Zinc Oxide Quantum Research Articles

Synthesis and characterization of fluorescent and thermochromic bifunctional composites: Polydiacetylene/zinc oxide quantum dots

Composites of polydiacetylenes (PDA) and zinc oxide (ZnO) find diverse applications in thermochromic inks, colorimetric sensors, and anticounterfeiting, albeit often with complex preparation methods, single functionality, and high color-changing temperature ranges. This study presents environmentally friendly aqueous composites exhibiting dual thermochromic and fluorescent properties, achieved by integrating ZnO quantum dots (QDs) with particle sizes below 10 nm with PDA. By varying the concentration ratio of ZnO QDs to PDA, the effects on fluorescence and thermochromic properties were systematically explored. The interaction between ZnO QDs and PDA interfaces causes alterations to the energy states in the conjugated π-orbital array within PDA molecules. In contrast to pure PDA solutions, the composite materials not only exhibit thermochromism but also fluorescence. Demonstratively, the composite was applied as functional ink or paste for writing, film production, and inkjet printing, maintaining robust thermochromic sensitivity and fluorescence properties in the resulting specimens. This methodology imparts excellent multifunctionality to composite materials, enhancing and broadening their application potential.

Enhancement of Optical Coherence Tomography for Early Diagnostics Through Ag-Decorated ZnO Quantum Dots-Induced Motion Analysis

Optical Coherence Tomography (OCT) stands as a pivotal imaging modality in medical diagnostics, providing intricate insights into microstructural alterations within biological tissues. This research delves into the augmentative impact of nanostructures on OCT, with a specific emphasis on their potential applications in early diagnostic scenarios. The article introduces a novel composite material, Silver-Zinc Oxide (Ag-ZnO) nano-structures, synthesized through the amalgamation of zinc oxide (ZnO) quantum dots and silver (Ag) particles. The study scrutinizes the enhancement effect of these nanostructures on the depth imaging capability and diagnostic precision of OCT. Employing the finite difference time domain method, the research simulates and calculates the extinction spectrum enhancement effect of Ag-ZnO quantum dots in OCT. Comparative analyses are conducted to evaluate the effectiveness and diagnostic accuracy of OCT imaging when enhanced with Ag-ZnO quantum dots against Magnetic Resonance Imaging (MRI) technology. The outcomes manifest a noteworthy improvement in diagnostic accuracy with the integration of Ag-ZnO quantum dots in OCT, underscoring their efficacy in heightening imaging depth and diagnostic precision for early diagnostic applications. This study not only accentuates the pivotal role played by quantum dots in amplifying the capabilities of OCT but also paves the way for the advancement of sophisticated diagnostic tools within the realm of medical imaging.

ZnSe nanoflakes/ ZnO quantum dots heterojunction-based bandgap engineered, flexible broadband photodetector on paper substrate

ZnO-based photodetectors exhibit high responsivity and high photon absorption coefficients. However, they show absorption in a narrow range and a low photogenerated carrier lifetime, limiting their potential applications in optoelectronics. This work demonstrates a high-performance broadband photodetector using Zinc Selenide nanoflakes (ZnSe) - Zinc Oxide (ZnO) quantum dots (QDs) heterojunction. Using a simple hydrothermal method on a flexible paper substrate, this work overcomes the complexity of previously reported fabrication techniques that involve electrospinning, electron beam lithography, spin coating, etc. Detailed chemical and structural characterization reveal the formation of cubic phase of ZnSe nanoflakes-like structure showing broad absorption in the visible region. In contrast, ZnO QDs show a hexagonal structure and absorption in the ultraviolet region, improving the photodetector's detection range. The device shows superior responsivity (Rʎ) of 17.2 µA/W, and 30 µA/W, with specific detectivity (D*) of 4.74×107 Jones, and 9.39×107 Jones, for ultraviolet, and visible, respectively. Detailed studies based on energy band diagrams are performed to understand the charge transport mechanism. The device shows excellent reliability and high stability for 500 bending cycles, thus, presenting a low-cost, facile approach for developing high-performance photodetectors that find utility in wearables, healthcare, and security/defense applications.

Towards bio-safe and easily redispersible bare ZnO quantum dots engineered via organometallic wet-chemical processing

Colloidal quantum dots (QDs) are of widespread importance for their unique combination of physicochemical properties and a number of prospective applications, and the search for efficient synthetic methods to produce readily dispersible, functionally stable and ligand-free quantum dot-based inks is a vital and timely area of research. We describe a convenient room-temperature and non-external-surfactant-assisted organometallic synthetic strategy for the reproducible preparation of solution-processable organic ligand-free zinc oxide (ZnO) QDs. The process involves the controlled transformation of a DMSO solution of commercially available diethylzinc upon exposition towards atmospheric air, where H2O and O2 act simultaneously as oxygen sources, and DMSO acts both as a solvent and a low-molecular-weight l-type surface protector. The resulting QDs with a narrow size distribution (4.7 ± 0.8 nm) were comprehensively characterized with a combination of various analytical techniques, which nicely documented their unique stabilities when dried, precipitated, re-dissolved or exposed to air. Moreover, to substantiate idealized surface passivation of the resulting QDs, we investigated their stability in the biological environment and nano-specific activity toward selected normal and cancer cell lines, and no significant toxic effect was revealed. Undoubtedly, the reported one-step-one-pot organometallic approach paves the way to high-quality and bio-stable ZnO QDs coated by an easily and reversibly removable organic shell, auguring applications in a vast array of devices and nanomedicine.

Down-shifting and antireflective effects of ZnO/PMMA thin films and their influence on silicon solar cells performance

The down-shifting effect of nanostructured II-VI semiconductors like zinc oxide (ZnO) is an attractive feature that can be exploited for the performance enhancement of silicon solar cells. The UV-region of the solar spectrum can be harvested more efficiently by the silicon solar cell after being absorbed by ZnO quantum dots (QDs) and re-emitted in the visible range (centered ⁓510 nm). Additionally, the polymeric matrix (PMMA) used for the fabrication of the ZnO/PMMA thin films can serve as an antireflective layer, enabling a better overall solar radiation absorption. The present study discusses the synthesis and characterization of photoluminescent ZnO QDs and their effect on the performance of in-house-fabricated single crystal silicon solar cells. The down-shifting effect of the colloidal quantum dots was characterized by collecting and analyzing their absorption and photoluminescence spectra. The structural characterization of the obtained ZnO QDs was performed employing X-ray diffraction (XRD) and transmission electronic microscopy (TEM). Before the deployment of the ZnO QDs thin film layers, the optimal thickness of the PMMA matrix was evaluated by ellipsometry seeking the optimal antireflective effect. The performance characteristics of the solar cells before and after the application of the ZnO/PMMA layers were determined from the J-V curves generated in a solar simulator and their spectral response was evaluated by external quantum efficiency (EQE) measurements achieving a maximum relative PCE increase above 19%.

Zinc oxide quantum dots/graphitic carbon nitride nanosheets based visible-light photocatalyst for efficient tetracycline hydrochloride degradation

Zinc oxide quantum dots/graphitic carbon nitride nanosheets based visible-light photocatalyst for efficient tetracycline hydrochloride degradation

Synthesis and Characterization of Polyvinylpyrrolidone-Modified ZnO Quantum Dots and Their In Vitro Photodynamic Tumor Suppressive Action.

Despite the numerous available treatments for cancer, many patients succumb to side effects and reoccurrence. Zinc oxide (ZnO) quantum dots (QDs) are inexpensive inorganic nanomaterials with potential applications in photodynamic therapy. To verify the photoluminescence of ZnO QDs and determine their inhibitory effect on tumors, we synthesized and characterized ZnO QDs modified with polyvinylpyrrolidone. The photoluminescent properties and reactive oxygen species levels of these ZnO/PVP QDs were also measured. Finally, in vitro and in vivo experiments were performed to test their photodynamic therapeutic effects in SW480 cancer cells and female nude mice. Our results indicate that the ZnO QDs had good photoluminescence and exerted an obvious inhibitory effect on SW480 tumor cells. These findings illustrate the potential applications of ZnO QDs in the fields of photoluminescence and photodynamic therapy.

Durable UV-blocking Property of Cotton Fabrics with Nanocomposite Coating Based on Graphene Oxide/ZnO Quantum Dot via Water-based Self-assembly

Yellow emission zinc oxide (ZnO) quantum dots were prepared by hydrolysis of zinc acetate dehydrate and potassium hydroxide in methanol solution. The structure and luminescence of the ZnO nanoparticles were investigated through X-ray diffraction, Fourier transform infrared attenuated total reflection and fluorescence spectrophotometer. The UV-blocking coating was deposited on the surfaces of cotton fabrics by water-based self-assembly between cationized cotton fabrics and ZnO quantum dots as well as graphene oxide. The UV-blocking property of as-coated cotton fabrics was evaluated by UV protection factor (UPF). Even after 20 consecutive launderings, the UPF value of the resultant cotton fabric still reached 57.6, suggesting promising potential as UV protective materials and excellent laundering durability.

A fast-response and transparent solution–processed ultraviolet photodetector based on ZnO quantum–sized nanoparticles

Solution-processed ultraviolet (UV) photodetectors with high performance have great potential in many practical applications. In this paper, quantum-sized zinc oxide (ZnO) nanoparticles (~ 5.5 nm) were synthesized by a simple and low-cost chemical reflux method. The crystalline structure, morphologies, and optical properties of ZnO nanoparticles were investigated in detail. The results showed that the as-synthesized ZnO nanoparticles were wurtzite-structured (hexagonal) ZnO and had specific surface area as high as 68.3 m2/g, the ZnO nanoparticulate thin films had a strong absorption in UV region and optical bandgap of 3.28 eV. Furthermore, an UV photodetector was fabricated using the as-prepared ZnO nanoparticles, the device revealed stable, rapid and repeatable photoresponse towards 365 nm UV light, the sensitivity (S), responsivity (R), rise time (Tr), and decay time (Td) of the photodetector was 11.4 at − 0.25 V, 22.1 A/W at 3 V, 1.8 s and 47.2 s, respectively. In addition, the photoresponsive mechanism of this UV photodetector was systematically illuminated according to the adsorption-photodesorption theory of oxygen in ZnO nanoparticles.

Enhanced green photoluminescence and dispersion of ZnO quantum dots shelled by a silica shell

Zinc oxide (ZnO) quantum dots (QDs) stabilized/functionalized with oleic acid and core-shelled with silicon dioxide (SiO2) are presented. A colloidal route, free surfactant was followed to synthesize ZnO QDs with an average size of 5 nm. After, the ZnO QDs were stabilized with oleic acid to avoid aggregation followed by (3-aminopropyl) trimethoxysilane functionalization. The X-ray diffraction patterns and transmission electron microscopy results indicated that the ZnO QD size and morphology did not suffer any change after functionalization. In addition, the photoluminescence measurements showed a strong green emission band related to particle size and the shell formation. Moreover, the quantum yield and z potential values were determined and the results showed an enhanced for those ZnO@SiO2 samples with 10 wt% of shell precursor. In this research, we report a high relationship between the stability and photoluminescence properties with the shell precursor concentration. Furthermore, we have developed a reliable method to obtain functionalized ZnO QDs which offer a great potential for future use as photoemission devices such as photonics, photocatalytic activities, biomedicine, optoelectronic devices, and chemical sensing.

A solution-processed ZnO quantum dots ultraviolet photodetector with high performance driven by low operating voltage

Solution-processed zinc oxide (ZnO) ultraviolet (UV) photodetector with high performance has great potential in practical applications. In this letter, ZnO quantum dots with diameters ranged in 4–6 nm were synthesized by a facile solution method. The results showed that the as-synthesized quantum dots were wurtzite structured ZnO and had specific surface area as high as 68.3 m2/g. Also, a solution-processed ZnO quantum dots-based ultraviolet photodetector was built. This UV photodetector exhibited a good photoresponse to 365 nm UV light at low operating voltage, under 48 μW/cm2 UV illumination, the responsivity (R), photocurrent gain (G), response time (Tr) and decay time (Td) of the photodetector were 21.6 A/W at 3.6 V, 85.8 at 4.0 V, 1.9 s and 51.1 s, respectively.

Stabilization of ZnO quantum dots by preferred 1:2 interaction with a liquid crystal molecule

Zinc oxide (ZnO) quantum dots were synthesized in the presence of a columnar liquid crystalline perylene derivative. The liquid crystal molecules did not influence the nanoparticles' growth, and surprisingly they were efficient in stabilizing the colloidal dispersion over several months. For the first time, the quantity of ZnO units present in the ~4 nm sized ZnO nanoparticles was determined from the supramolecular interaction between the nanoparticles and the liquid crystal molecules as well as by analyzing the stoichiometry of the mixture. The quantity of ZnO units was also confirmed by theoretical studies performed by means of DFT calculations. The mixture was efficiently applied for methylene blue photodegradation.

ZnO Quantum Dots Induced Oxidative Stress and Apoptosis in HeLa and HEK-293T Cell Lines.

Zinc oxide (ZnO) quantum dot (QD) is a promising inexpensive inorganic nanomaterials, of which potential toxic effects on biological systems and human health should be evaluated before biomedical application. In this study, the cytotoxicity of ZnO QDs was assessed using HeLa cervical cancer cell and HEK-293T human embryonic kidney cell lines. Cell viability was significantly decreased by treatment with 50 µg/ml ZnO QDs after only 6 h, and the cytotoxicity of ZnO QDs was higher in HEK-293T than in HeLa cells. ZnO QDs increased the level of reactive oxygen species and decreased the mitochondria membrane potential in a dose-dependent manner. Several gene expression involved in apoptosis was regulated by ZnO QDs, including bcl-2 gene and caspase. In HeLa cells, ZnO QDs significantly increased early and late apoptosis, but only late apoptosis was affected in HEK-293T cells. These findings will be helpful for future research and application of ZnO QDs in biomedicine.

Predicting the band gap of ZnO quantum dots via supervised machine learning models

Developing mathematical models for zinc oxide (ZnO) nanostructures can significantly accelerate the production of ZnO-based devices and applications. Herein, the implementation of supervised machine learning to predict the optical band gap energy of ZnO is presented. Different models such as Kernel Ridge Regression (KRR) and Artificial Neural Network (ANN) were trained with empirical features, including experimental time and temperature conditions during ZnO fabrication. Test results revealed high accuracy of the models (KRR with quadratic features), with root mean squared error = 0.0849 eV, and mean absolute error percentage = 1.7328 %. These results show the capabilities of machine learning models for automated prediction of semiconductor properties, which can be used to accelerate materials design and applications.

Carrier transport improvement in ZnO/MgZnO multiple-quantum-well ultraviolet light-emitting diodes by energy band modification on MgZnO barriers

Ultraviolet (UV) light-emitting diodes (LEDs) based on zinc oxide (ZnO) materials have been the subject of many investigations because of their potential applications. In this study, ZnO/MgZnO multiple-quantum-well UV LEDs with graded-composition barriers were developed and numerically analyzed. The simulation results demonstrate that an optimized LED with a Mg composition graded from 24% to 2% in each triangular barrier exhibits the highest internal quantum efficiency (IQE) (88.0%) at 200 A/cm2, showing a 31.3% increase compared with the conventional LED with square barriers. This enhancement is attributed to the modified energy band structures that improve the symmetry in carrier transportation and increase the radiative recombination rate in each ZnO quantum well, thus enhancing the IQE of the device. Additionally, the different band-offset ratios of the MgZnO/ZnO and InGaN/GaN heterojunctions, which lead to the different carrier transport and electroluminescence properties of the ZnO- and GaN-based LEDs, were discussed here, providing researchers new insights into device design of ZnO-based LEDs.

Fabrication and characterization of a ZnO quantum dots-based metal–semiconductor–metal sensor for hydrogen gas

This paper reports an interdigitated metal–semiconductor–metal (MSM) based hydrogen gas (H2) sensor using colloidal zinc oxide (ZnO) quantum dots (QDs) as the sensing material. The active layer is obtained by spin coating of as-synthesized colloidal ZnO QDs on a SiO2/Si substrate in which the SiO2 layer is grown by oxidation of the Si substrate. The surface morphology of a ZnO QDs -based active film is measured using scanning electron microscopy (SEM) and atomic force microscopy (AFM) support for enhanced gas response. The change in current is measured for different concentrations of H2 gas at 175 °C in an ambient air atmosphere. Reasonably good gas responses of ∼41% for 1% H2 gas and 83.2% for 4% H2 gas have been obtained in ambient air condition. A high selectivity of the proposed sensor with respect to ammonia, sulfur dioxide and organic vapours such as acetone, methanol, chlorobenzene, and chloroform has also been achieved due to nanostructure ZnO films.

Fluorescent ZnO quantum dots synthesized with urea for the selective detection of Cr6+ ion in water with a wide range of concentrations

Nearly monodisperse Zinc oxide (ZnO) quantum dots (QDs) displayed yellow fluorescence were synthesized using urea as dispersant. In this paper, urea-ZnO QDs were used as fluorescent probe to detect Cr6+ in solution. The emission from the as-synthesized urea-ZnO QDs is selectively quenched when Cr6+ ions were added. Moreover, there are two linear relationships between the quenching of fluorescence intensity and the Cr6+ concentrations ranging from 4 μM to 1000 μM, with the detection limit for Cr6+ at 19.53 nM (on basis of 3σ/slope criterion). The quenching of fluorescence is attributed to aggregation of the QDs and charge transfer between the QDs and Cr6+ by measurements of transmission electron microscopy (TEM) images, UV–visible absorption spectra and fluorescence lifetime.

Optical and structural properties of zinc oxide nanocrystalline

Zinc oxide (ZnO) is a wide band gap (~3.37 eV) semiconductor. Thin film ZnO has many attractive applications in optoelectronics and sensors. Recently, nanostructured ZnO (e.g. ZnO quantum dot) has been demonstrated as a hyperbolic material; its dielectric function has opposite signs along different crystal axes within the mid-infrared, making it an interesting material for metamaterials and nanophotonics. Conventional sputtering deposition usually leads to the formation of polycrystalline ZnO films with randomly oriented grains and rough surface. This work demonstrated a solution-based process to grow ZnO thin films with highly oriented nanocrystals. Low-temperature plasmas were employed to modulate the microstructure and optical properties of the films. Such highly anisotropic nanostructured transparent semiconductor films may lead to interesting material properties in developing new optoelectronic devices.

Enhanced brightness of methylammonium lead tribromide perovskite microcrystal-based green light-emitting diodes by adding hydrophilic polyvinylpyrrolidone with oleic acid-modified ZnO quantum dot electron transporting layer

In designing highly efficient perovskite light-emitting diodes (PeLEDs), the most significant process is to deposit perovskite film without pinholes and vacancies because discontinuous film results in high leakage current. To fabricate a continuous methylammonium lead tribromide (MAPbBr3) film, a hydrophilic polymer, polyvinylpyrrolidone (PVP), was added to the MAPbBr3 precursor solution. Due to the increased wettability of the precursor solution, a full surface coverage of MAPbBr3-PVP composite film without pinholes was produced. Moreover, zinc oxide (ZnO) quantum dot (QD) was synthesized by hydrothermal process in order to use as an electron transporting layer (ETL), and surface modification of QD was performed by oleic acid (OA) molecules in order to increase spatial distribution in the anti-solvent of perovskite. It was found that, due to the reduced agglomeration of QDs during a spin-coating process, a smooth and highly transparent OA-modified ZnO (OA-ZnO) QD layer was obtained. Thus, the PeLED prepared by using MAPbBr3-PVP composite film and OA-ZnO QD layer exhibited an excellent device performance of a maximum luminance of 11095.1 cd m−2 at 6 V and a maximum current efficiency of 6.79 cd A−1 at 4 V. Therefore, it is believed that adding PVP to perovskite materials and using OA-ZnO QD layer as an ETL are effective way to develop perovskite-based high performance LEDs.

Zinc oxide end-capped Fe3O4@mSiO2 core-shell nanocarriers as targeted and responsive drug delivery system for chemo-/ions synergistic therapeutics

Multifunctional core-shell nanocarriers based on zinc oxide (ZnO)-gated magnetic mesoporous silica nanoparticles (MMSN) were prepared for cancer treatment through magnetic targeting and pH-triggered controlled drug release. Under an external magnetic field, the MMSN could actively deliver chemotherapeutic agent, daunomycin (DNM), to the targeted sites. At neutral aqueous, the functionalized MMSN could stably accommodate the DNM molecules since the mesopores were capped by the ZnO gatekeepers. In contrast, at the acid intercellular environment, the gatekeepers would be removed to control the release of drugs due to the dissolution of ZnO. Meanwhile, ZnO quantum dots not only rapidly dissolve in an acidic condition of cancer cells but also enhance the anti-cancer effect of Zn2+. An in vitro controlled release proliferation indicated that the acid sensitive ZnO gatekeepers showed well response by the ‘on-off’ switch of the pores. Cellular experiments against cervical cancer cell (HeLa cells) further showed that functionalized MMSN significantly suppressed cancer cells growth through synergistic effects between the chemotherapy and Zn2+ ions with monitoring the treatment process. These results suggested that the ZnO-gated MMSN platform is a promising approach to serve as a pH-sensitive system for chemotherapies delivery and Zn2+ controlled release for further application in the treatment of various cancers by synergistic effects.