RESUMO
A series of Eu3+ doped NaCd1-xPO4: x Eu3+ (0 ≤ x ≤ 0.1) phosphors were synthesized and a systematic investigation of structural, morphological, optical and photophysical properties were carried out. Structural characteristics were analyzed both qualitatively as well as quantitatively to establish the phase purity, supported by FTIR and Raman spectroscopy methods. The valance state of the dopant, as well as surface elemental compositions were investigated by XPS technique. The optical characteristics were analyzed by employing UV-Visible DRS, which shows that the host bandgap is getting broadened upon doping as a result of the Burstein-Moss (BM) effect. Eu3+ doped phosphor exhibits emissions rich in red (617 nm) under suitable excitations at 393 nm while the optimal doping concentration was found to be around x = 0.06. The effective non-radiative transfer of energy from host to activator is governed by the dominant dipole-dipole transitions. The hypersensitive transition line 5D0 â 7F2 is observed owing to the induced electric dipole (ED) transition of Eu3+ centered at 617 nm. Local site symmetry has been analyzed to ascertain the environment around Eu3+ and presence of any non-equivalent cation sites. The concentration quenching effect of phosphors was explained on the basis of Dexter's theory and charge compensation mechanism. The Commission Internationale de l'Eclairage (CIE 1931) chromaticity coordinates for the prepared phosphors were estimated and found to lie in the red region of color space. The photoluminescence decay time was measured for the most intense emission line 5D0 â 7F2 at 617 nm under 393 nm excitation and the results indicate that Eu3+ activated NaCdPO4 can be a suitable red phosphor for white LED using UV-LED chip owing to it's near UV-excitation characteristics.
RESUMO
A detailed investigation of crystal structure, magnetic and electrical conduction properties of a low dimensional LaFeO3 is reported. The sample is synthesized by Sol-Gel method with a low preparation temperature. Synchrotron x-ray diffraction, Raman and FTIR spectroscopy methods were used to establish the structural phase and vibrational modes present in the sample. The low dimensionality and morphology of the prepared sample is probed through transmission electron microscopy. From the explicitly field and temperature dependent magnetization, the magnetic phase exhibited by the nanoparticle is weak ferromagnetic which is further evidencing from the Fe57 Mossbauer spectroscopy. To gain further understanding of electrical conduction mechanism and related features of AC conductivity, impedance spectroscopy techniques are used. It is noticed that, the grain effect is dominated while the electrode effect is suppressed with temperature. The activation energies due to grain and grain boundary effect are found to be 0.0780 eV, 0.175 eV for T < 90 °C and 0.451 eV, 0.525 eV for T > 90 °C respectively. Finally, jump relaxation model and Jonscher's power law are used to explain the frequency-dependent conduction behavior in the system.
RESUMO
The alterations in structure and function of photosystem II (PS II) during the senescence of primary leaves of wheat seedlings have been compared with the changes induced by ultraviolet-B (UV-B) radiation in the presence or absence of photosynthetically active radiation (PAR). The results indicated that the senescence-induced loss in pigment content, thylakoid membrane integrity and carotenoid-to-chlorophyll (Car-to-Chl) energy transfer efficiency was intensified by exposure to UV-B radiation. Different parameters for the measurement of PS II activity, such as Chl a fluorescence, O2-evolution and thermoluminescence intensity, were altered during senescence and these alterations were furthered by UV-B irradiation. The damage of photosynthetic apparatus by UV-B exposure in the presence of PAR was less than the damage in absence of PAR. The activation of molecular defense mechanisms could be a factor in the alleviation of UV-B damage in the presence of PAR.