A.F.M.Y. Haider

ESR study of transition metal ions in magnesium titanate

Trigonally symmetric electron spin resonance spectra have been observed for Co2+, Ni2+ and Mn4+ ions occupying single sites, and Cr3+ ions occupying two sites in ilmenite-structure MgTiO3. The fine-structure parameters at 295K for Cr3+(1), Cr3+(2), Mn4+ and Ni2+ ions are D=-1672, +364, -1769 and 1370*10-4 cm-1 respectively, whilst for Co2+ ions g/sub ///=2.867 and gperpendicular to =4.99. Previous results for Fe3+ and Mn2+ ions are substantially confirmed. Oxidation and reduction experiments show that the valence state of iron in MgTiO3 may be readily changed; the observed effects are consistent with the earlier proposal that Fe3+ ions are located at both the Mg2+ and Ti4+ sites. A comparison of experimental and calculated fine-structure splittings for Cr3+ ions suggests that Cr3+ (1) and Cr3+ (2) ions are located at sites which involve Cr3+-Ti4+ and Cr3+-Mg2+ ion pairs in nearest-neighbour cation sites respectively, although whether the Cr3+ ion in each pair occupies the Mg2+ or Ti4+ host lattice site is indeterminate. The calculations are based on the superposition model of crystal fields and existing data for ruby. The ESR data for MgTiO3 and Al2O3 containing Mn2+, Co2+ and Ni2+ ions suggests that the single-ion anisotropy in the layered antiferromagnets MnTiO3, CoTiO3 and NiTiO3 may be comparable with the dipolar anisotropy.

Elemental Analyses and Determination of Lead Content in Kohl (Stone) by Laser-Induced Breakdown Spectroscopy

Elemental analyses of kohl (stone) samples collected from three different parts of the world were performed using laser-induced breakdown spectroscopy (LIBS). The analyses indicated that lead (Pb), copper (Cu), silver (Ag), iron (Fe), calcium (Ca), aluminum (Al), silicon (Si), and sodium (Na) were present in all the kohl samples. In addition to these elements, the sample from Madina, Kingdom of Saudi Arabia (KSA), contained the elements tin (Sn), zirconium (Zr), and antimony (Sb). The sample from Mount Toor, Egypt, also contained Sn. Also, quantitative analysis for lead was carried out by the standard addition method using the LIBS technique. The result showed the presence of 14.12 ± 0.28% by weight of Pb in the sample from Madina, which compares well with the measurement done using atomic absorption spectroscopy (AAS) (13.31 ± 0.46%). The standard addition method used three calibration curves drawn for three emission lines of the LIBS spectra of Pb. The limits of detection (LoD) for these calibration curves varied from 0.27% to 1.16% by weight. The lead contents of the samples from Mount Toor and the local market of Bangladesh were also measured by the AAS technique, and the results were 14.61 ± 0.48% and 8.98 ± 0.35% by weight, respectively. The reason for determining only the lead content in kohl, which may be used as an eye cosmetic, is the adverse effect that lead has on health.

High conversion efficiency ultraviolet fiber Raman oscillator-amplifier system.

High efficiency UV frequency conversion by stimulated Raman scattering in a XeCl (λ = 308-nm) excimer laser-pumped multimode fiber is presented. The system consists of a first piece of fiber as a Stokes generator and a second as a power amplifier. Power conversion efficiencies up to 80% have been measured. Uses of fiber Raman amplifiers in the near UV are also discussed.

Measurement of in-plane motions and rotations using a simple electronic speckle pattern interferometer

We describe the construction and operation of a simple electronic speckle pattern interferometer which is sensitive to in-plane motions and rotations. The interferometer is extremely simple and easy to use. It uses a commercial digital still camera for image acquisition, and a personal computer for image storage and analysis. The interferometer was used to measure very small in-plane rotations of a rough surface, and the results were found to be in good agreement with the expected values. We propose to use this system as an instrument for the measurement of small-angle rotations.

Continuously tunable multiple-order stimulated four-photon mixing in a multimode silica fiber

Stimulated four-photon mixing (SFPM) has been observed up to four orders in a 300-m-long, low-loss, large-core multimode silica fiber pumped by a dual-frequency dye laser. The phase-matching condition for SFPM was uncritically achieved in the multimode fiber, so that, by varying the frequency separation of the two laser lines, it was possible to tune continuously an intense line generated by SFPM under the Raman-gain curve in the range of 350 to 495 cm(-1).

Trivalent transition metal ions and off-centre effects in strontium oxide

A calculation of the lattice energies involved in the displacements of Fe3+ and Cr3+ ions off the regular cation site in SrO is described. The model used comprises an FeO6 or CrO6 cluster, in which individual ionic interactions are considered using the simple shell mode, surrounded by a polarisable continuum. It is predicted that Fe3+ ions should be off-centre along (110) directions, whilst Cr3+ ions remain on-centre, consistent with experiment. The displacement magnitude for the Fe3+ ion is calculated to be 0.22 AA, and the stabilisation energy 0.68 eV.