In Situ versus ex Situ Assembly of Aqueous-Based Thioacid Capped CdSe Nanocrystals within Mesoporous TiO₂ Films for Quantum Dot Sensitized Solar Cells

We report a straightforward in situ deposition method to directly assemble aqueous thioglycolic acid capped CdSe colloidal quantum dots within mesoporous TiO₂ thin films by a low-temperature hydrothermal route. This approach integrates linker assisted adsorption and colloidal quantum dot synthesis in a single step due to the use of thioglycolic acid as the capping agent for the quantum dots and tethering agent for the TiO₂. It permits high loading and uniform distribution of colloidal quantum dots within mesoporous TiO₂ electrodes with a greatly improved photovoltaic performance as quantum dot sensitized solar cells, reaching efficiencies as high as 2.2% under one sun illumination conditions after ZnS treatment, compared to the ex situ assembly technique of adsorption of presynthesized semiconductor nanocrystals

Thickness-Dependent Full-Color Emission Tunability in a Flexible Carbon Dot Ionogel

Multicolor luminescent materials are of immense importance nowadays, while it still constitutes a challenge to achieve luminescence color tunability, transparency, and flexibility at the same time. Here we show how ultrasmall carbon dots (CDs) fluorescing strongly across the visible spectrum can be surface functionalized and incorporated into highly flexible hybrid materials by combination with ionic liquids within silica gel networks to form CD-ionogels with properties promising for fabrication of flexible displays and other optical technologies without the use of any toxic materials. We demonstrate how the emission from such hybrid materials can be tuned across a large range of the Commission Internationale de l’Enclairage (CIE) display gamut giving full-color performance. We highlight how the rich ladder of emissive states attributable to organic functional groups and CD surface functionalization supports a smooth sequential multiple self-absorption tuning mechanism to red shift continuously from blue emitting n-π* transitions down through the lower energy states

Photocurrent Enhancement of HgTe Quantum Dot Photodiodes by Plasmonic Gold Nanorod Structures

The near-field effects of noble metal nanoparticles can be utilized to enhance the performance of inorganic/organic photosensing devices, such as solar cells and photodetectors. In this work, we developed a well-controlled fabrication strategy to incorporate Au nanostructures into HgTe quantum dot (QD)/ZnO heterojunction photodiode photodetectors. Through an electrostatic immobilization and dry transfer protocol, a layer of Au nanorods with uniform distribution and controllable density is embedded at different depths in the ZnO layer for systematic comparison. More than 80 and 240% increments of average short-circuit current density (<i>J</i>_sc) are observed in the devices with Au nanorods covered by ∼7.5 and ∼4.5 nm ZnO layers, respectively. A periodic finite-difference time-domain (FDTD) simulation model is developed to analyze the depth-dependent property and confirm the mechanism of plasmon-enhanced light absorption in the QD layer. The wavelength-dependent external quantum efficiency spectra suggest that the exciton dissociation and charge extraction efficiencies are also enhanced by the Au nanorods, likely due to local electric field effects. The photodetection performance of the photodiodes is characterized, and the results show that the plasmonic structure improves the overall infrared detectivity of the HgTe QD photodetectors without affecting their temporal response. Our fabrication strategy and theoretical and experimental findings provide useful insight into the applications of metal nanostructures to enhance the performance of organic/inorganic hybrid optoelectronic devices

Shuttling Photoelectrochemical Electron Transport in Tricomponent CdS/rGO/TiO₂ Nanocomposites

Composite photoelectrodes consisting of CdS sensitizer, reduced graphene oxide (rGO) transporter, and TiO₂ acceptor were synthesized in a solvothermal synthesis. Under solvothermal conditions, the dimethyl sulfoxide (DMSO) solvent medium decomposed to form free sulfides, which facilitated the formation of CdS and, at the same time, which also reduced graphene oxide sheets by forming disulfide moieties. Compared to pure CdS and TiO₂, coupling of these materials either as bi- or tricomponent composites (including rGO) allowed efficient interfacial charge separation and prolonged electron lifetimes. In particular, in the CdS/rGO/TiO₂ tricomposite case, the rGO plays vital roles in alleviating trapped electrons at the heterojunction and serves as a platform for shuttling electrons between CdS and TiO₂. Taking into account all of the structure-related charge-transport characteristics, including interfacial contacts, the highest quantum efficiency (incident photon-to-current efficiency, IPCE, at 460 nm = 12%) was achieved for the CdS/rGO/TiO₂ tricomposite, and this was 6-fold that of CdS/TiO₂

Impact of D₂O/H₂O Solvent Exchange on the Emission of HgTe and CdTe Quantum Dots: Polaron and Energy Transfer Effects

We have studied light emission kinetics and analyzed carrier recombination channels in HgTe quantum dots that were initially grown in H₂O. When the solvent is replaced by D₂O, the nonradiative recombination rate changes highlight the role of the vibrational degrees of freedom in the medium surrounding the dots, including both solvent and ligands. The contributing energy loss mechanisms have been evaluated by developing quantitative models for the nonradiative recombination <i>via</i> (i) polaron states formed by strong coupling of ligand vibration modes to a surface trap state (nonresonant channel) and (ii) resonant energy transfer to vibration modes in the solvent. We conclude that channel (i) is more important than (ii) for HgTe dots in either solution. When some of these modes are removed from the relevant spectral range by the H₂O to D₂O replacement, the polaron effect becomes weaker and the nonradiative lifetime increases. Comparisons with CdTe quantum dots (QDs) served as a reference where the resonant energy loss (ii) a priori was not a factor, also confirmed by our experiments. The solvent exchange (H₂O to D₂O), however, is found to slightly increase the overall quantum yield of CdTe samples, probably by increasing the fraction of bright dots in the ensemble. The fundamental study reported here can serve as the foundation for the design and optimization principles of narrow bandgap quantum dots aimed at applications in long wavelength colloidal materials for infrared light emitting diodes and photodetectors

Solution-Processed Ambipolar Organic Thin-Film Transistors by Blending p- and n‑Type Semiconductors: Solid Solution versus Microphase Separation

Here, we report solid solution of p- and n-type organic semiconductors as a new type of p–n blend for solution-processed ambipolar organic thin film transistors (OTFTs). This study compares the solid-solution films of silylethynylated tetraazapentacene <b>1</b> (acceptor) and silylethynylated pentacene <b>2</b> (donor) with the microphase-separated films of <b>1</b> and <b>3</b>, a heptagon-embedded analogue of <b>2</b>. It is found that the solid solutions of (<b>1</b>)_<i>x</i>(<b>2</b>)_1–<i>x</i> function as ambipolar semiconductors, whose hole and electron mobilities are tunable by varying the ratio of <b>1</b> and <b>2</b> in the solid solution. The OTFTs of (<b>1</b>)_0.5(<b>2</b>)_0.5 exhibit relatively balanced hole and electron mobilities comparable to the highest values as reported for ambipolar OTFTs of stoichiometric donor–acceptor cocrystals and microphase-separated p-n bulk heterojunctions. The solid solution of (<b>1</b>)_0.5(<b>2</b>)_0.5 and the microphase-separated blend of <b>1:3</b> (0.5:0.5) in OTFTs exhibit different responses to light in terms of absorption and photoeffect of OTFTs because the donor and acceptor are mixed at molecular level with π–π stacking in the solid solution

Investigation of the Exchange Kinetics and Surface Recovery of Cd_<i>x</i>Hg_1–<i>x</i>Te Quantum Dots during Cation Exchange Using a Microfluidic Flow Reactor

Detailed analyses of coupled photoluminescence, emission lifetime, and absorption measurements have been made on the products of cation exchange reactions between CdTe nanocrystals and Hg²⁺ salt/ligand solutions in a microfluidic flow reactor and capillary measurement cell to probe the reaction kinetics over the seconds to hours time scale and to establish the influence of the reaction conditions on the spatial distribution of the mixed cations within the resulting Cd_<i>x</i>Hg_1–<i>x</i>Te colloidal quantum dots. The establishment of the evolution of the radiative and nonradiative rates allowed the recovery of the emission quantum yield in Cd_<i>x</i>Hg_1–<i>x</i>Te quantum dots to be quantified to almost 50% and the necessary time scales to be determined for each set of reaction conditions. The reaction kinetics showed clear indication of a fast surface exchange process followed by a slower internal rearrangement of the cation distribution

Aqueous Manganese-Doped Core/Shell CdTe/ZnS Quantum Dots with Strong Fluorescence and High Relaxivity

Core/shell CdTe/ZnS colloidal quantum dots with varying dopant levels (4.7–9.7%) of paramagnetic manganese ions spatially distributed within the thin ZnS shell are synthesized by the aqueous approach. They exhibit both strong fluorescence originating from the CdTe core (up to 45% room temperature emission quantum yield) and high ionic relaxivity in the range of 10.7–5.4 mM^–1 s^–1, which render them promising dual fluorescent/paramagnetic probes

Narrowing the Photoluminescence of Aqueous CdTe Quantum Dots via Ostwald Ripening Suppression Realized by Programmed Dropwise Precursor Addition

Ostwald ripening is the dominant particle growth mechanism in traditional routes to synthesize aqueous CdTe quantum dots (QDs), which results in a broadening of their size distribution and also their photoluminescence line width, in the case of prolonged reactions. We introduce a method to suppress the Ostwald ripening through the replenishment of precursors before size defocusing occurs in the aqueous synthetic system, which is realized through a programmed dropwise precursor (source) addition (denoted as PDPA) by a syringe pump arrangement that can control the precursor feed volume and rate. As a result, we have obtained a series of highly monodisperse CdTe QDs, with the emission full width at half-maximum in the red region (106 meV) being even narrower than that in the green region (160 meV). We monitored the conductivity of the reaction solution to follow the consumption of precursors, providing feedback as to whether the replenishment volume was matched. Correlations between the emission quantum yield and the fluorescence lifetime for different precursor source addition rates are provided. The influence of the respective sizes of the CdTe particles employed as precursors in PDPA on the growth rate, monodispersity, and emission characteristics of the resulting QDs is explored, and the underlying mechanisms are rationalized

Effect of \kur{Nosema apis} and \kur{Nosema ceranae} on colonyof bees

The work is aimed at assessing the influence of Nosema apis and Nosema ceranae on the hive. The literature contains only a limited degree of information about Nosema disease, which caused by both protozoa, that?s why the main aim of this work is to gather all available technical information from various sources, to compare and evaluate them. The result of evaluating the information gathered then is how this disease affects bee behavior, which has implications for breeding bees. The content of this work is first the general characteristics of Nosema apis and Nosema ceranae, their distribution, reproduction and development. A description Nosema disease, such as preventive and disinfecting measures to prezent it and how you can treat already established disease. The findings described by ptrotozoa Nosema apis imply that this protozoa is explored in the vast majority. Nosema ceranae is a recently discovered species and its research is not yet complete. Finally, the thesis summarizes the most important effects of Nosema apis and Nosema ceranae on the hive. These factors include, fluctuating number of individuals in a hive, honey yields lower, in some cases death of the colony and it also changed the behavior of honey bees