A series of new germanates was prepared and their structures were characterized with X-ray diffraction (XRD). We employed solid-state synthesis, flux growth, and crystallization from melts to obtain crystals of the new materials. The crystals were studied by means of single crystal XRD, providing the information on the structure and composition of the new materials. Germanates suitable to accommodate Mn4+ – a well-known activator ion for the preparation of the rare-earth-free red phosphors – were of a particular interest. The Ge4+ substitution for Mn4+ is possible if the crystal structure features octahedrally coordinated germanium atoms, and we indeed were able to prepare such germanates. The crystal structures of the following phases were characterized: Mg3Ge1-O4(1-)F2(1+2) ( ≈ 0.1), Mg14Ge4O20F4, Mg2Pb2Ge2O7F2, Sr3GeO4Cl2, Ba3GeO4Br2, Sr6Ge2O7Cl6, Ba5GeO4Br6, Na2BaGe8O18, Rb2BaGe8O18, Na0.36Sr0.82Ge4O9, Na2SrGe6O14, and K2SrGe8O18. Two phases, Mg3Ge1-O4(1-)F2(1+2) and Na0.36Sr0.82Ge4O9 demonstrate deficiency on certain crystallographic sites. We analyzed the connectivity of the GeO4 and GeO6 units in the new and reported tetra- and octagermanates. Despite the similar stoichiometry, the connectivity of GeOn polyhedra is different in RI2Ge4O9, RIIGe4O9 and RIRIIGe8O18 germanates (RI = alkali, RII = alkaline earth metal). The Ge4+ substitution for Mn4+ was successfully done for the Na2BaGe8O18, Rb2BaGe8O18, Na2SrGe6O14, and K2SrGe8O18 phases yielding new red phosphors. Based on the powder XRD data, the optimal synthetic strategies were developed yielding high purity (≈ 99 wt. %) samples. The photoluminescent excitation and emission spectra were collected for the new phosphors. Strong absorption of the UV light and emission in the far-red region of the visible spectra were confirmed, which is in a good agreement with the literature. The Mn4+ doping level was optimized to achieve the highest luminescence in the studied phases. Temperature-dependent luminescence spectra were collected for the Na2SrGe6O14 : Mn4+ and K2SrGe8O18: Mn4+, and the K2SrGe8O18: Mn4+ showed the highest resistance to temperature quenching. / Thesis / Doctor of Philosophy (PhD)

Abstract Not Provided / Thesis / Master of Science (MSc)

Abstract Not Provided / Thesis / Master of Science (MSc)

No description available.

<p>Silicon oxide films (oxygen-rich or silicon-rich) doped with various rare-earth (RE) [cerium (Ce), terbium (Tb), europium (Eu) and erbium (Er)] elements have been by deposited by electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD). The successful in-situ incorporation of high concentrations of RE elements has been confirmed by Rutherford backscattering spectrometry (RBS), and the optical properties of the films were analyzed by Photoluminescence (PL) spectroscopy.</p><p> Ce, Tb, Eu and Er related emission was observed from the films with corresponding doping and was found to be sensitive to RE concentration, the presence of Si nanoclusters (Si-ncs) and annealing induced structural evolution. The significant enhancement of Ce^3 + emission in Ce-doped oxygen-rich films under annealing in flowing N2 at 1200 °C was found to be related to the formation of cerium silicate whose presence was confirmed by Fourier transform infra-red (FTIR) spectra and high-resolution transmission electron microscopy (HR-TEM) images. The observation of intense Tb^3+ emission from Tb-doped oxygen-rich films under nonresonant excitation revealed the presence of indirect excitation processes. The organic ligands introduced from the Tb(tmhd)3 precursor during deposition was considered as the possible sensitizer. The presence of Si-ncs in Ce or Eu-doped silicon-rich films resulted in the quenching of both RE and Si-ncs PL, while in Tb or Er-doped silicon-rich films the coupling between Si-nes and RE ions can excite RE-related emission efficiently. The formation of Si-ncs with sizes of 2-3 nm in Tb-doped silicon-rich films under annealing in flowing N2 at 1100 and 1200 °C was revealed by HR-TEM images.</p> / Thesis / Master of Applied Science (MASc)

Silicon oxide and silicon oxynitride thin films with in-situ cerium (Ce) doping were deposited using electron-cyclotron-resonance plasma enhanced chemical-vapor deposition (ECR-PECVD) on p-type silicon substrates. Oxygen was gradually substituted by nitrogen to produce SiOxNy thin films with different layer compositions. Refractive indices extracted from variable-angle spectroscopic ellipsometry (VASE) measurements classified the thin films into two main groups, SiOx and SiOxNy. The thin film composition was studied by Rutherford Backscattering Spectrometry (RBS), verifying the gradual increase in nitrogen content. Photoluminescence (PL) spectra of samples were obtained using a 375 nm laser diode as an excitation source. All samples were subjected to post-deposition annealing treatment for 1 hour at different temperatures varying from 800 to 1200 °C in both 95% N2 and 5% H2 and pure N2 gas environment, to investigate the effect of hydrogen passivation on the PL irradiance. Samples subjected to annealing yielded considerably stronger blue/white PL emission than as-deposited ones, due to the formation of Ce-containing clusters at a temperature of 1200 °C. Optimum layer composition and annealing condition to produce SiOxNy thin films with maximized Ce3+ excitation efficiency were determined. Besides, the effect of hydrogen fluoride (HF) etching on PL irradiance was studied, showing that an HF (1%) etching duration of 90 s yields the highest PL irradiance. Electrical measurements were carried out for all Ce doped samples as preliminary work for light-emitting device fabrication. ITO and Al are coated as electrodes on the front side of the thin films and backside of the substrates, respectively, using a radio frequency (RF) magnetron sputtering system. I-V measurements were performed to investigate the carrier injection properties and the dominating mechanism of carrier conduction was determined. / Thesis / Master of Applied Science (MASc)

Macromolecular magnetic resonance imaging (MRI) contrast agents have unique localization and contrast enhancement properties. We have designed and studied a monodisperse paramagnetic β-cyclodextrin click cluster (Gd10) decorated with Gd-containing arms and unique contrast enhancing polymers. To synthesize Gd10, a novel alkyne-functionalized diethylenetriaminetetraacetic acid chelate was created and coupled to a per-azido-β-cyclodextrin core and chelated with Gd(III) to yield the precursor macromolecule. Luminescence measurements were carried out using an analogous structure Eu(III)-containing structure and indicated that each lanthanide has an average of 1.8 water exchange sites. Gd10 yields a high relaxivity profile (6.2 mM⁻¹ s⁻¹ per Gd(III) at 9.4 T). Gd10 shows toxicity higher than clinically used contrast agents such as Magnevist&trade in vitro in cardiomyoblast cells. No acute toxicity was observed in the rats (n = 9) and contrast enhanced image analysis indicates renal processes may be involved in clearance. The contrast enhancing polymers we developed are new macromolecular beacons that allow the delivery of nucleic acids to be visualized at different biological scales. They contain repeated oligoethyleneamines, for binding and compacting nucleic acids into nanoparticles, and Gd(III)/Eu(III) chelates. The chelated lanthanides allow the visualization of the delivery vehicle via microscopy and via magnetic resonance imaging (MRI). We demonstrate that these new delivery beacons effectively bind plasmid DNA(pDNA) and protect their cargo nucleic acids from nuclease damage. The lanthanide-chelate materials have been found to efficiently deliver pDNA into cultured cells and do not exhibit toxicity. Micrographs of cultured cells exposed to the nanoparticle complexes formed with fluorescein-labeled pDNA and the europium-chelated polymers reveal effective intracellular imaging of the delivery process. MRI of bulk cells exposed to the complexes formulated with pDNA and the gadolinium-chelated structures show bright image contrast, allowing visualization of effective intracellular delivery on the tissue-scale. Because of their versatility as imaging probes, these delivery beacons posses remarkable potential for tracking and understanding nucleic acid transfer in vitro and have promise for in vivo imaging applications. In later studies the Ln-chelating polymers were co-polymerized with dimethylgalacterate which definitively increases luciferase gene expression (up 50x enhancement) and cellular uptake (up to 2x enhancement). / Ph. D.

Metal-organic frameworks (MOFs) are crystalline materials composed of metal clusters and organic ligands. MOFs that exhibit photoluminescence are promising materials for a broad range of applications. Due to their structural tunability and crystalline nature, luminescent MOFs also provide an excellent platform for studying structure–property relationships of materials. The photophysical properties of three anthracene-dicarboxylic acids – 1,4-anthracene dicarboxylic acid (1,4-ADCA), 2,6-anthracene dicarboxylic acid (2,6-ADCA) and 9,10-anthracene dicarboxylic acid (9,10-ADCA) – were studied in a series of polar aprotic solvents using steady-state absorption, steady-state emission spectroscopy and time-correlated single photon counting (TCSPC) emission lifetime spectroscopy. The addition of carboxylic acid functional groups on the anthracene ring alters photophysical properties to varying degrees depending on the location and protonation state. Density functional theory (DFT) calculations reveal that the lowest-energy ground-state structures of both 2,6-ADCA and 1,4-ADCA have dihedral angles between the carboxylic acids and aromatic planes of θ = 0°, while the same dihedral angle increases to θ = 56.6° for 9,10-ADCA. Time-dependent DFT calculations suggest that the carboxyl groups of 1,4-ADCA and 2,6-ADCA remain coplanar with the anthracene ring system in the excited state. In contrast, the calculations reveal significant changes between the ground and excited geometries for 9,10-ADCA and puckering of the anthracene moiety of is observed. The three anthracene dicarboxylic acids were then incorporated into zirconium-based MOFs. The MOF structures were characterized using powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). The steady-state absorption and emission spectra as well as the fluorescence lifetimes of the MOFs were compared to that of the corresponding ligand in solution. The MOFs comprising 9,10-ADCA and 2,6-ADCA formed highly crystalline octahedral shaped crystals and were found to be isostructural with the well-known UiO-66 and UiO-67 frameworks. However, incorporation of the 1,4-ADCA ligand resulted in large rod-shaped crystals. The absorption spectra of the MOFs are broadened and redshifted compared with that of the corresponding free ligands. The emission spectra of the MOFs constructed from 9,10-ADCA and 1,4-ADCA display emission bands that resemble that of the free ligand in acidic solutions, but are slightly broadened and redshifted in the MOF. Little difference is observed between that of 2,6-ADCA within the MOF and in acidic solution. The broadening and redshift observed in the absorption and emission is indicative of intermolecular interactions between anthracene units and/or with the Zr4+ clusters. The fluorescence lifetimes measured for the anthracene-based MOFs show a long component, comparable to the lifetime of the free ligand, along with shorter component. This may also suggest intermolecular interactions between chromophores in the MOFs. Altogether, derivatization of anthracene was shown to have specific effects on the photophysical properties of the parent anthracene molecule. These properties are further altered when the ligand is incorporated into a metal organic framework. Such systematic studies can provide a guide in designing luminescent MOFs with the excited-state properties desired for a given application. / Master of Science

An electron microprobe equipped with a device for making luminescence measurements has been used to determine the concentration of luminescence activators in zoned cassiterites of hydrothermal origin. Micron-scale growth zones contain variable amounts of Ti, Fe, W and other impurities. The impurity ions replace Sn⁴⁺ to produce luminescence centers. The relative intensity of cathodoluminescence and the amount and kind of impurity activators were simultaneously measured while scanning the growth zones with a micro-focussed electron beam. Two distinct emission bands were observed, a yellow-green (λ ~ 565 mµ) band for Ti-activation and a blue (λ ~ 440 mµ) band for W-activation. Measurements made on a heated sample show strong thermal quenching of the Ti-activated cathodoluminescence. The decay time for the Ti-activated emission, which is independent of temperature from 21°c to 275°C, is 0.168 msec. The cathodoluminescence spectrum for W-activation closely resembles that of self-activated CaWO₄ (Leverenz, 1946) although a higher oxygen coordination (VI) for W in cassiterite is to be expected, Fe occurring with Ti appears to enhance the Ti-activated emission. Fe occurring with W or Si quenches luminescence. / Master of Science

M.S.