Electron Spin Resonance Studies Research Articles

An electron paramagnetic resonance study of the electron transport in heavily Si-doped high Al content AlxGa1−xN

High Al mole fraction AlGaN is an ultrawide bandgap semiconductor with potential applications in power electronics and deep UV detectors. Although n-type material is achievable with Si-doping, the role of Si is controversial, particularly for AlxGa1−xN with x > 0.8. For this paper, AlGaN films were grown by plasma-assisted molecular beam epitaxy onto bulk AlN substrates and doped with 1018–1020 cm−3 Si. We examine electron transport in heavily Si-doped AlxGa1−xN with x ≥ 0.65 using magnetic resonance, which allows us to probe the neutral donors directly rather than the free carriers and avoids complications due to electrical contacts. Transport was studied through the temperature-dependent linewidth of the electron paramagnetic resonance (EPR) signature for the neutral donor. Analysis shows evidence of hopping conductivity in the most lightly doped samples and impurity band formation in the most heavily doped ones. The EPR results, which are consistent with Hall measurements performed on the same samples, are promising for the development of highly conducting high Al content AlGaN.

Hierarchical MnO2-ZnO functionalized SiO2 nanofibrous membranes with enhanced Fenton-like catalytic performance for dye removal

In this work, flexible and hierarchical structured MnO2-ZnO/SiO2 nanofibrous membranes (NFMs) as easily recyclable Fenton-like catalysts have been developed utilizing the combination of electrospinning and a hydrothermal growth method. By capitalizing the advantages of the high specific surface area and synergism effects of bimetallic oxides, the optimal membranes exhibited prominent catalytic activity in the degradation of malachite green oxalate (MGO). Specifically, within a mere 15 min at an initial pH, 98.1% of MGO was degraded, demonstrating a remarkable degradation rate of 0.2744 min−1. Free radical scavenging experiments and Electron Paramagnetic Resonance studies conclusively identified superoxide radical species (O2•–) as the main reactive species for the degradation of MGO. Furthermore, the resultant flexible membranes displayed excellent stability and could be effortlessly recycled after catalytic process, surpassing the performance of conventional powdery Fenton-like catalysts. Notably, the resultant membranes could be used for dynamic catalyst for MGO removal and could efficiently treat 418 mL MGO with a flux of 5650.5 L m−2 h−1. The successful fabrication of these MnO2-ZnO/SiO2 membranes paves the way for the development of more efficient and applicable Fenton-like catalytic materials for water treatments and offers more inspirations for innovative designs of fiber-based or membrane-based catalysts.

Investigation of Surface Nanoclusters and Paramagnetic Centers of ZnO/Por-Si Structures as the Basis of Sensory Properties

The detection of particles with uncompensated charge and the determination of the features of their interaction during the formation of nanocrystals on substrates with a developed surface are an interesting area of research. The porous surface formed via the electrochemical etching of silicon acquired fractal properties as a result of the deposition of zinc oxide layers. Microscopy methods using different resolutions revealed a hierarchical structure of the surface, where each of the three consecutive levels contains uniformly distributed formations. The deposition of 20 layers of ZnO maximizes the concentration of nanocrystals at the pore boundaries, while the deposition of 25 layers leads to the formation of a continuous layer. The increase in photoluminescence intensity with an increase in the number of deposited layers is due to the saturation of surface nanostructures with electrons through several mechanisms. Electron paramagnetic resonance (EPR) studies have shown that the main mechanism of radiation recombination is the capture of electrons on oxygen vacancies. The different nature of the EPR saturation of the signal of interconnected paramagnetic centers revealed the formation of zinc oxide particles at the boundaries of pores with different sizes. The results of these studies of surface-active structures effectively complement the knowledge about sensory materials.

Electron spin resonance and photoluminescence studies of Co/Mg co‐doped ZnO nanoparticles

AbstractZn0.95−xMg0.05CoxO (x = 0.01–0.05 with an increment of 0.01) nanoparticles were synthesized by using the sol–gel technique to analyze structural and magnetic properties. The single phase was observed in the X‐ray diffraction measurements. To examine the surface morphology, elemental compositions, crystal quality, defect type, density, and magnetic behavior of the nanoparticles, SEM, energy dispersive X‐ray analysis (EDX), PL, and ESR were used, respectively. The PL has ultraviolet and a broad emission band including violet and a blue spectral region corresponding to the defect‐related and excitonic emissions. These emissions were strongly dependent on the synthesize condition and doping element and ratio. The effect of cobalt concentration on the line widths of pike to pike (ΔHPP) and the g‐factor of ESR spectra were investigated. By comparing the results of the ESR and PL measurements, it was determined which defect with a given g‐factor was responsible for the corresponding PL emission band. In addition, ESR spectra of Mg/Co co‐doped ZnO nanoparticles with different cobalt concentrations recorded at room temperature were presented. Since Mg/Co co‐doped ZnO nanoparticles reveal ferromagnetism at RT, they could be an appropriate material for new devices in spin‐based technologies.

Alteration in the molecular structure of the adenine base exposed to gamma irradiation: An ESR study

Abstract Adenine polycrystals were obtained from their powder form under effective crystallization conditions by adjustment of the concentration of chemical solutions. The adenine samples were irradiated with a 60Co gamma-ray source at room temperature for 12, 24, 48, and 72 h, and then these samples were investigated between 240 and 400 K using an electron spin resonance (ESR) spectrometer. No signals were observed in the non-irradiated samples irradiated for 12, 24, and 48 h; however, when irradiated for 72 h, the samples exhibited complex ESR spectra. The analysis indicated the presence of a radical structure, NH ̇ \dot{{NH}} . The hyperfine splitting and g-values were calculated from the spectra by simulation programs. Also, during the measurements, it was observed that the shapes of the ESR lines changed slightly with the temperature.

Superior photocatalytic and electrochemical activity of the MoSe2 modified ZIF-67 for the reduction and detection of Cr (VI)

The removal and detection of heavy metals from wastewater have proven to be challenging due to the limitations of the materials and technologies. Therefore, in this work, we have synthesized novel Z-scheme-based MoSe2-modified ZIF-67 by a two-step method and tested it for environmental safety by electrochemical detection and photocatalytic reduction of carcinogenic heavy metal pollutant (hexavalent chromium (Cr (VI)). The nanosheets and polyhedrons-like morphology of MoSe2 and ZIF-67 were confirmed using Field emission scanning electron microscope (FESEM) and High-resolution transmission electron microscope (HRTEM), respectively. The nanocomposite exhibited superior activity for photocatalytic reduction (∼89% within 30 min) towards Cr (VI) along with the detection (LOD-0.01 µM) with high stability. The superior activity of the MZ67 nanocomposite is attributed to enhanced recombination time (4.65 ns) with respect to pristine ZIF-67 (1.21 ns) as observed from time-correlated single photon counting (TCSPC) studies. The scavenger test and electron paramagnetic resonance (EPR) studies confirmed the Z-scheme of the nanocomposite. The electrochemical sensing for Cr (VI) combined with the photocatalytic reduction, tends to provide a trustworthy tool for wastewater management.

Influence of thermal annealing on silicon negative ion implanted SiO2 thin films

SiO2 thin film of thickness 300 nm grown on p-type silicon substrate was implanted with 100 keV silicon negative ions with fluences varying from 5×1015 to 1×1017 ions cm−2. The implanted samples were annealed at the temperature of 500 °C under N2 ambient. Electron spin resonance (ESR), Fourier transform infrared (FTIR), Photoluminescence (PL), and glancing angle X-ray diffraction (GXRD) techniques have been used to investigate the implanted SiO2 thin film after thermal annealing. ESR studies revealed the absence of vacancy defects after thermal annealing. FTIR studies showed variations in the vibrational modes, attributed to the formation of new structures after annealing at 500 °C. PL studies showed the presence of a peak at 720 nm with an intensity higher than that observed for the unannealed SiO2 samples. This effect showed a decrease in the non-radiative defect centers with an increase in the radiative Si:SiO2 interface states after thermal annealing. The presence of an additional peak at 692 nm may be attributed to the radiative recombination centers associated with silicon nanoclusters formed after annealing at 500 °C. GXRD studies showed a decrease in the intensity of the spectra for the samples implanted with 1×1016 and 5×1016 ions cm−2 after thermal annealing at 500 °C. This result reveals the formation of new SiOx structures in SiO2 thin film.

New visible-light-driven Bi2MoO6/Cs3Sb2Br9 heterostructure for selective photocatalytic oxidation of toluene to benzaldehyde

Herein, new Bi2MoO6/Cs3Sb2Br9 heterostructure (BiMo/CSB) was investigated for the first time as a visible-light-driven photocatalyst for C(sp3)–H bond activation using molecular oxygen as a green oxidant and toluene as a model substrate. The optimized BiMo/CSB photocatalyst exhibited enhanced toluene oxidation activity (2,346 μmol g-1h−1), which was almost two- and five-fold that of pristine CSB (1,165 μmol g-1h−1) and BiMo (482 μmol g-1h−1), respectively. The improved photocatalytic performance was essentially attributed to the formation of staggered band energy lineup in the BiMo/CSB hybrid, which promoted S-scheme charge transfer across the BiMo/CSB heterointerface as supported by ultraviolet photoelectron spectroscopy (UPS), density functional theoretical (DFT), time-resolve photoluminescence (TRPL), and photoelectrochemical studies. Spin–trapping electron paramagnetic resonance (EPR) and radical scavenging studies revealed that photoinduced hole, molecular oxygen, and superoxide radical are key active species in this photocatalytic system. The developed BiMo/CSB catalyst provided good selectivity toward benzaldehyde product (94–98 %), presumably due to the inhibiting effect of benzyl alcohol on benzaldehyde oxidation. No significant change in structure and morphology was observed for the spent catalyst, however small negative shift of Sb 3d and Bi 4f binding energy was found suggesting partial reduction of Sb3+ and Bi3+. This work not only provides a new visible-light-driven photocatalyst for C(sp3)–H bond activation but also opens the doors for exploitation of the conversion and functionalization of this inert bond toward the production of high value-added organic chemicals.

Evidence of ferromagnetic coupling for manganese pairs in a layered van der Waals GaS semiconductor

Using high-frequency electron paramagnetic resonance (EPR), we have observed the ferromagnetic coupling of manganese Mn2+ pairs in a layered van der Waals GaS semiconductor. The EPR spectra of Mn2+ pairs (Mn24+) [replacing covalently bonded Ga24+ pairs oriented along the chain axis (c axis) of two gallium ions and being situated in the center of the layer] were recorded at 94 and 130 GHz. The fine structure parameters for the lower multiplets with spin S = 5 and S = 4 were determined equal to D = −0.040 cm−1 and D ≅ −0.035 cm−1, respectively. Based on the observation of additional EPR lines in the region of intersection of the levels in the magnetic field of the multiplet with S = 5 and S = 4, the energy of the isotropic exchange interaction J was estimated to be ∼−0.5 cm−1. For all transitions, a well-resolved hyperfine structure was observed, due to the interaction with two equivalent 55Mn nuclei, leading to the appearance of 11 lines with a hyperfine interaction constant A = 30(1) × 10−4 cm−1, which is approximately half the hyperfine interaction constant for single Mn2+ ions. In addition, a signal from single manganese ions Mn2+ with spin S = 5/2 and a hyperfine interaction constant A = 60(1) × 10−4 cm−1 was observed, which are characterized by extremely large fine structure splitting of D = −0.15 cm−1. Simultaneously with EPR studies, the crystals were monitored by photoluminescence and micro-Raman scattering measurements using a microscope with confocal optics.

A Heterometallic Porphyrin Dimer as a Potential Quantum Gate: Magneto‐Structural Correlations and Spin Coherence Properties

AbstractIn the development of two‐qubit quantum gates, precise control over the intramolecular spin‐spin interaction between molecular spin units plays a pivotal role. A weak but measurable exchange coupling is especially important for achieving selective spin addressability that allows controlled manipulation of the computational basis states |00⟩ |01⟩ |10⟩ |11⟩ by microwave pulses. Here, we report the synthesis and Electron Paramagnetic Resonance (EPR) study of a heterometallic meso‐meso (m‐m) singly‐linked VIVO−CuII porphyrin dimer. X‐band continuous wave EPR measurements in frozen solutions suggest a ferromagnetic exchange coupling of ca. 8 ⋅ 10−3 cm−1. This estimation is supported by Density Functional Theory calculations, which also allow disentangling the ferro‐ and antiferromagnetic contributions to the exchange. Pulsed EPR experiments show that the dimer maintains relaxation times similar to the monometallic CuII porphyrins. The addressability of the two individual spins is made possible by the different g‐tensors of VIV and CuII‐ions, in contrast to homometallic dimers where tilting of the porphyrin planes plays a key role. Therefore, single‐spin addressability in the heterometallic dimer can be maintained even with small tilting angles, as expected when deposited on surface, unlocking the full potential of molecular quantum gates for practical applications.

A Heterometallic Porphyrin Dimer as a Potential Quantum Gate: Magneto-Structural Correlations and Spin Coherence Properties.

In the development of two-qubit quantum gates, precise control over the intramolecular spin-spin interaction between molecular spin units plays a pivotal role. A weak but measurable exchange coupling is especially important for achieving selective spin addressability that allows controlled manipulation of the computational basis states |00⟩ |01⟩ |10⟩ |11⟩ by microwave pulses. Here, we report the synthesis and Electron Paramagnetic Resonance (EPR) study of a heterometallic meso-meso (m-m) singly-linked VIV O-CuII porphyrin dimer. X-band continuous wave EPR measurements in frozen solutions suggest a ferromagnetic exchange coupling of ca. 8 ⋅ 10-3 cm-1 . This estimation is supported by Density Functional Theory calculations, which also allow disentangling the ferro- and antiferromagnetic contributions to the exchange. Pulsed EPR experiments show that the dimer maintains relaxation times similar to the monometallic CuII porphyrins. The addressability of the two individual spins is made possible by the different g-tensors of VIV and CuII -ions, in contrast to homometallic dimers where tilting of the porphyrin planes plays a key role. Therefore, single-spin addressability in the heterometallic dimer can be maintained even with small tilting angles, as expected when deposited on surface, unlocking the full potential of molecular quantum gates for practical applications.

An Electron Spin Resonance Study Comparing Nanometer-Nanosecond Dynamics in Diblock Copolymers and Their Poly(methyl Methacrylate) Binary Blends.

Block copolymers are a class of materials that are particularly interesting with respect to their capability to self-assemble in ordered structures. In this context, the coupling between environment and dynamics is particularly relevant given that movements at the molecular level influence various properties of macromolecules. Mixing the polymer with a second macromolecule appears to be an easy method for studying these relationships. In this work, we studied blends of poly(methyl methacrylate) (PMMA) and a block copolymer composed of PMMA as the first block and poly(3-methyl-4-[6-(methylacryloyloxy)-hexyloxy]-4'-pentyloxy azobenzene) as the second block. The relaxational properties of these blends were investigated via electron spin resonance (ESR) spectroscopy, which is sensitive to nanometric length scales. The results of the investigations on the blends were related to the dynamic behavior of the copolymers. At the nanoscale, the study revealed the presence of heterogeneities, with slow and fast dynamics available for molecular reorientation, which are further modulated by the ability of the block copolymers to form supramolecular structures. For blends, the heterogeneities at the nanoscale were still detected. However, it was observed that the presence of the PMMA as a major component of the blends modified their dynamic behavior.

Comprehensive in-vitro and magnetic hyperthermia investigation of biocompatible non-stoichiometric Zn0.5Ca0.5Fe2O4 and Mg0.5Ca0.5Fe2O4 nanoferrites on lung cancer cell lines

In this research, the suitability and potential of two biocompatible mixed valent non-stoichiometric spinel nanoferrites viz., Zn0.5Ca0.5Fe2O4 (ZCNF) and Mg0.5Ca0.5Fe2O4 (MCNF) with a minor impurity of CaCO3 have been explored for magnetic hyperthermia and in-vitro cytotoxicity against normal and lung cancer cell lines. Nanocrystalline samples of ZCNF and MCNF in fcc structure were synthesized using the citrate-based sol-gel method and characterized by a variety of standard techniques. 57Fe Mössbauer spectroscopy, electron spin resonance and dc-magnetometry studies revealed that ZCNF is dominantly superparamagnetic while, MCNF is a soft ferrimagnet at 300 K. The maximum specific absorption rate (SAR) for 1 mg/mL suspension of nanoferrite powder in de-ionized water was found to be 179 W/g and 338 W/g for ZCNF and MCNF, respectively. Further, the highest hyperthermia temperature of 41.5 °C and 52 °C was achieved in 900 s at 15.98 kA/m for ZCNF and MCNF, respectively. Both ZCNF and MCNF showed good cytocompatibility with a tested concentration of 0.5 mg/mL against the human embryonic kidney HEK-293 (>75% cell viability) cell line. Additionally, simulated in-vitro treatment at an optimum magnetic hyperthermia temperature of 45 °C for 30 min in the presence of ZCNF and MCNF powder (up to a concentration of 1 mg/mL) led to suppression of ∼55% lung cancer cell lines (A549) while, in similar simulated condition the cell viability of normal HEK 293 cell lines remain unaffected. In summary, ZCNF and MCNF are appropriate therapeutic nanomaterials for magnetic hyperthermia-related cancer therapies.

Spin Qubit in a 2D GdIII NaI -Based Oxamato Supramolecular Coordination Framework.

Qubits are the basic unit of quantum information and computation. To realize quantum computing and information processing, the decoherence times of qubits must be long enough. Among the studies of molecule-based electron spin qubits, most of the work focused on the ions with the spin S=1/2, where only single-bit gates can be constructed. However, quantum operations require the qubits to interact with each other, so people gradually carry out relevant research in ions or systems with S>1/2 and multilevel states. In this work, a two-dimensional (2D) oxygen-coordinated GdIII NaI -based oxamato supramolecular coordination framework, Na[Gd(4-HOpa)4 (H2 O)] ⋅ 2H2 O (1, 4-HOpa=N-4-hydroxyphenyloxamate), was selected as a possible carrier of qubit. The field-induced slow magnetic relaxation shows this system has phonon bottleneck (PB) effect at low temperatures with a very weak magnetic anisotropy. The pulse electron paramagnetic resonance studies show the spin-lattice and spin-spin relaxation times are T1 =1.66 ms at 4 K and Tm =4.25 μs at 8 K for its diamagnetically diluted sample (1Gd0.12 %). It suggested that the relatively long decoherence time is mainly ascribed to its near isotropic and the PB effect from resonance phonon trapped for pure sample, while the dilution further improves its qubit performance.

Transforming diapers into inorganic carbonate enriched Carbon catalyst for improved trimethoprim degradation performance

Waste-derived carbon materials are gaining popularity in persulfate/peroxymonosulfate activated water remediation process. In the present study, a carbon catalyst was prepared from baby diaper through simple pyrolysis step, and its catalytic activity was assessed through PMS activated trimethoprim (TMP) degradation. X-ray diffraction and Fourier-transform infrared spectroscopic characterization results revealed that the synthesized carbon material is complemented with sodium carbonate inorganic salt. The catalyst derived from diaper exhibits two important characteristics that make it practically applicable. Firstly, it has a high efficiency for removing TMP, and secondly, it maintains an ecological pH (7.5) level even after undergoing oxidation. Electron spin resonance and scavenging studies showed singlet oxygen was the predominant reactive oxygen species in the system. As a result, the system exhibited high tolerance to commonly found inorganic anions in the water bodies. These features make the diaper derived carbon catalysts a promising candidate for the degradation of TMP from wastewater, also providing an alternative solution for mitigating pollution of diapers in landfills.

Toward Silicon‐Matched Singlet Fission: Energy‐Level Modifications Through Steric Twisting of Organic Semiconductors

AbstractSinglet fission (SF) is a potential avenue for augmenting the performance of silicon photovoltaics, but the scarcity of SF materials energy‐matched to silicon represents a barrier to the commercial realization of this technology. In this work, a molecular engineering approach is described to increase the energy of the S1 and T1 energy levels of diketopyrrolopyrrole derivatives such that the energy‐level requirements for exothermic SF and energy‐transfer to silicon are met. Time‐resolved photoluminescence studies show that the silicon‐matched materials are SF active in the solid state, forming a correlated triplet pair 1(TT) – a crucial intermediate in the SF process – as observed through Herzberg‐Teller emission from 1(TT) at both 77 K and room temperature. Transient electron paramagnetic resonance studies show that the correlated triplet pair does not readily separate into the unbound triplets, which is a requirement for energy harvesting by silicon. The fact that the triplet pair do not separate into free triplets is attributed to the intermolecular crystal packing within the thin films. Nevertheless, these results demonstrate a promising route for energy‐tuning silicon‐matched SF materials.

Photosono catalytic behaviour of phthalocyanine when supported on electrospun nanofibers: The effect of radical initiators

In this study, two Zn phthalocyanine (ZnPc) complexes containing substituents with varying number of the methoxy groups were investigated when supported on TiO2 fibers in sono-, photo-, and photosono-catalytic degradation of Rhodamine 6 G. The ZnPc on fibers displayed higher activity than when alone. The photosonocatalytic process displayed higher degradation aptitude than sonocatalytic and photocatalytic processes. The electron paramagnetic resonance studies revealed that the photocatalytic process is instigated by singlet oxygen only. However, sonocatalytic and photosonocatalytic processes are instigated by both singlet oxygen and •OH radicals. The utilization of azo-bis-isobutyronitrile and tert-butyl hydrogen peroxide as radical initiators improved the degradation efficiency of photo-, sono- and photosono- catalytic processes. The re-used fibers from sonocatalytic process resulted in significant decrease in catalytic activity, whereas the fibers from photocatalytic process were highly reusable.

Tetravalent Terbium Chelates: Stability Enhancement and Property Tuning.

Coordination chemistry of rare-earth elements has been dominated by the +3 oxidation state. Complexes with higher-valence lanthanide ions are synthetically challenging but are of fundamental research interest and significance as advanced molecular materials. Herein, four tetravalent terbium complexes (2-5) of the common formula [Tb(OSiPh3)4L] (L = ethylene glycol dimethyl ether (DME), 2,2'-bipyridine (bpy), 2,2'-bipyrimidine (bpym), and 1,10-phenanthroline (phen)) are reported. Crystallographic analyses reveal in each of these complexes a hexacoordinate Tb(IV) ion situated in a distorted octahedral coordination environment formed by four triphenylsiloxido ligands and a bidentate chelating ligand. The use of chelating ligands enhances the stability of the resulting complexes over their THF solvate precursor. More significantly, the aromatic N-chelating ligands have been found to tune effectively the electronic structures of the complexes, as evidenced by the sizable potential shifts observed for the quasi-reversible redox Tb(IV/III) process and by the changes in their absorption spectra. The experimental findings are augmented with quantum theoretical calculations in which the ligand π-donation to the 5d orbitals of the Tb(IV) center is found to be primarily responsible for stability enhancement and the corresponding changes of physical properties observed. Magnetic measurements and results from electron paramagnetic resonance studies produced small absolute values of zero-field splittings of these complexes, ranging from 0.1071(22) to 1.1484(112) cm-1 and comparable to the values reported for analogous Tb(IV) complexes.

Novel azo metal chelates of 3-aminophthalhydrazide derivative: Structural investigation, evaluation of DNA cleavage, anticancer and molecular docking studies

Transition bivalent metal ion (Mn, Co, Ni, Cu, and Zn) complexes derived from an azo ligand (HLCU) having 1,3-diketone moiety with 3-aminophthalhydrazide were prepared and characterized by using elemental analyses, ultraviolet–visible, Fourier transform infrared, nuclear magnetic resonance (1H, 13C), electron spin resonance, molar conductivity and magnetic measurement studies. Molar conductivity value indicated the non-electrolytic nature of all complexes. The ligand coordinates with the metal ion as a tridentate pattern and the binding sites are carbonyl oxygen, hydrazo nitrogen and hydroxy oxygen of phthalhydrazide moiety. The fluorescence spectra of the compounds were recorded and the results revealed that ligand have higher emission intensity than metal complexes. The X-ray powder diffraction indicated that the ligand (HLCU) and nickel(II) complex have orthorhombic crystal lattices. The ligand and metal complexes were subjected to DNA cleavage activity on pUC18 plasmid DNA using the gel electrophoresis method. The cobalt(II) complex completely cleaved DNA and other compounds showing higher cleaving activity than the control. The antitumor activity of the compounds was screened using sulforhodamine B assay towards the breast cancer and leukaemia cancer cell lines. Manganese(II), cobalt(II) and nickel(II) complexes have more promising activity, and the IC50 value is < 10 μg/mL against the leukaemia carcinoma cell line, which is equally potent as the positive control (adriamycin). The molecular docking study was used to find the binding mode of ligand and complexes of cobalt(II) and nickel(II) towards the molecular target protein receptor. The binding affinity of these compounds is −9.8, −13.6 and −10.5 kcal/mol respectively. The cobalt(II) complex has a more effective binding nature than the ligand and nickel(II) complex. Drug-likeness character indicates moderate activity of HLCU, and [Co(HLCU)(H2O)3], [Ni(HLCU)H2O] complexes, in agreement with invitro results.

Optical and EPR studies of Fe-doped CaAl12O19 near-infrared emitting phosphor

In this article we report our results on optical and electron paramagnetic resonance studies of Fe-doped CaAl12O19. At room temperature, optical excitation in the ultraviolet region leads to highly intensive luminescence signal at around 810 nm that is ascribed to the emission of Fe3+. Measurements at low temperature revealed slight shift of the emission maximum and appearance of additional wide luminescence bands in the blue and near-infrared parts of spectrum. The dependence of the luminescence intensity and decay time on temperature and concentration of Fe3+ in the material has been studied. Electron paramagnetic resonance studies showed presence of at least two different paramagnetic centres related to Fe3+. The nature of the observed luminescence bands is discussed.