Low-temperature ultraviolet-excited photoluminescence (PL) and recombination luminescence (RL) properties of La-doped Ca2SnO4 have been investigated by luminescence, electron paramagnetic resonance ...(EPR) and optically-detected magnetic resonance (ODMR) techniques. Two PL and RL bands at 340 nm and 450 nm have been observed. PL excitation spectra measurements with a synchrotron source showed a significant difference between the 450 nm and the 340 nm PL bands. The 450 nm band has a long-lasting hyperbolic decay, while the 350 nm band shows a fast decay. Assuming an excitonic nature of the 340 nm band, the band gap of the Ca2SnO4:La has been estimated to be approximately 5.5 eV. ODMR measurements suggest that the low-temperature RL band at 450 nm is caused by tunnelling recombination of electron trap and hole trap centres, and the recombination energy is transferred to Sn2+ luminescence centres.
•Ca2SnO4:La exhibits a long-lasting afterglow at low temperatures.•ODMR techniques show that afterglow originates from recombination of F-type and V-type centres.•Band gap energy of 5.5 eV is estimated from luminescence excitation measurements.
TiO2 nanoparticles hazard is associated to their photocatalytic activity causing release of DNA damaging ROS (Reactive Oxygen Species), lipid peroxidation and skin damage. Various coatings have been ...proposed to minimize photocatalysis, while keeping the potential to block UV radiations. Uncoated and variously coated commercial nano-titania have been classified on the basis of UVB-induced lipoperoxidation of linoleic acid. A selection of the most and the least protective specimens was then examined by ESR (Electron Spin Resonance) to evidence the presence of surface paramagnetic centres and the release of ROS in aqueous suspensions (spin trapping). Paramagnetic centres and ROS were correlated with the extent of lipid peroxidation. When tested on porcine skin (mimicking the human one), titania acted as on linoleic acid. The combined use of lipid peroxidation of simple fatty acids with ESR analysis is here proposed as a possible screening tool for the evaluation of the potential toxicity of nano-titania in sunscreen preparations.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This study presents the preliminary results of investigation of the types and dynamics of paramagnetic centres in lime mortars from Sveta Petka church in Budinjak, Croatia, using Electron Spin ...Resonance (ESR) spectroscopy. The excavation in Budinjak discovered a very unique four lobed plan object Sveta Petka, with no additional finds or reliable historical records about the time of its construction. The lime mortars from the church were chosen for analysis in order to characterize the building material and to verify the site chronology by dating them. Lime mortar is valuable but problematic material for luminescence and radiocarbon dating. This type of material has not been dated before using ESR; therefore, careful studies are required to identify the useful paramagnetic centres. The ESR approach suggested in this work concentrates on a calcium carbonate signal. All samples were γ-irradiated in 60C bomb with the doses of 1, 10, 20, 50, 80 and 100kGy. In all spectra signals from Fe3+ and Mn2+ ions have been observed. Paramagnetic centres which give the ESR signals may be interpreted as CO2−, CO3−, CO33−, HCO32−, SO2−, SO3−, PO2− and PO32− species. However, all spectra are complex and signals are interfering; therefore, computer resolution enhancement method will be needed in further research. The changes in ESR signals amplitude measured at magnetic field range about 3440–3450G were analysed versus the dose of irradiation, using Mn2+ signals as a reference. Exponential growth of the curve and saturation for doses above 20kGy were observed; therefore, irradiation with smaller doses is required. These preliminary studies will be helpful in future attempts of dating lime mortars by ESR method.
► Lime mortars from Budinjak were investigated using ESR spectroscopy. ► In all spectra signals from Fe3+ and Mn2+ ions have been observed. ► Signals may be interpreted as CO2−, CO3−, CO33−, HCO32−, SO2−, SO3−, PO2−, PO32−. ► ESR amplitude grows exponentially with radiation dose and saturates at 20kGy. ► Those results will be helpful in future attempts of dating lime mortars by ESR.
The consequences of 50MeV Li3+ ion irradiation on the structural and magnetic behaviour of polycrystalline samples of spinel ferrite system Li0.5+0.5xTixAl0.1Fe2.4−1.5xO4 are investigated by using ...X-ray diffraction (XRD), magnetization and 57Fe Mössbauer spectroscopy. The Mössbauer spectra exhibit central enhancement after SHI-irradiation, which is attributed to the paramagnetic centres created due to the irradiation. The reduction observed in the saturation magnetic moment after SHI-irradiation is ascribed to the partial formation of paramagnetic centres and rearrangement of the cations in the lattice corroborated by XRD and Mössbauer Loretnzian intensity analysis. The presence of amorphous phase in the irradiated samples is ruled out.
The influence of oxidation on complex paramagnetic centres system of demineralized coal and coal free of pyrite was compared. Polish orthocoking coal with a carbon content of 87.8
wt% was studied. ...This coal was oxidized with nitric acid (HNO
3), peroxyacetic acid (PAA) and in O
2/Na
2CO
3 system. Multi-component structure of X-band EPR spectra of the coal samples was numerically analysed. The lineshape and the parameters of the component lines: linewidths and
g-factors, were determined. Concentrations of paramagnetic centres were measured. The three groups of paramagnetic centres belonging to different molecular units were found in the studied samples. They were responsible for broad Gauss (Δ
B
pp: 0.49–0.84
mT), broad Lorentz 1 (Δ
B
pp: 0.18–0.35
mT), and narrow Lorentz 3 (Δ
B
pp: 0.04–0.08
mT) EPR lines. Properties of paramagnetic centres of the simple molecular units with broad Gauss and Lorentz 1 lines were changed during demineralization of coal and after pyrite removing from coal.
g-Values of Gauss and Lorentz 1 lines increased, Lorentz 1 lines were broadened and concentrations of paramagnetic centres with Lorentz 1 lines increased. Oxidation of both demineralized coal and coal free of pyrite with nitric acid led to the highest decrease of the concentration of paramagnetic centres with Gauss lines, narrowing of these lines and increase of
g-factor. The higher effects of oxidation on paramagnetic centres responsible for broad lines were observed for coal free of pyrite. Paramagnetic centres with narrow Lorentz 3 lines belonging to multi-ring aromatic units in demineralized coal and coal free of pyrite were not susceptible for oxidation.
Microwave saturation of multi-component EPR spectra of oxidized lignite Mequinenza (Spain) with a carbon content of 65.1 wt % and with a high sulphur content of 10.3 wt % was studied. The coal was ...oxidized with nitric acid (NHO3), peroxyacetic acid (PAA), and in O2/Na2CO3 system. Three different groups of paramagnetic centres exist in the coal samples analyzed. The EPR spectrum of the demineralised coal was a superposition of broad Gauss (ΔB pp = 0.75 mT), broad Lorentz 1 (ΔB pp = 0.42 mT) and narrow Lorentz 3 lines (ΔB pp = 0.08 mT). The three EPR components with linewidths: 0.58–0.77 mT (Gauss line), 0.30–0.39 mT (Lorentz 1 line) and 0.05–0.06 mT (Lorentz 3 line) were recorded for the oxidized coal. The g-values were obtained for the samples studied in the ranges 2.0043–2.0046 (Gauss lines), 2.0035–2.0038 (Lorentz 1 lines) and 2.0032–2.0034 (Lorentz 3 lines). The broad Gauss and Lorentz 1 lines saturate at low microwave powers. The narrow Lorentz 3 lines of demineralised coal were not saturated at microwave power from the range considered. After the coal oxidation with HNO3, PAA and in O2/Na2CO3 system, the microwave saturation of the narrow Lorentz 3 lines was also observed, which indicated a degradation of the multi-ring aromatic structures upon oxidation.
The dynamic properties of the stable L-alanine radicals SAR1 and SAR2 induced by γ-irradiation of a L-alanine crystal have been investigated using the electron nuclear double resonance technique ...(ENDOR). The study was focused on the dynamic properties of these centres in the temperature range from 180 to 320 K. In this region, the motion of the
and CH
3
groups exhibits slow and fast motional dynamics in comparison with the nuclear and electron Larmor frequencies, respectively. The correlation rotation times of the CH
3
and
groups of the SAR2 CH
3
group and the neighbouring CH
3
group of the SAR1 paramagnetic centre were estimated from the spectral line broadening and spectral intensity.
Paramagnetic centres of thermally decomposed vitrinite from medium-rank Polish coal (85.6 wt.% C) were studied using X-band (9.3 GHz) electron paramagnetic resonance (EPR) spectroscopy. The aim of ...this work was to compare concentrations and properties of paramagnetic centres in vitrinite heated at different temperatures.
The vitrinite sample (92 vol.% vitrinite) obtained from vitrain was heated at 350 and 550 °C. The EPR measurements were performed for the evacuated (10
−4 Torr) samples. The line shape of the EPR spectra was numerically analysed. Amplitudes,
g-factors, and line widths Δ
B
pp of the EPR components were evaluated. The concentration of paramagnetic centres in the samples was determined.
Three different groups of paramagnetic centres exist in the studied vitrinite. EPR spectra of vitrinite were superposition of one broad Gaussian (Δ
B
pp: 0.80 mT,
g: 2.0030), and broad (Δ
B
pp: 0.56 mT,
g: 2.0029) and narrow Lorentzian (Δ
B
pp: 0.13 mT,
g: 2.0028) lines. The most active during thermal decomposition were paramagnetic centres with broad Lorentzian lines. The concentrations of the all types of paramagnetic centres in vitrinite increase with temperature of heating. Spin-lattice relaxation times in vitrinite decrease with increasing of temperature of thermal decomposition.
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