Diamond-based composite materials, which integrate the exceptional physical and chemical properties of diamond with functional additives, are of significant interest in advanced materials science, particularly for applications in photonics and ionizing radiation detection. The incorporation of rare-earth elements, such as europium (Eu), into a diamond matrix enables the development of materials with efficient X-ray-to-visible light conversion, which is critical for the design of robust scintillators for synchrotron radiation sources and freeelectron lasers. In this study, the beta-NaGdF4 matrix is used as a model system to investigate the mechanisms underlying the significant modifications in europium luminescence spectra upon embedding europium-doped nanoparticles into a diamond matrix under varying thermal processing conditions. Plasma-chemical interactions between the nanoparticles and the methane-hydrogen plasma are identified as the primary factor driving these spectral transformations. At lower processing temperatures (700-750 degrees C), partial reduction of europium to the +2 oxidation state is observed. At higher temperatures (800-900 degrees C), hydrogen incorporation into the nanoparticles induces an excess of surface hydrogen relative to the particle volume, leading to compositional anisotropy from the surface to the core. These effects result in modifications to the local coordination environment of europium ions, promoting the dominance of the 5D0 -> 7F2 luminescence transition at 613 nm and inducing a systematic shift in all luminescence bands. Additionally, the study establishes key synthesis parameters for precise spectral tuning, enabling controlled modulation of luminescence from broadband to narrowband emission.

Nanoparticles (NPs) exhibiting X-ray-excited UV-C luminescence can be used in radiation therapy to deactivate cancer cells through photochemical reactions of DNA with UV-C quanta. Colloidal solutions of monoclinic La1−xPrxPO4 NPs (x = 0.01–0.3), luminescent in the UV-C range (220–280 nm), with different morphologies, from nanofiber (diameter and length not larger than 15 and 600 nm, respectively) to short nanorod (diameter and length not larger than 8 and 35 nm, respectively), were obtained by a microwave-assisted hydrothermal method. For possible biomedical use, the synthesis parameters (pH = 8, anion excess coefficient = 2) were determined, at which nanorods of suitable sizes (diameter and length not larger than 10 and 80 nm, respectively) with the brightest UV-C luminescence among all synthesized nanorods were obtained. A gradual increase in the optimal concentration of Pr3+ ions with maximum luminescence brightness from 4 mol-

We report the high-resolution (0.1 cm(-1)) infrared (0.9-1.67 mu m) photoluminescence spectra of a KY3F10:Ho3+ (1 at. %) single crystal in the regions of the I-5(5) -> I-5(7), F-5(5) -> I-5(6), I-5(6) -> I-5(8), and F-5(5) -> I-5(7) optical transitions. We show that the luminescence of KY3F10:Ho3+ can be used to measure cryogenic temperatures. Temperature dependences (3.4 K -> 180 K) of the luminescence intensity ratios are studied in the region of the infrared transition F-5(5) -> I-5(6) (similar to 1.47 mu m, the S telecom band) and I-5(6) -> I-5(8) (similar to 1.16 mu m). A pair of spectral lines 6767-6799.7 cm(-1) is suggested for ratiometric Boltzmann thermometry with maximum absolute sensitivities at the temperature of 23.5 K and corresponding relative sensitivity 9 % K-1 at this temperature. The temperature dependences of the linewidths of the 6767 cm(-1) and 8598.8 cm(-1) lines can be used for measuring higher temperatures.

Solvothermal reaction of magnesium nitrate and boron oxide in N,N-dimethylformamide produced a number of particularly complex supramolecular magnesium borates.

The annealing treatment plays a crucial role in tailoring the properties of synthetic diamond materials, especially those doped with various elements in order to form specific color centers like nitrogen-vacancy (NV), siliconvacancy (Si-V), germanium-vacancy (Ge-V), etc. This study delves into the annealing of 175 mu m-thick Gedoped polycrystalline diamond (PCD) films grown by microwave plasma-assisted chemical vapor deposition (MPCVD). Large-area PCD plate was cut into smaller equivalent 5 x 5 mm2 pieces, which were separately subjected to annealing in microwave plasma in H2 atmosphere, to annealing in vacuum or to annealing under high-pressure high-temperature conditions (HPHT, 5.9 GPa, 2000 degrees C). The structure, phase composition and photoluminescence (PL) of samples before and after various annealing processes were investigated. All applied types of annealing enhance both the Si-V and Ge-V lines in PL at room temperature. Increasing annealing temperature leads to gradual decrease of full widths at half-maxima (FWHM) of diamond Raman peak (1332.5 cm-1), as well as Si-V (738 nm) and Ge-V (602 nm) PL peaks. In addition, the limitations for each type of annealing are established. The obtained results are crucial for the design of CVD-grown Ge-doped and Si-doped PCD materials that can be used for applications in photonics such as single photon sources, biomarkers, as well as for the fabrication of optical diamond thermometers.

The coupling between antiferromagnetic spins and infrared-active phonons in solids is responsible for many intriguing phenomena and is a field of intense research with extensive potential applications in the modern devices based on antiferromagnetic spintronics and phononics. Insulating rutile antiferromagnetic crystal CoF$_2$ is one of the model materials for studying nonlinear magnetophononics due to the strong spin-lattice coupling as a result of the orbitally degenerate ground state of Co$^{2+}$ ions manifested in the plethora of static and induced piezomagnetic effects. Here we report results on the complete infrared spectroscopy study of lattice and magnetic dynamics in CoF$_2$ in a wide temperature range and their careful analysis. We observed that infrared-active phonons demonstrate frequency shifts at the antiferromagnetic ordering. Furthermore, using first-principles calculations, we examined the lattice dynamics and disclosed that these frequency shifts are rather due to the spin-phonon coupling than geometrical lattice effects. Next we found that the low-frequency dielectric permittivity demonstrates distinct changes at the antiferromagnetic ordering due to the spontaneous magnetodielectric effect caused by the behavior of infrared-active phonons. In addition, we have observed magnetic excitations in the infrared spectra and identified their magnetodipole origin. To strengthen our conclusions, we analyze the theoretical phonon-magnon coupling overall phonons at the $\Gamma$ point. We conclude that the largest effect comes from the $A_{1g}$ and $B_{2g}$ Raman-active modes. As such, our results establish a solid basis for further investigations and more deeper understanding of the coupling of phonons with spins and magnetic excitations in antiferromagnets.

Crystals of bismuth fluoride BiF3 grown from a melt were studied for the first time by optical spectroscopy methods and calculated from first principles in the phonon excitations region. A study of IR reflectance spectra in polarized light was carried out. The parameters of optical phonons were obtained. In the IR reflectance spectra, a low-frequency rise in the range <500 cm–1, characteristic of conductive materials, is observed. The reflection spectra were analyzed within the framework of the Drude–Lorentz model, taking into account the contribution of ionic conductivity. An ab initio calculation of the phonon spectrum of a BiF3 crystal was carried out and the relationship between theoretical and experimental data was analyzed.

We explore the possibility of using the luminescence of LiYF4:Er3+ to measure cryogenic temperatures. Temperature dependences (2.5 K -> 190 K) of the luminescence intensity ratios and linewidths are studied in the regions of infrared transitions I-4(13/2) -> I-4(15/2) (similar to 1.5 mu m) and I-4(11/2) -> I-4(15/2) (similar to 0.98 mu m) using high-resolution Fourier spectroscopy. Pairs of spectral lines 6550-6510 cm(-1), 10176-10161 cm(-1), and 6482-6478 cm(-1) can be used for ratiometric Boltzmann thermometry with maximum absolute sensitivity at temperatures of 28.8, 10.8, and 2.9 K, respectively, and corresponding relative sensitivities of 6.9, 18.5, and 70% K-1 at these temperatures. The temperature dependence of the linewidth of 6510 cm(-1) line is favorable for measuring higher temperatures.

Here we present the study of spectral and kinetic characteristics of Er3+ ions in the heavily doped BaY1.8Lu0.2F8 mixed crystals, which are homologous to well-known fluoride host BaY2F8 with high value of crystal field splitting. Absorption and luminescence spectra were registered, and the luminescence decay was studied in the IR spectral range for BaY1.8Lu0.2F8 crystals doped with Er3+ ions at concentrations of 20.0 at. % and 30.0 at. %. Based on the Judd-Ofelt theory, the intensity parameters were determined from the absorption spectra with the use of two approaches, the standard theory (J -O), and the intermediate configuration interaction (ICI). It is shown that investigated BaY1.8Lu0.2F8:Er3+ crystals propose the value of stimulated emission cross-section at the wavelength around 2.7 pm higher than that for Er -doped YAG and at the level of Er -doped LiYF4 crystals. In addition, it was shown that for BaY1.8Lu0.2F8 crystals with a high doping level of Er3+ (more than 20.0 at. %), the radiative lifetime of the 4I13/2 state becomes shorter than the lifetime of the 4I11/2 state, which speaks for success on efficient laser oscillation at a wavelength of about 2.7 pm (the 4I11/2 -> 4I13/2 transition).

The paper presents the transmission spectra of hybrid perovskite MAPbI3 single crystals near the fundamental absorption edge in a wide temperature range. The absorption coefficient α of the single crystal samples is estimated at a temperature T = 150 K for the light with a photon energy E = 1.6 eV and at T = 40 K for E = 1.8 eV. The obtained values turned out to be several orders of magnitude smaller than the values of α for thin-film samples known from the literature. A sharp shift of the fundamental absorption edge by 100 meV was observed at a temperature T1 = 160 K of the structural phase transition from the tetragonal to the orthorhombic phase. The temperature hysteresis of the shift of the fundamental absorption edge near T1 was recorded, which is characteristic of a first-order phase transition.

We report high-resolution measurements and analysis of the optical transmission and emission spectra of a concentration series of La(1-x)PrxAlO3 (x=10-3, 9 10-3 and 2 10-2) single crystals in a wide frequency range ((2-27) 103 cm-1) at temperatures 5-300 K, below the structural phase transition from the cubic to the rhombohedral phase. Pr3+ ions substitute for La3+ ions at sites with point symmetry D3. All recorded spectral lines are assigned to specific initial and final crystal-field (CF) energy levels, the scheme of CF levels is constructed and described by an appropriate set of CF parameters. The structural phase transition is accompanied by shear strains and the formation of ferroelastic twin domains of four types compressed along one of the four C3 axes in the parent cubic crystal lattice. Specific features of the measured spectra, namely, anomalous broadening of spectral lines and doublet structure of some lines corresponding to transitions between CF singlets and doublets, are considered as a result of interaction of 4f electrons with the field of random shear deformations competing at the boundaries of twin domains. Modeling of the observed line shapes was performed taking into account both hyperfine interactions and random lattice strains, as well as the effect of temperature. The width (6.6±0.7)⋅10− 4 of the introduced two-dimensional distribution function of random strains was found from a comparison of simulated and measured profiles of the split spectral lines. The results of this work can be applied for quantitative assessment of crystal quality.

Rare-earth orthoferrites are a promising platform for antiferromagnetic spintronics with a rich variety of terahertz spin and lattice dynamics phenomena. For instance, it has been experimentally demonstrated that the light-driven optical phonons can coherently manipulate macroscopic magnetic states via nonlinear magnetophononic effects. Here using TbFeO3 as an example, we reveal the origin of the mode mixing between the LO and TO phonons, which is important for understanding of nonlinear phononics. We performed a comprehensive study of the lattice dynamics of the TbFeO3 single crystal by polarized infrared and Raman scattering spectroscopic techniques, and experimentally obtained and carefully analyzed the spectra of anisotropic complex dielectric functions in the far-infrared spectral range. This allowed us to reliably identify the symmetries and parameters of most infrared- and Raman-active phonons. Next, the experimental studies were supplemented by the lattice dynamics calculations which allowed us to propose the normal mode assignments. We reveal that the relation between LO and TO polar phonons is complex and does not strictly follow the "LO-TO rule" due to the strong mode mixing. We further analyze how displacements of different ions contribute to phonon modes and reveal that magnetic Fe ions are not involved in Raman-active phonons, thus shedding light on a lack of spin phonon coupling for such phonons. The obtained results establish a solid basis for further in-depth experimental research in the field of nonlinear phononics and magnetophononics in rare-earth orthoferrites.

This study develops regression models for predicting blood biochemical data using Fourier-transform infrared spectroscopy (FTIR) analysis. Absorption at specific wavelengths of blood serum is revealed to have strong correlations with biochemical parameters, such as ALT, amylase, AST, protein, bilirubin, Gamma-GT, iron, calcium, uric acid, triglycerides, phosphatase and cholesterol, were shown. The results consistently demonstrate that Random Forest Regression outperforms other models, delivering impressive outcomes for the majority of the analyzed parameters. For some parameters we obtained a coefficient of determination of 0.95 and more (amylase, AST, iron, calcium, protein, uric acid and cholesterol), which makes this approach to be applicable in clinical diagnostics. These findings highlight the potential of FTIR analysis combined with regression models for precise assessment of blood biochemistry.

The neutrally charged silicon-vacancy defect (SiV0) is a colour centre in diamond with spin S = 1, a zero-phonon line (ZPL) at 946 nm and long spin coherence, which makes it a promising candidate for quantum network applications. For the proper performance of such colour centres, all of them must have identical optical characteristics. However, in practice, there are factors that influence each individual centre. One of these factors is non-uniform isotope composition for both carbon atoms in diamond lattice and silicon atoms of dopant. In this work, we studied the isotopic shifts of SiV0 centres for CVD-grown epitaxial layers of isotopically enriched C-12 and C-13 diamonds, as well as for diamond with natural isotope composition but doped only with one isotope of Si (Si-28, Si-29 and Si-30). The detected shift was 1.60 meV for C-12/C-13 couple and 0.33 meV for Si-28/Si-29 and Si-29/Si-30 couples, which are close to the previously obtained values of the isotopic shift for the negatively charged silicon vacancy (SiV-), which indicates a similar model of interaction with the environment for these two charge states of the SiV colour centres.

The palmierite-type matrix with lanthanides is capable of producing customizable multicolored emission, and has characteristics such as long service life and high energy efficiency. This research explored the impact of synthesis method and composition on structural and luminescence properties of K5Eu1-xHox(MoO4)4 with the palmierite-type structure. Two modifications with space group (SG) R 3m (alpha-phase) and C2/m (beta-phase) were observed and characterized. This study underscores the critical role of co-doping of Eu3+ and Ho3+ cations in manipulating charge transfer and luminescence efficiency in visible and IR region. The existence of 5D0 -> 7F0 transition in the PL spectra indicates stable local environment of Eu3+ cations regardless of synthesis conditions.

A brief review of recent studies of crystals doped with rare-earth ions performed at the Institute of Spectroscopy of the Russian Academy of Sciences (ISAN) using high-resolution wide-range optical Fourier spectroscopy is presented. The results of a study of inhomogeneous broadening and the fine structure of lines in the absorption and luminescence spectra of crystals with rare-earth ions caused by random deformations, the isotopic structure in luminescence spectra associated with matrix isotopes, and anticrossings of the crystal hyperfine levels in a magnetic field are discussed. It is shown that the hyperfine structure in luminescence spectra can be used to implement a luminescence thermometer for the region of ultra-low temperatures.

We explore the possibility of using the luminescence of LiYF4:Er3+ to measure cryogenic temperatures. Temperature dependences (2.5 K → 190 K) of the luminescence intensity ratios and linewidths are studied in the regions of infrared transitions 4I13/2 → 4I15/2 (∼1.5 μm) and 4I11/2 → 4I15/2 (∼0.98 μm) using high-resolution Fourier spectroscopy. Pairs of spectral lines 6550–6510 cm−1, 10176–10161 cm−1, and 6482–6478 cm−1 can be used for ratiometric Boltzmann thermometry with maximum absolute sensitivity at temperatures of 28.8, 10.8, and 2.9 K, respectively, and corresponding relative sensitivities of 70, 18.5, and 6.9% K−1 at these temperatures. The temperature dependence of the linewidth of 6510 cm−1 line is favorable for measuring higher temperatures.

Solvothermal reaction of magnesium nitrate and boron oxide in N,N-dimethylformamide produced a number of particularly complex supramolecular magnesium borates. Five topologically different types of negatively charged {Mg@[B18φ34-35]}-clusters, φ = O, OH, were observed with the magnesium cation as a core and octadecaborate anions as shells. The clusters assemble via common borate polyhedra forming 1D chains, a 2D mesoporous layer, and 3D mesoporous frameworks with an effective channel width of up to 16 Å. Topological analysis of the clusters in combination with the modular crystallography approach indicates that numerous new functional materials can be obtained by varying their assembly mode. At least one compound containing such clusters exhibits a very strong luminescence.

Herewe present the spectral and kinetic characteristics of $\mathrm{Er}^{3+}$ ions in the heavily doped $\mathrm{BaY}_{1.8} \mathrm{Lu}_{0.2} \mathrm{~F}_{8}$ mixed crystals and evaluate the possibility of continuous laser oscillation at a wavelength of $2.7 \mu \mathrm{m}$.

Diamond synthesis with silicon-vacancy (SiV) color centers is of high interest to nanophotonics and optical quantum technologies. The methods to control and/or maximize concentration of Si atoms incorporated in diamond lattice, and coupled to vacancies, together with improving crystallinity of diamond structure, are in demand. Here, we studied the effect of heat treatment of electron-irradiated single crystal CVD diamond doped with S-28 isotope, on evolution of the neutral SiV0 and negatively charged SiV- centers. The crystal subjected to stepwise annealing at temperatures T-ann from 200 degrees C to 1640 degrees C has been analyzed with photoluminescence (PL) and optical absorption spectroscopies at room and low-temperature (T = 5 K). We found a complex non-monotonous behavior of SiV0 and SiV- intensity both in absorption and PL, with sharp rise at T-ann > 600 degrees C, reaching a maximum concentration peak, decline at 850 degrees C, and a repeated elevation to higher T-ann, reflecting creation and annihilation processes of these defects. Moreover, we detected a group of seven lines of a Si-related defect in the range 828-871 nm, which strongly correlate with annealing dynamics of the SiV- and, especially, of SiV0 centers, and estimated the isotope spectral shift. In parallel, dynamics of other optical centers such as NV, R11 and GR1, in course of the annealing is traced. The controlled annealing opens the way to preparation of the SiV color centers with optimized optical properties, promising for quantum technologies.