Photoluminescence studies on rare earth titanates prepared by self-propagating high temperature synthesis method

The laser-induced luminescence studies of the rare earth titanates (R2Ti2O7) (R = La, Nd and Gd) using 355 nm radiation from an Nd:YAG laser are presented. These samples with submicron or nanometer size are prepared by the self-propagating high temperature synthesis (SHS) method and there is no known fluorescence shown by these rare earths in the visible region. Hence, the luminescence transitions shown by the La2Ti2O7 near 610 nm and Gd2Ti2O7 near 767 nm are quite interesting. Though La3+ ions with no 4f electrons have no electronic energy levels that can induce excitation and luminescence processes in the visible region, the presence of the Ti3+ ions leads to luminescence in this region.

Optical-limiting response of rare-earth metallo-phthalocyanine-doped copolymer matrix

The nanosecond optical-limiting characteristics (at 532 nm) of some rare-earth metallo-phthalocyanines (Sm(Pc)2, Eu(Pc)2, and LaPc) doped in a copolymer matrix of poly(methyl methacrylate) and methyl-2-cyanoacrylate have been studied for the first time to our knowledge. The optical-limiting response is attributed to reverse saturable absorption due to excited-state absorption. The performance of LaPc in a copolymer host is studied at different linear transmissions. The laser damage thresholds of all the samples are also reported.

Studies on development of novel rare earth doped (Bi,Pb)-2212 superconductors with enhanced properties

The objective of the present work is to study the effect of rare-earth (RE) doping on the superconducting properties of (Bi,Pb)-2212 system and to develop novel superconductors in the system with improved properties, especially, the self- and in-field critical current densities so as to use them for practical applications. This dissertation describes a range of findings in Bi-based superconductor using the cationic substitution of rare earth (RE) elements. Most of the experiments reported here take advantage of the difference in the valency and ionic radii of dopant and doping site.

Studies on the catalysis by sulfated mixed oxides of tin with some rare earth elements

A comparative study of acid-base properties and catalytic activity of Sn-La and Sn-Sm mixed oxides and their corresponding sulfate modified analogues are reported in this thesis. The catalytic activity and product selectivity in the decomposition of alcohols are correlated with the acid-base and redox properties of the catalyst systems under study The effect of catalyst preparation, pretreatment and various reaction parameters on the catalytic activity of sulfate modified oxides is investigated in the oxidative dehydrogenation reactions The experimental conditions are optimised to synthesise industrially important organic chemicals viz. 2,6 xylenol, o-cresol, N-methylanilne and N,N-dimethylaniline employing the mixed oxide systems. The effect of sulfate treatment on the catalytic activity of these systems in the alkylation reactions of phenol, anisole and aniline is also investigated and the merits and demerits of sulfate treatment are highlighted.

Nitrogen laser excited fluorescence of some rare earth doped alkaline earth fluorides

The present study is mainly concéntrated on the visible fluorescence of Ho3+ ,nd 3+ and Er 3+rare earths in alkaline earth fluoride hosts(caF2,srF2,BaF2) using a nitrogen laser excitation. A nitrogen laser was fabricated and its parametric studies were first carried out.

Acid-Base. Surface Electron Donatin6 &.Catai.Ytlc Properties Of Some Binary Mixed Oxides Containing Rare Earth Elements

Catalysis research underpins the science of modern chemical processing and fuel technologies. Catalysis is commercially one of the most important technologies in national economies. Solid state heterogeneous catalyst materials such as metal oxides and metal particles on ceramic oxide substrates are most common. They are typically used with commodity gases and liquid reactants. Selective oxidation catalysts of hydrocarbon feedstocks is the dominant process of converting them to key industrial chemicals, polymers and energy sources.[1] In the absence of a unique successfiil theory of heterogeneous catalysis, attempts are being made to correlate catalytic activity with some specific properties of the solid surface. Such correlations help to narrow down the search for a good catalyst for a given reaction. The heterogeneous catalytic performance of material depends on many factors such as [2] Crystal and surface structure of the catalyst. Thermodynamic stability of the catalyst and the reactant. Acid- base properties of the solid surface. Surface defect properties of the catalyst.Electronic and semiconducting properties and the band structure. Co-existence of dilferent types of ions or structures. Adsorption sites and adsorbed species such as oxygen.Preparation method of catalyst , surface area and nature of heat treatment. Molecular structure of the reactants. Many systematic investigations have been performed to correlate catalytic performances with the above mentioned properties. Many of these investigations remain isolated and further research is needed to bridge the gap in the present knowledge of the field.

Tailoring the microwave dielectric properties of BaRE2Ti4O12 and BaRE2Ti5O14 ceramics bycompositional variations

Ceramic dielectric resonators in the BaO-RE2O3-TiO2 (RE=rare earth) system have been prepared by the conventional solid state ceramic route. The dielectric properties have been tailored by substitution of different rare earth oxides and by bismuth oxide addition. The dielectric constants increased with Bi addition whereas the Q decreased. The temperature coeffecient of the resonant frequency improved with bismuth addition.

Tailoring the Microwave Dielectric Properties of BaRE2Ti4012 and BaRE2Ti5014 Ceramics by Compositional Variations

Ceramic dielectric resonators in the BaO-RE2O3-TiO2 (RE = rare earth) system have been prepared by the conventional solid state ceramic route. The dielectric properties have been tailored by substitution of different rare earth oxides and by bismuth oxide addition. The dielectric constants increased with Bi addition whereas the 0 decreased. The temperature coefficient of the resonant frequency improved with bismuth addition

Fabrication of thin films and nano columnar structures of Fe-Ni amorphous alloys and modification of its surface properties by thermal annealing and swift heavy ion irradiation for tailoring the magnetic properties

Department of Physics, Cochin University of Science and Technology