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We report a study of upconversion luminescence in BaF2–HoF3 crystals in the visible spectral region under excitation to the 5I5 level of Ho3+ ions by laser radiation with a wavelength of 890 nm. For these excitation conditions, we propose mechanisms responsible for upconversion luminescence from the 5F3, 5S2(5F4) and 5F5 levels of Ho3+ ions.

The characteristics of upconversion luminescence of CaF2:Er crystalline powders upon laser excitation of Er3+ ions to the 4I13/2 level at a wavelength of 1531.8 nm are studied. The upconversion luminescence energy yields for the spectral regions of 380–780 and 380–1100 nm are determined. It is found that upconversion luminescence of CaF2:Er powders with Er3+ concentrations of 0.5, 2, 4, 6, 8, 10, 11, 13, 15, and 17% is characterized by correlated color temperatures of 5100, 2142, 1726, 1738, 1773, 1757, 1762, 1765, 1735, and 1714 K, respectively.

Upconversion luminescence of fluoride phosphors SrF2:Er,Yb co-precipitated from aqueous solutions is studied. Under excitation of Er3+ ions to the 4I13/2 level, upconversion luminescence spectra are recorded in the visible and near-IR spectral regions, which correspond to the 4G11/2 → 4I15/2, 2H9/2 → 4I15/2, 4F5/2 → 4I15/2, 4F7/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2 → 4I15/2, 4I9/2 → 4I15/2, and 4I11/2 → 4I15/2, electronic transitions of Er3+ ions and to the 2F5/2 → 2F7/2 transition of Yb3+. The absolute quantum yields of visible upconversion luminescence under excitation in the region of 1.5 μm are determined for SrF2:Er,Yb phosphors with different concentrations of Er3+ and Yb3+ ions and analyzed comparatively with the corresponding values for SrF2:Er phosphor. A study of chromaticity coordinates showed that the yellow-green upconversion luminescence of SrF2:Er,Yb phosphors is characterized by color temperatures of 3037–3526 K at an incident power density of 850 W/cm2.

The purpose of the article is to discuss methods of air disinfection in passenger aircraft cabins during flight. In the course of the study, a comparative analysis of modern methods of cleaning and disinfecting air in closed rooms was carried out. The efficiency, mass characteristics and energy consumption of UV sources are compared. The use of photocatalytic filters based on the phenomenon of oxidation of organic substances under the influence of sunlight in the presence of a catalyst is proposed. As a result, the authors compare the efficiency of disinfection and energy consumption when using various methods of air purification. In addition, the authors draw conclusions about the prospects of the proposed method of air disinfection using photocatalytic filters in relation to the cabins of passenger aircrafts. The schemes of rational placement of UV sources are proposed, which allow obtaining the maximum efficiency of air disinfection.

In this work, the polymer film based on the upconversion particles doped Er3+ and Yb3+ ions and polyethylene was obtained byusing extrusion and hot pressing methods. Upconversion luminescence spectra of polymer films were recorded in the visible spectral range upon excitation by laser radiation at wavelengths of 972 nm and 1532 nm. The applications of a polymer film in various areas of photonics are discussed.

In preset paper, for the first time upconversion luminescence (UCL) of SrF2:Er,Tm phosphors upon excitation of 4I13/2 level of Er3+ were investigated. Fluorite-type SrF2:Er,Tm phosphors were synthesized by co-precipitation from aqueous nitrate solution technique. Tuning the UCL by SrF2:Er through Tm3+ ions co-doping was demonstrated. Also we estimated the UCL energy yield in the visible and near-infrared spectral range.

In present work, the spectral-luminescent properties of CaF2-SrF2-ErF3 (CaF2-SrF2:Er) single crystals were investigated. The upconversion luminescence (UCL) of CaF2-SrF2: Er in the visible and infrared spectral regions upon excitation of the 4I13/2 level Er3+ ions were studied for the first time. The absolute energy yields of the UCL upon laser excitation at 1.5 μm are determined for CaF2-SrF2:Er. The possible application of fluoride crystals for increasing the efficiency of solar cells was discussed.

The article deals with information-diagnostic systems of detection of defects and malfunctions as applied to aircraft structures and units. Methods. Analysis of modern methods of nondestructive testing is carried out. It is suggested to use the combined diagnostics of aircraft structures and systems with the use of vibrometry in combination with the determination of the appearance of metal particles in the oil, their quantity and size. The possibility of using acoustic emission is considered. Results. The article compares the accuracy and reliability of the inspection of aircraft parts, assemblies and systems by different methods. Conclusion. We have drawn conclusions about the prospects of the proposed method of diagnostics. It is shown that trained neural networks are able to provide information about the presence of defects, their size and location when working in the software of information-diagnostic systems.

Fluorite-type SrF2:Er powders were synthesized by using a co-precipitation from the aqueous solution technique. X-ray powder diffraction, scanning electron microscopy, absorption and luminescence spectroscopy were used to characterize the samples. For the first time upconversion luminescence of SrF2:Er powders in the visible and near-infrared spectral region upon excitation of 4I13/2 level Er3+ ions was investigated. The decrease in the slopes of the visible upconversion luminescence with increasing excitation power density and concentration of Er3+ ions were experimentally observed and discussed. The most intensive visible luminescence was obtained for SrF2:Er (8.8%) with a maximum quantum yield of 0.19%. Chromaticity coordinates and color temperature of yellow-green upconversion luminescence of SrF2:Er were calculated.

Mechanisms of upconversion luminescence (UCL) of SrF2:Er phosphors corresponding to the G411/2→I415/2, H29/2→I415/2, F45/2→I415/2, F47/2→I415/2, H211/2→I415/2, S43/2→I415/2, F49/2→I415/2, and I49/2→I415/2 transitions upon excitation of the I411/2 level of Er3+ ions were investigated. Energy transfer upconversion processes are responsible for the populating of the H29/2, H211/2, S43/2, and F49/2 levels. Cooperative process is the dominant mechanism of luminescence from S43/2 and F49/2 levels for SrF2:Er with high concentrations of Er3+ ions. The UCL from G411/2 and F45/2 is explained by excited-state absorption. Cross-relaxation processes take part in the population of F49/2 and I49/2 levels. For quantifying material performance, the Er3+-concentration dependence of UCL and the absolute quantum yields of SrF2:Er were studied. The most intensive visible luminescence was obtained for SrF2:Er (14.2%) with 0.28% maximum quantum yield.

Low-temperature thermal properties of superconductors have been studied. It is shown that the symmetry group influences the thermal conductivity and the anomalous acoustic damping, and the directions of maximum thermal conductivity and acoustic damping factor are indicated. For crystals, the general conclusion is reached that the absence of a center of symmetry is a necessary condition for the existence of these properties.