051 to 2016 nm, and the PL bands from 1165 to 2095 nm. Upon the dwelling time 10 h, the crystallization of glass host required relatively higher heating temperature (∼490 °C) than the formation of PbSe QDs (∼480 °C). With the heat treatment at 490 °C for10 h, the PLQY from PbSe QDs in glass-ceramics reached ∼38.7 %. Phase separation induced the glass crystallization and had a significant effect on the distribution of PbSe QDs. To study the growth kinetics of PbSe QDs, the glasses were heat treated at 480 °C and 500 °C for various durations. The average diameters of PbSe QDs (D) showed exponential relationship to the growth time (t), described by the equation D(t)∼ t x. In rapid growth stage, the growth exponents x is ∼0.56 at 480 °C and ∼0.47 at 500 °C, and then decrease to ∼0.13 and ∼0.10, respectively. The formation of a large number of LiAlO2 crystals in glass hindered the diffusion of semiconductor ions, which is the main reason for the decreasing in the growth rate of PbSe QDs.

Stacked Encapsulation Structure for Discretely Distributed Quantum Dot Array

The performances of quantum-dot (QD) based photoluminescent devices are highly restricted by the application environment, especially the moisture and oxygen. However, current external encapsulation structures are not applicable to the devices with discrete QD distribution, especially for some rough profiles. To address this issue, an encapsulation method for discretely distributed quantum-dot arrays (DQDA) is proposed for liquid crystal display (LCD) backlight applications, in which the DQDA can be well fabricated by printing the QD slurry onto a light guiding substrate (LGS), and then covered with a thin UV glue layer and a barrier film. By specially optimizing the UV glue and barrier film, this ultra-thin encapsulation structure cannot only improve the surface defects of the QD morphology without affecting the original light path and the output optical performance, but also significantly suppress the fluorescence decay and isolate moisture and oxygen by almost 100 times compared with unencapsulated one. The water vapor transmission rate (WVTR) was measured to be 1.29 × 10−4 g/m2/day after fabricated the stacked encapsulation structure. After a long period of aging test, the encapsulated sample kept its luminance for 1000 hours. This method also has potential to widely used for discrete structures in other device applications due to its easy fabrication process, high reliability, and low manufacturing costs.

Mechanisms of GaN quantum dot formation during nitridation of Ga droplets

We have examined the formation mechanisms of GaN quantum dots (QDs) via annealing of Ga droplets in a nitrogen flux. We consider the temperature- and substrate-dependence of the size distributions of droplets and QDs, as well as the relative roles of Ga/N diffusivity and GaN nucleation rates on QD formation. We report on two competing mechanisms mediated by Ga surface diffusion, namely, QD formation at or away from pre-existing Ga droplets. We discuss the relative roles of nucleation- and coarsening-dominant growth, as well as zincblende vs wurtzite polytype selection, on various substrates. These insights provide an opportunity for tailoring QD size distributions and polytype selection for a wide range of III-N semiconductor QDs.

Imaging of X-Ray-Excited Emissions from Quantum Dots and Biological Tissue in Whole Mouse

Optical imaging in clinical and preclinical settings can provide a wealth of biological information, particularly when coupled with targetted nanoparticles, but optical scattering and absorption limit the depth and resolution in both animal and human subjects. Two new hybrid approaches are presented, using the penetrating power of X-rays to increase the depth of optical imaging. Foremost, we demonstrate the excitation by X-rays of quantum-dots (QD) emitting in the near-infrared (NIR), using a clinical X-ray system to map the distribution of QDs at depth in whole mouse. We elicit a clear, spatially-resolved NIR signal from deep organs (brain, liver and kidney) with short (1 second) exposures and tolerable radiation doses that will permit future in vivo applications. Furthermore, X-ray-excited endogenous emission is also detected from whole mouse. The use of keV X-rays to excite emission from QDs and tissue represent novel biomedical imaging technologies, and exploit emerging QDs as optical probes for spatial-temporal molecular imaging at greater depth than previously possible.

Laser precipitation of PbS quantum dots in glass rods to achieve broadband near‐infrared emission

AbstractContinuous‐wave laser (λ = 532 nm) was irradiated on Ag+‐exchanged glass surfaces to precipitate PbS quantum dots (QDs) of various diameters. TEM images combined with element mapping results confirmed the formation and size distribution of PbS QDs. Photoluminescence spectra red‐shifted from 1336 nm to 1635 nm with increases in power density and duration of laser irradiation. Three representative irradiation conditions are proposed to realize broadband photoluminescence from one glass rod to cover the 1.3‐1.7 μm communication window.

Correlations between optical properties and Voronoi-cell area of quantum dots

A semiconductor quantum dot (QD) can generate highly indistinguishable single-photons at a high rate. For application in quantum communication and integration in hybrid systems, control of the QD optical properties is essential. Understanding the connection between the optical properties of a QD and the growth process is therefore important. Here, we show for GaAs QDs, grown by infilling droplet-etched nano-holes, that the emission wavelength, the neutral-to-charged exciton splitting, and the diamagnetic shift are strongly correlated with the capture zone-area, an important concept from nucleation theory. We show that the capture-zone model applies to the growth of this system even in the limit of a low QD-density in which atoms diffuse over $\mu$m-distances. The strong correlations between the various QD parameters facilitate preselection of QDs for applications with specific requirements on the QD properties; they also suggest that a spectrally narrowed QD distribution will result if QD growth on a regular lattice can be achieved.

Theoretical study of stress and strain distribution in coupled pyramidal InAs quantum dots embedded in GaAs by finite element method

Stress and strain distributions in and around a single or two-coupled pyramidal InAs quantum dots (QDs) embedded in GaAs are calculated by finite element methods according to the continuum elasticity theory. By changing the quantum dot spacing and thickness of cap layer, the results about strain and stress distributions show compressive strain and stress distribution in the QDs and relaxation undergoes two stages with different speeds for different quantum dot height, quantum width and thickness of cap layer. The stress and strain distributions of pyramidal QDs would not vary monotonously with geometric dimensions. The height of quantum dot and cap layer thickness can effectively adjust the vertical correlation of self-assembly QDs according to the calculation. The shape of stress distribution at surface of cap layer can be tuned from a quadrangle into a circle by increasing the thickness of cap layer or decreasing the height of quantum dot. Also, a new approach to grow quantum ring is found in this paper. The calculations of two-coupled QDs show that the self-assembly technology might fail if the horizontal distance between two QDs is not large enough. The stress induced by upper QDs will be relaxed to zero with a longer distance downwards is found in this paper.

Facile synthesis of molybdenum disulfide (MoS2) quantum dots and its application in humidity sensing

Molybdenum disulfide (MoS2) quantum dots (QDs) are successfully synthesized by facile synthesis using ultrasonication assisted liquid exfoliation technique. The high and low boiling point solvents: N-methyl-pyrrolidone (NMP) and ethanol-water solution have been used for synthesis of MoS2 QDs. Similar size distribution of MoS2 QDs synthesized in two different solvents have been observed from the transmission electron microscopy and average size of these QDs are ∼5 nm. The film of MoS2 QDs is used to fabricate humidity sensor. The large edge to volume ratio and high surface active sites of QDs enhanced the water adsorption even at low humidity environment (<37% RH). The humidity sensing analysis shows that sensing film of MoS2 QDs synthesized in ethanol-water has an average sensitivity of 2.78 MΩ/%RH with fast response time (11 s), good repeatability and high stability. In view of these results, the work is highly applicable to fabricate high performance MoS2 QDs humidity sensor.

Clarifying photoluminescence decay dynamics of self-assembled quantum dots

We studied the temperature-dependent photoluminescence (PL) and time-resolved PL spectra of multilayer CdTe/ZnTe quantum dots (QDs) to understand their carrier dynamics. We demonstrated a method of enhancing the confinement of carriers in CdTe QDs by modulating the number of stacked layers, leading to enhanced acoustic phonons up to 67 μeV and reducing the optical phonon coupling to 20 meV with an average phonon energy of 20 meV. The temperature-dependent decay time could be explained using a simple model of the thermal redistribution of carrier states. Thermal escape from hole states during multiphonon scattering occurred only at high temperatures, whereas blue shifts and enhanced PL intensity were expected to enhance the electron–phonon coupling and confinement-induced mixing among discrete state and continuum states with separation energies of 3.5–7.4 meV. Time-resolved PL measurements probed the electric field screening effect as a function of the strain distribution in QDs and was established to be 2.5 ± 0.2 MV/cm.

The targeting ability of fluorescent quantum dots to the folate receptor rich tumors.

Quantum dots (QDs) bring new insights in cancer theranostics. Exceptional brightness together with the simple possibility to modify surface with targeting molecules make QDs attractive agents in fluorescence guided surgery and photodynamic therapy. Currently, many targeted QDs have been developed for theranostic purpose. However, their targeting ability was tested mainly in two dimensional monolayer tumor cell models, while our study includes 3D tumor model reflecting the specificity of in vivo tumor environment. Core/multilayer shell CdSe/CdS/ZnS QDs were conjugated with folic acid (FA) and characterized spectroscopically. Cytotoxicity of QDs on KB and A549 cells lines were evaluated using the MTT assay. Cellular uptake of QDs was assessed by epifluorescent microscopy. To study the distribution of QDs in tumor tissue, KB spheroids were prepared by means of the liquid overlay technique and then frozen cut of spheroids treated with QDs were imaged by epifluorescence microscopy. We confirmed the specificity of QD-FA for the folic acid receptor positive KB cells. In 3D tumor spheroid model we demonstrated uptake enhancement of QD-FA compared with non-targeted QD. It was demonstrated that penetration profiles were similar for both QDs with penetration depth never exceeding 100 μm. We have demonstrated the effectiveness of FA conjugated QDs to target tumor spheroids thus confirming the crucial role of FRα receptor as a target. Further improvement of QD-FA targeting ability could be performed using dual targeting different targeting agents, such as FA and cyclic RGD.

Interaction of carboxylated CdSe/ZnS quantum dots with fish embryos: Towards understanding of nanoparticles toxicity

Due to colloidal instability even with protective coatings, nanoparticles tend to aggregate in complex environments and possibly interact with biota. In this study, visualization of quantum dots (QDs) interaction with rainbow trout (Oncorhynchus mykiss) embryos was performed. Studies on zebrafish (Danio rerio) and pearl gourami (Trichogaster leerii) embryos have shown that QDs interact with embryos in a general manner and their affects are independent on the type of the embryo. It was demonstrated that carboxylated CdSe/ZnS QDs (4 nM) were aggregating in accumulation media and formed agglomerates on the surface of fish embryos under 1–12 days incubation in deep-well water. Detailed analysis of QDs distribution on fish embryos surface and investigation of the penetration of QDs through embryo's membrane showed that the chorion protects embryos from the penetration through the chorion and the accumulation of nanoparticles inside the embryos. Confocal microscopy and spectroscopy studies on rainbow trout embryos demonstrated that QDs cause chorion damage, due to QDs aggregation on the surface of chorion, even the formation of the agglomerates at the outer part of the embryos and/or with the mucus were detected. Aggregation of QDs and formation of agglomerates on the outer part of the embryo's membrane caused the intervention of the aggregates to the chorion and even partially destroyed the embryo's chorion. The incorporation of QDs in chorion was confirmed by two methods: in living embryos from a 3D reconstruction view, and in slices of embryos from a histology view. The damage of chorion integrity might have adverse effects on embryonic development. Moreover, for the first time the toxic effect of QDs was separated from the heavy metal toxicity, which is most commonly discussed in the literature to the toxicity of the QDs.

Developing Wrinkled Surface to Achieve Low-Cost Photoelectrochemical Biosensor and Study the Interplay between LSPR of Nanoparticles and Semiconductive Quantum Dots

The emergence of photoelectrochemical (PEC) biosensors has opened the door to achieve biosensors with a low limit-of-detection as PEC technique offers reduced background signals 1,2. As a result, researchers are trying to use PEC technique to achieve low-cost and ultrasensitive biosensors. In this work, we proposed a novel method for fabricating flexible, low-cost PEC sensor substrates. Exploiting wrinkled surfaces, we have shown an increase in the photocurrent density of more than 700%. We investigated photocurrent density of CdTe Quantum dots (QD) on top of wrinkled and planar ITO surface. The quality of the substrates has been also verified by measuring sheet resistance and electron mobility. Moreover, these substrates, with an enhanced PEC response, have been used to investigate the interplay between localized surface plasmonic effects (LSPR) and photoactive semiconductor materials using DNA as spacer and gold nanoparticle as plasmonic materials. The wrinkled structure has been achieved by thermally shrinking (heating at 140°C for 5 minutes) pre-stretched PS substrates modified using various surface treatments. RF sputtering technique has been used to deposit ITO on planar and wrinkled PS. The thicknesses of the ITO film used for this study are 50nm and 100nm. Two methods have been used to prepare the wrinkled electrodes. In the first method, thermal shrinking has been done after putting ITO on PS, whereas for other method, PS substrates were cleaned using UV-Ozone (UVO) and then heated to shrink. ITO was sputtered on those shrunk substrates. CdTe QDs have been deposited using the layer-by-layer method. The photocurrent was measured by using chronoamperometry in a three-electrode setup illuminated using an LED excitation source. Scanning electron microscopy (SEM) has been used to visualize the structure of the electrodes. Cross-sectional Transmission electron microscopy (TEM) is used to probe the QD distribution in both planar and wrinkled ITO surface. To investigate the interplay between LSPR of metallic nanoparticles and the photo-activity of semiconductor quantum dots, a material architecture based on a DNA spacer was developed on the optimized wrinkled electrode. The length of DNA spacer was adjusted to tune the distance between the nanoparticles and the QDs. Substrates created by ITO deposition following the shrinking process showed the highest photocurrent density (more than 700% enhancement) among the analyzed samples. SEM images showed that when the substrates were heated after depositing ITO, it tends to break in places, which creates more surface defects, whereas more uniform ITO is obtained if the thin film is applied after wrinkling. TEM images showed much higher QD density on the wrinkled substrate compared to the planar one. By controlling the distance of the QD and Au-NP, the photocurrent can be enhanced or quenched. Quenching of the photocurrent have been observed when longer DNA was used as probe, whereas photocurrent enhancement was achieved by using shorter oligonucleotide. The substrates developed here are ideally suited for enhancing the limit of detection of biosensors. Moreover, this platform has enabled us to study the interaction between plasmonic nanoparticles and photoactive semi-conductive QDs to understand the underlying mechanisms for enhancing or quenching the photocurrent. Devadoss, A., Sudhagar, P., Terashima, C., Nakata, K. & Fujishima, A. Photoelectrochemical biosensors: New insights into promising photoelectrodes and signal amplification strategies. Journal of Photochemistry and Photobiology C: Photochemistry Reviews 24, 43–63 (2015).Fan, G., Han, L., Zhang, J. & Zhu, J. Enhanced Photoelectrochemical Strategy for Ultrasensitive DNA Detection Based on Two Different Sizes of CdTe Quantum Dots Cosensitized TiO 2 /CdS:Mn Hybrid Structure. Analytical Chemistry (2014). doi:10.1021/ac503043w

Molecular-Level Hybridization of Nafion with Quantum Dots for Highly Enhanced Proton Conduction.

Nanophase-separated membranes hold promise for fast molecule or ion transfer. However, development and practical application are significantly hindered by both the difficulty of chemical modification and nanophase instability. This can be addressed by organic-inorganic hybridization of functional fillers with a precise distribution in specific nanophase. Here, a molecular-level hybridization for nanophase-separated Nafion using 2-5 nm quantum dots (QDs) as a new smart filler is demonstrated. Two kinds of QDs are prepared and used: hydrophilic polymer-like QDs (PQDs) and hydrophobic graphene oxide QDs (GQDs). Because of selective interactions, QDs offer advantages of matched structural size and automatic recognition with the nanophase. A distinctive synthesis of subordinate-assembly, in which QDs are driven by the self-assembly of Nafion affinity chains, is reported. This results in a precise distribution of QDs in the ionic, or backbone, nanophases of Nafion. The resulting PQDs in the ionic nanophase significantly increase membrane proton conduction and device output-power without loss of mechanical stability. This is difficult to realize with conventional fillers. The GQDs in the backbone nanophase reduce the crystallinity and significantly augment membrane water uptake and swelling capacities.

Time resolved femtosecond spectroscopy of nanocomposites

Characterization methods of nanocomposites consisted of semiconductor metal-oxide quantum dots (QD) incorporated into a dielectric matrix have been elaborated on the base of time resolved four-wave mixing and photon echo. Large permanent dipole moment, inherent to QDs under study, local field effect, the QD spatial dispersion and distribution function of the transition dipole moments in QDs are taken into account. New responses at multiple frequencies in directions differed from spatial synchronism conditions of well-known signals have been predicted.

CdS QDs-Decorated Self-Doped γ-Bi2MoO6: A Sustainable and Versatile Photocatalyst toward Photoreduction of Cr(VI) and Degradation of Phenol.

In this work, CdS quantum dots (QDs)-sensitized self-doped Bi2MoO6 has been synthesized using glucose as reducing agent by hydrothermal method, followed by in situ deposition of the QDs. The synthesized catalyst has been employed to reduce toxic Cr(VI) and degrade phenol from the aqueous solution. The structural, optical, and electrochemical characterizations are performed using X-ray diffraction, UV–vis diffuse reflection, photoluminescence (PL), scanning electron microscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and electrochemical impedance spectroscopy. The optical properties were precisely investigated by calculating the Urbach energy, PL, and photoluminescence excitation spectra. The orderly distribution of QDs is confirmed from the correlation between full width at half-maximum of PL spectra, Urbach energy, and TEM analysis. The versatile photocatalytic activity has been tested toward Cr(VI) reduction and degradation of phenol. 3% CdS QDs-sensitized self-doped Bi2MoO6 showed highest activity, i.e., 97 and 47.5% toward reduction of Cr(VI) and degradation of phenol under solar light. The reduction of Cr(VI) by the catalyst is supported by the kinetics and determination of the pHPZC value. In addition to this, the photostability and reusability test showed that the catalyst can be reused up to five cycles without diminishing its activity.

Ultrathin GaAsN matrix-induced reduced full width at half maximum of GaAsN/InAs/GaAsN dot-in-a-well heterostructures with extended emission wavelength

We grew InAs quantum dots (QDs) embedded in a GaAs0982N0.018 quantum well—a dot-in-a-well (DWELL) structure—that exhibits emission at wavelengths of up to 1.31µm at 19K and the full width at half maximum (FWHM) of 59meV which are lower those of the InAs/GaAs QDs (1.09µm and 82meV, respectively), the reference sample. Our results can be explained as follows: modified strain field at the GaAsN matrix/InAs QDs due to insertion of ultrathin GaAsN matrix, or nitrogen-induced point defects formed in the ultrathin GaAsN matrix during growth, could promote the homogeneous distribution of InAs QDs on the surface. The GaAsN capping layer evidently enhances the emission wavelength by reducing the overall compressive strain within the QDs. DWELL with ultrathin matrix layer annealed at 800°C exhibited 130-fold improvement in PL intensity, as compared to the as-grown sample, attributed to annihilation of N-related point defects. The results of this study are expected to be useful in fabricating DWELL-based infrared photodetectors with narrow spectral linewidth.