Thesis (M.S.)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: Max Deibert. Includes bibliographical references (leaves 56-58).

Nanocrystalline praseodymium oxide films have been successfully generated on stainless steel substrates. The electrochemical deposition was performed in the cathode compartment of a divided electrochemical cell with a regular three-electrode configuration. The green films obtained by electrodeposition were then annealed at high temperatures for 1-3 hours. X-ray diffraction revealed the fluorite structure of Pr6O11 and the crystallite size was calculated. X-ray photoelectron spectroscopy was employed to study the composition of the oxide films and also the oxidation state of Pr. Scanning electron microscopy was utilized to study the surface texture and microstructure of deposits. Fourier transform infrared spectrometery was used to investigate the composition of the films. The effects of different conditions on the green films were also studied such as different pH values of the electrolyte solution, different deposition modes, different supporting electrolytes and different applied current densities. Sintering experiments were conducted to investigate the properties of the green films. Praseodymium oxide powders were also successfully prepared by combining electrochemical methods with sintering processes. The praseodymium oxide powders were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The crystallite sizes of the powders were evaluated.

UV radiation is utilized in a number of environmental technologies, most notably for the disinfection of water, air, and surfaces through the use of UVC fluorescent lamps. Recently, our group developed a luminescent material that could emit germicidal UVC simply by irradiating it with a household fluorescent lamp, thus introducing a new type of antimicrobial surface powered by low-intensity visible light. The materials were doped with praseodymium ions (Pr3+) which have the unique capability of converting visible light to higher energy UV using an optical mechanism called upconversion. While visible-to-UV upconversion materials appeared promising for environmental application—particularly because solar irradiation could be used for their activation—their practical application was thwarted by low light conversion efficiencies. Herein we discuss the pursuit of new material forms and modifications designed to improve the efficiency of Pr3+-based upconversion systems. These enabled successful enhancement of antimicrobial activity and led to a proof of concept for upconversion-sensitized TiO2 photocatalysis. Correlations between material properties and optical behavior will be presented, followed by commentary on how these strategies might be used to further advance upconversion systems toward environmental application.

Using the parallel disk method of activation analysis, the (n,2n) reaction cross section in 141-Pr was measured as a function of neutron energy in the range 15.4 to 18.4 MeV. The bombarding neutrons were produced from the 3-T(d,n)4-He reaction, where the deuterons were accelerated by the 3-MV Van de Graff generator of the North Texas Regional Physics Laboratory in Denton, Texas.

Orientador: Alexandre Mesquita / Resumo: O titanato de cálcio CaTiO3 é um material com estrutura de tipo perovskita que tem sido aplicado como luminóforo. É bem estabelecido que a inserção de íons de terra rara no sítio ocupado pelo Ca2+ provoca mudanças significativas nas suas propriedades estruturais e produz efeitos luminescentes na faixa do visível. Entretanto não existem trabalhos reportando a inserção do La3+ no sítio do Ca2+ no que se refere às características estruturais e luminescentes desses materiais. Portanto, o presente trabalho estuda as propriedades fotoluminescentes apresentadas pela matriz à base de titanato de cálcio dopada com praseodímio, lantânio e alumínio. O material foi sintetizado a partir do método Pechini, que se mostrou um método eficaz na preparação de acordo com a caracterização estrutural realizada. A técnica de difração de raio X permitiu identificar que todas as amostras de CaTiO3 apresentam-se na fase cristalina com simetria ortorrômbica. Através da espectroscopia de absorção de raio X na borda K do Ti4+ constatamos a ocorrência de maior simetria do Ti4+ em relação aos átomos ao seu redor quando aumentamos a temperatura de calcinação e que a substituição de íons no sítio do Ca2+ não altera essa simetria. Em razão do aumento da concentração dos dopantes, tanto no sítio do Ca2+ quanto no sitio do Ti4+, foram observados alterações nos modos de vibração dos espectros Raman. Constatou-se o aumento da torção entre os octaedros de TiO6 em relação ao aumento da concentração dos dopantes. No... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The calcium titanate CaTiO3 is a perovskite structure material which has been used as phosphor. It is well established that the incorporation of rare earth ions in the place occupied by Ca2+ cause significant changes in their structural properties and produce luminescent effects in the visible range. However, there are no studies reporting the insertion of La3+ on the Ca2+ site with respect to structural and luminescent characteristics of these materials. So, this work studies the photoluminescent properties presented by the matrix based on calcium titanate doped with praseodymium, lanthanum and aluminum. The material was synthesized by the Pechini method, which proved an effective method of preparation according to the structural characterization performed. The technique of X-ray diffraction showed that all samples are organized and exhibit orthorhombic symmetry. Using X-ray absorption spectroscopy at the K edge of Ti4+, we found that the occurrence of major symmetry of Ti4+ with respect to the neighbor atoms when the calcination temperature was increased and that the substitution of ions Ca2+ by Pr3+ does not change this symmetry. With the concentration of dopants increasing at the Ca2+ and Ti4+ sites, changes of the vibration modes in the Raman spectra were observed. It was found an increased torque between the TiO6 octahedra as a function of the increase in concentration of dopants. In the luminescence spectra, increasing the structural defect density enhanced the light e... (Complete abstract click electronic access below) / Mestre

Thesis (M.S.)--University of Texas at El Paso, 2007. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--University of Pennsylvania, 1903. / Includes bibliographical references.

Thesis (Ph. D.)--University of Pennsylvania, 1903. / Includes bibliographical references.

The technique of detecting EPR spectra and measuring spin-bath relaxation times by the megneto-optical Faraday rotation has been applied to carefully grown crystals of praseodymium ethylsulphate (PrES). This method has been successfully applied to neodymium ethylsulphate by Rieckhoff and Griffiths. PrES was chosen because Pr³⁺ is an ion having an even number of unpaired hf electrons and thus possesses a non-degenerate ground state, the removal of any degeneracy in zero magnetic field being due to low symmetry components of the crystalline electric field. All experiments were done' at liquid helium temperatures (1.4 ≤ T ≤ 4.2°K) and in external magnetic fields up to 12 kilogauss. Successful measurements were made with the optic axis of the crystal aligned parallel to the polarized light beam and the external magnetic field. It was necessary to orient the magnetic field component of-the microwave power parallel to the external magnetic field in order to induce spin transitions. Theory shows that the magnitude of the Faraday rotation is proportional to the difference in population of the ground state doublet. The EPR spectrum and spin-bath relaxation times were measured in terms of saturation, the saturation being defined by s = [formula omitted], where Θ and Θ₀ are the rotation in the presence and absence of microwave power. The EPR spectrum at X band of undiluted PrES is a broad band Extending over several kilogauss with no evidence of hyperfine structure. The band decreases at 8400 φ and covers 800 φ from its maximum to half power point. Pr¹⁴¹ has nuclear spin 1 = [formula omitted] and the absence of any hyperfine structure indicates that crystal field distortion is the main source of line broadening. This result agrees with work done by Baker and Bleaney who in examining the low field side of this spectrum at K band found no trace of hyperfine structure. The empirical dependence of saturation on the relative microwave power is found to be s = [formula omitted]. This relationship cannot be explained theoretically. Since homogeneous line broadening predicts s = [formula omitted], we conclude that the resonance line is inhomogeneously broadened. The relaxation times measured as a function of temperature over the ranee 1.4 to 2.18°K and at 4.22°K and as a function of the external magnetic field, range from 0.1 to 10 msec. For 1.40 ≤ T ≤ 1.80°K, T decreases from 0.4 to 0.15 msec; is proportional to T[symbol omitted] and is consiaered to be the phonon-bath relaxation time. Values of T show a scatter within 0.20 ± 0.02 msec for 1.80 ≤ T ≤ 1.95°K. As the λ -point is approached (1.95 ≤ T ≤ 2.18°K), T exhibits a very rapid increase, having a value of 0.20 msec at 2.155°K and 0.85 msec at 2.165°K. This behaviour appears to be related to the energy exchange between the crystal and helium bath. Measurements of T at 2.18°K and 4.22°K indicate that the return to thermal equilibrium of the spin-phonon system is limited by the thermal conductivity of the liquid helium bath. The magnetic field dependence of T is interpreted in terms of phonon scattering by the paramagnetic Pr³⁺ ions. The effect is strongest at the lowest temperatures (i.e. ~ 1.4°K) where there is an increase in T from 0.5 to 2.0 msec for the magnetic field H increasing from 3.5 to 11.5 kilogauss. The effect of the magnetic field on T decreases with increasing temperature and at 2.15°K T appears to be independent of field. An unsuccessful attempt to detect electron spin resonance in neodymium ethylsulphate oriented with its optic axis .perpendicular to the light path (and external magnetic field) is described. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第18380号 / 人博第693号 / 新制||人||166(附属図書館) / 25||人博||693(吉田南総合図書館) / 31238 / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 田部 勢津久, 教授 加藤 立久, 教授 杉山 雅人, 教授 森本 芳則, 教授 山本 行男 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DGAM