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

An up-conversion luminophore with high quantum yield and brightness based on BaF<inf>2</inf>:Yb³⁺,Er³⁺single crystals

Up-conversion (UC) of near-infrared radiation to visible light has received much attention because of its use in the conversion of solar radiation, luminescence thermometry, biosensing, and anti-counterfeiting applications. However, the main issue hindering the successful utilization of UC is the relatively low quantum efficiency of the process. In order to design new UC systems with high quantum yield (ϕUC) values, we synthesized two series of co-doped BaF2single crystals with nominal concentrations of Yb3+(2-15 mol%)/Er3+(2 mol%) as well as Yb3+(3 mol%)/Er3+(2-15 mol%). The highestϕUCvalue of 10.0% was demonstrated for the BaF2:Er3+(2 mol%) and Yb3+(3 mol%) sample under 490 W cm−2of 976 nm excitation. To study the natural limit of UC efficiency, quantum yield values upon direct excitation (ϕDS) of the4S3/2(ϕDS≤ 4%) and4F9/2(ϕDS≤ 26%) levels were measured. Comparison of experimental values of quantum yields to the ones obtained using Judd-Ofelt theory reveals strong quenching of the4S3/2state for all investigated compositions. In addition, we observed an unusually strong contribution of the Er3+:4I9/2excited state to both UC and down-shifting luminescent processes. This contribution becomes possible due to the very low maximum phonon energy of BaF2crystals (240 cm−1)

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

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