The Li9Mg3[PO4]4F3 fluorophosphate, which is considered as a promising dosimetric material, was prepared by the conventional solid-phase and microwave-assisted methods. The dosimetric properties of the obtained materials were examined and compared. The results revealed that the microwave-assisted synthesis leads to a fourfold enhancement of the thermoluminescence. Analysis of structural data showed that prolonged contact with the atmosphere can cause the loss of fluorine, resulting in the deterioration of material properties. This effect is also evidenced by the increase in the ESR signal, which is associated with a larger number of antisite defects, for the fluorophosphate obtained by the microwave-assisted method. The additional synthesis of Li9Mg3[PO4]4F3 with an excess of LiF allowed us to suppress the fluorine losses, thereby leading to an additional manifold increase of the thermoluminescence.

We report an experimental study on intrinsic defects in pure and rare-earths doped lithium-magnesium phosphate LiMgPO4. A wide range of optical methods were used in the work, including photoluminescence, thermoluminescence, radioluminescence and optical absorption. A detailed investigation made it possible to conclude that the main type of intrinsic defects responsible for all kinds of luminescence in LiMgPO4 is neutral oxygen vacancy (VO0), i.e., a vacancy with two trapped electrons. Lithium magnesium phosphate has been shown to be a thermoluminescent (TL) material. The TL response of LiMgPO4 is significantly enhanced by doping with praseodymium, cerium or europium. At the same time, the spectra of LiMgPO4: RE (RE - Ce, Pr, Yb) do not contain the lines associated with f-f transitions in RE3+ but are completely identical to the TL spectrum of the phosphate host. The energy transfer from RE to the host is suggested as an explanation for the observed effect.

Lithium-magnesium fluorophosphate with the formula Li9Mg3[PO4](4)F-3 has recently been proposed as a new thermoluminescent material capable of storing ionizing radiation energy and emitting photons after additional thermal stimulation. Pure and sodium-doped fluorophosphates were obtained by microwave-assisted synthesis. Using X-ray and neutron diffraction methods, it was shown that sodium occupies only one of the three nonequivalent lithium positions. This conclusion was confirmed by a MAS NMR study and ab initio calculations. A significant increase in the thermoluminescence intensity of sodium-containing fluorophosphates in comparison to the undoped compound was found. Analysis of the kinetic parameters obtained from glow curves showed that they are similar for the undoped and sodium-doped samples. This indicates that the addition of sodium does not result in the emergence of novel types of traps, but rather in a change in their number. The effect of sodium on the formation of intrinsic defects, which can be responsible for the enhanced thermoluminescence, is considered using ab initio modelling.

The aim of this work was to elucidate the role of defects in energy storage and transfer in X-ray irradiated MgB4O7. Pure and terbium- and erbium-doped magnesium tetraborate was synthesized by the solid state reaction method. The band gap value Eg = 9 eV was estimated using the method of X-ray photoelectron spectroscopy (XPS). Absorption attributed to defects with energy levels located in the forbidden band was found from UV-vis spectroscopy. An interpretation of the thermoluminescence and radioluminescence spectra of pure and doped magnesium tetraborate was proposed. Two different mechanisms for enhancing the thermoluminescent response of MgB4O7 upon doping with rare earth elements were demonstrated.

Lithium magnesium phosphate LiMgPO4 is one of the most promising materials for luminescence dosimetry. In this paper, we consider methods for the synthesis or additional processing of this material, such as microwave, hydrothermal, and flux techniques, as well as melting followed by quenching, which makes it possible to enhance its thermoluminescence by increasing the crystallinity of the samples and improving grain contacts. The best properties are shown by the LiMgPO4–Na2B4O7 composite.

Fluorine-doped lithium magnesium phosphate has been studied for the first time. It has been shown that fluorine significantly enhances the intensity of thermally stimulated luminescence. To find the preferred positions of fluorine and structural distortions caused by aliovalent substitution, ab initio calculations have been performed, which demonstrate that fluorine is not included into the (PO 4 ) 3– anion; rather, it promotes the formation of clusters simultaneously containing lithium and fluorine ions.

In this work, radioluminescence (RL), thermoluminescence (TL) and photoluminescence (PL) of fluorophosphate Li9Mg3[PO4](4)F-3 as a possible dosimetry material are studied for the first time. It was found that the irradiated sample exhibits significant thermoluminescence in the temperature range of 100-300 degrees C with the main peak at 205 degrees C. The RL, PL and TL spectra consist of one broad band centered at 400 nm which was attributed to defects in the structure of Li9Mg3[PO4](4)F-3 . The energy required to excite defects in Li9Mg3[PO4](4)F-3 determined by UV-vis spectroscopy is 4.4 eV (lambda approximate to 280 nm). Additional evidence for intrinsic defects was obtained from the electron paramagnetic resonance (EPR) in Li9Mg3[PO4](4)F-3 . The DFT method was employed to simulate various defects including single and complex, neutral and charged vacancies. The formation energies of vacancies were predicted and their effect on the electronic structure and optical properties was established. These intrinsic defects introduce additional electronic states into the band gap and absorption bands in the visible region, the position and intensity of which strongly depend on the type of defect. Our experimental and theoretical studies reveal that Li9Mg3[PO4](4)F-3 can be a promising optical matrix suitable for dosimetric applications. As evidence, the main functional characteristics of the new material are given.

Fluorine-doped lithium magnesium phosphate has been studied for the first time. It has been shown that fluorine significantly enhances the intensity of thermally stimulated luminescence. To find the preferred positions of fluorine and structural distortions caused by aliovalent substitution, ab initio calculations have been performed, which demonstrate that fluorine is not included into the (PO4)3– anion; rather, it promotes the formation of clusters simultaneously containing lithium and fluorine ions.

Lithium magnesium phosphate LiMgPO 4 is one of the most promising materials for luminescence dosimetry. In this paper, we consider methods for the synthesis or additional processing of this material, such as microwave, hydrothermal, and flux techniques, as well as melting followed by quenching, which makes it possible to enhance its thermoluminescence by increasing the crystallinity of the samples and improving grain contacts. The best properties are shown by the LiMgPO 4 –Na 2 B 4 O 7 composite.

Solid solutions Li1-xNaxMgPO4 (0 < x < 0.20) with olivine-type orthorhombic structure were synthesized by the conventional solid state reaction route and their optical properties and defect structure were examined by experimental and theoretical methods. A significant gain in the thermoluminescence of phosphate was found with an increase in sodium concentration up to 6%. The ab initio calculations and the study of the ESR spectra made it possible to attribute this effect to an increase in the number of defects, primarily oxygen vacancies. It was established that partial substitution of sodium for lithium can increase the solubility of rare earth elements in LiMgPO4, and this contributes to the development of materials with improved dosimetric characteristics.

The TL and RL signals in LiMgPO4:Sm, Gd, Tb, Dy, Tm originate from f–f transitions in rare earth elements, while the rare earths in LiMgPO4:Er, Ho, Nd only greatly enhance the signals of the phosphate matrix as a result of energy transfer.

The Ca(Ba)RE2Ge3O10 germanates are currently considered as a promising class of active optical media emitting in the visible and infrared spectral region. Herein, a new series of BaY2-x-yTmxDyyGe3O10 phosphors was synthesized using the solid-state reaction and characterized by X-ray diffraction, scanning electron microscopy, diffuse reflectance and luminescence spectroscopy. All the studied compounds crystallize in the monoclinic system, space group P21/m, Z = 2. Under 808 nm excitation, BaY2-xTmxGe3O10 germanates demonstrate a broad emission in 1.3–2.2 µm range owing to a series of cascade 3H4 → 3F4 and 3F4 → 3H6 transitions in Tm3+ ions. The BaY2-xTmxGe3O10 phosphors exhibit a high thermal stability over a wide temperature range and belong to promising infrared luminescence materials. The intensity of these emission bands decreases with an increase in the dysprosium content in the BaY1.97-yTm0.03DyyGe3O10 germanates. The magnetic properties measurements have been also carried out since Dy3+ ions exhibit a large magnetic anisotropy and non-collinearity of the magnetization easy axes. The magnetization curve of Tm3+-doped BaY2Ge3O10 shows the effects of saturation typical of paramagnetics, while the magnetization of germanates doped with Dy3+ ions occurs with hysteresis which is observed for single-ion magnets.

A phase transition from a quasi-one-dimensional hexagonal structure (1D) to a two-dimensional layered structure (2D) of the second homolog of the Ruddlesden-Popper series was detected in the Sr3ScCoO6+delta complex oxide. The transition is unique since it occurs when the temperature increases without the use of high pressures and changes in the oxygen partial pressure. Using high-temperature X-ray diffraction and differential scanning calorimetry in situ, a transition temperature range 1296 K-1433 K was established. It is shown that in the quasi-one-dimensional phase the scandium and cobalt cations are ordered by prismatic and octahedral positions, while in the two-dimensional perovskite-like oxide they are statistically distributed by octahedral positions. Sr3ScCoO6+delta is the only compound in the Sr3ScMO7-delta (M = Ni - Cr) morphotropic series, which exists in two structural types. The 1D -> 2D transformation is associated with the ability of cobalt to be in various combinations of oxidation states and spin states. The temperature dependence of the magnetic susceptibility of oxides of both types of structure in the Sr3ScMO7-delta (M = Ni - Cr) series is paramagnetic due to magnetic dilution with Sc ion. The tetragonal modification of Sr3ScCoO6+delta has a significantly larger magnetic moment compared to the hexagonal one.

A new method for the synthesis of various types of copper(II) formates with Cu(NO3)(2)center dot 3H(2)O and formic acid, orthorhombic (alpha) and monoclinic (beta) modifications of anhydrous copper(II) formate, as well as Cu(HCOO)(2)center dot 2H(2)O and Cu(HCOO)(2)center dot 4H(2)O. The identity of the obtained compounds was confirmed by Xray phase analysis, optical microscopy and thermogravimetry methods. It was shown that Cu(HCOO)(2)center dot 4H(2)O can be used as a precursor for producing copper powders with particle size of the order of 150 nm. The results of investigation of vibration and absorption spectra of alpha and beta modifications of anhydrous copper(II) formate are presented. Their magnetic behavior in the temperature interval 2 -300 K was estimated, and comparative analysis of magnetic properties was carried out. First-principle calculations of electronic band structure for anhydrous alpha and beta modifications were performed. The results obtained correspond to experimentally observed structural instability of beta-Cu(HCOO)(2) , fundamental absorption edge enhancement during transition from alpha to beta modification, and low-temperature ferromagnetic ordering in alpha-Cu(HCOO)(2). Simulation for beta modification is indicative of antiferromagnetic ordering of magnetic moments inside chains formed by copper-oxygen octahedra. (C) 2020 Elsevier B.V. All rights reserved.

A perovskite-like CaV1-xMoxO3-delta (x = 0.2 divided by 0.6) were prepared by a formate solution method with the final annealing at 1473 K in an H-2 atmosphere. X-ray diffraction analysis was used for sample characterisation. Metallike electric conductivity was observed using a 4-probe DC technique from 573 to 1123 K in dry H-2. Magnetic susceptibility measurements showed the absence of localised V and Mo valence electrons. The Seebeck coefficient was measured between temperatures of 573-1123 K in dry H-2, supporting the hypothesis that electronic conductivity is predominant. Thermal expansion coefficients (TEC) are obtained by dilatometry from 373 to 1123 K in dry H-2. TEC values increase with temperature from 10 ppm to 15 ppm K-1 and decrease with Mo concentration.

The standard formation enthalpy of the Bi 12.5 Er 1.5 CoO 22.3 phase has been determined as following: Δ f H 0 (Bi 12.5 Er 1.5 CoO 22.3 , s, 298.15 K) = −5203.9 ± 14.5 kJ mol –1 . Solution calorimetry, using 1 mol dm –3 HCl as a solvent, has been used to study the thermochemistry of Bi 12.5 Er 1.5 CoO 22.3 . The lattice energy for Bi 12.5 Er 1.5 CoO 22.3 has been calculated on the basis of Born-Haber cycle using the standard formation enthalpy of the phase and literature data. For the first time, we measured the magnetic characteristics of Bi 12.5 Er 1.5 CoO 22.3 and established that the Bi 12.5 Er 1.5 CoO 22.3 phase has paramagnetic properties.

Phosphor Ca2La6.8Eu1.2(SiO4)6O2−δ is obtained via coprecipitation and the nitrate-citrate pyrolysis method. The structure and phase composition of the synthesized apatite silicates are studied using XRD. The luminescence spectra of the sample are registered before and after pressing at pressures above 5 GPa. The magnetic properties are analyzed by means of ESR spectroscopy and vibration magnetometry. The concentrations of Eu2+ ions and constants (λ) of optical splitting between 7FJ levels in the initial sample, and in the sample after hot pressing, are calculated.

Pure and terbium-doped lithium-magnesium phosphate LiMgPO4 was investigated with respect to its thermoluminescent properties. The samples were synthesized by solid state, ultrasonic spray pyrolysis, as well as by melting and quenching methods. To predict the terbium site, ab initio calculations were carried out. Additional treatment in atmospheres with different oxygen partial pressures was used. The larger is the concentration of oxygen in the atmosphere and, accordingly, the smaller is the quantity of surface oxygen vacancies, the greater is the intensity of thermoluminescence. For a better understanding of thermoluminescence in LiMgPO4 and LiMgPO4:Tb, the TL spectra were recorded. It was concluded that the thermoluminescence of LiMgPO4:Tb is additively composed of the signals of the matrix and activator ions.