Fe₃O₄@SiO₂ core-shell nanoparticles (NPs) were synthesized with the co-precipitation method and functionalized with NH₂ amino-groups. The nanoparticles were characterized by X-ray, FT-IR spectroscopy, transmission electron microscopy, selected area electron diffraction, and vibrating sample magnetometry. The magnetic core of all the nanoparticles was shown to be nanocrystalline with the crystal parameters corresponding only to the Fe₃O₄ phase covered with a homogeneous amorphous silica (SiO₂) shell of about 6 nm in thickness. The FT-IR spectra confirmed the appearance of chemical bonds at amino functionalization. The magnetic measurements revealed unusually high saturation magnetization of the initial Fe₃O₄ nanoparticles, which was presumably associated with the deviations in the Fe ion distribution between the tetrahedral and octahedral positions in the nanocrystals as compared to the bulk stoichiometric magnetite. The fluorescent spectrum of eosin Y-doped NPs dispersed in water solution was obtained and a red shift and line broadening (in comparison with the dye molecules being free in water) were revealed and explained. Most attention was paid to the adsorption properties of the nanoparticles with respect to three dyes: methylene blue, Congo red, and eosin Y. The kinetic data showed that the adsorption processes were associated with the pseudo-second order mechanism for all three dyes. The equilibrium data were more compatible with the Langmuir isotherm and the maximum adsorption capacity was reached for Congo red.

Praseodymium sulfate was obtained by the precipitation method and the crystal structure was determined by Rietveld analysis. Pr₂(SO₄)₃ is crystallized in the monoclinic structure, space group C2/c, with cell parameters a = 21.6052 (4), b = 6.7237 (1) and c = 6.9777 (1) Å, β = 107.9148 (7)°, Z = 4, V = 964.48 (3) ų (T = 150 °C). The thermal expansion of Pr₂(SO₄)₃ is strongly anisotropic. As was obtained by XRD measurements, all cell parameters are increased on heating. However, due to a strong increase of the monoclinic angle β, there is a direction of negative thermal expansion. In the argon atmosphere, Pr₂(SO₄)₃ is stable in the temperature range of T = 30–870 °C. The kinetics of the thermal decomposition process of praseodymium sulfate octahydrate Pr₂(SO₄)₃·8H₂O was studied as well. The vibrational properties of Pr₂(SO₄)₃ were examined by Raman and Fourier-transform infrared absorption spectroscopy methods. The band gap structure of Pr₂(SO₄)₃ was evaluated by ab initio calculations, and it was found that the valence band top is dominated by the p electrons of oxygen ions, while the conduction band bottom is formed by the d electrons of Pr³⁺ ions. The exact position of ZPL is determined via PL and PLE spectra at 77 K to be at 481 nm, and that enabled a correct assignment of luminescent bands. The maximum luminescent band in Pr₂(SO₄)₃ belongs to the ³P₀ → ³F₂ transition at 640 nm.

The crystal structure of YAl₃(BO₃)₄ is obtained by Rietveld refinement analysis in the present study. The dynamical properties are studied both theoretically and experimentally. The experimental Raman and Infrared spectra are interpreted using the results of ab initio calculations within density functional theory. The phonon band gap in the Infrared spectrum is observed in both trigonal and hypothetical monoclinic structures of YAl₃(BO₃)₄. The electronic band structure is studied theoretically, and the value of the band gap is obtained. It was found that the YAl₃(BO₃)₄ is an indirect band gap dielectric material.

In this work, we report on the synthesis, in-depth crystal structure studies as well as optical and magnetic properties of newly synthesized heterometallic quaternary selenides of the Eu⁺²Ln⁺³Cu⁺¹Se₃ composition. Crystal structures of the obtained compounds were refined by the derivative difference minimization (DDM) method from the powder X-ray diffraction data. The structures are found to belong to orthorhombic space groups Pnma (structure type Ba₂MnS₃ for EuLaCuSe₃ and structure type Eu₂CuS₃ for EuLnCuSe₃, where Ln = Sm, Gd, Tb, Dy, Ho and Y) and Cmcm (structure type KZrCuS₃ for EuLnCuSe₃, where Ln = Tm, Yb and Lu). Space groups Pnma and Cmcm were delimited based on the tolerance factor t’, and vibrational spectroscopy additionally confirmed the formation of three structural types. With a decrease in the ionic radius of Ln³⁺ in the reported structures, the distortion of the (LnCuSe₃) layers decreases, and a gradual formation of the more symmetric structure occurs in the sequence Ba₂MnS₃ → Eu₂CuS₃ → KZrCuS₃. According to magnetic studies, compounds EuLnCuSe₃ (Ln = Tb, Dy, Ho and Tm) each exhibit ferrimagnetic properties with transition temperatures ranging from 4.7 to 6.3 K. A negative magnetization effect is observed for compound EuHoCuSe₃ at temperatures below 4.8 K. The magnetic properties of the discussed selenides and isostructural sulfides were compared. The direct optical band gaps for EuLnCuSe₃, subtracted from the corresponding diffuse reflectance spectra, were found to be 1.87–2.09 eV. Deviation between experimental and calculated band gaps is ascribed to lower d states of Eu²⁺ in the crystal field of EuLnCuSe₃, while anomalous narrowing of the band gap of EuYbCuSe₃ is explained by the low-lying charge-transfer state. Ab initio calculations of the crystal structures, elastic properties and phonon spectra of the reported compounds were performed.

We report on the novel heterometallic quaternary sulfides SrLnCuS₃ (Ln = La, Nd, Tm), obtained as both single crystals and powdered samples. The structures of both the single crystal and powdered samples of SrLaCuS₃ and SrNdCuS₃ belong to the orthorhombic space group Pnma but are of different structural types, while both samples of SrTmCuS₃ crystallize in the orthorhombic space group Cmcm with the structural type KZrCuS₃. Three-dimensional crystal structures of SrLaCuS₃ and SrNdCuS₃ are formed from the (Sr/Ln)S₇ capped trigonal prisms and CuS₄ tetrahedra. In SrLaCuS₃, alternating 2D layers are stacked, while the main backbone of the structure of SrNdCuS₃ is a polymeric 3D framework [(Sr/Ln)S₇]_n, strengthened by 1D polymeric chains (CuS₄)_n with 1D channels, filled by the other Sr²⁺/Ln³⁺ cations, which, in turn, form 1D dimeric ribbons. A 3D crystal structure of SrTmCuS₃ is constructed from the SrS₆ trigonal prisms, TmS₆ octahedra and CuS₄ tetrahedra. The latter two polyhedra are packed together into 2D layers, which are separated by 1D chains (SrS₆)_n and 1D free channels. In both crystal structures of SrLaCuS₃ obtained in this work, the crystallographic positions of strontium and lanthanum were partially mixed, while only in the structure of SrNdCuS₃, solved from the powder X-ray diffraction data, were the crystallographic positions of strontium and neodymium partially mixed. Band gaps of SrLnCuS₃ (Ln = La, Nd, Tm) were found to be 1.86, 1.94 and 2.57 eV, respectively. Both SrNdCuS₃ and SrTmCuS₃ were found to be paramagnetic at 20–300 K, with the experimental magnetic characteristics being in good agreement with the corresponding calculated parameters.

A new multicationic structurally disordered K₅FeHf(MoO₄)₆ crystal belonging to the molybdate family is synthesized by the two-stage solid state reaction method. The characterization of the electronic and vibrational properties of the K₅FeHf(MoO₄)₆ was performed using density functional theory calculations, group theory, Raman and infrared spectroscopy. The vibrational spectra are dominated by vibrations of the MoO₄ tetrahedra, while the lattice modes are observed in a low-wavenumber part of the spectra. The experimental gap in the phonon spectra between 450 and 700 cm⁻¹ is in a good agreement with the simulated phonon density of the states. K₅FeHf(MoO₄)₆ is a paramagnetic down to 4.2 K. The negative Curie–Weiss temperature of −6.7 K indicates dominant antiferromagnetic interactions in the compound. The direct and indirect optical bandgaps of K₅FeHf(MoO₄)₆ are 2.97 and 3.21 eV, respectively. The K₅FeHf(MoO₄)₆ bandgap narrowing, with respect to the variety of known molybdates and the ab initio calculations, is explained by the presence of Mott-Hubbard optical excitation in the system of Fe³⁺ ions.