Transmission electron microscopy and flow cytometry study of cellular uptake of unmodified Pr³⁺:LaF<inf>3</inf> nanoparticles in dynamic

The article represents the transmission electron microscopy (TEM) and flow cytometry study of A-549 (human lung carcinoma) cellular uptake of unmodified Pr3+:LaF3 nanoplates and nanospheres after 2, 10, and 24 h of nanoparticles exposure. The studied Pr3+:LaF3 (CPr = 1 mol.%) nanoplates (length = 64.0 ± 1.0 nm) and nanospheres (diameter = 13.0 0.4 nm) are hexagonal structured nanocrystals without amorphous phase. Both morphotypes of nanoparticles (nanoplates and nanospheres) are easily internalized by A-549 cells via macropinocytosis after 2, 10, and 24 h of nanoparticle exposure. The nanoparticles were not observed in cell nuclei and other organelles. During macropinocytosis, relatively large vesicles (0.2–5 μm) are formed. The flow cytometry experiments revealed that the internalized nanoparticles increase the cells’ optical inhomogeneous that leads to an increase of side scattered light intensity by ~ 10% without any dynamic during 24 h (for both morphotypes of nanoparticles). Probably, it can be explained by the fact that macropinocytosis is a dynamic process and some macropinosomes appear and move in the cytoplasm, in turn, other macropinosomes travel back to the cell surface of the membrane and release the content to the extracellular space, consequently, the equilibrium is achieved

Tetrahydrobiopterin Photooxidation: a Key Process in Vitiligo Phototherapy

Abstract: The processes of the autooxidation and photooxidation of tetrahydrobiopterin (Н4Bip) (a coenzyme present in a three- to fivefold excess in vitiligo) were studied in the context of vitiligo pathology and treatment. The study of the kinetics of Н4Bip autooxidation and analysis of the reaction products via high-performance liquid chromatography (HPLC) demonstrated that autooxidation was intensive at a rate constant of 1 × 10–3 s–1 with the formation of dihydrobiopterin, dihydropterin, and their oxidized derivatives. Analysis of the autooxidation data led to a new conclusion that the oxidation of the excess of Н4Bip in melanocytes obviously triggers an autocatalytic cycle of the synthesis of the excess of hydrogen peroxide (Н2О2). This, in turn, activates interferon-inducible GTP cyclohydrolase, which synthesizes an excess of Н4Bip. The autocatalytic cycle of excess Н2О2 synthesis apparently underlies the pathology of vitiligo. The excess Н2О2 is also partly spent to activate the immune system. The autocatalytic cycle can be broken via the conversion of Н4Bip into dihydropterin dimers during its UV photooxidation. The kinetics of Н4Bip was studied, the reaction products were identified, and the quantum yields of the formation of dihydropterin dimers were calculated. The action spectrum of UV radiation was constructed based on the quantum yield data. It shows that the range of 300–325 nm is efficient for vitiligo phototherapy

Spectral-Kinetic Properties and Energy Transfer in Nanoparticles of Y<inf>0.5–x</inf>Ce<inf>0.5</inf>Tb<inf> x</inf>F<inf>3</inf> Solid Solution

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Crystalline nanoparticles of Y0.5–xCe0.5TbxF3, doped with various concentrations (x = 0, 0.005, 0.01, 0.05, 0.1, 0.15, and 0.2) of Tb3+ ions were synthesized by co-precipitation. The crystal structure and chemical composition of nanoparticles were studied using transmission electron microscopy, scanning electron microscopy, and X-ray diffractometry. The obtained nanoparticles of solid solutions had an elliptical shape with a size of 10–15 nm along the long axis and good crystallinity with the structure of a CeF3 crystal. The spectral-kinetic properties of the obtained nanoparticles, and the effect of the concentration of Tb3+ activator ions on the energy transfer from Ce3+ to Tb3+ ions were investigated. Energy transfer from Ce3+ to Tb3+ ions in nanocrystals of the Y0.5–xCe0.5TbxF3 solid solutions occurs mainly through the dipole–dipole interaction. The results of evaluating the efficiency of energy transfer from Ce3+ to Tb3+ ions show its increase with increasing concentration of Tb3+ ions

Characterization of perspective active medium based on mixed crystals Ce3+:LiCaXSr1-XAlF6

© 2020 IEEE. The aim of this work is characterization of perspective active media based on mixed crystals Ce3+:LiCaXSr1XAlF6. Also the optical studies ions in the UV spectral range and effect of the various types of the doping centers on the laser characteristics in the Ce3+:LiCaXSr1-XAlF6 mixed crystals were studied

Down-conversion luminescence of Yb³⁺ in novel Ba<inf>4</inf>Y<inf>3</inf>F<inf>17</inf>:Yb:Ce solid solution by excitation of Ce³⁺ in UV spectral range

© 2020 Elsevier B.V. The down-conversion luminescence under UV excitation was demonstrated in single-phase Ba4Y3F17 solid solution nanoparticles codoped with Ce3+/Yb3+. The complex photodynamic processes occurred in the samples including excited state absorption, excitons and color centers formation. The Yb doping suppressed the solarization effect. The efficiency of down-conversion from UV to near IR luminescence of Yb3+ appeared to be high due to Ce4+-Yb2+ charge transfer mechanism responsible for energy transfer between Ce3+ and Yb3+ ions. The direct measurements of down-conversion luminescence quantum yield by means of integrating sphere and calculations of energy transfer efficiency from luminescence spectra data were carried out. The down-conversion luminescence quantum yield reached the maximum value of about 1% for the sample with 0,1 mol.% of Ce3+ and 5,0 mol.% of Yb3+ ions contents, whereas energy transfer coefficient reached its maximum of about 6,3% for 0,05 mol.% of Ce3+ and 5,0 mol.% of Yb3+ ions

Growth, spectroscopy and continuous-wave laser performance of Nd³⁺:LiLu_0.65Y_0.35F₄ crystal

A mixed fluoride crystal of LiLu0.65Y0.35F4 doped with Nd3+ ions was grown by the Bridgman–Stockbarger method. Polarized absorption and luminescence spectra as well as luminescence lifetime were measured at room temperature. Emission probabilities, branching ratios and radiative lifetime were studied within the Judd–Ofelt theory and the emission cross section spectra were calculated. Efficient continuous wave laser operation was demonstrated with the crystal. A maximum output power of 7.7 W and slope efficiency of 60% were achieved at 1047 nm for the TEM00 mode

The study of the luminescence of solid solutions based on yttrium fluoride doped with ytterbium and europium for photonics

© 2020 Voronezh State University. All right reserved. The majority of the global market for solar photovoltaic devices is based on silicon technology. It is very important to increase their effi ciency through the use of luminescent coatings, including those converting radiation from the UV-blue region of the spectrum into the near-infrared range, where silicon absorbs radiation most effi ciently (Stokes or downconversion luminescence), or from the infrared region of the spectrum in the near-infrared range (up-conversion luminescence). The aim of this research was to synthesize and study the spectral-kinetic characteristics of single-phase solid solutions of Y1-x-yEuxYbyF3 and to determine the quantum yield of down-conversion luminescence. Using the method of high-temperature melting, single-phase samples of solid solutions of Y1-x-yEuxYbyF3 with orthorhombic system were synthesized. For the series of samples with different Eu3+/Yb3+ ratios, upon double doping with these ions, the formation of the corresponding solid solutions with a crystal lattice of the b-YF3 phase was confi rmed. Their chemical composition was determined using the energy dispersion analysis, and it was established that it corresponds to the nominal one. It was shown that both Eu3+ and Yb3+ ions become luminescent upon excitation at wavelengths of 266 nm and 296 nm. This indicates these compounds as promising sensitisers of UV radiation. In this case, upon excitation at a wavelength of 266 nm, luminescence of Eu2+ ions was recorded. The maximum quantum yield values (2.2 %) of the ytterbium downconversion luminescence in the near-infrared wavelength range upon excitation at a wavelength of 266 nm were recorded for YF3:Eu:Yb with the Eu3+:Yb3+ ratios of 0.1:10.0 and 0.05:5.00

Magnon Bose-Einstein condensation in CsMnF<SUB>3</SUB> and MnCO<SUB>3</SUB>

International audienceThe Spin Supercurrent and Bose-Einstein condensation of magnons, similar to an atomic BEC, was observed in 1984 in superfluid 3He-B. The same phenomena should exist in solid magnetic systems. We describe here the first observation of magnon BEC in solid easy plain antiferromagnets CsMnF3 and MnCO3. We have observed magnon BEC on a mode of coupled Nuclear-Electron precession. The dynamical properties of this mode have many similarities with NMR of superfluid 3He-A. The frequency changes with deflection of nuclear magnetization. Furthermore, the involvement of electron ordered subsystem gives the magnon-magnon interaction, spin waves and spin supercurrent, while the nuclear subsystem gives the relatively long time of relaxation

Down-conversion luminescence studies of CaF2, SrF2, Ba4Y3F17, GdF3, YF3, NaYF4 doped Yb or Pr/Ce/Eu ions for photonics

© 2020 IEEE. We determined compositions with high down-conversion characteristics from UV and blue spectral range to Yb luminescence based on luminescence studies, which are promising for efficiency increasing of silicon solar cells