Search

We present a rapid and energy-efficient microwave-assisted approach to prepare a single-phase full-color phosphor based on Ba 3 MgSi 2 O 8 . The samples were prepared using a citric acid based sol–gel preparation pathway with a microwave-assisted heating step, which reduces the time required for the final heat treatment to less than 30 min. Thermogravimetric analysis was utilized to optimize the solution-based preparation prior to microwave heating. The structural properties of the obtained luminescent materials have been thoroughly investigated by means of X-ray powder diffraction and Rietveld analyses. To study the optical behavior, the excitation and emission spectra were recorded. Full-color emission is achieved using Eu 2+ (blue), Tb 3+ (green), and Mn 2+ (red) as the activator ions. The thermally robust emission was investigated using temperature-dependent luminescence spectroscopy. The energy-transfer processes within the samples were studied using time-dependent spectroscopy, and the quantum yield of this true color phosphor as a function of the composition was determined.

This article in the form of “reflections” is devoted mainly to the image-building of Heidegger in Russia as a thinker of Being, a conservative critic of late modernity and a “post” philosopher. On the one hand, due to French post-modernism influence on late Soviet and post-Soviet philosophy Russia has developed a special interest in Heidegger’s deconstruction theory. On the other hand, the reception of Heidegger’s criticism of European nihilism, totalitarianism and machine technology as the manifestations of modernity has shaped significantly the account of the “political”. The specifics of Russian reception of Heidegger can also be traced in the rejection of strict division between the “core” of Heidegger’s philosophy and “accidental” conditions related to social and political aspects of his work in 1930s. The current discussion about recently published “Black notebooks” shows not only the fact of existence of a separate language of description and analysis in Russian philosophical field but also an original tendency to holistic consideration of Heidegger’s thinking including not only his existential and historical reflections but also political passages and criticism of civilizational discourse. In addition to the reviews of “Black notebooks” by N.V. Motroshilova, V.V. Mironov and D. Mironova in the last year’s issues of the magazine “Voprosy filosofii” there are earlier works by N.V. Motroshilova, V.V. Bibikhin and A.V. Gulyga related to the debate on Heidegger’s political and ideological commitment which are in focus of attention.

A rapid and energy efficient microwave assisted solid state preparative route for europium-doped Akermanite (Ca{sub 2}MgSi{sub 2}O{sub 7}) has been developed. This method reduces the reaction time and energy needed by more than 90%, compared to the preparation carried out in a conventional furnace. The obtained samples are phase pure as has been determined using synchrotron X-ray powder diffraction data and Rietveld analyses. Scanning electron microscopy was employed to investigate the morphology of the microwave prepared compounds whilst energy dispersive X-ray spectroscopy (EDX) was used to verify the elemental composition of the specimens. A systematic investigation of the influence of the utilized microwave setup is presented. Finally, the microwave prepared materials were subject to temperature dependent photoluminescence measurements in order to investigate the thermal quenching of the luminescence.

Here we report a new approach for the preparation of anode buffer layer for efficient polymer light-emitting devices (PLEDs) by using glycerol to modify relative low conductivity poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). This new type of anode buffer layer allows for a 50–90% increase in device performance for green emitting phosphorescent PLEDs in terms of luminous efficiency, and external quantum efficiency, while 90–150% in power efficiency, as compared to devices fabricated using commercially available PEDOT:PSS. The green emitting phosphorescent PLEDs with this modified anode buffer exhibit very high efficiencies, representing a significant step forward to matching and exceeding the efficiencies reported to date with vacuum-deposited small molecular devices. We anticipate that these findings can provide a simple experimental procedure for improvement of PLEDs.

We have investigated the upconversion properties of the rare-earth doped systems La 2 BaZnO 5 ( I 4/ mcm ) and Gd 2 BaZnO 5 ( Pbnm ). The dependence of the luminescence properties on the identity and the concentration of the dopants, Er 3+ and Er 3+ co-doped with Yb 3+ , as well as on the synthetic route, was examined. Following coherent excitation at 975 nm, strong upconversion emission was observed in the visible region (525, 550 and 660 nm). Power dependence studies revealed a two photon process for these emissions. In the co-doped samples, a blue emission (410 nm) could also be observed. For this emission, the power dependence studies confirmed a three photon process.

We report on the anisotropic reflectance (R), transmittance (T) and photoluminescence (PL) properties of stretch-oriented free standing films of poly( p -phenylene-vinylene) (PPV) at different temperatures. The PL quantum efficiency is strongly dependent on the pump polarization, being higher when the pump is polarized perpendicular to the polymer chain orientation. Independently of the pump polarization, we find that the PL emission spectra are mainly polarized along the polymer chain direction. The PL spectra have been corrected both for the number of absorbed photons and for self-absorption of the emitted light. Frank-Condon analysis of the oscillator strength for absorption and corrected emission spectra suggest that two different “chromophores” contribute to the optical properties.

Liposomes have been evaluated as drug delivery vehicles for decades. However, it is hard to prepare liposomes to both balance enhanced drug retention and rapid and targeted content release. The challenge is to initiate the release of encapsulated drugs at the diseased site at a controlled rate. We recently developed a novel photo-activated approach by which near-complete contents release from liposomes can be completed within seconds by irradiating encapsulated or tethered hollow gold nanoshells (HGN) with a near infrared (NIR) pulsed laser. The rapid heating of the gold nanoshells leads to unstable microbubble formation and collapse, the same type of cavitation events associated with ultrasound. Our approach is conceptually analogous to the use of optically triggered nano-“sonicators” deep inside the body for drug delivery. We demonstrate that even though the local temperature surrounding HGNs can be very high, the bulk temperature of the solution only rises by ∼1°C. Results from electrophoresis and quantitative PCR all show no damage to DNA molecules mixed with HGNs after NIR irradiation. These results confirm the potential of using this optical approach to permeabilize lipid membranes and facilitate the cellular uptake of DNAs for gene therapy. Since DNAs are relatively robust macromolecules, we also investigated the more delicate dye molecule, carboxyfluorescein (CF), which contains a double bond; liquid chromatography followed by mass spectral analysis shows that ∼95% of CF molecules are intact. These results agree well with our hypothesis that only an few nanometer thick layer surrounding HGNs reach temperatures above the explosive boiling temperature (∼ 650 K), so that only CF molecules close to HGNs are damaged. Other NIR responsive materials, such as carbon nanotubes and solid gold nanoparticles were used as triggering agent for liposome release, and their release efficiencies are compared with those of HGNs.