Lead Sulfide Quantum Dots Research Articles

Highly Photosensitive Vertical Phototransistors Based on a Poly(3-hexylthiophene) and PbS Quantum Dot Layered Heterojunction

We fabricated a vertical field effect phototransistor with Au/Ag nanowires as the transparent source electrode and with vertically stacked layers of poly(3-hexylthiophene) (120 nm) and lead sulfide quantum dots (380 nm), which formed heterojunctions. The built-in electric field in the layered heterojunction aids the separation of photoinduced excitons, while the short channel enables efficient carrier transport across the active region. Both of these benefits enable a high photoperformance and fast photoresponse. This vertical phototransistor can be operated at room temperature with a low operation voltage of −1 V and is therefore energy-efficient. Further, it has a wide response spectrum from 400 to 2100 nm, a high photoresponsivity of more than 9 × 104 AW–1, and a high detectivity of up to 2 × 1013 Jones (cm Hz1/2 W–1) under infrared illumination. Additionally, this vertical phototransistor had a response time of 9 ms, which is faster than a previously reported lateral field effect phototransistor based...

Effect of heat treatment on absorption and fluorescence properties of PbS-doped silica optical fibre

The effect of heat treatment on the optical properties of a PbS-doped silica optical fibre was investigated. The experimental results showed that the absorption peak of the fibre red shifted from 1032 to 1133 nm when the heat treatment temperatures were carried out at 900, 950, 1000, and 1100 °C for 1 h, respectively. At the same time, when the heat treatment at 900 °C was carried out for 2, 5, 10, 20, and 40 h, the absorption spectra of the fibre showed a red shift from 1074 to 1143 nm. In addition, the intensity of the absorption peak increased from 0.258 to 1.384 dB/m and the full width at half maximum (FWHM) became narrower (from 130 to 50 nm) as the heat treatment proceeded. Moreover, the photoluminescence (PL) intensity in the wavelength range of 1100–1500 nm decreased with an increase in the heat treatment temperature. The theoretical analysis, using an effective mass method, showed that the effective band gap energy and average size of the lead sulphide (PbS) quantum dots (QDs) in the silica fibre core varied from 1.199 to 1.083 eV and from 4.28 to 4.81 nm, respectively. The results indicate that the size of the PbS QDs present in the silica fibre core could be controlled by a proper heat treatment, which is of great interest in optical fibre amplifiers and other fibre optic devices.

Difference in hot carrier cooling rate between Langmuir-Blodgett and drop cast PbS QD films due to strong electron-phonon coupling.

The carrier dynamics of lead sulphide quantum dot (PbS QD) drop cast films and closely packed ordered Langmuir-Blodgett films are studied with ultra-fast femtosecond transient absorption spectroscopy. The photo-induced carrier temperature is extracted from transient absorption spectra and monitored as a function of time delay. The cooling dynamics of carriers in PbS QDs suggest a reduction of the carrier energy loss rate at longer time delays through the retardation of the longitudinal optical (LO) phonon decay due to partial heating of acoustic phonon modes. A slowed hot carrier cooling time up to 116 ps is observed in the drop cast film. A faster cooling rate was also observed in the highly compact Langmuir-Blodgett film due to the enhanced carrier-LO phonon coupling strength arising from the Coulombic interaction in neighboring QDs, which is verified by temperature dependent steady state PL measurements.

Red green blue emissive lead sulfide quantum dots: heterogeneous synthesis and applications.

Visible emission colloidal quantum dots (QDs) have shown promise in optical and optoelectronic applications. These QDs are typically composed of relatively expensive elements in the form of indium, cadmium, and gallium since alternative candidate materials exhibiting similar properties are yet to be realized. Herein, for the first time, we report red green blue (RGB) photoluminescences with quantum yields of 18% from earth-abundant lead sulfide (PbS) QDs. The visible emissive property is mainly attributed to a high degree of crystallinity even for the extremely small QD sizes (1-3 nm), which is realized by employing a heterogeneous reaction methodology at high growth temperatures (>170 °C). We demonstrate that the proposed heterogeneous synthetic method can be extended to the synthesis of other metal chalcogenide QDs, such as zinc sulfide and zinc selenide, which are promising for future industrial applications. More importantly, benefiting from the enlarged band gaps, the as-prepared PbS solar cells show an impressive open circuit voltage (∼0.8 V) beyond that reported to date.

Formation of channels containing lead sulfide quantum dots using continuous-wave laser for active planar waveguides in glasses

PbS quantum dots (QDs) and channels containing QDs were fabricated by irradiation with a continuous-wave (cw) laser at λ = 532 nm. Channels with diameters of 36 ~52 μm were formed by scanning with the laser at 6-8 μm•s−1. Photoluminescence centered at λ = 1290 nm was recorded. Precipitation of PbS QDs inside glasses increased their refractive indices by as much as ~0.002. These channels are expected to provide active waveguides that operate in telecommunication windows once the diameters of PbS QDs can be controlled precisely.

The influence of silver ion exchange on the formation and luminescent properties of lead sulfide molecular clusters and quantum dots

PbS molecular clusters and quantum dots are formed by heat treatment in fluorophosphate glasses of the Na2O3–Р2O5–Ga2O3–AlF3–ZnO(S)–PbF2 system with different lead concentrations. PbS molecular clusters are characterized by optical absorption in the range of 300–800 nm and low quantum yields, which decrease from 8.9 to 2.7% with a semiconductor component concentration. It is shown that the parameters of formation of quantum dots luminescing in the wavelength range of 1000–1500 nm are considerably different at different semiconductor component concentrations. The influence of silver ion exchange on the formation of PbS nanoparticles is studied. Introduction of silver stimulates the growth of molecular clusters, which is seen in the absorption spectra. A possible mechanism of interaction of silver nanoparticles with PbS quantum dots is presented.

Versatile PbS Quantum Dot Ligand Exchange Systems in the Presence of Pb-Thiolates.

A robust solution phase ligand exchange system for lead sulfide (PbS) quantum dots (QDs) in the presence of Pb-thiolate ligands is presented that can better preserve the excitonic absorption and emission features as compared to the conventional ligands. The photoluminescence after ligand exchange of PbS QDs with Pb-thiolate ligand is preserved up to 78% of the original oleate capped PbS QDs.

Ligand-Dependent Morphology and Optical Properties of Lead Sulfide Quantum Dot Superlattices

Small angle X-ray scattering, atomic force microscopy, optical microscopy, and absorption and luminescence spectroscopy have shown that the type and amount of surface organic ligands have a strong impact on the morphology and optical properties of 2D superlattices formed by lead sulfide quantum dots (QDs) of different sizes deposited on a glass substrate. This allows control of the process of QD self-assembly, the homogeneity of the superlattices, and the interparticle distance by optimization of the amount of surface ligands. It has been found that annealing and aging also influence the stability of the structural and optical properties of the superlattices.

Highly Monodispersed PbS Quantum Dots for Outstanding Cascaded-Junction Solar Cells.

High-performance cascaded-junction quantum dot solar cells (CJQDSCs) are fabricated from as-prepared highly monodispersed lead sulfide QDs. The cells have a high power conversion of 9.05% and a short-circuit current density of 32.51 mA cm–2. A reliable and effective stratagem for fabricating high-quality lead sulfide quantum dots (QD) is explored through a “monomer” concentration-controlled experiment. Robust QDSC performances with different band gaps are demonstrated from the as-proposed synthesis and processing stratagems. Various potential CJQDSCs can be envisioned from the band edge evolution of the QDs as a function of size and ligands reported here.

Quantum dot solar cells hit record efficiency

Researchers led by Edward H. (Ted) Sargent of the University of Toronto have built the first colloidal quantum dot solar cells certified to convert sunlight into electricity with greater than 10% power conversion efficiency (Nano Lett. 2016, DOI: 10.1021/acs.nanolett.6b01957). Although quantum dots have played a role in solar cells with efficiencies better than 11%, the nanoscopic spheres in those cases are used only as a light-absorbing material, says Oleksandr Voznyy, a researcher in Sargent’s group. The new cells use thin films of lead sulfide quantum dots deposited from solution as light-sensitive layers that also conduct electric charges between electrodes. Using these multitasking quantum dots unlocks simpler design approaches for this brand of solar cell, but the team will need to continue improving the efficiency to compete with or complement other promising materials, such as perovskites, Voznyy says. To beat the 10% benchmark, the researchers tweaked the surface chemistry of their

Recycled Synthesis of Whey-Protein-Capped Lead Sulfide Quantum Dots as the Second Near-Infrared Reporter for Bioimaging Application

Owing to their high emission intensity and size-based tunability, lead sulfide (PbS) quantum dots (QDs) have been employed in a broad spectrum of biological applications especially for the second near-infrared (NIR-II) biological imaging. However, the toxicity of Pb2+ ions remains an unavoidable risk factor during both preparation and biological applications. Here, we have developed an economical and environmentally friendly synthetic route with a recycle setup to prepare whey-protein-capped PbS QDs. Furthermore, the final Pb2+ ions were allowed to react with excess S2– ions and produce nontoxic precipitate in the end, which helped to avoid polluting the environment. After surface modification with protein, both our prepared QDs and the final reaction wastes demonstrated low toxicity in following both in vitro and in vivo experiments. Notably, the conversion efficiency of Pb2+ ions into PbS QDs in this study was almost 3 times than that of a one-time reaction without recycle. In addition, each batch of as...

Highly Fluorescent Ribonuclease-A-Encapsulated Lead Sulfide Quantum Dots for Ultrasensitive Fluorescence in Vivo Imaging in the Second Near-Infrared Window

Ribonuclease-A (RNase-A) encapsulated PbS quantum dots (RNase-A@PbS Qdots) which emit in the second near-infrared biological window (NIR-II, ca. 1000–1400 nm) are rapidly synthesized under microwave heating. Photoluminescence (PL) spectra of the Qdots can be tuned across the entire NIR-II range by simply controlling synthesis temperature. The size and morphology of the Qdots are examined by transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS). Quantum yield (Φf) measurement confirms that the prepared Qdots are one of the brightest water-soluble NIR-II emitters for in vivo imaging. Their high Φf (∼17.3%) and peak emission at ∼1300 nm ensure deep optical penetration to muscle tissues (up to 1.5 cm) and excellent imaging contrast at an extremely low threshold dose of ∼5.2 pmol (∼1 μg) per mouse. Importantly, this protein coated Qdot displays no signs of toxicity toward model neuron, normal, and cancer cells in vitro. In addition, the animal’s metabolism results in thorough elimination of intravenously injected Qdots from the body within several days via the reticuloendothelial system (RES), which minimizes potential long-term toxicity in vivo from possible release of lead content. With a combination of attractive properties of high brightness, robust photostability, and excellent biocompatibility, this new NIR-II emitting Qdot is highly promising in accurate disease screening and diagnostic applications.

PbS Quantum Dots Sensitized TiO2 Solar Cells Prepared by Successive Ionic Layer Absorption and Reaction with Different Adsorption Layers.

Lead sulfide (PbS) quantum dots (QDs) have been synthesized via successive ionic layer adsorption and reaction (SILAR) on a titanium dioxide (TiO2) nanoporous film for the fabrication of quantum dot-sensitized solar cells (QDSCs). The reaction is environmental friendly and energy saving. The green synthesized PbS QDs match the maximum remittance region of the solar spectrum and are suitable as sensitizers for TiO2 electrodes for cell devices application. PbS QDs were adsorbed in different adsorption layers in order to improve the solar cell performance. The optical properties of PbS sensitized TiO2 films were studied by scanning electron microscopy and UV-Vis absorbance spectroscopy. The photovoltaic characteristics of the PbS QDSCs were analyzed by I-V characteristics and electrochemical impedance spectroscopy. As a result, the light harvesting was enhanced with increasing SILAR adsorption layers. The maximum photovoltaic conversion efficiency of the PbS QDSCs (3.14%) was obtained at the 12 adsorption layers with the highest short circuit current density and lowest charge transfer resistance.

Influence of interparticle electronic coupling on the temperature and size dependent optical properties of lead sulfide quantum dot thin films

We report on the quantum dot (QD) size, temperature, and inter-dot coupling dependence on the optical absorption and emission for PbS QD thin films. Inter-dot coupling is induced by ligand exchange from oleic acid to 1,2-ethanedithiol, and the expected band gap red-shift observed for coupled QD thin films is accompanied by a modification to the temperature-dependence of the band gap energy. The amplitude and temperature dependence of the photoluminescence (PL) Stokes shift support recombination via a mid-gap state and also indicate that the application of band gap-specific models to fit the temperature dependence PL peak energy is inadequate. Electronically coupled QD thin films show PL quenching with decreasing temperature, following a Boltzmann model which is consistent with thermally activated carrier transport. Enhancing the inter-dot coupling results in the dynamic PL decay signal changing from single- to bi-exponential behavior, reveals a size-dependent transport activation energy, and yields a negative temperature dependent band gap energy for the smallest QD diameters.

Work-Function Engineering in Lead Sulfide and Cadmium Sulfide Quantum Dots incorporated into Zeolite Y using Ion Exchange

The work function is a key property that should be considered to enhance the performance of quantum-dot (QD) applications. Here, the ability to effectively control the work-function value of zeolite-encapsulated PbS and CdS QDs by choosing the type of cation in the framework is reported. This study will provide new insight for developing applications of the QD-zeolite composites. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Simple Molecular Reactive Force Field for Metal-Organic Synthesis.

For colloidal quantum dots to transition from research laboratories to deployment as optical and electronic products, there will be a need to scale-up their production to large-scale manufacturing processes. This demand increases the need to understand their formation via a molecular representation of the nucleation of lead sulfide (PbS) quantum dot systems passivated by lead oleate complexes. We demonstrate the effectiveness of a new type of reactive potential, custom-made for this system, that is drawn from simple Morse, Lennard-Jones, and Coulombic components, which can reproduce reactions across a broad range of PbS quantum dot sizes with good accuracy. We validate the capability of this model to capture reactive systems by comparison to ab initio calculations for a reaction between two dots.

Optical Response of Lead Sulfide Quantum Dots on Gamma Radiation

Here we show the changes occur in the optical response of lead sulfide quantum dots when irradiated with gamma radiation. Gamma Radiations are presently being detected using Single Crystal Scintillators. Where, sodium iodides are used. At which the absorbed radiations (High Energy) and converts it into light pulses which are converted into electrical pulses. Apart from this type of single crystal scintillators, Quantum dots of materials like lead sulfide can be used for detection of gamma radiation only on concentrating the optical property of the material. Here we have synthesized lead sulfide quantum dots of size 4-6 nm which is been proved by particle size analyzer then the optical property of the material is characterized using FTIR Spectroscopy in the mode of absorbance, DLS, PL as essential characterization for QD’s. Sample is irradiated using Co-60 gamma source of 1 KGy, 2 KGy, 3 KGy as varying dose rate and then again the FTIR Spectroscopy study is done to observe the variation in optical study and it’s been observed.

Ultrasensitive PbS quantum-dot-sensitized InGaZnO hybrid photoinverter for near-infrared detection and imaging with high photogain

Lead sulfide (PbS) quantum dots (QDs) have great potential in optoelectronic applications because of their desirable characteristics as a light absorber for near-infrared (NIR) photodetection. However, most PbS-based NIR photodetectors are two-terminal devices, which require an integrated pixel circuit to be practical photosensors. Here we report on PbS QD/indium gallium zinc oxide (InGaZnO, IGZO) metal oxide semiconductor hybrid phototransistors with a photodetection capability between 700 and 1400 nm, a range that neither conventional Si nor InGaAs photodetectors can cover. The new hybrid phototransistor exhibits excellent photoresponsivity of over 106 A W−1 and a specific detectivity in the order of 1013 Jones for NIR (1000 nm) light. Furthermore, we demonstrate an NIR (1300 nm) imager using photogating inverter pixels based on PbS/IGZO phototransistors at an imaging frequency of 1 Hz with a high output voltage photogain of ~4.9 V (~99%). To the best of our knowledge, this report demonstrates the first QD/metal oxide hybrid phototransistor-based flat panel NIR imager. Our hybrid approach using QD/metal oxide paves the way for the development of gate-tunable and highly sensitive flat panel NIR sensors/imagers that can be easily integrated. A hybrid near-infrared photoinverter based on lead sulphide quantum (PbS) dots and InGaZnO that exhibits a high photogain has been made. PbS quantum dots have promising properties for near-infrared detection, but two-terminal devices based on them require an integrated pixel circuit. Now, Do Kyung Hwang at Korea University of Science and Technology and co-workers have demonstrated a hybrid near-infrared detector that employs PbS quantum dots to sensitize InGaZnO. The detector covers a wavelength range of 700–1,400 nanometres, which is not covered by conventional photodetectors. It also exhibits an excellent photoresponsivity of over 106 amperes per watt. The researchers consider that this approach will open up the way to develop highly sensitive, flat-panel near-infrared sensors and imagers that are both gate tunable and readily integrable. We propose hybrid approach of two classes of PbS QD as NIR light absorber and IGZO as the photogenerated charges acceptor/transport semiconductor to create phototransistor for near infrared (NIR) detection/imaging. Such hybrid phototransistor shows photodetection capability between 700 and 1400 nm. We demonstrate a NIR (1300 nm) imager using photogating inverter pixel based on PbS/IGZO hybrid phototransistor.

A filterless, visible-blind, narrow-band, and near-infrared photodetector with a gain.

In many applications of near-infrared (NIR) light detection, a band-pass filter is needed to exclude the noise caused by visible light. Here, we demonstrate a filterless, visible-blind, narrow-band NIR photodetector with a full-width at half-maximum of <50 nm for the response spectrum. These devices have a thick (>4 μm) nanocomposite absorbing layers made of polymer-fullerene:lead sulfide (PbS) quantum dots (QDs). The PbS QDs yield a photoconductive gain due to their hole-trapping effect, which effectively enhances both the responsivity and the visible rejection ratio of the external quantum efficiency by >10 fold compared to those without PbS QDs. Encouragingly, the inclusion of the PbS QDs does not increase the device noise. We directly measured a noise equivalent power (NEP) of 6.1 pW cm(-2) at 890 nm, and a large linear dynamic range (LDR) over 11 orders of magnitude. The highly sensitive visible-blind NIR narrow-band photodetectors may find applications in biomedical engineering.

Direct water-phase synthesis of lead sulfide quantum dots encapsulated by β-lactoglobulin for in vivo second near infrared window imaging with reduced toxicity.

Compared to conventional fluorescence imaging in the visible (400-700 nm) and NIR-I regions (700-900 nm), optical fluorescence imaging in the second near infrared window (NIR-II, 1000-1400 nm) offers reduced photon scattering, deeper tissue penetration and lower auto-fluorescence. Despite excellent imaging capabilities, current NIR-II probes have not yet reached their full potential due to weak quantum yield, low water solubility and suboptimal biocompatibility. To address these problems, we report herein a new NIR-II fluorescent PbS quantum dots (QDs) that are fabricated in water using β-lactoglobulin (LG) as a biological template. The LG-PbS QDs exhibit satisfactory dispersibility, relatively high quantum yield and favorable biocompatibility, and therefore are suitable for high-resolution in vivo imaging applications.