One-pot synthesis of poly(vinylpyrrolidone)-encapsulated color-emitting silicon quantum dots for sensitive and selective detection of 2,4,6-trinitrophenol

Here, we illustrate an efficient, convenient, and simple method for the sensitive and selective detection of nitro explosive 2,4,6-trinitrophenol (TNP) in 100% water medium by bright cyan-blue color emitting colloidal...

In situ reduction triggers the highly sensitive detection of pesticide by classic gold nanoparticle and quantum dots nanocomposite

Fluorescence "turn on" method is always preferable for target detection under the urgent demand to develop point-of-care portable sensors in practical applications due to its higher selectivity and less false positives. However, there is only few reports of pesticide monitoring based on this strategy so far most probably ascribed to its poor hydrophilicity and reactivity. In this work, triggered by reductant tris (2-carboxyethyl) phosphine hydrochloride (TCEP), initially fluorescence-quenched gold nanoparticles (Au NPs)-decorated quantum dots (QDs)-embedded nanobead shows obvious fluorescence "turn on" signal response to thiram with concentration response range of 0.01-20 μM and limit of detection (LOD) of 7 nM due to the target-induced dissociation of Au NPs from the surface of probe nanobead. Moreover, paper sensor has been successfully developed by immersing commercial drainage membrane in probe solution for visual detection of thiram with the ultrahigh LOD (50 nM) by the naked eye. More importantly, this work, for the first time, reported an in situ reduction strategy to improve the interaction between target and nanoprobe and thus bring obvious signal output for pesticide detection with high sensitivity, demonstrating the potential to expand the detection scope of nanomaterials.

Fabrication of CdS-SBA-15 nanomaterials and their photocatalytic activity for degradation of salicylic acid under visible light

CdS-SBA-15 nanomaterials were synthesized by solvothermal method using cadmium nitrate as cadmium source and thiourea as sulfur source. The properties of as-prepared materials were characterized by means of XRD, FTIR, TEM, XPS, N₂ physisorption, UV-Vis DRS and PL spectra, etc. The results show as-synthesized materials have partially ordered mesoporous structure, larger specific surface area, and higher content of CdS and good crystallinity. The combination of SBA-15 and CdS did almost no reduction in the absorption light range of CdS, but greatly increased the photocapacity of the composite. The synergistic effect of CdS and SBA-15 leads to improving the photocatalytic degradation activity of salicylic acid under visible light. When the photocatalyst was 30 mg (0.75 g/L) and the concentration of salicylic acid was 10 mg/L, the maximum degradation efficiency of salicylic acid was 84.93% after 6 h of light. Photocatalytic reaction has a lower activation energy (2.90 kJ/mol), activation enthalpy (3.13 kJ/mol) and activation entropy (-281.00 J/(mol K)). The photocatalytic mechanism study demonstrates that superoxide radicals (O₂^•-) are the most key active species, e^- and h⁺ have something to do with the photocatalytic reaction, while ·OH has little to do with the photocatalytic reaction. In sum, the protection effect of SBA-15 on CdS nanomaterials makes the composite have a higher photolumination intensity and a higher photocatalytic activity.

Highly Stabilized Gradient Alloy Quantum Dots and Silica Hybrid Nanospheres by Core Double Shells for Photoluminescence Devices

This Letter reports the synthesis approach and application of colloidal suspensions containing gradient alloy quantum dots (QDs) and silica hybrid spheres with improved thermal and photostability, invisible QD aggregation, and high material compatibility. These hybrid nanospheres are characterized by using silica spheres as cores, adsorbing QDs as one shell, and then coating a silica layer as another shell (termed SiO₂-QD-SiO₂). They were synthesized by using Stöber and adsorption methods. The experimental conditions affecting the optical properties were fully investigated. A light-guiding microstructure array (LGMA) was fabricated and tested for photoluminescence demonstration. After accelerated aging tests for 240 h under 85 °C, 40% relative humidity, and 450 nm blue light excitation, the luminance of the SiO₂-QD-SiO₂ LGMA remained stable, which was 1.6 times greater than that of untreated QD samples. This structure with long-term photothermal stability could pave the way for displays or lighting applications.

Al atomistic surface modulation on colloidal gradient quantum dots for high-brightness and stable light-emitting devices

Quantum-dot (QD) light-emitting devices (QLEDs) have been attracting considerable attention owing to the unique properties of process, which can control the emission wavelength by controlling the particle size, narrow emission bandwidth, and high brightness. Although there have been rapid advances in terms of luminance and efficiency improvements, the long-term device stability is limited by the low chemical stability and photostability of the QDs against moisture and air. In this study, we report a simple method, which can for enhance the long-term stability of QLEDs against oxidation by inserting Al into the shells of CdSe/ZnS QDs. The Al coated on the ZnS shell of QDs act as a protective layer with Al₂O₃ owing to photo-oxidation, which can prevents the photodegradation of QD with prolonged irradiation and stabilize the device during a long-term operation. The QLEDs fabricated using CdSe/ZnS/Al QDs exhibited a maximum luminance of 57,580 cd/m² and current efficiency of 5.8 cd/A, which are significantly more than 1.6 times greater than that of CdSe/ZnS QDs. Moreover, the lifetimes of the CdSe/ZnS/Al-QD-based QLEDs were significantly improved owing to the self-passivation at the QD surfaces.

Surface Coating of Gradient Alloy Quantum Dots with Oxide Layer in White-Light-Emitting Diodes for Display Backlights

Recently, quantum dots (QDs) have been successfully developed as efficient color converters for light-emitting diodes (LEDs) display due to excellent optical properties of QDs. Herein, we demonstrate a new approach to form metal oxide layers (or metal oxide coating) on the exterior surface of gradient alloy QDs (the most advanced chemical architecture QDs developed thus far wherein the lattice parameter from the core to shell is changing in a gradient fashion) in order to improve the photochemical stability and photoluminescence efficiency. The resulting CdO-treated QDs are incorporated into polymer matrix films to fabricate a backlight unit as a part of display panel wherein CdO-treated gradient alloy QDs are utilized as color converters upon the blue-LED excitation. The fabricated 9.7 in. iPad 2 tablet liquid crystal display panel exhibited an excellent uniformity in terms of CIE chromaticity, luminance, and bright variation and superb durability test results (maintenance of ca. 110% brightness compared to initial value even after 3 weeks of operation).

Highly luminescent silica-coated CdS/CdSe/CdS nanoparticles with strong chemical robustness and excellent thermal stability

We present facile synthesis of bright CdS/CdSe/CdS@SiO₂ nanoparticles with 72% of quantum yields (QYs) retaining ca 80% of the original QYs. The main innovative point is the utilization of the highly luminescent CdS/CdSe/CdS seed/spherical quantum well/shell (SQW) as silica coating seeds. The significance of inorganic semiconductor shell passivation and structure design of quantum dots (QDs) for obtaining bright QD@SiO₂ is demonstrated by applying silica encapsulation via reverse microemulsion method to three kinds of QDs with different structure: CdSe core and 2 nm CdS shell (CdSe/CdS-thin); CdSe core and 6 nm CdS shell (CdSe/CdS-thick); and CdS core, CdSe intermediate shell and 5 nm CdS outer shell (CdS/CdSe/CdS-SQW). Silica encapsulation inevitably results in lower photoluminescence quantum yield (PL QY) than pristine QDs due to formation of surface defects. However, the retaining ratio of pristine QY is different in the three silica coated samples; for example, CdSe/CdS-thin/SiO₂ shows the lowest retaining ratio (36%) while the retaining ratio of pristine PL QY in CdSe/CdS-thick/SiO₂ and SQW/SiO₂ is over 80% and SQW/SiO₂ shows the highest resulting PL QY. Thick outermost CdS shell isolates the excitons from the defects at surface, making PL QY relatively insensitive to silica encapsulation. The bright SiO₂-coated SQW sample shows robustness against harsh conditions, such as acid etching and thermal annealing. The high luminescence and long-term stability highlights the potential of using the SQW/SiO₂ nanoparticles in bio-labeling or display applications.

Highly efficient Blue-Emitting CdSe-derived Core/Shell Gradient Alloy Quantum Dots with Improved Photoluminescent Quantum Yield and Enhanced Photostability

Highly efficient blue-emitting CdSe-derived core/shell gradient alloy quantum dots (CSGA QDs) with photoluminescence quantum yield (PL QY) of ca. 90% have been synthesized through a facile "one-pot" approach. CdSe nuclei are initially formed as core and gradient alloy shells such as CdSe_xS_1-x/ZnSe_yS_1-y simultaneously encapsulate the preformed CdSe core in an energy-gradient fashion eventually followed by coating with ZnS shells due to the faster precursor reaction kinetics of Cd and Se compared to analog of Zn and S. During the formation of core/shell structure, red-shifting of absorption/emission peaks followed by blue-shifting of analogues were observed due to the intradiffusion of sulfur anion to CdSe luminescent center. In this gradient architecture, interfacial lattice strain can be effectively alleviated, and thus high PL QY (ca. 90%) and enhanced photochemical stability can be achieved. The synthesized blue-emitting gradient alloy QDs with superior optical properties tunable in the range of 450-490 nm can be used for highly efficient blue-emitters and potentially applicable for the fabrication of white-light LEDs.