We report on a temperature-, time-, and spectrally resolved study of the photoluminescence of type-I InP/ZnS colloidal nanocrystals with varying core size. By studying the exciton recombination ...dynamics we assess the exciton fine structure in these systems. In addition to the typical bright–dark doublet, the photoluminescence stems from an upper bright state in spite of its large energy splitting (∼100 meV). This striking observation results from dramatically lengthened thermalization processes among the fine structure levels and points to optical-phonon bottleneck effects in InP/ZnS nanocrystals. Furthermore, our data show that the radiative recombination of the dark exciton scales linearly with the bright–dark energy splitting for CdSe and InP nanocrystals. This finding strongly suggests a universal dangling bonds-assisted recombination of the dark exciton in colloidal nanostructures.
By careful engineering of the core and shell dimensions in CdSe/CdS colloidal hetero‐nanocrystals, amplified spontaneous emission can be triggered from either the core, shell, or both states ...simultaneously. The ASE threshold is almost constant over a temperature interval of 5–325 K. This feature is unique to quantum dots and highlights their potential as a gain material, suitable for lasing at elevated temperatures.
The paper describes all stages of synthesis and characterization of biocompatible CdSe-based core/shell quantum dots (QDs) and their application as fluorescent label for immunoassay. Special ...attention was focused on development of maleic anhydride-based amphiphilic polymers for QDs solubilization in aqueous media. In this work two PEG-amines were tried for polymer modification: monoamine Jeffamine M 1000 used previously in some researches and diamine Jeffamine ED-2003 applied for the first time for QDs solubilization. The use of different Jeffamines allows us to obtain QDs with carboxyl or amine functional groups available for conjugation. The influence of polymer composition on optical properties of the nanocrystals and their stability in aqueous solutions as well as on their conjugation with biomolecules was studied. QDs with different coatings were used as biolabels in quantitative fluorescence microtiter plate immunoassay and qualitative on-site column test. It was found that quantum dots covered with amphiphilic polymer prepared from poly(maleic anhydride-alt-1-octadecene) and Jeffamine ED-2003 retained up to 90% of their initial brightness, easily conjugated with protein and showed low non-specific adsorption. In optimized conditions the obtained QDs were successfully used for determination of mycotoxin deoxynivalenol in wheat and maize samples by fluorescence microtiter plate immunoassay with an IC50 of 220 μg kg(-1) and by on-site column test with cut-off of 500 μg kg(-1).
This work reports on ABA triblock copolymer microparticles encoded with CdSe/CdS core–shell quantum dots (QDs) realized by electrospraying. This method allows for simple but efficient embedding of ...QDs in polymer beads while retaining the fluorescent properties of the original QDs. The creation of poly(styrene‐ethylene‐butylene‐styrene) (SEBS) monodisperse spherical microparticles with a tunable morphology for applications of the final QD‐loaded product is attainable via solvent variation. By varying the selectivity of the solvent for one of the distinct blocks in the polymer, the final particle morphology can be selectively altered while maintaining the same overall process conditions, allowing to tailor the particles from homogeneously flat in a nonselective solvent to dense spherical particles in an endblock selective solvent system. The mechanism responsible for this transition in morphology can be related to differences in mass transfer in the droplets and thus solvent evaporation rates arising from particular microphase structures. Finally, fluorescence characteristics of the final QD‐embedded polymer particles and photodegradation stability are investigated by spectrophotometry and are compared to the temporal evolution of the original QDs, indicating significant stability improvement and well‐dispersed QDs in an optimized polymer matrix morphology.
Embedding of quantum dots (QDs) in polymer particles can improve various undesirable properties such as poor biocompatibility and cytotoxicity for in vivo and in vitro applications. Electrospraying of poly(styrene‐ethylene‐butylene‐styrene) proves to be an excellent technique to achieve well‐dispersed QD‐encoded polymer particles with a tunable particle morphology from dense spherical to uniformly flat depending on the utilized solvent system.
The absorption cross section of colloidal quantum dots in close-packed monolayers shows a 4 (CdSe) to 5-fold (PbS) enhancement compared to quantum dots in a dilute dispersion. Quantitative agreement ...is demonstrated between the value and the size dependence of the enhancement and theoretical model predictions based on dipolar coupling between neighboring quantum dots. This collective optical behavior offers a new degree of freedom in the custom design of optical properties for electro-optical devices.
We determine the optical properties of PbS/CdS core/shell QDs, addressing the energy and the oscillator strength of the first exciton transition and the intrinsic absorption coefficient at short ...wavelengths. It follows that the intrinsic absorption coefficient at wavelengths of 350 and 400 nm agrees with theoretical numbers predicted using the Maxwell–Garnett model. Moreover, close correspondence is demonstrated between the energy and the oscillator strength of the first exciton transition of PbS/CdS core/shell and PbS QDs with a similar core size. This provides a straightforward way to estimate the PbS core diameter in PbS/CdS core/shell quantum dots by means of the PbS sizing curve, and it indicates that PbS/CdS QDs exhibit a type 1 band alignment.
We report on the synthesis of luminescent CdSe/CdS@SiO2 nanoparticles and their application to cell labeling. The main novelty of these nanoparticles is the use of newly developed “flash” CdSe/CdS ...quantum dots (QDs), which are obtained through a new fast and efficient synthesis method recently reported. These core–shell QDs are encapsulated in silica nanoparticles through a water-in-oil microemulsion process, resulting in CdSe/CdS@SiO2 nanoparticles with good morphology and controlled architecture. The main asset of these luminescent nanoparticles is their high photoluminescent quantum yield, which is equal to that of the original CdSe/CdS QDs and remains unchanged even after several months of storage in water. Thanks to the remarkable stability of their optical property in aqueous environment and to their low levels of toxicity, the high potential of these nanoparticles for long-term cell labeling is demonstrated.
We report on the synthesis of core–shell CuInS2/ZnS quantum dots (QDs) in organic solution, their encapsulation with a PEG-containing amphiphilic polymer, and the application of the resulting ...water-soluble QDs as fluorescent label in quantitative immunoassay. By optimizing the methods for core synthesis and shell growth, CuInS2/ZnS QDs were obtained with a quantum yield of 50% on average after hydrophilization. After conjugation with an aflatoxin B1-protein derivative, the obtained QDs were used as fluorescent labels in microplate immunoassay for the quantitative determination of the mycotoxin aflatoxin B1. QDs-based immunoassay showed higher sensitivity compared to enzyme-based immunoassay.
Imaging in the infrared wavelength range has been fundamental in scientific, military and surveillance applications. Currently, it is a crucial enabler of new industries such as autonomous mobility ...(for obstacle detection), augmented reality (for eye tracking) and biometrics. Ubiquitous deployment of infrared cameras (on a scale similar to visible cameras) is however prevented by high manufacturing cost and low resolution related to the need of using image sensors based on flip-chip hybridization. One way to enable monolithic integration is by replacing expensive, small-scale III-V-based detector chips with narrow bandgap thin-films compatible with 8- and 12-inch full-wafer processing. This work describes a CMOS-compatible pixel stack based on lead sulfide quantum dots (PbS QD) with tunable absorption peak. Photodiode with a 150-nm thick absorber in an inverted architecture shows dark current of 10
A/cm² at -2 V reverse bias and EQE above 20% at 1440 nm wavelength. Optical modeling for top illumination architecture can improve the contact transparency to 70%. Additional cooling (193 K) can improve the sensitivity to 60 dB. This stack can be integrated on a CMOS ROIC, enabling order-of-magnitude cost reduction for infrared sensors.
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