Papers by Keyword: Quantum Dots

Abstract: Semiconductor quantum dots (QDs) exhibit significant potential for laser applications, where a thorough understanding of their optical gain properties and excitonic dynamics is crucial for performance optimization. In this study, state-resolved pump-probe transient spectroscopy was employed to investigate the optical gain and exciton dynamics in CdSe QDs. The results reveal that the gain threshold increases with pumping photon energy, attributed to the competition between surface trapping and intraband relaxation, as well as to the increased biexciton binding energy associated with higher-energy excitonic charge distributions. Notably, the biexciton binding energy reverses from negative to positive values with increasing pump energy, a transition that underpins the observed rise in gain threshold. Additionally, time-resolved decay curves demonstrate accelerated excitonic recombination at higher pump fluences, indicating a greater proportion of biexcitons relative to single excitons. These findings provide valuable insights for tailoring optical gain in quantized nanostructures and optimizing QD-based laser devices.

Abstract: This study examined the impact of silica-coating on the luminescence characteristics of indium phosphide (InP) nanoparticles. Silica-coated InP nanoparticles were prepared using three different techniques. The first method utilized tetraethoxysilane (TEOS) as the silica source, resulting in the encapsulation of multiple InP nanoparticles within silica spheres. This approach caused a red-shift in the luminescence peak wavelength of the InP colloidal solution post-TEOS coating, compared to the original InP colloidal solution. Conversely, the second method employed tetramethoxysilane (TMOS), resulting in the formation of irregularly shaped silica-coatings on multiple InP nanoparticles, which reduced the red-shift in the luminescence peak wavelength of the silica-coated InP colloidal solution. The third method involved pre-coating InP nanoparticles with TMOS, followed by thickening the silica shells using TEOS. This technique successfully encapsulated multiple InP nanoparticles within silica spheres, maintaining the luminescence peak wavelength of the InP colloid solution post-coating with TMOS and TEOS nearly identical to that of the original solution. This method merged the advantageous outcomes of the first two methods. Additionally, silica spheres containing InP nanoparticles synthesized using both TMOS and TEOS exhibited the highest luminescence intensity. In summary, this study introduces a novel approach in nanoparticle engineering, enhancing the functional properties of InP nanoparticles and expanding their potential applications in optoelectronic devices.

Abstract: This work reported the successful fabrication of a low-cost electrospun PAN nanofiber coated with Cu₂O QDs. Our works reveal that the spray coating method was effective in applying a homogenous distribution of Cu₂O QDs on the surface of PAN nanofiber. The as-synthesized Cu₂O QDs have an absorption edge at 510 nm and band gap energy of 2.5 eV indicating a light-sensitive photocatalyst. The SEM image showed an even distribution of Cu₂O QDs on the top of PAN nanofibers with an average diameter of 454.45 ± 124.732 nm. The wettability of the as-made nanofibers was determined using the contact angle method. Our PAN/Cu₂O QDs nanofibers showed hydrophilic behavior. The reactive oxygen species generation study also indicated the ability of our PAN/Cu₂O to generate singlet oxygen. Our results indicate the promising potential of PAN/Cu₂O as wound healing fabric due to the advantageous natural properties of copper and hydrophilic fabric.

Abstract: The near-field direct writing technology represents a cutting-edge micro-nano additive manufacturing technique capable of printing intricate lattice structures with high precision. Leveraging the nanoscale self-luminous properties of quantum dots (QDs), a novel RGB QDs ink is developed by integrating QDs with polycaprolactone (PCL), specifically tailored for near-field direct writing applications. Based on the synergistic benefits offered by the aforementioned materials and technology, we present a groundbreaking approach to fabricating lattice structures patterns featuring RGB quantum dots. Firstly, a specialized printing ink is formulated for the production of lattice structures, aiming to achieve precise and intricate patterns. Subsequently, comprehensive investigations are conducted to determine the optimal parameters for the RGB quantum dots ink. Finally, an in-depth analysis is performed to evaluate the deposition process and luminescence properties of the resulting lattice structures pattern. The micron-scale lattice structures, incorporating quantum dots, hold great potential for applications in displacement encoders.

Abstract: Liquid crystal-quantum dot (LC-QD) composites are promising new materials for a number of applications in displays, energy harvesting, and photonics. In the present work, quantum dispersion in the mixture of LCs of cholesteric and nematic phases is reported. The combination of two LCs, namely Cholesteryl Palmitate (cholesteric 97%) and 4′-Pentyl-4-biphenylcarbonitrile (nematic, 98%), were used in equal proportion while CdS quantum dots were added in this mixture. The thermal, optical, and structural properties of this new LC-QD composite system were analyzed using differential scanning calorimetry (DSC), ultra-violet visible (UV-VIS) spectroscopy, Fabry-Perot scattering studies (FPSS), and Fourier transform infrared (FTIR) spectroscopy. Structural studies indicate that the QDs are uniformly dispersed inside the LC matrix rather than on the surface area. It was observed that quantum dot dispersion increases the strength of the LC mixture. It also changes the phase behavior of the LC mixture affecting the overall performance of LC-QD composite systems. The present findings would be very helpful for the design of the display and photonic devices with an improved optical response.

Abstract: Copper sulphide quantum dots were synthesized by a simple chemical route using ammonia (aq.) as a complexing agent in PVA matrix. Copper acetate monohydrate and thiourea were used as precursors. The particle sizes as obtained from XRD results were found to be in good agreement with those of HRTEM. The UV-Vis. absorption and PL emission spectra exhibited a systematic blue shift of absorption and emission respectively confirming quantum confinement effect in the synthesized quantum dots. The band gap as estimated from Tauc-plot increased from 3.26eV to 3.92eV with change of concentration of complexing agent. The FTIR spectra exhibited Cu-S stretching peaks characteristic of CuS. Ionic contributions of the electrolytic ionic CuS solution as measured by a standard conductivity cell clearly showed the semiconducting behavior of the product material. The synthesized material may be exploited in fabrication of an optoelectronic device in UV-blue region.

Abstract: Improving the conversion efficiency of solar cells is a key way to make solar cells cost-competitive with conventional sources of energy because the cost of electricity produced from solar cells depends on their efficiency. According to Shockley-Queisser limit, all single junctions cells have a theoretical efficiency limit of 33.7%. Efficiency losses are associated with light that either is not energetic enough or too energetic for the generation of an electron-hole pair. In other words, the two most important loss mechanisms in single bandgap solar cells are the inability to convert photons with energies below the bandgap energy (Eg) into electricity and the thermalization of photon energies exceeding Eg. These two mechanisms alone represent the loss of about half of the incident solar energy during the conversion. Intermediate band (IB) located inside the forbidden band of the host semiconductor, making it possible to increase the absorption of photons with energy lower than the band gap energy Eg, can be a solution for the first problem. The effect of IB on the efficiency of solar cells was discussed. Our aim is to show how IB can improve the efficiency of solar cells based on Quantum Dots (QDs), i.e, the efficiency of a solar cell can be greatly increased through additional optical absorption. In this paper, two cases were discussed applying a numerical model. Our model, used to calculate solar cells efficiency and to plot the current-voltage (I-V) characteristics and the power-voltage (P-V) characteristics curves, is mainly based on the principles of the detailed balance between absorption and emission of solar light and well separated quasi-Fermi levels. The first case is an idealized case where the recombinations are assumed to be entirely radiative. In the second case, the model takes into account the non-radiative recombinations introduced by the increase in the density of defects caused by the increase in the size of the QDs. It has been shown that Consideration of size leading to the reduction of the defects is one of important key solution to increase the efficiency of intermediate band solar cells (IBSC).

Abstract: A CdTe quantum dot modified with thioglycolic acid as stabilizer was prepared. The structure of CdTe quantum dots was characterized by IR, UV and fluorescence spectra, transmission electron microscopy (TEM) scanning and X-ray diffraction (XRD). The effects of reactants, temperature, time and PH on the luminescence properties of the quantum dots were investigated. It is found that the quantum dots have strong fluorescence intensity. The synthesized QDS have small and uniform particle size and high crystallinity. The optimum conditions were determined as follows: n (Cd²⁺): n (Te^2-): n (TGA) = 2:1:4, heating temperature 140°C, reaction time 60min, pH 11.

Abstract: Cuprous Oxide (Cu₂O) is a semiconductor material with excellent photocatalytic properties, a broad range of applications, low fabrication costs, and is non-toxic. We concentrated on the impact of two different synthesis methods in this study. Cu₂O synthesis was carried out using two different techniques, which are chemical deposition and hot-soap method. The chemical deposition (CD) method used a copper sulfate pentahydrate precursor in a room temperature reaction. Hot-soap (HS) method employed copper acetylacetonate with reaction at higher temperature. The X-Ray Diffraction analysis reveals a sharp peak with a size of 53.8 nm and a broaden peak with a size of 26.24 nm for particles synthesized by (Cu₂O-CD) and (Cu₂O-HS), respectively. Using the Tauc Plot method, the band gap of Cu₂O-HS is estimated to be 2.65 eV and that of Cu₂O-CD to be 1.7 eV. Cu2O-HS emits a noticeable photoluminescence peak at 425 nm, whereas Cu₂O-CD emits no peaks in photoluminescence spectra analysis. These findings indicate that Cu₂O-HS has a high potential for use in photocatalytic mechanisms.

Abstract: By fixing Quantum Dots (QDs) on gold electrodes with dithiol compounds, a novel Ascorbic Acid sensor without any redox mediator was desighed. First, the fabrication process of sensor was described.Sencond, the characteristics of the sensor were investigated. Third,the sensor was tested in Ascorbic Acid solutions of different concentrations.From the results,it shows that the performance of photoelectrochemical sensor were influenced by the bias voltage and the amplitude of photocurrent changed with the Ascorbic Acid concentration linearly in detection range.