In recent studies, amorphous silica (SiO2) has been used as a host matrix for rare-earth ions to prepare luminescent materials that can be used in various light emitting devices. Sol-gel glasses have the potential to hold up to â¥10% dopants without losing their amorphous structure. However, before rare earth (RE) - doped sol-gel glasses can be used as luminescent material, several fluorescence quenching mechanisms must be overcome. There are several quenching mechanisms which are present in all materials that are more serious in sol-gel glasses. The first is cross relaxation which involves energy transfer between RE elements; the others are energy transfer through lattice vibrations and to hydroxyl (OH) groups which are present due to the use of water as the solvent during the preparation process. A few studies have demonstrated that the luminescence intensity of rare-earth doped silica can be improved through incorporation of co-dopants such as Al, TiO2, B and by annealing at high temperatures (e.g. > 500ºC). Following their footsteps and in order to make comparisons, we used aluminum as the codopant in some samples to investigate the effects on luminescence yield for various RE concentrations. We also investigated the effects of magnesium co-dopant and high temperature annealing on the luminescence intensity of rare-earth doped silica. In this work, the highest emission intensity was observed for the sample with a composition of 0.5 mol% Ce3+. Cerium doped silica glasses had broad blue emission corresponding to the D3/2- FJ transition at 445 nm but exhibited apparent concentration quenching after higher concentrations of 0.5 mol% Ce3+. Silica containing Mg2+ or Al3+ ions displayed an increase in luminescence intensity as the Mg2+ or Al3+ to Ce3+ ratio increases for the range investigated but significant luminescence enhancement was observed for Mg2+:Ce ratio greater than 20, while that of Al3+ co-doping had the highest luminescent intensity when the ratio of Al:Ce is 10:1. This enhanced photoluminescence was assigned to an energy transfer from the Mg nanoparticles, to result in enhanced emission from Ce3+. The Al3+ or Mg2+ ions disperses the Ce3+ clusters, enhancing 2F5/2 and 2F7/2 emissions due to increased ion-ion distances and decreased cross-relation.

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Melt compounding was used to prepare polycarbonate (PC) and poly(methyl methacrylate) (PMMA) nanocomposites with different amounts of metal-oxide fillers (silica, zirconia and titania). Zirconia and two types of titania were prepared by a sol-gel method, whereas a commercial hydrophobic silica having chemically surface bonded methyl groups was used. Titania nanoparticles were annealed at 200 and 600 °C to obtain the anatase and rutile phases, respectively. The effect of filler amount, in the range 1-5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics was investigated by means of transmission electron microscopy (TEM), X-ray diffractometry (XRD), small-angle X-ray scattering (SAXS), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), 13C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (13C{1H}CP-MAS NMR) and measures of proton spin-lattice relaxation time in the rotating frame (T1Ï(H)), in the laboratory frame (T1(H)) and cross polarization times (TCH). Results showed that the nanoparticles were well dispersed in the polymers whose structure remained amorphous, except for zirconia in a PC matrix, which showed the appearance of a local lamellar order around the nanoparticles. The silica, titania and zirconia nanopaticles increased the thermal stability of the polymers, except for the highest silica and zirconia contents in the PC system which showed a decrease. A similar trend in the activation energies of thermal degradation was observed. The presence of zirconia and silica showed a decrease in the storage and loss moduli at lower temperatures, probably due to a plasticization effect. The two types of titania nanoparticles influenced the rigidity of the polymers in different ways because of their different carbon contents, particle sizes and crystal structures. NMR results suggested that, in the presence of a metal oxide, the observations in the PMMA systems could be related to heteronuclear dipolar interactions between the carbonyl carbons and the surrounding hydrogen nuclei, and in the PC systems to intermolecular interactions involving the carbonyl groups.

This work comprises of several aspects of calcium-aluminate phosphor activated with rare earth metal ions i.e. (CaAl2O4:Eu2+, Nd3+, and Dy3+). In particular the luminescent and structural properties of the long afterglow CaAl2O4:Eu2+,Nd3+,Dy3+ phosphors prepared by urea-nitrate solution-combustion method were investigated. The solution-combustion method is more efficient because phosphors with high efficiency were obtained at low temperature (500 oC) in a very short period of time (5 min). The effects of varying concentration of host matrix composition (Ca:Al), flux i.e. boric acid (H3BO3), activator (Eu2+) and co-activator (Nd3+/Dy3+) mass ratios and urea ((NH2)2CO) on the structural, luminescent, and thermoluminescent(TL) properties of the CaAl2O4:Eu2+, Nd3+, Dy3+ phosphors were studied. It was observed that Ca:Al mass ratios greatly affect the crystalline structure of the material. The results of the X-ray diffraction (XRD) analysis reveal that the formation of several crystalline phases depends on the ratios of the host material. The XRD peaks show the presence of other phases such as Ca3Al2O6 and CaAl4O7 but the predominant phase formed was that of CaAl2O4. However it was found that the crystalline structure is generally not affected by the variation of the co-dopants concentration. Photoluminescence (PL) studies revealed a general rise in intensity with an increase in the mass ratio of Ca:Al. The highest PL intensity was observed with 0.7% Ca. The luminescent intensities vary from each other when co-doped with various proportions of Nd3+ and Dy3+. The addition of H3BO3 favored the formation of pure monoclinic CaAl2O4 phase while the variation of the amount of ((NH2)2CO) showed mixed phases although still predominantly monoclinic. Both boric acid and urea to some extent influence the luminescence intensity of the obtained phosphor but unlike the case of CO(NH2), the emission peak for H3BO3, does not shift evidently because the energy level difference of 4f-5d does not change obviously. The broad blue emissions consisting mainly of symmetrical bands having maxima between 440â445 nm originate from the energy transitions between the ground state (4f7) and the excited state (4f65d1) of Eu2+ ions while the narrow emissions in the red region 600-630 nm arise from the f-f transitions of the remnant unreduced Eu3+ions. High concentrations of H3BO3 generally reduce both intensity and lifetime of the phosphor powders. The optimized content of H3BO3 is 5.8 mol % for the obtained phosphor with excellent properties. XRD analysis of the influence of Eu2+ and Nd3+ doping concentrations on the morphological, structural and PL properties of the CaAl2O4: Eu2+; Nd3+ phosphor, depict a dominant monoclinic phase that indicates no change in the crystalline structure of the phosphor even with high concentration of Eu2+ or Nd3+. The Energy Dispersive x-ray Spectroscopy (EDS) and Fourier Transform Infra-Red Spectroscopy (FTIR) spectra showed the expected chemical components of the phosphor. The excitation spectra show one broadband from 200 nm to 300 nm centered around 240 nm corresponding to the crystal field splitting of the Eu2+ d-orbital. The prepared phosphor compositions exhibit PL emission in the blue region with a maximum around 440 nm. This is a strong indication that there was dominantly one luminescence centre, Eu2+ which represents emission from transitions between 4f7 (8S7/2) ground state and the 4f6-5d1 excited state configuration. Two other, minor peaks, at 580 and 614 nm indicate the presence of remnants of Eu3+ ions as a result of incomplete reduction during sample preparation. High concentrations of Eu2+ and Nd3+ generally reduce both intensity and lifetime of the phosphor powders. The optimized content of Eu2+ is 0.36 mol % and for Nd3+ is 0.09 mol % for the obtained phosphors with good properties. The decay characteristics exhibit a significant rise in initial intensity with increasing Eu2+ doping concentration while the decay time increased with Nd3+ co-doping. Analysis of the TL glow curves is one of the most significant ways to measure the number of traps and also the activation energy of the trap levels in luminescent materials. In the present study TL properties of the CaAl2O4:Eu2+, Nd3+,Dy3+ phosphors were investigated above room temperature by use of Nucleonix 1009I TL reader. The trap depths were estimated with the aid of the peak shape method. The glow curve of CaAl2O4:Eu2+ with a first peak at 50 °C was found to correspond to several traps. The ratio of Nd3+:Dy3+ ions were observed to influence the position, concentration and type of traps formed. The observed afterglow can be ascribed to the generation of suitable traps due to the presence of the Nd3+ trap levels. Trivalent rare earth ions (Nd3+/Dy3+) are thought to play the role of hole traps in calcium aluminate phosphors (CaAl2O4:Eu2+). In these phosphors, Eu2+ ions act as luminescent centre emitting in the blue (λ max = 440 nm) region. Despite a large number of research on the phenomenon the mechanism of the persistent luminescence of CaAl2O4:Eu2+,Nd3+,Dy3+ has not been well presented. A proper understanding of the exact luminescence mechanisms and the identification of trap levels or locations in long phosphorescent materials is required for their use in areas such as detection of radiation, sensors for cracks in buildings, fracture of materials and temperature among others.

This work consists of several aspects of phosphor materials. Strontium, calcium and yttrium aluminate doped with rare earth (Ce, Tb and Eu) have been synthesized by solution combustion method using urea as a fuel for investigations of the luminescent, structure and morphological properties. The phosphors were characterized by several techniques such as X-ray diffraction (XRD), energy dispersive electroscopy (EDS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Photoluminescence (PL), PL data were collected using a Cary Eclipse Photoluminescence Spectrophotometer equipped with a 150 W xenon lamp. Cerium doped strontium aluminum oxide (SrAl2O4:Ce3+) were synthesizes. The effects of different concentration of cerium were investigated. X-ray diffraction results confirmed the formation of the SrAl2O4 monoclinic phase (Powder Diffraction Standards (JCPDS) file No 34-0379). The particle sizes of different peaks were estimated and the average particle size was 47 nm. SEM results showed agglomerated as well as small elongated-egg-like shape on particles when taken to higher magnification. The PL spectra show a broad emission consisting of two bands peaking at 374 and 384 nm, corresponding to the transitions from the lowest 5d excited state to the 2F5/2 and 2F7/2 states. The excitation and emission peak position shifted with varying the cerium concentration. This maybe due to uncontrollable electrospinning conditions like air and wetness, which influence the cristal field that surround Ce3+. SrAl2O4:Tb3+ XRD peaks confirmed the formation of the SrAl2O4 monoclinic phase and some impurities were also observed. The photoluminescence characteristics show the emission peaks at 415, 436 and 459 nm which correspond to the 5D3 to 7FJ (J=5, 4, and 3) level and 489, 543, 585, and 622 nm corresponding to 5D4 to 7FJ (J= 6, 5, 4, 3) under excitation at 229 nm and the terbium concentration was varied. The elements of the phosphor SrAl2O4:Tb3+ were shown by energy dispersive spectroscopy. The decay curves were also observed and the decay constants show a higher value at a concentration of 0.25 mol% and lower value at a concentration of 2 mol%. CaAlxOy:Tb3+ green phosphors were obtained at low temperature (500 oC) by a solution- combustion method. The structural analysis revealed the presence of both monoclinic CaAl4O7 and CaAl2O4. The main parent structure of CaAl2O4 monoclinic was revealed when varying the concentration of terbium. The characteristic luminescence properties were investigated using emission spectra. The emission peaks are from transition of the 5D4 state to the 7FJ (J = 6, 5, 4, 3) state. The optimal intensity was obtained when the concentration of Tb3+ was increased to 2 mol%. FTIR was used to identify all the chemical bands. Absorption bands of the condensed matter AlO4 located in the range of 700 cm-1-900 cm-1 and condensed matter AlO6 at 500 cm-1-680 cm-1 are attributed to AlO4 liberation at 600 cm-1-900 cm-1. The decay curves of the phosphor were investigated and showed a higher intensity and longer afterglow time at higher concentration of terbium 2 mol%.Y3Al5O12 known as Yttrium aluminum garnet (YAG) phosphor doped with different concentration of Eu was synthesized by the solution combustion method. The crystalline structure, morphology and luminescent properties of the phosphors were studied. The SEM revealed the agglomerated morphology containing small spherical particles around the pores. FTIR spectra reveal all bonds that exist in the phosphor. The emission spectra revealed three major emission peaks at 592, 615, and 628 nm, corresponding to the 5D0â7F1 (592 nm), 5D0â7F2 (615 nm) and 5D0â7F3 (628 nm) transitions respectively. The luminescence intensity increased with an increase in Eu concentration at 0.7 mol% and then decreases with an increasing of concentration further.

This paper deals with the explanation of what seemed, under the circumstances, a rather surprising activity of about 30 minutes induced in crystals of potassium iodide when bombarded at 40 Mev in the McGill cyclotron. It is shown that the activity is, in reality, complex and arises from (1) C134 (32 min) formed from the K nuclei and (2) I128 127 (25 min) formed by neutron capture in I127. This is the first example of a strong activity so formed in the McGill cyclotron by capture of the numerous neutrons known to be released in all targets at high energies. In the fall of 1950, D. E. Tilley, J. D. Keys and W. S. Boyle, all members of the McGill Radiation Laboratory, bombarded, in the McGill cyclotron, crystals of iodine and iodine salts with protons of various energies. In newly bombarded crystals (i.e. before any separation of the elements was attempted) they noticed, among other things, an activity of half-life approximately 30 minutes. This particular activity appeared most markedly when the bombarding protons had energies from 30 to 50 Mev. The purpose of the work reported here is to identify this 30 minute activity. Iodine, atomic number 53, has only one stable isotope, I127. Some of the present published knowledge(l, 2, 3, 4, 5, 6, 7, 8) about the active iodine isotopes, and about the isotopes of xenon (atomic number 54) and other nearby elements, is summarized in Figure 1. The chart shows the relative abundances of the stable isotopes [...]

Finite difference equations abound in all areas of physics and engineering. In particular, linear difference equation eigenvalue problems define an important class of systems which have been studied through various traditional approaches adapted from continuum space methods. We studied an important subclass of problems involving strong coupling potential interactions which are not amenable to conventional analysis, such as ordinary perturbation theory. We worked with a powerful eigenvalue moment method, developed by Handy et al (C.R. Handy, D. Bessis and T. Morley, Atlanta University preprint, 1987), for generating rapidly converging lower and upper bounds to the eigenvalues of such systems, as previously described. This type analysis focuses on the signature structure of the intended solution in order to define a moment problem. Through the relevant “moment problem” theorems, tight constraints can be defined which serve to determine (quantize) the physical parameters of the system.

<p> Superconducting niobium accelerating cavities are devices operating in radiofrequency and able to accelerate charged particles up to energy of tera-electron-volts. Such accelerating structures are though limited in terms of quality factor and accelerating gradient, that translates&mdash;in some cases&mdash;in higher capital costs of construction and operation of superconducting rf accelerators. Looking forward for a new generation of more affordable accelerators, the physical description of limiting mechanisms in superconducting microwave resonators is discussed. In particular, the physics behind the dissipation introduced by vortices in the superconductor, the ultimate quench limitations and the quality factor degradation mechanism after a quench are described in detail. </p><p> One of the limiting factor of the quality factor is the dissipation introduced by trapped magnetic flux vortices. The radio-frequency complex response of trapped vortices in superconductors is derived by solving the motion equation for a magnetic flux line, assuming a bi-dimensional and mean free path-dependent Lorentzian-shaped pinning potential. The resulting surface resistance shows the bell-shaped trend as a function of the mean free path, in agreement with the experimental data observed. Such bell-shaped trend of the surface resistance is described in terms of the interplay of the two limiting regimes identified as pinning and flux flow regimes, for low and large mean free path values respectively. The model predicts that the dissipation regime&mdash;pinning- or flux-flow-dominated&mdash;can be tuned either by acting on the frequency or on the electron mean free path value. The effect of different configurations of pinning sites and strength on the vortex surface resistance are also discussed. </p><p> Accelerating cavities are also limited by the quench of the superconductive state, which limits the maximum accelerating gradient achievable. The accelerating field limiting factor is usually associated to the superheating field, which is intimately correlated to the penetration of magnetic flux vortices in the material. Experimental data for N-doped cavities suggest that uniform Ginzburg-Landau parameter cavities are statistically limited by the lower critical field, in terms of accelerating gradient. By introducing a Ginzburg-Landau parameter profile at the cavity rf surface&mdash;dirty layer&mdash;the accelerating gradient of superconducting resonators can be enhanced. The description of the physics behind the accelerating gradient enhancement as a consequence of the dirty layer is carried out by solving numerically the Ginzburg-Landau equations for the layered system. The enhancement is showed to be promoted by the higher energy barrier to vortex penetration, and by the enhanced lower critical field. </p><p> Another serious threat to the quality factor during the cavity operation is the extra dissipation introduced by the quench. Such quality factor degradation mechanism due to the quench, is generated by the trapping of external magnetic flux at the quench spot. The purely extrinsic origin of such extra dissipation is proven by the impossibility of decrease the quality factor by quenching in a magnetic field-free environment. Also, a clear relation of the dissipation introduced by quenching to the orientation of the applied magnetic field is observed. The full recover of the quality factor by re-quenching in compensated field is possible when the trapped flux at the quench spot is modest. On the contrary, when the trapped magnetic flux is too large, the quality factor degradation may become irreversible by this technique, likely due to the outward flux migration beyond the normal zone opening during the quench.</p>

<p> Accelerating cavities are devices resonating in the radio-frequency (RF) range used to accelerate charged particles in accelerators. Superconducting accelerating cavities are made out of niobium and operate at the liquid helium temperature. Even if superconducting, these resonating structures have some RF driven surface resistance that causes power dissipation. In order to decrease as much as possible the power losses, the cavity quality factor must be increased by decreasing the surface resistance. </p><p> In this dissertation, the RF surface resistance is analyzed for a large variety of cavities made with different state-of-the-art surface treatments, with the goal of finding the surface treatment capable to return the highest Q-factor values in a cryomodule-like environment. This study analyzes not only the superconducting properties described by the BCS surface resistance, which is the contribution that takes into account dissipation due to quasi-particle excitations, but also the increasing of the surface resistance due to trapped flux. When cavities are cooled down below their critical temperature inside a cryomodule, there is always some remnant magnetic field that may be trapped increasing the global RF surface resistance. </p><p> This thesis also analyzes how the fraction of external magnetic field, which is actually trapped in the cavity during the cooldown, can be minimized. This study is performed on an elliptical single-cell horizontally cooled cavity, resembling the geometry of cavities cooled in accelerator cryomodules. The horizontal cooldown study reveals that, as in case of the vertical cooldown, when the cooling is performed fast, large thermal gradients are created along the cavity helping magnetic flux expulsion. However, for this geometry the complete magnetic flux expulsion from the cavity equator is more difficult to achieve. This becomes even more challenging in presence of orthogonal magnetic field, that is easily trapped on top of the cavity equator causing temperature rising. </p><p> The physics behind the magnetic flux expulsion is also analyzed, showing that during a fast cooldown the magnetic field structures, called vortices, tend to move in the same direction of the thermal gradient, from the Meissner state region to the mixed state region, minimizing the Gibbs free energy. On the other hand, during a slow cool down, not only the vortices movement is limited by the absence of thermal gradients, but, also, at the end of the superconducting transition, the magnetic field concentrates along randomly distributed normal-conducting region from which it cannot be expelled anymore. </p><p> The systematic study of the surface resistance components performed for the different surface treatments, reveals that the BCS surface resistance and the trapped flux surface resistance have opposite trends as a function of the surface impurity content, defined by the mean free path. At medium field value, the BCS surface resistance is minimized for nitrogen-doped cavities and significantly larger for standard niobium cavities. On the other hand, Nitrogen-doped cavities show larger dissipation due to trapped flux. This is consequence of the bell-shaped trend of the trapped flux sensitivity as a function of the mean free path. Such experimental findings allow also a better understanding of the RF dissipation due to trapped flux. </p><p> The best compromise between all the surface resistance components, taking into account the possibility of trapping some external magnetic field, is given by light nitrogen-doping treatments. However, the beneficial effects of the nitrogen-doping is completely lost when large amount of magnetic field is trapped during the cooldown, underlying the importance of both cooldown and magnetic field shielding optimization in high quality factors cryomodules. </p>

<p> Effective field theories (EFTs) provide frameworks to systematically improve perturbation expansions in quantum field theory. This improvement is essential in quantum chromodynamics (QCD) predictions, both at low energy in the description of low momentum hadron-hadron scattering and at high energy in the description of electron-positron, proton-proton, proton-electron collisions. It is also important in quantum electrodynamics (QED), when electrons interact with a high-intensity, long-wavelength classical field. I introduce the principles and methods of effective field theory and describe my work in three EFTs: First, in the perturbative QCD region, I use soft collinear effective theory (SCET) to prove that strong interaction soft radiation is universal and to increase the QCD accuracy to next-to-next-to-next-to leading logarithm order for new particle searches in hadron colliders. I also compute a new class of non-perturbative, large logarithmic enhancement arising near the elastic limits of deep inelastic scattering and Drell-Yan processes. Second, in the QCD confinement region, I use heavy hadron chiral perturbation theory to study near-threshold enhancements in the scattering of <i>D</i> and &pi; mesons near the threshold for the excited <i>D</i>-meson state, <i> D*,</i> as well as in the scattering of <i>D</i> and <i> D*</i> mesons near the threshold for the exotic hadron X(3872). This work provides a clear picture of the hadronic molecule X(3872) and more profound understanding of the nuclear force between hadrons. Finally, inspired by SCET, I construct a new electron-laser effective field theory to describe highly-relativistic electrons traveling in strong laser fields, extract the universal distribution of electrons in strong electromagnetic backgrounds and its evolution in energy from the separated momentum scales of emitted photons and classical radiation, and predict the rate of wide angle photon emission. I conclude with limitations of EFT methods and some perspectives on what new work may be achieved with these EFTs.</p>