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The linear photochemical response of materials depends on two critical parameters: the size of the optical band gap determines the onset of optical excitation, whereas the absolute energetic positions of the band edges define the reductive or oxidative character of photo-generated electrons and holes. Tuning these characteristics is necessary for many potential applications and can be achieved through changes in the bulk composition or particle size, adjustment of the surface chemistry or the application of electrostatic fields. In this contribution the influence of surface chemistry and fields is investigated systematically with the help of standard DFT calculations for a typical case, namely composites prepared from ZnS quantum dots and functionalized carbon nanotubes. After comparing results with existing qualitative and quantitative experimental data, it is shown conclusively, that the details of the surface chemistry (especially defects) in combination with electrostatic fields have the largest influence. In conclusion, the development of novel or improved photoresponsive materials therefore will have to integrate a careful analysis of the interplay between surface chemistry, surface charges and interaction with the material environment or substrate.

Cornflower is a flowering weed and ornamental plant whose blue flowers have been used for food, decorative and colouring purposes. In this study, the upper (edible flowers) and lower (non-edible receptacle and involucre) parts of the capitulum were studied and compared for their chemical composition and bioactive properties. The flowers were richer in tocopherols, organic acids, and apigenin derivatives (mainly apigenin-7-O-glucuronide-4′-O-(6-O-malonylglucoside)) than the non-edible bristly part (where syringic acid predominated). Four cyanidin derivatives were identified in the flowers. The extract of the non-edible part was more efficient in inhibiting the formation of thiobarbituric acid reactive substances (TBARS), the bleaching of β-carotene, and the haemolysis of the erythrocytes membrane. In general, the extracts were more active against Gram-positive bacteria and had no cytotoxicity against non-tumour liver PLP2 cells. Therefore, while flowers are a potential source of natural cyanidin-based colorants, the lower part of the capitulum has bioactive properties to be exploited in different food or pharmaceutical formulations. The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO ( UID/AGR/00690/2013 ); to FCT for the grants of C.L. Roriz ( SFRH/BD/129551/2017 ) and C. Pereira ( SFRH/BPD/122650/2016 ) (awarded under the Programa Operacional Capital Humano (POCH) supported by the European Social Fund and National Funds of MCTES (Ministério da Ciência, Tecnologia e Ensino Superior) , and the research contracts of J. Pinela (Project AllNatt , POCI-01-0145-FEDER-030463 ) and L. Barros. This work is also funded by the European Regional Development Fund (ERDF) through the Regional Operational Program North 2020, within the scope of Project NORTE-01-0145-FEDER-023289: DeCodE and project Mobilizador Norte-01-0247-FEDER-024479: ValorNatural®; and FEDER-Interreg España-Portugal through the project 0377_Iberphenol_6_E. info:eu-repo/semantics/publishedVersion

An aqueous route based on electrostatics for preparing heterostructures from carbon nanotubes (CNT) and Zinc Sulfide doped with manganese (ZnS:Mn) is demonstrated. This was achieved by one-pot synthesis of negatively charged multiwalled carbon nanotubes and positively charged ZnS quantum dots, in a reaction driven by the electrostatic interaction between the binary components. The structural and optical properties of the heterostructures were characterized by particle size, zeta potential, x-ray diffraction, transmission and scanning electron microscopy, and photoluminescence measurements. A size-restriction effect of the CNTs on the growth of the ZnS nanoparticles during synthesis was observed, particle sizes of the prepared composites were smaller with higher amounts of CNT. Remarkably, all ZnS:Mn/CNT composites showed a blue shift of in the excitation spectra compared to ZnS:Mn only. Further experiments attributed the blue shift to an increased band gap of the ZnS:Mn, originating from an effective electrostatic interaction between the CNT and the attached ZnS:Mn. This effect was indicative of an intimate contact between the CNTs and the ZnS:Mn which was affirmed by images obtained from Transmission Electron Microscopy as well. Composites with such controlled morphology between the binary components are relevant in the fabrication of inorganic nanomaterial-carbon nanotube heterostructures, directed towards applications in optoelectronics.

Polymer electrolyte membrane fuel cells (PEMFCs) operating at low temperature (60–80 °C, up to 110 °C) are mostly limited in their performance by the kinetics of the oxygen reduction reaction (ORR), leading to high loadings of platinum (Pt) in the cathode. Pt catalysts are without alternative in numerous industrial applications, and since Pt resources are limited, the associated high costs for low temperature fuel cells are hindering among other factors their commercialization. In order to increase the fraction of electrocatalytically available Pt towards ORR, this work is devoted to the factors responsible for the microstructure of the PEMFC cathodes. Typically, the active layers are coated by processes like spraying, doctor blading, printing etc. Therefore, the final structure actually is strongly dependent on the coating process and the physicochemical properties of the catalyst dispersions used. Selecting commercially available electrocatalysts from Johnson-Matthey and Tanaka as active material and ultrasonically assisted spraying as the coating method, systematic variations of the surface chemistry of the catalyst particles and their influence on catalyst layer morphology and therefore electrical and electrochemical properties of resulting membrane electrode assemblies (MEA) have been investigated. It could be shown, that the colloid–chemical properties of the catalyst dispersions have a profound influence not only on the microstructure of the MEAs but also on the performance under operating conditions.

In this work, the heteroaggregation kinetics between positively and negatively charged variants of multiwalled CNTs with positively charged zinc sulfide (ZnS) nanoparticles was studied. Through time-dependent size measurements, we observed an increasing rate of heteroaggregation between negatively charged nanotubes and positively charged ZnS nanoparticles with increasing ZnS/CNT ratios. The heteroaggregation rate increases to a maximum at a ZnS/CNT weight ratio of 4.8, then reverses in trend. Time-dependent zeta potential measurements also revealed that during heteroaggregation, the negatively charged nanotubes are continuously coated by the positively charged ZnS nanoparticles. When the surface of the CNTs is oversaturated with ZnS nanoparticles, the aggregates behave as single positively charged entities hindering further growth in size through inter-aggregate repulsion. No heteroaggregation was observed between positively charged CNTs and positively charged ZnS nanoparticles. TEM imaging supported the notion of ZnS nanoparticles attached to CNTs. Using heteroaggregation, we further successfully prepared composites from functionalized CNT and ZnS phosphors with good distribution of the nanotubes on the phosphors.

Manganese-doped ZnS quantum dots (QDs) stabilized by cysteamine hydrochloride were successfully synthesized. Their thorough physicochemical characteristics were acquired using UV-Vis absorption and photoluminescence spectroscopy, X-ray diffraction, dynamic light scattering (DLS), transmission electron microscopy (HR-TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared (FT-IR) spectroscopy. The average particle size, derived from HR-TEM, was 3.1nm, which agrees with the hydrodynamic diameter acquired by DLS, that was equal to 3-4nm, depending on ionic strength. The quantum dots also exhibited a large positive zeta potential varying between 75 and 36mV for ionic strength of 10-4 and 10-2M, respectively (at pH 6.2) and an intense luminescent emission at 590nm. The quantum yield was equal to 31% and the optical band gap energy was equal to 4.26eV. The kinetics of QD monolayer formation on silica substrates (silica sensors and oxidized silicon wafers) under convection-controlled transport was quantitatively evaluated by the quartz crystal microbalance (QCM) and the streaming potential measurements. A high stability of the monolayer for ionic strength 10-4 and 10-2M was confirmed in these measurements. The experimental data were adequately reflected by the extended random sequential adsorption model (eRSA). Additionally, thorough electrokinetic characteristics of the QD monolayers and their stability for various ionic strengths and pH were acquired by streaming potential measurements carried out under in situ conditions. These results were quantitatively interpreted in terms of the three-dimensional (3D) electrokinetic model that furnished bulk zeta potential of particles for high ionic strengths that is impractical by other experimental techniques. It is concluded that these results can be used for designing of biosensors of controlled monolayer structure capable to bind various ligands via covalent as well as electrostatic interactions.

Different from negatively charged CuInS2 (CIS) based quantum dots (QDs), positively charged QDs are difficult to obtain in good optical quality, but are desirable for certain applications. We herein present a general synthesis strategy that allows for a universal surface modification of ternary CIS based QDs with thiol containing ligands. The idea behind the synthesis design is, to apply a ZnS shell first for passivating and protecting the core QDs, and then add a second ZnS shell for the functionalization via ligand exchange. Whereby easy ligand exchange with thiolated molecules is systematically set up, by using a weak bonding amine ligand for the second shell. Molecules with various terminal groups were used to functionalize the nanoparticles and stabilize them in different media making any surface charge and polarity accessible. Surface defect chemistry seemed to play an important role in our synthesis strategy, therefore to gain a deeper understanding how these defect sites can alter the electronic structure of core/shell nanoparticles theoretical calculations based on density functional theory were performed, whilst structural, colloidal and optical properties were characterized experimentally (by dynamic light scattering, x-ray diffraction, infrared spectroscopy, zeta potential, absorption- and (time resolved) photoluminescence measurements).

Quantum dots that efficiently emit white light directly or feature a "candle-like" orange photoluminescence with a high Stokes shift are presented. The key to obtaining these unique emission properties is through controlled annealing of the core Cu-In-Ga-S quantum dots in the presence of zinc ions, thus forming Zn-Cu-In-Ga-S solid solutions with different distributions of the substitution and dopant elements. The as-obtained nanocrystals feature excellent quantum yields of up to 82% with limited or even eliminated reabsorption and a color rendering index of bare particles of up to 88, enabling the production of high-quality white LEDs using a single color converter layer. Furthermore, the color properties can be tuned by changing the experimental conditions as well as by varying the excitation wavelength. The multicomponent luminescence mechanism is discussed in detail based on similar literature reports. White LEDs with unparalleled color quality and competitive luminous efficacies are presented herein.

Light emitting diodes (LEDs) have become a very important source for ultraviolet light (UV) in various technical areas, the near UV range (NUV in the following) being particularly attractive due to the availability of high power emitters at very competitive cost for the spectral range between 350 and 400 nm. While numerous Eu3+ complexes are known now that can efficiently be exploited in this excitation range, corresponding green Tb3+ emitter complexes are hard to find. Tb3+ salts of fenamic acid and derivatives thereof are shown to be interesting candidates for applications using NUV excitation: on additional co-coordination with e.g. 5,5′‑dimethyl‑2,2′‑bipyridine, excitation maxima at 380 nm, at the same time maintaining high efficiencies, can be accomplished. Such coordination compounds hold the promise of being useful as versatile marker molecules in a variety of ‘soft’ chemical environments.

In this study, we report on the influence of organic solvents on the dissolution and reduction of elemental selenium for the phosphine-free synthesis of metal selenide nanoparticles. To this end, elemental selenium was reduced with sodium borohydride in the presence of a hydrophobic unsaturated alkylamine (oleylamine) and an alkene (1-octadecene) in different ratios. These varying conditions affect the optical properties of the prepared ZnSe:Mn nanoparticles (which was chosen as the test case) in a systematic way. The characterization with UV-vis absorption, photoluminescence measurements and nuclear magnetic resonance (NMR) shows the importance of the bifunctionality of oleylamine for the reduction and dissolution of elemental selenium for the scalable synthesis of highly crystalline nanoparticles. NMR data indicate that (in addition to the amine group) the double bond in the center of the molecule plays an important role as well. A proposed reaction pathway describes the specific actions of the amine group and the double bond in oleylamine for the synthesis of selenide nanoparticles. Consequently, oleylamine as solvent has a pronounced positive effect on the optical properties of the synthesized ZnSe:Mn nanoparticles.

We present a facile one-pot synthesis and simple surface modification strategies to prepare ternary CuInS2/ZnS quantum dots (CIS/ZnS QDs) functionalized with alkyl-, carboxyl- and hydroxyl-terminated ligands. Photoluminescence quantum yields (PLQY) up to 60% can be achieved for CIS/ZnS QDs synthesized on a gram scale. Aqueous mercaptopropionic acid (MPA) capped QDs are used as a base for further surface modification. On the one hand ligand–solvent interactions have been found to play a major role in the luminescence quenching mechanism of aqueous CIS/ZnS QDs. On the other hand, solvent extraction, immobilization in a polymer matrix or phase transfer greatly enhances the photoluminescence. Quantum yields in solution and in solid matrices differ greatly in the case of aqueous QDs both in polymers and in sol–gel silica. Surface engineered QDs are assessed for their usefulness in LED down-conversion experiments. We demonstrate that down-converter layer properties are not only dependent on the QD type and PLQY, but also on the matrix and the type of ligand shell. Despite significant (up to a factor of two) differences in PLQY between the hydrophobic and hydrophilic dots, their LED conversion efficiencies are comparable and up to 49% and 46% for hydrophobic and for hydrophilic QDs, respectively. Additionally, sol–gel nanocomposites incorporating CuInS2/ZnS QDs with OH-terminated ligands that can withstand 200 h high power blue LED irradiation are presented for the first time.

Highly luminescent Mn doped ZnSeS nanoparticles have been synthesized using a modified Se/S-precursor solution in a facile one-pot approach. The main challenge of the phosphine-free synthesis of metal selenide nanoparticles is the solubility and reduction of elemental selenium in organic solvents without the use of alkylphosphine. Herein, we report on a highly reactive Se/S precursor solution with NaBH4, which is suitable for the reproducible synthesis of alloyed structures like ZnSeS in a one-pot approach. Hitherto, the synthesis of core/shell and alloyed ZnSe nanoparticles like ZnSe:Mn/ZnS has required at least two steps with time consuming purification steps. This modified Se/S-precursor facilitates the synthesis of highly luminescent alloyed nanostructures in view of time and purification steps. The as-synthesized alloyed ZnSeS:Mn nanoparticles possess small size and high quality optical properties with up to 42% photoluminescence (PL) quantum yield (QY). Distinctive features in the PL spectra indicate the usability of the modified Se/S-precursor solution for the synthesis of alloyed structures. Besides this, the ratio of S to Se significantly affected the PL QY of the nanoparticles. ICP-MS/ICP-OES, EDX and XPS measurements indicate the formation of alloyed ZnSeS:Mn nanoparticles, using the modified precursor.

This paper deals with development of a novel ZnSe:Mn/ZnS@PMMA nanocomposites fabricated via simple film casting methods using commercial available PMMA resin (DEGALAN® Evonik). Hydrophobic ZnSe:Mn/ZnS nanoparticles were successfully produced by the hot-injection method using high boiling point organic solvents. ZnSe:Mn colloidal nanoparticles were protected from luminescence quenching and degradation by overcoating with a ZnS shell. The coverage of the nanoparticles with three layers of the ZnS shell effectively protected them against photooxidation and quenching in organic solvents. The crucial step in the production of highly transparent and luminescent ZnSe:Mn/ZnS@PMMA polymer nanocomposites was the purification of the ZnSe:Mn/ZnS nanoparticles from by-products and unreacted precursors. The optical properties of ZnSe:Mn/ZnS@PMMA nanocomposites were characterized by UV–Vis and spectroscopic ellipsometry measurements. All nanocomposite films demonstrated high transmittance in the visible range (70–90%), an intense orange emission originating from homogeneously dispersed ZnSe:Mn/ZnS nanoparticles. The intensity of the orange emission increased with increasing ZnSe:Mn/ZnS nanoparticle concentration in the nanocomposite up to a quantum yield (QY) of 19% ± 5 for a nanocomposite with nanoparticles content up to 7% wt. These novel polymer nanocomposites exhibited good optical properties (high refractive index of 1.59 at 450 nm) and stability under ambient conditions and can be easily deposited over large areas by printing process.

In this study, the formation of zinc sulphide-carbon nanocomposite layers by electrophoretic deposition (EPD) was investigated with various compositions. Under the addition of Mg(NO3)2 and Al(NO3)3 the approach allowed to form stable and thick porous deposits for potential application as electrocatalyst. Vulcan XC-72R carbon was used as carbon source and oxidized to provide dispersibility in isopropyl alcohol (IPA). Zinc sulphide nanoparticles were synthesized with cysteamine as capping agent by a precipitation method. Different compositions of these materials were used and electrodeposited to analyse the structural differences in the resulting layers. We showed that the use of cations such as Mg 2 + or Al3＋ allowed to increase the deposition rates in most cases and to avoid agglomeration which could be characterized by zeta potential measurements. Structural analysis of the resulting layers revealed a decreased density with increasing amount of carbon in presence of salt. This is attributed to different interactions in the final stages of the deposition process which are discussed in this work.

We have synthesised a neutral, water-soluble, Pt(II) complex able to aggregate more efficiently in aqueous solutions than in organic solvents. The aggregates are luminescent and are not quenched by molecular oxygen. Further, we have prepared phosphorescent hydrogels utilising host-guest interactions between cyclodextrins and the tetraethylene glycol tails of the Pt(II) complex. The soft assemblies feature host-dependent emission properties.

The electrophoretic deposition (EPD) method has been adapted for the deposition of ceramic green bodies from aqueous nanodispersions of alumina, yttria, yttrium aluminium garnet and lutetium aluminium garnet. These materials have been selected, since they are promising candidates for optically transparent ceramics. Films as well as cylindrical bodies have been successfully prepared by application of pulsed direct current (pDC) EPD. To guarantee constant deposition yield during pDC, a variant with variable pulse widths and pulse heights has been developed. The obtained green bodies were studied by surface area analysis, scanning electron microscopy, optical transmittance measurements, determination of pycnometric density and sintering behaviour. The effect of colloid-chemical dispersion properties on green and sintered ceramics is discussed as well. The green ceramics received are nanoporous and dense, providing excellent properties for further processing under mild conditions to optical materials. For comparison, EPD-formed green bodies were either processed directly to ceramic bodies or after additional compacting by hot-pressing in a piston-cylinder apparatus.

Low temperature fuel cells consuming ethanol without reformation would be a major step toward the use of renewable energy sources from biomass. However, the necessary electrodes and electrocatalysts still are far from being perfect and suffer from various poisoning and deactivation processes. This work describes investigations on systems using carbon/ZnS-based electrocatalysts for ethanol oxidation in complete membrane electrode assemblies (MEAs). MEAs were built on Nafion membranes with active masses prepared from ZnS nanoparticles and Vulcan carbon support. Under operation, acetic acid and acetaldehyde were identified and quantified as soluble oxidation products, whereas the amount of CO 2 generated could not be quantified directly. Overall conversion efficiencies of up to 25% were estimated from cells operated over prolonged time. From polarization curves, interrupt experiments and analysis of reaction products, mass transport problems (concentration polarization) and breakthrough losses were found to be the main deficiencies of the ethanol oxidation electrodes fabricated so far.

Nanocomposites combining functional nanoparticles and transparent polymers allow for stabilization of filler properties over long periods of time while retaining transparency of the polymer matrix. Here we employ CuInS2/ZnS quantum dots (QDs), ternary visible- and NIR-emitting semiconductors as wavelength-tunable luminescent fillers. Luminescence in the near infrared (NIR) is of particular interest in medicine which allows deep penetration into human tissue enabling in vivo diagnostics and treatment, while visible emitters may serve as color converters in displays or lighting. To stabilize the optical properties of QDs and prevent agglomeration, polymethyl metacrylate (PMMA) was chosen as a matrix. These novel polymer nanocomposites (PNCs) show good optical properties and stability under ambient conditions, and can be easily deposited over large areas. High-quality QDs and hydrophobic functionalization with long-chain hydrocarbons are a prerequisite for embedding into a PMMA matrix. Transparent PNC films without visible scattering losses were obtained for 1 wt-% QD loading with respect to the polymer. Partial transparency is retained up to 10 wt-% QD loading and vanishes rapidly at higher loading. Luminescence properties increase up to 5 wt-% and then decrease rapidly due to QD agglomeration and reabsorption between adjacent particles. Potential applications include converter materials for medical applications, laser layers, displays and white LEDs.

The present study describes an economic and scalable approach to aqueous mesophases from bola-amphiphiles (BA) obtained via nucleophilic addition of dimer fatty acid based α,ω-polyesterdiols (PES) on cyclic acid anhydrides and conversion of the carboxylic end groups into ammonium salts. Novel bola-amphiphilic head groups are introduced using alkenyl succinic anhydrides (ASA). The additional terminal hydrophobic side chains favour the self-assembly of polymeric BA of different molecular weights into nanoscale anisotropic objects, their shape and ordering into nematic or lamellar-like phases being dependent on the length and structural uniformity of the ASA chains. Corresponding diester based on C15 (hydrogenated bisphenol-A, HBA) and C8 (1,4-cyclohexanedimethanol, CHDM) spacers have been prepared and the self-assembly of the resulting BA in water has been studied using SAXS, (2)H-NMR and optical polarization microscopy. While the rigid C8 spacer impedes any ordering, ASA capped C15 tends to form ordered hydrogels over extended regions of the phase diagram that resemble mesh phases and L(α)/L(3) polymorphism. Rheological and simulation results confirm the presence of elastically responding bicontinuous morphologies and biased porous assemblies resembling interconnected mesh phases. Both the use of the dimer fatty acid based spacer as well as of ASA head groups open up large-scale applications of ordered liquids (or hydrogels) as a formulation basis for e.g. films, coatings and adhesives.

Preparation methods and optical properties of silica sol–gel microparticles functionalized with [Eu(ntac)3][pphendcn] and [Eu(phen)2](NO3)3 [ntac = 1-(2-naphthoyl)-3,3,3-trifluoroacetone, pphendcn = pyrazino[2,3-f][1,10-phenanthroline-2,3-dicarbonitrile, phen = 1,10-phenanthroline] complexes displaying an energy transfer are discussed. Adsorption of [Eu(ntac)3][pphendcn] on the silica surface leads to strong red emitting samples. A method for functionalization of SiO2:Eu3+ with 1,10-phenanthroline is described. Diffuse reflectance spectra, excitation/emission spectra and quantum yield measurements of the investigated solids are presented. The studies are supported by chemical analysis, NMR data, IR spectra and X-ray diffraction measurements of the functionalized powders.

Electrocatalytic materials for applications, e.g. in fuel cells are often composites of (conducting) carbon variants and nanosized metal particles, typically from the family of platinum or nickel. They share some common problems (most notably a tendency to agglomeration and poisoning, e.g. by CO or H2), which prevent their use in contact with, e.g. raw biogenic methane or ethanol. Highly purified fuels or reformation to hydrogen are therefore necessary for such purposes. As a potential alternative, this study describes electrocatalytic activity of composites of undoped and Mn-doped Zn(S,Se) nanoparticles and carbon in contact with ethanol. The results on ethanol oxidation on such electrodes in short-circuit mode are reported, as well as values for the open circuit voltage achieved so far. The focus of this report is the variation of the Se/S ratio in mixed nanocrystals of ZnS and ZnSe. The influence on the electrocatalytic activity by the varying band gap energy and absolute positions of the electronic levels of the doped as well as undoped chalcogenide nanoparticles is reported.

The semiconductor properties of titanium dioxide (TiO2) offer an interesting alternative to convert sunlight into electrical energy by water splitting. This is because of its band gap, a high photogenerated charges mobility and the possibility to be doped both n-type and p-type. However, it has been found that charge recombination and low visible radiation sensitivity are the bottlenecks in the efficient solar energy conversion. Although in the last decade important advances in the synthesis of nanostructured morphologies with high interaction area like nanotubes have been achieved, the conversion efficiency growth has decreased. This is a logical result because there are intrinsic limitations imposed by the electronic properties of TiO2. One of the alternatives to modifying the TiO2’s band gap and improving its photoactivity under visible light irradiation is to dope the nanotubes with transition metals. This option requires fabricating efficient nanostructured photoelectrodes with controlled morphology and specific properties able to offer a suitable surface area for metallic doping. Also, transition-metal oxides and hydroxides are frequently applied as low-cost water-splitting catalysts because they reduce the needed activation energy to overcome the kinetic barrier and increase the electrochemical reaction rate. There are thus important challenges and opportunities from the material science point of view that require a substantial effort for developing new knowledge and advancing in the controlled synthesis of this type of nanostructures. This research focuses on the synthesis and characterization of Ni doped titanium dioxide nanotubes (TNTs) for improving its photocatalytic activity in solar energy conversion applications. Initially, TNTs with controlled morphology were synthesized by two-step potentiostatic anodization of titanium foil. The anodization was carried out at room temperature in an electrolyte composed of ammonium fluoride, deionized water and ethylene glycol. Consequent thermal annealing of as-prepared TNTs was conducted in the air between 450 °C - 550 °C. Afterwards, the nanotubes were superficially modified by nickel deposition. Studies of the morphology and crystalline phase of the samples, before and after nickel deposition, were carried out by SEM, EDS and XRD analysis. Determining the photoelectrochemical performance of photoelectrodes is based on typical electrochemical characterization techniques (OCP, EIS, LSV). Also, the morphological characterization associated electrochemical behavior analysis were discussed to establish the effect of nickel nanoparticles modification on the TNTs. The methodology proposed in this research allows using other transition metal for nanotube surface modification and studying new routes for improving the performance of low cost water-splitting catalysts.

At present, thick film (powder based) alternating current electroluminescence (AC-EL) is the only technology available for the fabrication of large area, laterally structured and coloured light sources by simple printing techniques. Substrates for printing may be based on flexible polymers or glass, so the final devices can take up a huge variety of shapes. After an introduction of the underlying physics and chemistry, the review highlights the technical progress behind this development, concentrating on luminescent and dielectric materials used. Limitations of the available materials as well as room for further improvement are also discussed.

Composites from ZnS:Mn nanoparticles and modified silicas are of interest for a broad range of potential applications in the form of films, structured particles, and self-assembled structures (e.g., colloidal crystals). They combine the versatility of silica sol gel chemistry with the wealth of functionalities available from doped nanoparticulate semiconductors (e.g., optical, electrical, and magnetic). In this work, ZnS:Mn nanoparticles have been prepared and modified in such a way that they can be incorporated seamlessly, either by inclusion or by covalent bonding into silicas. Functionalization was achieved through the use of silanes or thioles. Further processing by standard sol gel chemistry then either led directly to covalent conjugation with the silica network formed after condensation, or to isolated particles encapsulated in a silica shell. The results are heavily loaded (up to 30 wt%), transparent (including semiconductor particles that are smaller than 15 nm) and luminescent films, and massive bodies. In this work, the progress of nanocomposite formation was followed mainly by luminescence spectroscopy. Further work will have to address the electrical and magnetic properties of these nanocomposites as well.

“Bulk heterojunctions” from polymers and inorganic molecules or nanoparticles offer simple internal structures for organic photovoltaic cells. Systems proposed so far need quite expensive or instable materials, often with limited availability; open-circuit voltages are well below 1 V. In this work, a system prepared from poly-3-hexyl-thiophene in contact with ZnS nanoparticles is described. Its almost perfect match of the electronic levels leads to a very high open-circuit voltage, not available until now in similar systems.

The introduction of luminescent materials into a sol–gel-derived silica layer is a promising way for the creation of optical applications on the basis of UV-sensitive waveguides. In this work, the preparation of tetraethylorthosilicate (TEOS)-derived silica layers doped with terbiumtrisbenzoate is described. Results with respect to the layer thickness, the photoluminescence of doped bulk silica materials compared to doped silica layers, the influence of ultrasonic treatment during preparation, and the temperature stability are given. Atomic force microscopy measurements show that the withdrawal speed during the sol–gel process can be optimized in order to minimize the surface roughness of the films deposited. Nanoindentation experiments reveal that the hardness of layers cured at 200 °C is comparable to that of ordinary glass.

Carboxylic acid complexes of lanthanide ions may show an excellent sensitivity to UV radiation and often a luminescence quantum yield near unity. By incorporating them into an inert matrix such as a sol–gel layer, it is possible to prevent degradation of the complexes under atmospheric conditions or by UV irradiation. This work focuses on the lateral structuring of thin sol–gel layers which have been doped with two different luminescent complexes, namely terbium picolinate and europium picolinate. It is demonstrated that structuring of the doped layers with standard photolithographic processes is possible, without harming the luminescent properties of the incorporated complexes. Best results are achieved in an image reversal process, while the lift-off approach with a thick layer of photoresist leads to inhomogenities in the layer. Smallest features of 40 μm were reproduced with excellent edge quality.

Since glassfibres are a common method for transport of information, this study examines the application of glassfibres in UV sensors. To this end, the glassfibres have been coated with a silica-xerogel doped with lanthanide carboxylate complexes, especially terbium picolinate (TbPic). Different pretreatments of the glassfibres have been tested in order to enhance the signal to background ratio of the terbium line emission of 545 nm wavelength. It has turned out that the signal to background ratio can be increased by a factor of nine by etching the surface of the glassfibre with concentrated hydrofluoric acid.

Die Verwendung von Laserstrahlung zur Reinigung kunsthistorischer Objekte etabliert sich in den letzten Jahren zunehmend. Ein besonders verbreitetes und schwieriges Problem sind dabei Farbfassungen. Sie reagieren sehr empfindlich auf Laserstrahlung. In dieser Studie wurde untersucht, mit welchen Parametern (Wellenlange, Energiedichte) und in welchem Ausmas reine Pigmente unter Laserbestrahlung verandert werden. Es wurde gezeigt, dass die Farbveranderungen unterschiedliche Grunde haben kann: Sie konnen z.B. durch laserinduzierte Oxidation, Reduktion oder Phasenumwandlung verursacht werden. The possibility to use laser radiation to clean historical objects has been established for several years. A complex case and widely met problem are polychromes. They react very sensitive towards laser radiation. In this study the reaction of pigments was investigated in dependency on the incident wavelength and energy density. The chemical and also the physical interactions were investigated. It turned out, that the colour change of the pigments can have multiple origins (laser induced oxidation, reduction, phase changing).

Luminescence and excitation spectra of sol–gel derived silica co-doped with Ge and Tb and treated in reducing atmosphere are reported. Energy transfer from Ge-related defects to Tb centers is demonstrated with an efficiency close to unity, resulting in all-inorganic sol–gel-derived materials with up to 30% quantum efficiency upon excitation under 254 nm radiation.

Various approaches to prepare sol–gel-derived silica doped with luminescent lanthanoid complexes have been already demonstrated in several studies. The applicability of these materials as phosphors for practical purposes depends on the quantum efficiencies achievable as well as on the excitation characteristics. This work describes the excitation spectrum of such hybrid materials down to the VUV region and gives quantitative figures for the quantum efficiencies under 254 nm excitation.

Sol-gel chemistry offers a possibility for preparation of optical materials like xerogels, aerogels, or thin films doped with rare earth ions [1–5]. In the case of silicabased materials the physical properties of the produced xerogels depend on the physicochemical processes accompanying the hydrolysis and gelation of tetraethylorthosilicate (TEOS) at different temperatures and time durations. In our previous contributions we demonstrate a higly efficient germanium–terbium energy transfer in silica sol-gel derived glasses [4, 5], the synthesis of transparent holmium-doped silica xerogels [3], as well as the luminescence of silica gels doped with terbium benzoate complexes [4]. The aim of the present investigation is the study of the preparation and luminescence of Ce3+/Tb3+ codoped silica xerogels. Optical materials containing Tb3+ and Ce3+ are important green emitting phosphors due to Ce3+ (5d1) → Tb3+ (4f75d1) energy transfer [6–8]. Despite the intense investigations of polycrystalline Ce3+/Tb3+-doped materials [8], the luminescence of amorphous xerogels remains unexplained so far. The silica xerogels in the present contribution were prepared by acid-catalyzed hydrolyzation of TEOS dissolved in ethanol (EtOH), and then gelation and drying (Techne 3D dry block with 5.6 ml starting amount of TEOS for all samples). Both ethanol addition and doping, followed by hydrolysis with HCl at pH 2 were performed under stirring. The molar ratios were TEOS:EtOH:H2O:HCl = 1:1:4:0.003. The pH of the 0.45 M Tb3+ nitrate solution is 4–5. For the cerium codoping a 1.8 M Ce3+ nitrate solution with pH 4–5 was added to the terbium containing sol. The duration and temperature conditions for all samples of the different sol-gel steps following the cerium codoping are: hydrolysis—1 hr at room temperature, gelation—48 hr at 50 ◦C and drying—120 hr at 50 ◦C. Samples containing 1 mol% Tb/Si and codoped with 0.5, 1, 2, 3, 4, 5, and 7.5 mol% Ce/Si as well as 1, 2, and 5 mol% Ce/Si were

Refractory and chemically inert nanoparticulate solids like yttria, yttrium aluminium garnet or lutetium aluminium garnet are notoriously difficult to disperse in aqueous solution, although such dispersions might prove useful for 2D- and 3D-printing, deposition of films or other shaping procedures for ceramic green bodies. This work reports on experiments to prepare such dispersions from nanopowders, using a range of selected carboxylic acids as ligands for electrostatic charging and stabilization of the various nanomaterials. The assessment of the system properties achieved combines ζ-potential and viscosity (flow curve) measurements in the resulting colloidal systems. Calculations of the molecular electrostatic potential of the ligands were used to correlate the molecular structure of the ligands and their capability to dock to the surface of the solid particles. The colloid chemical data received have then been interpreted on this background; citric acid and polyacrylic acid have been identified as the most attractive dispersants.

Strontium can be substituted into the calcium sublattice of hydroxyapatite without a solubility limit. However, recent ab initio simulations carried out at 0 K report endothermic nature of this process. There is also striking discrepancy between experimentally observed preference of Sr doping at Ca-II sites and the first principles calculations, which indicate that a Ca-I site is preferred energetically for the Sr substitution. In this paper we combine insights from Density Functional Theory simulations and regular configurational entropy calculations to determine the site preference of Sr doping in the range of 0-100 at% at finite temperatures. In addition, samples of Sr-HA are synthesized and refinement of the relevant structural information provides benchmark information on the experimental unit cell parameters of Sr-HA. We find that the contribution of the entropy of mixing can efficiently overcome the endothermic excess energy at a temperature typical of the calcining step in the synthesis route of hydroxyapatite (700-950 degrees C). We observe that the most preferential substitution pattern is mixed substitution of Sr regardless of the concentration. For a wet chemical method, carried out at a moderate temperature (90 degrees C), the mixed doping is still slightly favourable at higher Sr-concentrations, except the range at 20% Sr, where Site II substitution is not restricted energetically and equally possible as the mixed doping. We observe a close correspondence between our theoretical results and available experimental data. Hence it should be possible to apply this theory to other divalent dopants in HA, such as Zn2+, Mg2+, Pb2+, Cu2+, Ba2+, Cd2+ etc.

Mit den Leuchtstoffen ZnS:Cu, Au, Al (grun), ZnS:Ag (blau) und Y2O2S:Eu (rot) stehen nach uber vierzigjahriger Entwicklung fur konventionelle Farbfernseh- und Computer-monitor-Anwendungen optimierte Materialien zur Verfugung, deren Lumineszenzeigenschaften kaum Wunsche offen lassen. Verbessert werden konnte allenfalls das Sattigungsverhalten des grunen Leuchtstoffs, wobei allerdings auch die Elektronenkanonen effizienter werden musten. Durch den Ersatz Cadmium-haltiger Zinksulfide ist ein weiterer Schritt in Richtung Umweltvertraglichkeit gelungen. Daher liegen die Herausforderungen zur Zeit eher im Bereich der Pulvertechnologie, z. B. bei der Kontrolle der Morphologie (Korngrose) und bei kontrasterhohenden Masnahmen (Ummantelungen/Pigmentierungen) zur weiteren Verbesserung von Auflosungsvermogen, Brillanz und optimaler Anpassung an die Produktionsbedingungen. Bei den Projektionsfernsehrohren konnten das Alterungsverhalten und die Sattigung des blauen Phosphors, ZnS:Ag, noch verbessert werden; nach Alternativen wird gesucht. Neue Displaykonzepte befinden sich noch im Entwicklungsstadium; die zugehorigen Leuchtstoffspezifikationen sind zum Teil noch nicht bekannt. Bei ihnen wird in Zukunft vermutlich ein Schwerpunkt der industriellen Lumineszenz- bzw. Leuchtstoff-Forschung liegen.

Highly luminescent ZnS:Cu nanoparticles were synthesized in a coprecipitation route using aqueous salt solutions and thiopropionic acid as stabilizer. The method yields a stable, transparent particle dispersion in water and allows for a good control over particle size in the range of 3–10 nm as determined by dynamic light scattering, small angle X-ray scattering and transmission electron microscopy. Strong luminescence of the nanoparticles was observed under UV-excitation and emission colors could be adjusted in the range of blue to green by varying the Cu-doping concentration. The phase transfer of the ZnS:Cu nanoparticles into non-polar solvents using octylamine was used for a hydrophobic surface functionalization. The hydrophobic particles were used for the fabrication of transparent bulk nanocomposites via in situ -polymerization of dispersions in laurylacrylate. A high transparency of the composite materials, and the luminescence of the ZnS:Cu nanoparticles is retained during the phase transfer and the polymerization process allowing for the integration of a new luminescent functionality into the polymer material.

ZnS is a versatile wide-gap semiconductor that shows remarkable chemical stability against oxidation and hydrolysis. These properties are retained when the particle size steps down to 10 nm and below, and thus ZnS nanoparticles are interesting entities for optical and catalytic functions, where they might be exposed to quite aggressive environments. Moreover, ZnS may be doped by a host of elements, so that the electrical and optical properties can be tuned over an extended range. Neither Zn nor S are in short supply, and ZnS as compound or in view of the constituting elements is not toxic. Therefore, functional materials based on ZnS will be ideal for "green chemistry" applications, since they are suited also for large scale manufacture and will pose no additional problems when released into the environment. The article describes first results for ZnS-nanoparticles acting as electrocatalysts, a field that has not been covered so far by ZnS-derived materials. The catalytic action is evaluated for the decomposition of ethanol, a potentially abundant fuel for mobile electricity generation, since it can be fabricated by fermentation from a broad range of organic materials.

Enhanced photoluminescence (PL) is reported from Mn-doped ZnS nanocrystals (NCs) capped with ZnS (ZnS:Mn/ZnS core-shell NCs) and thioglycolic acid (TGA) (ZnS:Mn/ZnS core-shell NCs dispersed in an alkaline TGA solution). The NCs were prepared using a reverse micelle route. Comparing with initial ZnS:Mn core NCs, the ZnS:Mn/ZnS core-shell NCs exhibit much stronger orange PL (~580 nm). This is presumably the result of effective passivation of quenching ZnS:Mn NCs surface states by a pure ZnS shell. As for TGA-capped ZnS:Mn/ZnS core-shell NCs, the parallel decrease of a defect-related emission of ZnS is associated with the formation of a shell surface layer of TGA-Zn complexes. In summary, the combination of ZnS shells with TGA ligands was demonstrated to yield ZnS:Mn NCs with narrow size distribution and intense PL.

In this work, transparent luminescent nanocomposites were obtained using manganese – doped ZnS nanoparticles with crystallite sizes of about 10 nm, dispersed in the monomer isobornyl acrylate (IBOA). Suited nanocrystals of Mn2+-doped ZnS have been prepared by arrested precipitation in the presence of capping agents like cysteamine, combined with hydrophobization. Transparent ZnS: Mn/PIBOA nanocomposites were subsequently prepared via in situ polymerization. Nanocomposites were produced by adding different percentages of nanoparticles up to 30% by weight. The structural properties of the ZnS:Mn nanoparticles were studied in detail using X-ray diffractometer (XRD), Fourier transform IR spectrometer (FT-IR), spectroscopy (UV-VIS) and dynamic light scattering (DLS). The X-ray diffraction pattern exhibited peaks corresponding to the cubic phase of ZnS. The emission spectrum (at 320 nm excitation) of the composites showed the same broad band as bulk ZnS:Mn, centered at 590 nm.

Recent investigations in the systems Ga2Te3/CdTe and Ga2Se3/CdSe have shown, that some quasibinary II—VI/III—VI-systems may possess an ordered phase as well as a thermodynamical miscibility gap. Therefore in these systems the interaction coefficient for the calculation of the excess enthalpy must be strongly concentration-dependent, since ordering and demixing are requiring interaction coefficients of opposite sign. The thermodynamical miscibility gap in the region of non-ordered solid solutions of II—VI-and III—VI-chalcogenides can be described by a regular model, which leads to good agreement with experimental data. The free enthalpy of the ordered phase is approximated by a very simple model, that takes into account an additional enthalpy contribution by the ordering process. After the evaluation of the phase diagram by minimizing the free enthalpy the calculations are compared with experimental results.