The modulated structure and frequency upconversion properties of CaLa2(MoO4)4:Ho3+/Yb3+ phosphors prepared by microwave synthesis

CaLa2_x(MoO4)4:Ho3+/Yb3+ phosphors with the doping concentrations of Ho3+ and Yb3+ (x = Ho3+ + Yb3+, Ho3+ = 0.05; Yb3+ = 0.35, 0.40, 0.45 and 0.50) have been successfully synthesized by the microwave sol-gel method. The modulated and averaged crystal structures of CaLa2_x(MoO4)4:Ho3+/Yb3+ molybdates have been found by the Rietveld method, and the upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 °C for 16 h, showed a highly crystallized state. Under the excitation at 980 nm, CaLa2_x(MoO4)4:Ho3+/Yb3+ particles exhibited strong 545 and 655 nm emission bands in the green and red regions. When the Yb3+ :Ho3+ ratios are 9 : 1 and 10: 1, the UC intensity of CaLai.5(MoO4)4:Yb045/Ho0.05 and CaLai45(MoO4)4:Yb0.50/Ho0.05 particles is the highest for different bands. The CIE coordinates calculated for CaLa2_x(MoO4)4:Ho3+/Yb3+ phosphors are related to the yellow color field. The Raman spectrum of undoped CaLa2(MoO4)4 has revealed about 13 narrow lines. The strongest band observed at 906 cirT1 was assigned to the n1 symmetric stretching vibration of MoO4 tetrahedra. The spectra of the samples doped with Ho and Yb, as obtained under the 514.5 nm excitation, were dominated by Ho3+ luminescence over the wavenumber range of >700 cm-1 preventing the recording of the Raman spectra

Raman scattering study of δ-BiB3O6 crystal

The total set of polarized Raman spectra have been obtained at room temperature, and an assignment of observed modes based on the lattice dynamics simulation and polarization selection rules is proposed. An LO-TO splitting of A1 Raman bands have been observed

Anisotropic crystal of the δ-BiB3O6 investigated by vibrational spectroscopy

The vibrational spectroscopy has been applied to investigate the structure the BiB3O6 (BIBO) crystal. Based on the experimental results, the total set of phonons mode of the polarized Raman spectra was proposed. To verify the obtained experimental data have been performed theoretical calculation in software package LADY

Exploration of structural, thermal, vibrational and spectroscopic properties of new noncentrosymmetric double borate Rb3NdB6O12

New noncentrosymmetric rare earth borate Rb3NdB6O12 is found in the ternary system Rb2O–Nd2O3–B2O3. The Rb3NdB6O12 powder was fabricated by solid state synthesis at 1050 K for 72 h and the crystal structure was obtained by the Rietveld method. Rb3NdB6O12 crystallized in space group R32 with unit cell parameters a = 13.5236(4), c = 31.162(1) Å, Z = 3. From DSC measurements, the reversible phase transition (I type) in Rb3NdB6O12 is observed at 852–936 K. The 200 μm thick tablet is transparent over the spectral range of 0.3–6.5 μm and the band gap is found as Eg ∼ 6.29 eV. Nonlinear optical response of Rb3NdB6O12 tested via SHG is estimated to be higher than that of K3YB6O12. Blue shift of Nd luminescent lines is found in comparison with other borates. The vibrational parameters of Rb3NdB6O12 are evaluated by experimental methods

High-refractive index and mechanically cleavable non-van der Waals InGaS3

The growing families of two-dimensional crystals derived from naturally occurring van der Waals materials offer an unprecedented platform to investigate elusive physical phenomena and could be of use in a diverse range of devices. Of particular interest are recently reported atomic sheets of non-van der Waals materials, which could allow a better comprehension of the nature of structural bonds and increase the functionality of prospective heterostructures. Here, we study the optostructural properties of ultrathin non-van der Waals InGaS3 sheets produced by standard mechanical cleavage. Our ab initio calculation results suggest an emergence of authentically delicate out-of-plane covalent bonds within its unit cell, and, as a consequence, an artificial generation of layered structure within the material. Those yield to singular layer isolation energies of around 50 meVA-2, which is comparable with the conventional van der Waals material's monolayer isolation energies of 20 - 60 meVA-2. In addition, we provide a comprehensive analysis of the structural, vibrational, and optical properties of the materials presenting that it is a wide bandgap (2.73 eV) semiconductor with a high-refractive index (higher than 2.5) and negligible losses in the visible and infrared spectral ranges. It makes it a perfect candidate for further establishment of visible-range all-dielectric nanophotonics

Nature of phase transitions in ammonium oxofluorovanadates, a vibrational spectroscopy study of (NH4)3VO2F4 and (NH4)3VOF5

Two ammonium oxofluorovanadates, (NH4)3VO2F4 and (NH4)3VOF5, have been in-vestigated by temperature-dependent infrared and Raman spectroscopy methods to determine the nature of phase transitions (PT) in these compounds. Dynamics of quasioctahedral groups was simulated within the framework of semi-empirical approach, which justified the cis-conformation of VO2F43– (C2v) and the C4v geometry of VOF53–. The observed infrared and Raman spectra of both compounds at room temperature (RT) revealed the presence at least of two crystallographically independent octahedral groups. The first order PT at elevated temperatures is connected with a complete dynamic disordering of these groups with only single octahedral state. At lower temperatures, the octahedra are ordered and several octahedral states appear. This PT is the most pronounced in the case of (NH4)3VOF5, when at least seven independent VOF53– octahedra are present in the structure below 50 K, in accordance with the Raman spec-tra. Ammonium groups do not take part in PTs at higher and room temperatures but their reorientational motion freezes at lower temperatures

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies

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. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Funding: The research was supported by the Tyumen region within the framework of the grant agreement in the form of a grant to non-profit organizations no. 89-don dated 07.12.2020. This study was supported by the Ministry of Science and Higher Education of the Russian Federation (project no. FEUZ-2020-0054). This work was supported by state assignment of the Ministry of Science and Higher Education of the Russian Federation (Project Reg. No. 720000Ф.99.1.БЗ85АА13000). The work was conducted within the framework of the budget project № 0287-2021-0013 for the Institute of Chemistry and Chemical Technology SB RAS

SI: Advances in Density Functional Theory (DFT) Studies of Solids

This summary is a review on articles published in the Special Issue “Advances in Density Functional Theory (DFT) Studies of Solids” from the section “Materials Simulation and Design” of the MDPI journal Materials [...

Microwave sol-gel synthesis, microstructural and spectroscopic properties of scheelite-type ternary molybdate upconversion phosphor NaPbLa(MoO4)3:Er3+/Yb3+

New ternary molybdate NaPbLa(1-x-y)(MoO4)3:xEr3+,yYb3+ (x = y = 0, x = 0.05 and y = 0.35, 0.4, 0.45 and 0.5) phosphors were successfully fabricated by the MSG (microwave sol-gel) method, and the microstructural and spectroscopic properties were characterized. The crystal structure of NaPbLa(MoO4)3 (NPLM) was defined by Rietveld analysis in space group I41/a with unit cell parameters a = 5.3735(2) and c = 11.8668(4) Å, V = 342.65(3) Å3, Z = 4 (RB = 6.64 %). The unit cell volume of NaPbLa(MoO4)3 (NPLM) was intermediate between those of NaLa(MoO4)2 and PbMoO4. Under the 980 nm excitation, upconverted yellowish-green emissions at transitions from 2H11/2 and 4S3/2 were observed. No concentration quenching in the subsystem of donor ions at the content up to 50 at.% and no cross-relaxation losses in the subsystem of acceptor ions at the concentrations as high as 5 at. % were verified. The individual chromaticity points for the NaPbLa(MoO4)3:Er3+,Yb3+ phosphors, corresponding to the equal-energy point in the standard CIE diagram, revealed yellowish-green emissions