Fe3+Fe^{3+} ions in alkali lead tetraborate glasses-an electron paramagnetic resonance and optical study

Glass systems of composition $90R_{2}B_{4}O_{7} + 9PbO + 1Fe_{2}O_{3}$ (R = Li, Na and K) and $90Li_{2}B_{4}O_{7} + (10-x)PbO + xFe_{2}O_{3}$ (x = 0.5, 1, 3, 4, 5, 7 and 9 mol%) have been investigated by means of electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra exhibit three resonance signals at g=6.0, 4.2 and 2.0. The resonances at g=6.0 and 4.2 are attributed to $Fe^{3+}$ ions in rhombic and axial symmetry sites, respectively. The g=2.0 resonance signal is due to two or more $Fe^{3+}$ ions coupled together with dipolar interaction. The EPR spectra of 1 mol% of $Fe_{2}O_{3}$ doped in lithium lead tetraborate glass samples have been studied at different temperatures (123-433 K). The intensity of g=4.2 resonance signal decreases and the intensity of g=2.0 resonance signal increases with the increase of temperature. The line widths are found to be independent of temperature. The EPR spectra exhibit a marked concentration dependence on iron content. A decrease in intensity for the resonance signal at g=4.2 with increase in iron content for more than 4 mol% has been observed in lithium lead tetraborate glass samples and this has been attributed to the formation of $Fe^{3+}$ ion clusters in the glass samples. The paramagnetic susceptibility (\chi) is calculated from the EPR data at various temperatures and the Curie constant (C) has been evaluated from 1/\chi versus T graph. The optical absorption spectrum of $Fe^{3+}$ ions in lithium lead tetraborate glasses exhibits three bands characteristic of $Fe^{3+}$ ions in an octahedral symmetry. The crystal field parameter Dq and the Racah interelectronic repulsion parameters B and C have also been evaluated. The value of interelectronic repulsion parameter B (825 $cm^{-1}$ obtained in the present work suggests that the bonding is moderately covalent

EPR and Optical Studies of Vanady Ions in Alkali Lead Borotellurite Glasses

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of $VO^{2+}$ ions in different alkali lead borotellurite glasses have been studied. The spin-Hamiltonian parameters (g and A), bonding parameter $\beta_{2}.^{2}$ and Fermi contact interaction parameter k have been calculated. The values of spin-Hamiltonian parameters confirm that the vanadyl ions are present in the glasses as $VO^{2+}$ molecular ions in an octahedral site with a tetragonal compression. The number of spins (N) participating in resonance is calculated as a function of temperature (123-393 K) for 9 mol% of $VO^{2+}$ ions in lithium lead borotellurite glass sample. It is observed that N obeys the Boltzmann law. From EPR data, the paramagnetic susceptibility (\chi) is calculated at various temperatures and the Curie constant has been evaluated from $1/\chi$ graph. The optical absorption spectrum exhibits two bands characteristic of $VO^{2+}$ ions in tetragonal symmetry. The band gap $(E_{opt})$ and the Urbach energies $(\triangle E)$ have been determined from the ultraviolet absorption edges and are found to be dependant on the size of the alkali ion. The theoretical values of optical basicity $(A_{th})$ of these glasses have also been evaluated

Determination of Copper in Water, Vegetables, Foodstuffs and Pharmaceuticals by Direct and Derivative Spectrophotometry

Abstract: The quantification of copper in water, vegetables, foodstuffs, human hair and pharmaceutical samples was determined by a simple more sensitive and selective spectrophotometric method. Cu(II) forms an orange -red color complex with 5-{ά -methyl-3-hydroxy benzylidene} rhodanine [5M, 3H-BR], at pH 5.5 in sodium acetate and acetic acid buffer. The maximum absorbance was measured at 430 nm. The Beer's law is obeyed in the range of (0.05 µg -13 µg/mL). The molar absorptivity (ε) and the Sandell's sensitivity of the complex were 0.6027× 10 4 mol -1 cm -1 and 0.01054 µg cm -2 respectively. First, second and third derivative spectrophotometry were also proposed and employed successfully for the determination of copper in the supra. The performance of the present method was also evaluated in terms of RMSEP, REP and RSD, students t-test. This indicates the greater importance of the method than other methods reported in the literature