Measurement of stress build-up of ion-exchange strengthened lithium aluminosilicate glass.

A recently developed non-destructive method was used to investigate the stress build-up in chemically strengthened lithium aluminosilicate glass. We utilized an updated version of the gradient scattered light method, which now enables more precise determination of the depth coordinates, recovering a more detailed stress profile around the knee. The main motivation of the work was to characterize and optimize the development of the knee-shaped breaking point in stress profile in lithium aluminosilicate glass using Saunders-Kubichan method of 1-step strengthening in a mixture of KNO3+NaNO3 molten salt bath. In the industry, a 2-step process is still commonly used to build such a stress profile. 1-step strengthening will simplify the process as well as save the cost. Compared to previous studies, which used a destructive method based on transmitted light photoelasticity, we found that in the samples ion-exchanged for 24h the knee-shaped breaking points were situated two times deeper whereas the case-depths were 28% shallower. The measured stress profiles were validated by stress equilibrium and by comparison to Na+ ion concentration profiles.

An energy transfer kinetic probe for OH-quenchers in the Nd(3+):YPO4 nanocrystals suitable for imaging in the biological tissue transparency window.

Tetragonal xenotime-type yttrium orthophosphate (YPO4) Nd(3+) doped nanoparticles suitable for biomedical applications were prepared by microwave-hydrothermal treatment. We applied the energy transfer probing based on the analysis of kinetics of impurity quenching to determine the presence and spatial position of -OH fluorescence quenching acceptors in the impurity-containing nanoparticles. We show that the impurity quenching kinetics of the 0.1 at% Nd(3+) doped YPO4 nanoparticles is a two stage (ordered and disordered) static kinetics, determined by a direct energy transfer to the -OH acceptors. Analyzing the ordered stage, we assume that the origin of the -OH groups is the protonation of the phosphate groups, while analyzing the disordered stage, we assume the presence of water molecules in the mesopores. We determine the dimension of the space of the -OH acceptors as d = 3 and quantify their absolute concentration using the disordered Förster stage of kinetics. We use the late stage of kinetics of fluorescence hopping (CDD ≫ CDA) quenching (the fluctuation asymptotics) at 1 at% Nd(3+) concentration as an energy transfer probe to quantify the relative concentration of -OH molecular groups compared to an optically active rare-earth dopant in the volume of NPs, when energy migration over Nd(3+) donors to the -OH acceptors accelerates fluorescence quenching. In doing so we use just one parameter α = γ(A)/γ(D) = n(A)√[C(DA)]/n(D)√[C(DD)], defined by the relation of concentration of the -OH acceptors to the concentration of an optically active dopant. The higher is the α, the higher is the relative concentration of -OH acceptors in the volume of nanoparticles. We find α = 2.95 for the 1 at% Nd(3+):YPO4 NPs that, according to the equation for α, and the results obtained for the values of the microparameters CDD(Nd-Nd) = 24.6 nm(6) ms(-1) and CDA(Nd-OH) = 0.6 nm(6) ms(-1), suggests twenty times higher concentration for acceptors other than donors. As the main result we have established that the majority of -OH acceptors is located not on the surface of the Nd(3+):YPO4 nanoparticles, as many researchers assumed, but in their volume, and can be either associated with crystal structure defects or located in the mesopores.

Reusable magnetic mixture of CuFe2O4-Fe2O3 and TiO2 for photocatalytic degradation of pesticides in water.

Photocatalysis is a promising treatment method to remove pollutants from water. TiO2-P25 is a commercially available model photocatalyst, which very efficiently degrades organic pollutants under UVA light exposure. However, the collection and the recovery of TiO2-P25 from cleaned water poses significant difficulties, severely limiting its usability. To address this challenge, we have prepared a sintered mixture of TiO2-P25 nanomaterials and magnetic CuFe2O4-Fe2O3 nanocomposites. The mixture material was shown to contain spinel ferrite, hematite and maghemite structures, copper predominantly in Cu2+ and iron predominantly in Fe3+ state. The CuFe2O4-Fe2O3 and TiO2-P25 mixture demonstrated magnetic collectability from processed water and photocatalytic activity, which was evidenced through the successful photodegradation of the herbicide 2,4-D. Our findings suggest that the sintered mixture of CuFe2O4-Fe2O3 and TiO2-P25 holds a promise for improving photocatalytic water treatment, with the potential to overcome current photocatalyst recovery issues.

Comparison of Toxicity and Cellular Uptake of CdSe/ZnS and Carbon Quantum Dots for Molecular Tracking Using Saccharomyces cerevisiae as a Fungal Model.

Plant resource sharing mediated by mycorrhizal fungi has been a subject of recent debate, largely owing to the limitations of previously used isotopic tracking methods. Although CdSe/ZnS quantum dots (QDs) have been successfully used for in situ tracking of essential nutrients in plant-fungal systems, the Cd-containing QDs, due to the intrinsic toxic nature of Cd, are not a viable system for larger-scale in situ studies. We synthesized amino acid-based carbon quantum dots (CQDs; average hydrodynamic size 6 ± 3 nm, zeta potential -19 ± 12 mV) and compared their toxicity and uptake with commercial CdSe/ZnS QDs that we conjugated with the amino acid cysteine (Cys) (average hydrodynamic size 308 ± 150 nm, zeta potential -65 ± 4 mV) using yeast Saccharomyces cerevisiae as a proxy for mycorrhizal fungi. We showed that the CQDs readily entered yeast cells and were non-toxic up to 100 mg/L. While the Cys-conjugated CdSe/ZnS QDs were also not toxic to yeast cells up to 100 mg/L, they were not taken up into the cells but remained on the cell surfaces. These findings suggest that CQDs may be a suitable tool for molecular tracking in fungi (incl. mychorrhizal fungi) due to their ability to enter fungal cells.

Alkoxide-based precursors for direct drawing of metal oxide micro- and nanofibres.

The invention of electrospinning has solved the problem of producing micro- and nanoscaled metal oxide fibres in bulk quantities. However, until now no methods have been available for preparing a single nanofibre of a metal oxide. In this work, the direct drawing method was successfully applied to produce metal oxide (SnO2, TiO2, ZrO2, HfO2 and CeO2) fibres with a high aspect ratio (up to 10 000) and a diameter as small as 200 nm. The sol-gel processing includes consumption of precursors obtained from alkoxides by aqueous or non-aqueous polymerization. Shear thinning of the precursors enables pulling a material into a fibre. This rheological behaviour can be explained by sliding of particles owing to external forces. Transmission (propagation) of light along microscaled fibres and their excellent surface morphology suggest that metal oxide nanofibres can be directly drawn from sol precursors for use in integrated photonic systems.

Graphene-Enhanced Raman Scattering from the Adenine Molecules.

An enhanced Raman scattering from a thin layer of adenine molecules deposited on graphene substrate was detected. The value of enhancement depends on the photon energy of the exciting light. The benzene ring in the structure of adenine molecule suggests π-stacking of adenine molecule on top of graphene. So, it is proposed that the enhancement in the adenine Raman signal is explained by the resonance electron transfer from the Fermi level of graphene to the lowest unoccupied molecular orbital (LUMO) level of adenine.

Angular shaping of fluorescence from synthetic opal-based photonic crystal.

Spectral, angular, and temporal distributions of fluorescence as well as specular reflection were investigated for silica-based artificial opals. Periodic arrangement of nanosized silica globules in the opal causes a specific dip in the defect-related fluorescence spectra and a peak in the reflectance spectrum. The spectral position of the dip coincides with the photonic stop band. The latter is dependent on the size of silica globules and the angle of observation. The spectral shape and intensity of defect-related fluorescence can be controlled by variation of detection angle. Fluorescence intensity increases up to two times at the edges of the spectral dip. Partial photobleaching of fluorescence was observed. Photonic origin of the observed effects is discussed.

Gilded nanoparticles for plasmonically enhanced fluorescence in TiO2:Sm3+ sol-gel films.

Silica-gold core-shell nanoparticles were used for plasmonic enhancement of rare earth fluorescence in sol-gel-derived TiO2:Sm3+ films. Local enhancement of Sm3+ fluorescence in the vicinity of separate gilded nanoparticles was revealed by a combination of dark field microscopy and fluorescence spectroscopy techniques. An intensity enhancement of Sm3+ fluorescence varies from 2.5 to 10 times depending on the used direct (visible) or indirect (ultraviolet) excitations. Analysis of fluorescence lifetimes suggests that the locally stronger fluorescence occurs because of higher plasmon-coupled direct absorption of exciting light by the Sm3+ ions or due to plasmon-assisted non-radiative energy transfer from the excitons of TiO2 host to the rare earth ions. PACS: 78; 78.67.-n; 78.67.Bf.