Abstract

Crystals of tungstates and molybdates are widely used to create scintillation detectors of ionizing radiation and are of interest for the search and study of neutrinoless double beta decay. Such experiments require high precision and impose strict requirements on the optical quality and purity of scintillator crystals.

Single crystals Li₂WO₄ and Li₂W_1-xMo_xO₄ doped with molybdenum (x = 0.0125, 0.05) were grown by the Chokhralsky method with a low temperature gradient, which allows obtaining the required crystals.

Method

The Czochralski method with a low temperature gradient was developed for growing large oxide crystals for use in scintillators (LTG Cz).

During melting of the charge, the temperature in the growth furnace was elevated at a rate of 100 degrees/hour to a value of 760 °C and was kept at this temperature for 5 hours until the melt was completely homogenized. Before seeding, the temperature was decreased to 733 °C. The first growth experiments were carried out on a platinum seed holder, and subsequently on monocrystalline seeds cut from the obtained Li₂WO₄ crystals.

Results

The crystal, in which 1.25% of tungsten was replaced by molybdenum, visually completely repeated the appearance of pure Li₂WO₄: it was transparent, optically homogeneous, without visible defects and was characterized by a convex shape of the crystallization front.

A single crystal with a molybdenum content of 5 mol.% reached 65 mm in length and 40 mm in diameter. Its upper part remained transparent, however, at a distance of 25 mm from the seed, macroscopic structural defects began to form, the crystal acquired a yellowish tint, and a general deterioration in its optical quality was recorded.

Conclusion

The LTG Cz method has successfully grown a series of visually defect-free single crystals of Li₂WO₄, both unalloyed and with partial replacement of [WO₄]^2- by [MoO₄]^2- (1.25 mol.% and 5 mol.%, respectively).

Plasma spray pyrolysis is an advanced technique for the synthesis of ceramic and metallic particles through the interaction of powder precursors with a high-temperature gas flow. In this research, the process was implemented using an experimental plasma-chemical reactor operated with a direct-current (DC) plasma torch to generate an atmospheric-pressure air plasma jet. Aluminum hydroxide (Al(OH)₃) was used as a precursor material. Under plasma heating, Al(OH)₃ decomposes into Al₂O₃ after the melting, drying, and crystallization processes within the reactor, resulting in the production of aluminum oxide particles.
Experiments were carried out with plasma torch powers ranging from 30 to 35 kW, when the gas temperature was sufficient to induce Al₂O₃ melting. The formed particles were analyzed using scanning electron microscopy (SEM) to determine their morphology and X-ray diffraction (XRD) to identify their crystalline phases and structural composition. The obtained Al₂O₃ particles exhibited a narrow size distribution (50–150 µm), spherical shape, and predominantly hollow internal structure with smooth hexagonal surfaces. Plasma spray technology enables the controlled formation of uniform, spherical granules: the morphology and size of the produced Al2O3 particles can be controlled by adjusting flow parameters, residence time, and injection geometry. Al2O3 particles prepared by this method exhibit excellent characteristics, including a fine size, narrow size distribution, pure phase, and hollow spherical morphology. The morphological analysis demonstrates the ability to manufacture powders with controlled characteristics for specific applications. The produced hollow spherical Al₂O₃ granules are promising as lightweight ceramic fillers, high-temperature insulators, catalyst supports, and feedstock materials for plasma spraying or thermal barrier coatings, where controlled particle morphology and narrow size distribution are essential.

In this work, two novel zigzag one–dimensional Co(II) and Cu(II) coordination polymers (CP1 and CP2) derived from 2,5–dihydroxyterephthalic acid and 2,2'–bipyridine ligands were synthesized and characterized by multispectroscopic (UV–vis, FTIR, EPR, sc–XRD) and analytical techniques. Single crystal X–ray diffraction studies revealed a monoclinic crystal system with I2/a and P2₁/m space group for CP1 and CP2, respectively. The DFT studies were performed to study the structural and electronic properties of CP1 and CP2 and the results revealed that HOMO electron density was localized around the central metal ions whereas, LUMO electron density is diffused throughout the polymeric structures and was mostly localized on 2,2'–bipyridine ligand. Additionally, the Hirshfeld studies analysis was carried out to study the various intra–/intermolecular interactions that stabilize the crystal structure and our results showed that CP1 and CP2 were majorly stabilized by H‒H interactions. The chemotherapeutic efficacy of CP1 and CP2 were explored by studying the in vitro DNA binding interactions utilizing multispectroscopic techniques including UV−visible, fluorescence, circular dichroism and cyclic voltammetry. The synthesized coordination polymers were also evaluated for their biosensing activity and the finding revealed that CP1 showed selective sensing for levofloxacin (LVF) whereas, CP2 proved to be an efficient sensor for chloramphenicol (CLAM), LVF and nitrofurantoin (NFT). We have further evaluated the catechol oxidase activity of CP1 and CP2 was assessed by using 3,5−DTBC as a potential substrate. The chemotherapeutic potential of CP1 and CP2 was ascertained by carrying out in vitro cytotoxic activity against neuroblastoma (SH–SY5Y) cell line employing cisplatin as a reference and the results displayed better anticancer activity of CP2 which was evident from their IC₅₀ values.

Currently, 3d metal complexes are of great importance in modern research and industrial processes of organic synthesis, allowing for the efficient and sustainable synthesis of organometallic compounds. Most metals with acceptor properties have become a pressing issue. Also, copper (Cu) stands out as a promising method due to its low cost, relatively low toxicity, and rich redox properties [1]. Copper ions are widely used in catalysis and coordination chemistry because they exhibit different oxidation states, have flexible coordination geometries, and form stable complexes with donor atoms of ligands [2]. In recent years, the synthesis of new derivatives of 1,2,3-triazole derivatives has been rapidly developing due to their pharmacological and biological activity; because of this, ligands containing a 1,2,3-triazole fragment, one of the 5-membered heterocyclic compounds, have attracted particular interest in the synthesis of Cu-based complexes due to their strong N-donor properties [3]. In this study, we synthesized the Cu-based compound C₃₄H₂₆Br₄Cl₂CuN₆O₆ (1) with (1-(2-bromophenyl)-1H-1,2,3-triazol-4-yl)methyl 2-(4-bromophenoxy)acetate and characterized it by single-crystal X-ray diffraction, and performed conformational calculations based on quantum chemical analyses. For this complex compound, supramolecular and Hirshfeld surface analysis were performed to determine the intermolecular interactions. According to our results, intermolecular and intramolecular hydrogen bonds: C—H···O and C—H···N and C—Br···π stacking interactions are associated. Three-dimensional Hirshfeld surface analysis and two-dimensional fingerprint plots showed that the structures are dominated by H···H, H···C/C···H and H···O/O···H contacts; these interactions present in the determined molecular structure were characterized as stabilizing factors in the unit cell. Quantum chemical analysis revealed that the N atom located at the 3^rd position in the triazole ring of the ligands has electron-rich donor properties in this complex.

1. Mendoza-Espinosa et al. Dalton Trans. 2014. 43, 7069–7077.
2. Hakimov et al. Acta Cryst. 2025. E81, 271–274.
3. Hakimov et al. Acta Cryst. 2024. E80, 910–912.

Mononuclear and dinuclear cobalt(II) complexes C1 and C2 were synthesized, characterized and examined for their potential biological studies. The structural validation of C1 and C2 was ascertained by various analytical and spectral methods which corroborated well with single-crystal X−ray diffraction studies. DFT/TD−DFT investigations of C1 and C2 were performed to understand their electronic and structural properties. In vitro DNA/BSA interactions of synthesized complexes were conducted using a range of biophysical techniques including UV−vis, fluorescence, circular dichroism (CD), cyclic voltammetry (CV) and electron paramagnetic resonance (EPR). The binding strength of complexes C1 and C2 with DNA were calculated to be 8.06(±0.84) × 10⁴ and 8.63(±1.03) × 10⁵ M⁻¹, and with BSA, were found to be 2.8(±0.31) × 10⁴ and 6.7(±0.54) × 10⁴ M⁻¹, respectively. The catechol oxidase activity of complexes C1 and C2 were assessed employing 3,5−di−tert−butylcatechol (3,5−DTBC) as a substrate, and its subsequent conversion to 3,5−di−tert−butylquinone (3,5−DTBQ) product was validated. We also validated the antioxidant potential of C1 and C2 via a DPPH assay. Furthermore, the cytotoxic activity of C1 and C2 was measured against A549 (lung), MCF−7 and MDA−MB−231 (breast), MIA−Pa−Ca−2 (pancreas) and Hep−G2 (liver), employing ADR (adriamycin) as a standard. The results specified that the complexes C1 and C2 demonstrated cytotoxicity against A549 cell lines with relatively low GI₅₀ values (8−10 µg mL^‒1).

Inorganic chemistry is rapidly producing novel molecules and useful materials. Mixed-ligand complexes of copper (II) ions with 1,10-phenanthroline (Phen) have been developed, and their optical and magnetic properties, stability, antibacterial activity, and crystal structures have all been comprehensively explored [1-2]. Based on these findings, Phen-containing mixed-ligand complexes were created. Their crystal structures, IR and UV-visible spectra, and how the copper ion coordinated and remained stable at high temperatures were next examined by the researchers [3].

This work synthesized a mixed-ligand complex, [Cu(C₁₂H₈N₂)(C₆H₅CONHO)·NO₃]·H₂O, from Phen and benzhydroxamic acid. The crystal structure and physicochemical characteristics were studied using UV-Vis and IR spectroscopy, thermogravimetric (TG) analysis, and Hirshfeld surface analysis.

A mixed-ligand complex was synthesized by dissolving 1 mmol of Phen 1 mmol of benzhydroxamic acid and 1 mmol of Cu(NO₃)₂·5H₂O (0.20 g) in ethanol to obtain 0.05 M solutions. The Cu(NO₃)₂ and BA solutions were first mixed, followed by dropwise addition of the Phen solution under magnetic stirring. The mixture was heated at 50 °C for 20 min and then allowed to evaporate at room temperature. After 20 days, dark-green single crystals were obtained.

The Cu(II) complex was found to possess a square-pyramidal coordination geometry. The Cu(II) ion is coordinated in the equatorial plane by two nitrogen atoms from the Phen ligand (Cu1—N1 1.986(3) Å, Cu1—N2 1.986(3) Å) and two oxygen atoms from the benzhydroxamic acid ligand (Cu1—O1 1.919(2) Å, Cu1—O2 1.920(2) Å). In the axial position, an oxygen atom from the nitrate ion is coordinated (Cu1—O4 2.580(4) Å). According to the Hirshfeld surface analysis of the complex compound, the two-dimensional fingerprint plots indicate that H···H and O···H/H···O interactions make the major contributions to the intermolecular contacts. In the UV–visible spectrum, a low-intensity absorption band corresponding to d–d transitions was observed at 634 nm.

Abstract

Crystals of alkali metal tungstates are widely used as photonic materials due to their physico-chemical stability, wide transmission range, and relatively low cost. Since bulk boules with a size of 40 mm are required for the creation of scintillators, it is necessary to develop new approaches to crystal growth under conditions of low temperature gradients. This method is the low-gradient Czochralski method, which allows for the production of homogeneous crystals with a lower number of structural defects and thermoelastic stresses.

Method

The feedstock was loaded into a crucible, then melted in a sealed chamber with a thermoinsulation installed above the crucible with a pipe. Immediately before the crystal growth process, the melt was kept at a temperature slightly above the melting point to homogenize the melt. The seed is a single crystal of high structural perfection with a minimum density of dislocations, which is cut in a strictly defined crystallographic direction. The seed was immersed in the melt. The process of crystal stretching began with the formation of a monocrystalline neck, immersing the seed into the melt. The neck was formed by simultaneously lowering the melt temperature at a high linear velocity and large axial temperature gradients. Once the crystal reaches the desired diameter, the growing conditions should be stabilized to ensure a constant crystal diameter and high structural perfection.

Results

We have successfully grown Na₂W₂O₇ crystals using the low-temperature gradient Chochralski method and measured the excitation and emission spectra of the crystal.

Conclusion

Growing crystals of alkali metal tungstates using the Chochralski method with low temperature gradients is a effective method for growing single crystals. The advantages of this method include the ability to change the crystal's geometric shape and the reduction of temperature gradients, which allows for the production of larger crystals with high optical quality.

Background. Scintillators are employed in a wide range of applications, spanning from medical imaging to radiation detectors operating under extreme temperature conditions or high radiation flux. In this context, systematic investigation of their luminescence response as a function of temperature and or radiation flux is of significant importance. In this sense, this study examined the influence of temperature on the luminescence efficiency of a bismuth germanate (Bi₄Ge₃O₁₂-BGO) single crystal. Results were compared with a barium fluoride (BaF₂) single-crystal scintillator.

Materials and Methods. The experimental setup, comprised of a medical X-ray unit, for crystal irradiation was set to a voltage of 90 kVp. The crystal light output measurements were performed under temperatures ranging from 19 to 174 ^oC. The BGO crystal under investigation has a light yield of 8.2-8.9 × 10³ photons/MeV, a decay time of 300 ns and a timing resolution of 2500-6000 ps @ FWHM.

Results. The luminescence efficiency values of BGO are 2.96 EU at 21.0 ^oC and 0.37 EU at 172.4 ^oC. The corresponding values for BaF₂ decrease with increasing temperature, ranging from 1.56 EU at 19.5 ^oC to 0.32 EU at 174.2 ^oC. BGO appears with clearly higher luminescence efficiency values across the examined temperature range; however, for temperatures reaching 174 ^οC, the efficiencies of BaF₂ and BGO scintillators converge with each other, despite their initial differences.

Conclusion. Despite the higher luminescence efficiency values of BGO, an interesting finding of this work is that BaF₂​ maintains a performance profile that is comparable to BGO, especially as temperatures approach 174°C where the differences between the two materials are minimized. This combination of economic accessibility and thermal stability at high temperatures renders it an good choice for harsh environments and large-scale applications where budget and durability are as critical as performance.

We present a study of 18 adsorption sites found on metal nanoparticles and surfaces that have either a Face-Centred Cubic (FCC) or Hexagonal Close-Packed (HCP) structure. Most metals in the periodic table have these structures, and we determine using a geometric approach the adsorption site geometry on a nanoparticle made using physical magnetic ball-and-stick models. These geometric models include the existence of an octahedral or tetrahedral hole beneath the adsorption site, as these can affect the adsorption site strength of adsorbates. Furthermore, these adsorption sites are a combination of the three-fold hollows and four-fold hollows, which are adsorption sites known to activate diatomic molecules (e.g. N2, CO). In addition, adsorption of larger molecular weight adsorbates can be defined on these sites as they provide multiple contact points in contrast to the typical, four-fold hollow, three-fold hollow, bridge and atop adsorption. We find that there are 9 geometrically distinct adsorption site topologies that are composed of square (i.e. 100) and triangular (i.e. 111) motifs. These adsorption site topologies when combined with a characteristic angle (ζ) result in 18 distinct adsorption site geometries that can be found on metal nanoparticles and surfaces. A systematic naming system for these adsorption sites is provided that explicitly defines the adsorption site geometry. Using this approach we find that there are five different type of B5 sites, an adsorption site that has been previously found to activate dinitrogen on ruthenium for the ammonia synthesis reaction.

ZnO is a multifunctional semiconductor material, with a wide band gap (~3.37eV), high coupling energy (60 meV), excellent chemical and thermal stability, and enhanced optical, electronic and structural properties, enabling its wide range of applications. In this study, crystalline ZnO films were deposited on silicon substrates, obtained by a chemical method, using Zn(NO₃)₂ as the Zn precursor, NaOH as the precipitating agent, and SDS as the surfactant. The deposited ZnO films were initially treated at 150°C, followed by RTA at 550 and 900°C, for 300 sec. Morphological and structural analyses were compared with conventionally treated samples to highlight the changes induced by RTA. SEM analysis showed that temperature influenced the morphology of ZnO NPs, obtaining particles with spherical shapes and sizes between 15 and 60 nm in a short time. In addition, the tendency agglomeration increases with increasing temperature. Structural analysis indicated a high degree of crystallinity and a hexagonal wurtzite structure; the size of the surface boundaries decreased as the temperature increased from 550°C to 900°C. The FTIR spectra show absorption bands that can be associated with the vibration mode of the Zn-O bonds, and confirm the improvement of crystallinity by enhancing the intensity of the peaks. The surface properties exhibit high wetting capacity, through contact angles with an average value of 45°, regardless of the RTA applied. The results obtained highlight the potential of the RTA process as an efficient alternative to classical thermal methods for improving the quality of crystalline ZnO films, increasing their potential for various technological applications, by controlling the thermal cycle parameters.

Acknowledgments: This work was supported from a grant of the Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, project number PN-IV-P2-2.1-TE-2023-0417, within PNCDI IV, and by the Core Program within the National Research Development and Innovation Plan 2022-2027, project no. 2307.