For the first time, translucent NaLa9(GeO4)6O2 ceramics were obtained using thermobaric treatment of polycrystalline oxyapatite. The initial powder of NaLa9(GeO4)6O2 germanate was prepared by the citrate method. High-pressure high-temperature sintering was performed at 8 GPa, 600 degrees C for 10 min. The proposed technology for producing ceramics is unique for germanates and differs from the traditional technology of quenching GeO2 melt used to produce germanium glass-ceramics. Two ways of heat treatment of the initial powder are compared from the point of view of the optical properties of ceramics. It is shown that more transparent ceramics are obtained from a polycrystalline sample with a grain size of 40 nm. The total forward transmittance is 55% at 500 nm and 80% at 1200 nm. The difference in the local structure of the initial polycrystalline phase and NaLa9(GeO4)6O2 apatite ceramics was revealed using EPR for Gd3+ as a paramagnetic probe.

Oxyapatites A10(GeO4)6O2 (A – alkaline, rare‐earth elements) are considered promising materials for applications in solid‐state lighting and non‐contact thermometry. The temperature dynamics of the oxygen sublattice have a crucial influence on the luminescent properties of these optical hosts. Here, the structural evolution with temperature of germanates with the general formula ALa9(GeO4)6O2 (A – Li, Na, K, Rb) is investigated, using X‐ray and neutron powder diffraction methods. These compounds crystallize in space‐group P63/m. NPD experiments helped to determine the oxygen and alkaline metal positions. Thermally‐induced reentrant structural transitions relating to the oxygen in the apatite channel are discovered for the first time. In the example of Eu‐doped RbLa9(GeO4)6O2 and KLa9(GeO4)6O2, it is demonstrated that the luminescence of the Eu3+ ion is influenced by small changes in the crystal structure.

Both pristine and Eu3+-doped scandium-potassium complex sulfate KSc(SO4)(2) has been obtained with 99% yield via crystallization from solutions. The high-temperature XRPD and thermal studies revealed an enantiotropic first-order phase transition at 700-725 K and standard pressure. In the temperature region 724-754 K, the low-temperature stable monoclinic polymorph, beta-KSc(SO4)(2) (sp.gr. & Scy;2/m), coexists with the high-temperature trigonal modification, alpha-KSc(SO4)(2) (sp.gr. P321), with decomposition at similar to 1120 K. DFT calculations confirmed this rank of polymorphs and a low hospitality of their Sc-sublattices for Eu3+ cations. Under UV excitation, the KSc0.98Eu0.02(SO4)(2) sample exhibits Eu3+ luminescence at 570-720 nm. Heating of the sample from 298 K to 423 K leads to a luminescence fading of 13% and to its a sharp decline at elevated temperatures. Kinetic studies have shown that the lifetime depends on the chosen excitation wavelength and temperature. An & KHcy;-band resonance in the sample of KSc(SO4)(2):Eu3+ has been detected in the temperature range of 299-500 K. The EPR spectra are interpreted assuming the presence of sulfate radicals.

Two series of NaY1-xTmxGeO4 olivines with x = 0.005-0.04 and x = 0.0-0.2 have been prepared by the solid state reaction method and citrate technique, respectively. These germanates crystallize in olivine structure and have the orthorhombic lattice, space group Pnma, Z = 4. The diffuse reflectance spectra have been measured and the optical band gap has been estimated. Under 808 nm laser diode excitation, the NaY1-xTmxGeO4 samples yield luminescence in the range of 1300-1600 nm (3H4 - 3F4) and 1600-2200 nm (3F4 - 3H6). The maximum of luminescence integrated intensity has been achieved for the composition NaY0 & sdot;85Tm0.15GeO4. The luminescence decay kinetics has been explained using migration. The parameters of the cross-relaxation process: 3H4 + 3H6 3F4 + 3F4 were obtained taking into account the energy transfer rate between thulium ions. It is shown that the presented materials are characterized by an effective migration-accelerated cross-relaxation process, which occurs as a result of dipole-dipole interactions.

A new series of BaRE6(Ge2O7)2(Ge3O10) (RE = Tm, Yb, Lu) germanates and activated phases BaYb6(Ge2O7)2(Ge3O10):xTm3+ and BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ have been prepared using a solid-state reaction. An XRPD study has revealed that the compounds crystallize in the monoclinic system (space group P21/m, Z = 2). The crystal lattice consists of zigzag chains of edge-sharing distorted REO6 octahedra, bowed trigermanate [Ge3O10] units, [Ge2O7] groups, and eight-coordinated Ba atoms. The density functional theory calculations have confirmed a high thermodynamic stability of the synthesized solid solutions. According to the results of vibrational spectroscopy studies and diffuse reflectance measurements, the BaRE6(Ge2O7)2(Ge3O10) germanates are promising compounds for the creation of efficient lanthanide ion activated phosphors. Under 980 nm laser diode excitation, the BaYb6(Ge2O7)2(Ge3O10):xTm3+ and BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ samples exhibit upconversion luminescence corresponding to the characteristic 1G4 → 3H6 (455-500 nm), 1G4 → 3F4 (645-673 nm) and 3H4 → 3H6 (750-850 nm) transitions in Tm3+ ions. Heating of the BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ phosphor with the optimal composition up to 498 K leads to the enhancement of a broad band at 673-730 nm, caused by 3F2,3 → 3H6 transitions. It has been revealed that the fluorescence intensity ratio between this band and the band at 750-850 nm may be used for temperature sensing. The absolute and relative sensitivities in the studied temperature range reach 0.021% K-1 and 1.94% K-1, respectively.

Two new high-pressure modifications of sodium yttrium germanate NaYGeO4 are described. A reversible pressure-induced phase transition of olivine-type NaYGeO4 to new phases has been studied in the pressure range of 4-10 GPa at temperatures from 400 to 1000 degrees C. It was shown that NaYGeO4 olivine is stable at 400-600 degrees C up to 10 GPa. A high-pressure polymorph of NaYGeO4 with NaNdSiO4 crystal structure is formed at 800 degrees C starting from 6 GPa. Along with this polymorph, another new high-pressure modification of NaYGeO4 with NaSmSiO4 crystal structure was found in small amount. In addition, a yet undescribed polymorph of Y2Ge2O7 with pyrochlore-type structure was isolated at 8 GPa and 800 degrees C. The crystal structures of the new phases were determined by X-ray powder diffraction. The results of DFT calculations confirmed the experimental crystallography and gave a preliminary insight into the relative thermodynamic stability and electronic properties for all three new compounds.

An intense electron paramagnetic resonance (EPR) spectrum has been unexpectedly observed at room temperature in polycrystalline samples of NaYGeO4 with olivine crystal structure. Signals were registered in a wide range of fields up to 6000 G. Along with strongly broadened unresolved resonance lines, the relatively narrow spectral components were found. It is shown that the spectrum profile depends on synthesis conditions and mechanical treatment of samples, all suggesting a partial orientational order of microcrystallites in the powders. The spectra are interpreted under the assumption of strong superhyperfine interaction between the oxygen-deficient centers like [GeO3](3-)and the nuclei of Na+ cations. In addition, a sharp anisotropic resonance at g-values exceeding free -electron value is attributed to oxygenic-hole centers. The density functional theory (DFT) calculations are employed for the estimation of the thermodynamic stability of various intrinsic defects.

The ball-like ZnS microparticles assembled of nanoparticles with the size of 3-5 nm were synthesized by chemical bath deposition using thiourea as sulfur agent. Their defectiveness was examined by electron paramagnetic resonance (EPR) and high-resolution transmission electron microscopy (HRTEM). Multiple imperfections of ZnS lattice were visualized using HRTEM, where the patterns of the grain boundaries between sphalerite and wurtzite appear the most legible and often. Inherency of such a grain boundary to individual nanoparticle, hence, the Janus morphology of synthesized ZnS nanoparticles, was confirmed using molecular dynamics simulations of their stability. The extremely intense EPR response was obtained, which interpretation assumes the presence of intrinsic electric field arising due to a giant dipole moment across the interface within Janus nanoparticle. The powders of such sedimented ZnS particles exhibited an enhanced photocatalytic activity in reaction of hydroquinone oxidation under visible light irradiation, employing neither alteration of the band gap of ZnS nor any doping of ZnS lattice.

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.

Pseudo-crystals of vanadyl(iv) citrate [(VO)3(C6H5O7)2]·H2O have been obtained after addition of V2O5 to citric acid solution. Composition of the compound has been established by thermal analysis and confirmed by IR, UV-VIS, Raman and ESR spectra.

Solid solutions Zn1-xCuxO and/or hybrid materials Zn1-xCuxO/CuxO of the "core-shell" type were obtained by one-step thermolysis of Zn1-xCux(HCOO)(OCH2CH2O)(1/2) complexes. Precursors the Zn1-xCux(HCOO)(OCH2CH2O)(1/2) complexes were synthesized under solvothermal method from the corresponding formates and ethylene glycol. It was established that copper in these materials is a promoter of the photoactivity and morphology of aggregates. Zn1-xCuxO solid solutions (0 < x < 1) have 1D-morphology of aggregates, Zn1-xCuxO/CuxO hybrid materials are spherical. According to TEM, XPS, optical spectroscopy and voltammetry data, Cu+ prevails in the solid solution samples and its concentration increases with transition to hybrid materials. It was shown that solid solutions with tubular particle morphology exhibit the maximum photoactivity of As3+ in UV and blue light. The expansion of the spectral range of Zn1-xCuxO irradiation to the visible region is explained by the formation of acceptor levels (Cu2+ + e(-) -> Cu+/V-O(+) + e(-) -> V-O) in the band gap of ZnO, which increases the efficiency of separation of photogenerated electron-hole pairs. The presence of Cu+ in the material intensify photoactivity due to the formation of an overactive oxygen radical O-center dot(2)-.

New germanate ALa9(GeO4)6O2 (A = Li, Na, K, Rb, Cs) oxyapatites, showing promise as host lattices for phosphors with emission in the visible and infrared spectral ranges, have been obtained for the first time by ultrasonic spray pyrolysis. The discussion is focused on native defectiveness and optical properties of these compounds, depending on the nature of alkaline ions. Spray pyrolysis method was consciously used to obtain the compounds with intrinsic defects as confirmed by electron paramagnetic resonance. Reviewing available EPR data, the registered EPR response was assigned to the paramagnetic centers related to germanium tetrahedra embracing the oxygen vacancies. According to quantum-chemical calculations the oxygen-deficient centers in ALa9(GeO4)6O2 are presumably stabilized by antisite defects in the cation sublattice. Diffuse reflectance and pulse cathodoluminescence spectra of the compounds were investigated in detail, establishing a distinct dependence of optical properties on the type of alkaline ion. The observed optical absorption maxima at 275 and 370 nm were attributed to the F-like centers. The inverse dependence of luminescence intensity on the degree of defectiveness was interpreted on the assumption that these centers were involved in non-radiative energy relaxation.

New apatite-type NaLa9-xTmx(GeO4)(6)O-2 (x = 0.025-0.8) germanates (space group P6(3)/m, Z = 1) have been prepared using both the citrate technique and the conventional solid state method. The samples were characterized by powder X-ray diffraction, scanning electron microscopy, diffuse reflectance and photoluminescence spectroscopy. Photoluminescence measurements of NaLa9-xTmx(GeO4)(6)O-2 compounds were carried out both in the 425-850 nm range under 356 nm excitation and in the infrared region under 808 nm excitation. The most intensive lines at 453 nm, 478 nm and in 625-850 nm wavelength range are associated with the D-1(2) -> F-3(4), (1)G(4) -> H-3(6) and a series of (1)G(4) -> F-3(4), F-3(2) -> H-3(6), H-3(4) -> H-3(6) transitions in Tm3+ ions. The spectra measured in the infrared spectral range consist of two broad emission bands centered at 1440 nm and 1810 nm, which correspond to the cascade( 3)H(4)degrees ->degrees F-3(4) and F-3(4)->degrees H-3(6) transitions in Tm3+. The influence of dopant content and temperature on possible mechanisms promoting the population of Tm3+ excited states has been studied.

A series of Sr3La2-xEux(Ge3O9)(2) (x = 0.1-1.8) cyclogermanates has been prepared by the citrate method. The powder XRD study has shown that the compounds crystallize in the monoclinic space group C2/c, Z = 4. An increase in the dopant content causes a morphotropic phase transition: at x = 0.1-0.7 the samples are isostructural to Sr3La2(Ge3O9)(2), while at x = 0.9-1.8 the germanates have a crystal structure of Sr3Eu2(Ge3O9)(2). In all compounds, strontium and rare earth ions occupy three symmetry independent cation sites and form layers alternating along the [10 (1) over bar] direction. The relationships between the crystal structure and the luminescence characteristics: the energy of the charge transfer transition, the values of 4f-4f/CTB and D-5(0) -> F-7(2)/D-5(0) -> F-7(1) intensity ratios have been revealed. CIE chromaticity coordinates for Sr3La1.4Eu0.6(Ge3O9)(2) and Sr3La0.8Eu1.2(Ge3O9)(2) phosphors under 393 nm excitation have been measured.

The phase formation of Sr3RE2(Ge3O9)(2) (RE = Dy, Ho, Er, Tm, Yb, Lu) cyclogermanates was studied at 1000 and 1100 degrees C in air. It was shown that these compounds did not exist under these conditions, in contrast to cyclogermanates with large RE3+ ions, such as La, Pr, Nd, Sm, Eu and Gd. Using the thulium-based system SrO-T-m(2)O(3)-GeO2 as an example, it was established that compounds with Sr/RE atomic ratio other than 3/2 were formed instead of the expected Sr3RE2(Ge3O9)(2). Single phase Sr4TmGe5.667O16.834 was prepared and characterized by X-ray powder diffraction. The quantum-chemical calculations confirmed the thermodynamic instability of strontium germanates Sr3RE2(Ge3O9)(2) with RE3+ cations smaller than Gd3+. It is suggested that the prototypic structure of mixed strontium and Dy, Ho, Er, Tm, Yb and Lu rare earth germanates stems from the crystal structure of walstromite BaCa2Si3O9.

AbstractCyclogermanate Sr_3La_2(Ge_3O_9)_2, isostructural to silicate Sr_3Er_2(Si_3O_9)_2, activated by neodymium and holmium is obtained for the first time by the precursor method. Ion Nd^3+ in the structure of Sr_3La_2(Ge_3O_9)_2 is a sensitizer of the infrared luminescence of Ho^3+. Excitation by radiation with a wavelength of 808 nm leads to a series of emission lines in the luminescence spectra of Sr_3La_2- x Nd_ x (Ge_3O_9)_2 : Ho^3+ in the short-wave and middle-IR ranges (1.0–3.4 μm). The highest intensity of lines at 2.1 and 2.7 μm, associated with the ^5 I _7 → ^5 I _8 and ^5 I _6 → ^5 I _7 transitions in the Ho^3+ ion, is found for compositions containing traces of holmium. Based on the analysis of the concentration dependences of the luminescence intensity, an optimal composition of the phosphor is determined, which ensures the maximum efficiency of conversion of laser radiation energy. The data obtained are interpreted in the assumption of cross-relaxation energy transfer from Nd^3+ to Ho^3+.

Cyclogermanate Sr 3 La 2 (Ge 3 O 9 ) 2 , isostructural to silicate Sr 3 Er 2 (Si 3 O 9 ) 2 , activated by neodymium and holmium is obtained for the first time by the precursor method. Ion Nd 3+ in the structure of Sr 3 La 2 (Ge 3 O 9 ) 2 is a sensitizer of the infrared luminescence of Ho 3+ . Excitation by radiation with a wavelength of 808 nm leads to a series of emission lines in the luminescence spectra of Sr 3 La 2- x Nd x (Ge 3 O 9 ) 2 : Ho 3+ in the short-wave and middle-IR ranges (1.0–3.4 μm). The highest intensity of lines at 2.1 and 2.7 μm, associated with the 5 I 7 → 5 I 8 and 5 I 6 → 5 I 7 transitions in the Ho 3+ ion, is found for compositions containing traces of holmium. Based on the analysis of the concentration dependences of the luminescence intensity, an optimal composition of the phosphor is determined, which ensures the maximum efficiency of conversion of laser radiation energy. The data obtained are interpreted in the assumption of cross-relaxation energy transfer from Nd 3+ to Ho 3+ .

A new group of cyclogermanates has been characterized using XRD, DFT calculations, photoluminescence spectroscopy and magnetic study.

Nanocrystalline ZnS is a well-recognized semiconducting material for photocatalysis, current photogeneration, white luminophors and efficient fluorescence sensorics. Chemical bath deposition from aqueous solutions is an affordable method for fabrication of ZnS nanostructures and composite materials thereof. Here, the one-step route is proposed for deposition of nitrogen-doped ZnS nanoparticles, prepared formerly only via high-temperature ZnS nitridation. The nanoparticles are characterized by XRD, EPR and UV/Vis spectroscopic methods. The origin, chemical state and localization of nitrogen impurity within the ZnS lattice are elucidated using quantum-chemical calculations. The emergence of nitrogen in ZnS lattice is related to NH4+ ions grabbed to the Zn sublattice from parent aqueous solution.

The photoluminescence properties of nanodimensional γ-Al2O3 produced by the thermolysis of aluminum hydroxoformate Al(OH)(HCOO)2 under different conditions have been studied. In the EPR spectrum of γ-Al2O3 prepared by thermohydrolysis, a low-field signal was detected, whose shape depends on the amount of sample. The data were interpreted assuming the existence of paramagnetic centers having no inversion center.