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The optical properties of a photoluminescent material based on CsPbBr3 perovskite nanocrystals were studied in this work. The laser heating of the obtained samples was studied under three different regimes of laser excitation: the photoluminescence band appears in the Stokes region, in the anti-Stokes region, and coincides with the excitation line. It was found that under laser excitation of a certain wavelength, this material is able to demonstrate predominantly anti-Stokes (upconversion) photoluminescence. A method is proposed for estimating the PL quantum yield from data on absorption, photoheating, and the position of the photoluminescence band of a sample at two different wavelengths. The external photoluminescence quantum yield of CsPbBr3 nanocrystals was experimentally determined to be 91 ± 4%. The results of this work can be useful for the development of optical cooling technology and can be used in the development of laser devices based on perovskite materials. [ABSTRACT FROM AUTHOR]

MXenes are a new material in the family of 2D materials and exhibit striking physical properties common to both dielectrics, conductors, and semiconductors. MXenes are the product of the MAX-phase after aluminum etching. Due to different synthesis techniques and a variety of starting precursors in the synthesis of MAX-phases, the properties of MXenes can also be controlled over a wide range. In this work, we have shown that depending on the presence of aluminum oxide with a small amount of chromium, the structure of MXenes exhibits intense narrow-band luminescence with half-width less than 1 nm under excitation at 532 and 633 nm. Moreover, aluminum oxide is formed naturally because of incomplete etching of aluminum from the structure of the MAX phase. The intensity of narrow band photoluminescence is temperature dependent. The work unambiguously identifies MXenes with and without the presence of aluminum oxide. In relatively pure MXenes, narrowband photoluminescence is absent. [ABSTRACT FROM AUTHOR]

The method for obtaining the MAX phase Ti2AlC by spark plasma sintering of mechanically milled elemental powders using Al4C3, TiC, Ti has been optimized. Ti2AlC is currently considered the most used MAX phase at high temperatures due to its good mechanical properties as well as good resistance to oxidation at high temperatures. When analyzing the literature, no method was found for obtaining Ti2AlC using Al4С3. The selection of the ratio of precursors and the condition for their activation directly affects the final content of the MAX phase and impurities. The series of experiments was carried out with different ratios of Al4С3 and TiС, in a liquid medium and in the atmosphere, as well as with different sintering temperatures. Analysis of experimental data showed that the maximum of the MAX phase was obtained at a sintering temperature of 1300°C and a molar ratio of Ti : TiС : Al4С3 = 7 : 1 : 1.3. Synthesis in acetone did not improve the result. By this method, obtaining the MAX phase with a purity of >90% is possible. [ABSTRACT FROM AUTHOR]

The optical properties of nanocomposite particles consisting of silicon cores about 100 nm in size with smaller gold nanoparticles deposited on their surface have been studied. An increase in the absorption of light in the nearinfrared region of the spectrum for the obtained nanoparticles is observed in comparison with that for nanoparticles of pure silicon or gold. Experiments on measuring the temperature of aqueous suspensions showed significantly higher rates of photoheating of nanocomposite particles upon irradiation with laser radiation at a wavelength of 810 nm compared to the case of pure silicon nanoparticles. Calculations of the distribution of the electric field showed multiple increases in its strength near nanocomposite particles upon irradiation with light in the visible and near-infrared ranges and also made it possible to find the scattering and absorption contributions to the extinction spectra of nanoparticle suspensions. The observed enhanced photoheating of nanocomposite particles can be used for application in antibacterial treatment and cancer hyperthermia. [ABSTRACT FROM AUTHOR]

The photoluminescent properties of nanocrystalline layers of organometallic perovskites deposited on various semiconductor and dielectric substrates are studied. It has been established that, depending on the substrate, both one and two maxima can be observed in the exciton photoluminescence spectrum for CH3NH3PbBr3 nanocrystals with dimensions of tens and hundreds of nanometers at room temperature. The photoluminescence of nanocrystals deposited on an array of silicon nanowires has a longer wavelength of the spectrum maximum as compared to nanocrystals on a flat surface of a single-crystal silicon substrate. The results obtained are explained by the influence of electric fields of bound charges at the interfaces and by processes of photoluminescence absorption. [ABSTRACT FROM AUTHOR]

Nanostructures made from transition metal dichalcogenides represent unique platform for realization of light-matter interaction at the nanoscale. This work is dedicated to laser engineering of spherical resonant Mie-excitonic nanoparticles from layered molybdenum disulfide (MoS2). We demonstrate the laser-based approach for synthesis of water-dispersed ultra-stable spherical MoS2 nanoparticles of variable size 10–150 nm. Such nanoparticles demonstrate exciting optical and electronic properties inherited from the initial crystal, due to preserved crystalline structure, which offers a unique combination of pronounced excitonic response and high refractive index value, making possible a strong concentration of electromagnetic field in nanoparticles. Moreover, it was found that laser fragmentation of produced colloidal solutions of MoS2 nanoparticles leads to its oxidation accompanied by evolution of its optical response. Such partially oxidized MoSxOy nanoparticles provide efficient absorption of near-infrared radiation making them perfect candidates for biomedical theranostics applications. [ABSTRACT FROM AUTHOR]

The previously unknown aluminum-containing solid solution 312 Mn + 1AXn phases (Ti0.5,V0.5)3AlC2, (Ti0.5,Ta0.5)3AlC2 and (Ti0.5,Nb0.5)3AlC2 were successfully synthesized by the standard non-pressure sintering method. The composition of the MAX-phase was confirmed by complementary methods: XRD, SEM and EDS. Rietveld analysis of the powder X-ray diffractograms was used to calculate the lattice parameters and phase compositions. Heating of pure Ti, Al, C powders with Ta, Nb added in 1.5 : 1.5 : 1.1 : 2 molar ratio up to 1450°C for 8 h under dynamic vacuum resulted in samples with dominant MAX phase volume fraction. All new MAX phases were then successfully converted to MXenes using the standard MILD protocol-chemical etching of aluminum layers in a mixture of HCl acid and LiF. The obtained MXenes were characterized using several techniques, including: XRD, SEM, TEM, EDS, AFM, and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Quasi one-dimensional materials are technologically very important due to their extraordinary properties. The properties are enhanced when these materials are exfoliated into single or few layers. In this work, we present the laser etching of TiS3 nanoribbons synthesized by chemical vapor transport technique. The experiments were carried out using the TiS3 nanoribbons with thicknesses ranging from 100 to 150 nm. These nanoribbons were transferred on a silicon substrate via mechanical exfoliation technique prior to the laser treatment for the etching process followed. The resulting etching depth was in the range of 20–25 nm with no oxidation. Through the experiments, it was found that the etching depth was independent of the initial thickness of the nanoribbons, which suggests that if samples had a smaller initial thickness, a monolayer can be obtained. We also observed significant (up to 3–4 nm) improvement of the surface roughness of the etched samples, which makes the laser etching technique promising for the development of flexible, efficient, and reliable optoelectronic devices. [ABSTRACT FROM AUTHOR]

The growing family of two-dimensional crystals has been recognized as a promising platform for investigation of rich low-dimension physics and production of a variety of devices. Of particular interest are recently reported atomic sheets of non-van der Waals materials, which reshape our understanding of chemical bonds and enable heterostructures with novel functionality. Here, we study the structural and optical properties of ultrathin non-van der Waals InGaS3 sheets produced by standard mechanical cleavage. Our ab initio calculations reveal weak out-of-plane covalent bonds, responsible for the layered structure of the material. The energy required for isolation of a single layer is as low as ~50 meVÅ–2, which is comparable with the conventional van der Waals material's monolayer isolation energies of 20–60 meVÅ–2. A comprehensive study of the structural, vibrational, and optical properties of the material reveals its wide bandgap (2.73 eV), high refractive index (>2.5) and negligible losses in the visible and infrared spectral ranges. These properties make it a perfect candidate for visible-range all-dielectric nanophotonics. [ABSTRACT FROM AUTHOR]

Abstract: This work is devoted to the wear nature of Fe-Ni-Cr-W-Mo-Co-C-B metal glass coatings on steel 1035 substrate via electrospark deposition in various granules mediumcompositions. The microhardness, roughness, and wear resistance of the coatings under dry abrasive and dry sliding wear conditions in the load range of 2.2 to 50 N were studied. During dry abrasive friction, the minimum specific wear rate of the coatings was 1.4 to two times lower than that of steel 1035 in all load ranges. Tests of the Fe33Ni8Cr8W8Mo8Co8C16B11 coating resistance to dry friction against P6M5 steel showed that its wear at 30 km was 1.5 to two times lower than steel 35, but, with a decrease in the normal load, the greatest effect of steel hardening was observed. The results show that the method used in the electrospark deposition of the Fe33Ni8Cr8W8Mo8Co8C16B11 granules mixture can protect the steel substrate from abrasive and sliding wear at low loads and speeds. [ABSTRACT FROM AUTHOR]

It was shown that, without entering the structure of the crystal, boron can change the structure of the melt and have a significant effect on the fine features of the structure and the physical characteristics of lithium niobate crystals. Crystals grown from a charge doped with boron by the direct solid-phase method have a stronger photorefractive effect and a smaller forbidden band width than crystals grown from the re-extract doped homogeneously with boron at the niobium pentoxide extraction stage. [ABSTRACT FROM AUTHOR]

Photoinduced light scattering and optical spectroscopy have been used to study the photorefractive effect and determine the band gap in nominally undoped congruent and stoichiometric lithium niobate crystals, as well as in a series of congruent LiNbO3 crystals doped with Mg, Zn, B, Gd, Y, and Er cations and LiNbO3 single crystals codoped with Mg:Gd, Mg:Fe, Mg:Y, and Mg:Ta. [ABSTRACT FROM AUTHOR]

A stoichiometric lithium niobate crystal (LiNbO) and congruent lithium niobate crystals grown from a charge prepared using cyclohexanone as an extractant (LiNbO(CHN)) and a charge prepared using cyclohexanone and carboxylic acid dimethylamides as extractants (LiNbO(CHN + A)) have been characterized by photoinduced light scattering and laser conoscopy. The results demonstrate that the LiNbO(CHN + A) crystals are rather homogeneous along their growth direction and possess good optical properties, similar to those of the LiNbO(CHN) crystal. At the same time, the LiNbO(CHN + A) crystal offers significantly better electro-optical properties ( r = 29.3 pm/V). [ABSTRACT FROM AUTHOR]

Photovoltaic and diffusion fields in nominally pure single crystals of stoichiometric composition (R = Li/Nb = 1) grown in the presence of 6 wt% KO flux (LiNbO stoich. KO) in nominally pure single crystals of complementary composition (LiNbO), complementary single crystals doped with Zn, Er at wavelength of 476, 514.5, 530 nm are defined according to parameters of photo induced light scattering indicatrix. Photo induced changes of crystals' refractive index are defined. [ABSTRACT FROM AUTHOR]

The article discusses the investigations into photorefractive light scattering (PRLS) in nominally pure single crystals of stoichiometric composition (Li/Nb = 1) grown from a melt with 58.6 mol % Li2O. It is demonstrated that the asymmetric pattern of the scattering indicatrix depends on radiation intensity up to 160 mW. When the radiation intensity increases, the crystal is heated, resulting in a decrease in the scattering indicatrix. [ABSTRACT FROM AUTHOR]

Crystalline FeWMoCrBC electrode materials were prepared by conventional powder metallurgy. Metallic glass (MG) coatings were produced by electrospark deposition onto AISI 1035 steel in argon atmosphere. X-ray diffraction and scanning electron microscopy verified the amorphous structure of the as-deposited coatings. The coatings have a thickness of about 40 microns and a uniform structure. The results of dry sliding wear tests against high-speed steel demonstrated that Fe-based MG coatings had a lower friction coefficient and more than twice the wear resistance for 20 km sliding distance with respect to AISI 1035 steel. High-temperature oxidation treatment of the metal glass coatings at 1073 K in air for 12 h revealed that the oxidation resistance of the best coating was 36 times higher than that for bare AISI 1035 steel. These findings are expected to broaden the applications of electrospark Fe-based MG as highly protective and anticorrosive coatings for mild steel. [ABSTRACT FROM AUTHOR]

We have investigated the photorefractive (photoinduced) light scattering in lithium niobate single crystals: LiNbO, LiNbO:B, LiNbO:Y(0.46 mas %), LiNbO:Y(0.24):Mg(0.63 mas %), and LiNbO:Ta(1.13):Mg(0.0109 mas %) that were grown from congruent melts. We have found that the shape of the speckle structure of this scattering and the kinetics of the development of its indicatrix depend substantially on the type of the impurity dopant in the lithium niobate crystal. We have observed that, upon laser irradiation of crystals doped with Y, Ta:Mg, and Y:Mg, the shape of their scattering indicatrix changes with time. At the same time, the LiNbO:B crystal is characterized by a complete absence of time changes in its speckle structure, which indicates that the photorefractive effect in this crystal is substantially lowered. [ABSTRACT FROM AUTHOR]

The conversion of the broadband thermal radiation in stoichiometric ( R = 1) lithium niobate single crystals that are grown from melt with 58.6 mol % of LiO, congruent ( R = Li/Nb = 0.946) melt with the KO flux admixture (4.5 and 6.0 wt %), and congruent melt and in congruent single crystals doped with the Zn, Gd, and Er cations is studied. It is demonstrated that the conversion efficiency of the stoichiometric crystal that is grown from the melt with 58.6 mol % of LiO is less than the conversion efficiency of congruent crystal. In addition, the stoichiometric and almost stoichiometric crystals and the doped congruent crystals exhibit the blue shift of the peak conversion intensity in comparison with a nominally pure congruent crystal. For the congruent crystals, the conversion intensities peak at 520 and 495 nm, respectively. [ABSTRACT FROM AUTHOR]

Using the methods of photorefractive and Raman light scattering, we study subtle features of the structure of LiNbO single crystals with different Li/Nb ratios (pure and doped with nonphotorefractive cations) grown by different methods. We reveal that, upon the irradiation of a single crystal with visible laser light, locally fluctuating micro- and nanostructures are initially formed in it, with their physical parameters being different from the corresponding parameters of the single crystal in the absence of the photorefractive effect. Upon an increase in the irradiation intensity and in the course of time, more and more such micro-structures are formed, and they are transformed into static micro- and nanoformations, which are subsequently converted into a continuous laser track. The speckle structure of photorefractive scattering is studied in detail. We show that the photorefractive effect in single crystals of the stoichiometric composition is fairly strong for their use as materials for recording and storing information. [ABSTRACT FROM AUTHOR]

The photovoltaic and diffusion fields in nominally pure single crystals of stoichiometric composition ( R = Li/Nb = 1) grown from the melt with 58.6 mol % of LiO (LiNbO stoich), in the nominally pure single crystals of congruent composition (LiNbO), and in congruent single crystals doped with Cu, Zn, and Gd are found from the parameters of the photoinduced light scattering indicatrix obtained with the use of a 60-mW He-Ne laser. [ABSTRACT FROM AUTHOR]

The time dependence of the photorefractive light scattering in lithium niobate single crystals of the congruent composition (LiNbO3) doped by “photorefractive” Cu cations (0.015 wt %) is studied for a radiation power of 160 mW. The data for the photorefractive scattering are confirmed by changes in Raman scattering spectra. [ABSTRACT FROM AUTHOR]