published_or_final_version / Physics / Master / Master of Philosophy

Cancer currently represents one of the greatest burdens on human health in the world, claiming in excess of 7 million lives a year worldwide. Advances in both our understanding of the disease as well as our ability to diagnose it before it has had a chance to metastasize will lead to a reduction in its burden on society. To these ends, optical imaging techniques are particularly attractive. The ability to resolve cellular details noninvasively is paramount to improved cancer detection and to research on diseased tissue and cells. Lanthanoid nanoparticles, a group of photoluminescent contrast agents developed within the last two to three decades, have numerous unique optical properties that enable their use in improved and novel optical techniques. They possess large Stokes and anti-Stokes shifts, sharp electronic transitions, long luminescence lifetimes, and exceptional photostability. For these reasons, they are a good choice for biomedical applications that benefit from low background fluorescence or long illumination times. The major goal of the research presented in this dissertation was to synthesize functional lanthanoid nanoparticles for optical imaging modalities, and to explore their potential uses in a variety of biomedical applications. To this end, the research can be broken up into three specific aims. The first aim was to successfully and reproducibly synthesize downconverting and upconverting lanthanoid nanoparticles, and to functionalize these nanoparticles for use in optical techniques that would aid in the research and diagnosis of cancer. The second aim was to conduct a thorough investigation of the optical properties of these nanoparticles, and the third aim was to explore the utility of these nanoparticles in a variety of biomedical applications. First, both downconverting and upconverting lanthanoid nanoparticles were synthesized using several different methods, resulting in nanoparticles of varying size and surface functionality. Novel methods were employed to improve the utility of these nanoparticles for specific applications, including the incorporation of a mixed surface ligand population in downconverting lanthanoid nanoparticles and the use of a biomimetic surface coating to render upconverting nanoparticles water dispersible. These coated particles were further functionalized by the addition of folic acid and an antibody for epidermal growth factor receptor, both of which bind to cell surface receptors overexpressed in a number of cancers. Second, the spectral properties of lanthanoid nanoparticles were explored in detail, with special attention paid to many of the unique optical properties of upconverting lanthanoid nanoparticles. This included the discovery of one such unique property, the excitation frequency dependent emission of NaYF₄ nanocrystals codoped with Yb³⁺ and Er³⁺. Third, lanthanoid nanoparticles were used as contrast agents in a number of biomedical applications, including the development of a homogenous assay based on diffusion enhanced luminescence resonance energy transfer, a wide-field luminescence lifetime microscope, and a super resolution microscope based on the aforementioned excitation frequency dependent emission of NaYF₄:Yb³⁺,Er³⁺ nanoparticles. Specific binding of functionalized upconverting lanthanoid nanoparticles was investigated with laser scanning multiphoton microscopy, and an image processing technique was developed to overcome the challenge of working with long lived luminescent contrast agents using this imaging modality.

This dissertation focuses on the synthetic exploratory synthesis of molybdenum chalcogenides and rare earth metal-rich ternary tellurides as a part of an effort to produce molecular building blocks of molybdenum chalcogenide clusters and to explore their structural relationships with solid state cluster networks. The tightly cross-linked Mo3nSe3n+2(n = 2, 3, ...∞) clusters and chain compounds react with alkali metal cyanide or cyanide salt mixtures at temperatures of 450-675 °C to yield reduced, cyanide-terminated molybdenum chalcogenide clusters that are thermodynamically stable. At temperatures of 650-675 °C, linear chain compounds I6[Mo6Se8(CN)4(CN)2/2] (MI = K, Cs) were prepared from reactions of Mo6Se8 or elemental starting materials, Mo and Se with excess molten cyanide (KCN, CsCN). These are the first known compounds to feature linking of Mo6Se8 clusters via cyanide bridges. Magnetic susceptibility and EPR measurements indicate that there is one unpaired electron per cluster. A new reduced molecular octahedral complex, Na8[Mo6Se8(CN)6]•20H2O was prepared by the reduction of [Mo6Se8(CN)6]7-with Zn in an aqueous NaCN solution. Single crystal structure was determined. Cyclic voltammetric measurements in basic aqueous media show multiple reversible redox waves corresponding to [Mo6Se8(CN)6]6-/7-, [Mo6Se8(CN)6]7-/8-, [Mo6Se8(CN)6]8-/9-redox couples with half-wave potentials of E1/2 = -0.442 V, -0.876 V, and 11.369 V respectively versus the standard hydrogen electrode (SHE). UV-Vis studies support the presence of the reduced cluster compound. New reduced molecular tetrahedral complexes, K7Na[Mo4Se4(CN)12]•5H2O•MeOH, Na4Cs7[Mo4Se4(CN)12]Cl3, Na8[Mo4Se4(CN)12], and Na4K4[Mo4Se4(CN)12]•12H2O were prepared. Preparation of Na8[Mo4Se4(CN)12] is an improved method for the synthesis of the Mo4Se4 core. Half-wave potentials of E1/2 for the [Mo4Se4(CN)12]6-/7-and [Mo4Se4(CN)12]7-/8-couples are 0.233 V, and -0.422 V respectively versus SHE. The molecular cubane clusters [Mo4Se4(CN)12]7-/8-play an essential role in the process by which the discrete [Mo6Se8(CN)6]6-and [Mo6Se8(CN)6]are excised from the CN-linked chain compound, K6Mo6Se8(CN)5. A new rare-earth telluride compound with the empirical composition of Gd4NiTe2 was synthesized from a high-temperature solid-state reaction. Gd4MTe2 (M = Ni) crystallizes in the orthorhombic space group Pnma. This unprecedented structure consists of a cluster condensation of Ni-centered gadolinium tricapped trigonal prisms along the rectangular faces of the trigonal prism such that the Ni atoms act as two of the caps to the trigonal prisms.

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Two sets of nanostructured Zinc Oxide (ZnO) thin films doped with varying nominal concentrations of rare earth (RE) ions were prepared by pulsed laser deposition (PLD). One set was doped with europium ions (ZnO:Eu³⁺) while the other was doped with erbium ions (ZnO:Er³⁺). The nominal concentration of RE ions ranged from 0.025 to 5 atomic %. The produced films were structurally, morphologically and optically characterised using different techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), combined excitation and emission spectroscopy (CEES) and X-ray photoelectron spectroscopy (XPS). All films were found to possess a single-crystal hexagonal structure and were strongly oriented along the c-axis. However, the crystallinity of the investigated films seemed to deteriorate as the concentration of the rare earth ions increased. This deterioration is assumed to be due to the local distortion of the ZnO structure (host material) caused by the insertion of the relatively large RE ions, hence inducing structural stresses. Importantly, XRD measurements showed that no other crystalline phases related to europium or erbium, such as Eu₂O₃ or Er₂O₃, were observed. Surprisingly, the ZnO lattice constant (c) tended to become smaller as more RE³⁺ ions were added to the films. An explanation is offered whereby this observation can be taken as further evidence that Zn²⁺ ions were successfully substituted by RE³⁺ ions. Interestingly, doping ZnO films with RE³⁺ ions of a nominal concentration of ≥ 0.5 at.% or higher exhibited a drastic effect on the optical properties of the host matrix (ZnO) in which the near band edge luminescence characteristic of pure ZnO completely disappeared. According to SEM images, morphological changes also occur as dopant concentrations increase. Well-defined grains (crystallites) were clearly seen in films doped with ˂ 0.5 at.% of RE ions. However, these grains became hardly distinguishable at higher RE ion concentrations. Typical intra-4f shell transitions of RE³⁺ ions were observed when these ions were non-resonantly excited with UV radiation, indicating that energy had been efficiently transferred from ZnO to the rare earth ions. A plausible physical mechanism for this energy transfer is proposed. The radiative optical centres of rare earth ions were studied by CEES. In these experiments, both sets of films exhibited multiple optical sites. ZnO:Eu³⁺ thin films were found to have two distinct optical sites with differing site symmetries, whereas up to four optical sites were detected in the ZnO:Er³⁺ films.

The synthesis of yttrium phenalenide complexes 129-132 was achieved by salt metathesis reactions between ligand anions and YCI3. Ytterbium phenalenide complexes 133-137 were synthesized by protonolysis reactions between neutral ligands and Yb[N(SiMe3)2]2(THF)2. The solid state structure of (Pni1Bu)2Yb(THF) 136 reveals a unique n3 bonding pattern, however the electrons of the phenalenide ligand remain delocalized even when bonded to the metal center. Mono-alkyl complexes (PCpR)2Y(CH2SiMe3)(THFSiMe3)(THF) 147-149 (R = Me. Ph. H) and bis-alkyl complexes (PCp*)Y(CH2SiMe3)2(THF) 150 and (sCp)Y(CH2SiMe3)2(THF) 152 were synthesized by direct protonolysis reactions between Y(CH2SiMe3)3(THF)2 and neutral ligands. When treated with phenylsilane, complex 148 generated the crowded hydride dimer [(PCpPh)2Y(u-H)]2 161. Complexes 150 and 152 undergo acid-base. metallation. insertion reactions and polymerization of small substrates. A variable temperature `H NMR study of 150 and 152 at low temperature reveals an equilibrium between 150/152-THF and 1501152. The THF-free complexes. 150/152-THF. appear to undergo inversion of a pyramidal ground state structure to generate a C2 symmetric intermediate. The X-ray structures of 136, 147, 150. 152, (sCp)Y(CH2SiMe3)2(bipy) 154, 161. [PCp*Y(CCSiMe3)(THF)]2(u2-CCSiMe3)2] 167, acetylide cluster 169 and bis-(Me3Si)2Cp yttrium chloride dimer 176 were determined and structural features discussed.

A combination of 169Tm-Mo??ssbauer spectroscopy and inelastic neutron scattering (INS) has been used to investigate the crystal field (CF) interaction at the rare earth site for the tetragonal series RT2Si2 (where R = rare earth) and the orthorhombic series RNiAl4. Single phase specimens were prepared in an argon arc furnace and characterised using x-ray powder diffraction, specific heat and magnetic measurements. For the RT2Si2 series previous investigations were extended to include T = Mn and Cr whose sub-lattices are antiferromagnetic well above room temperature. However, the rare earth sub-lattices were confirmed to order close to liquid helium temperature. With the assistance of the lattice electric field gradient (EFG) for isostructural GdCr2Si2 (determined elsewhere using 155Gd-Mo??ssbauer spectroscopy) and the within-rank CF parameter ratios for HoCr2Si2 (determined elsewhere using INS), the experimental 169Tm quadrupole interaction data were analysed to arrive at CF parameters for the Tm3+ site in TmCr2Si2. The final CF parameters match well with the trend observed for other members of the series RT2Si2 (T = Fe, Co, Ni, Cu). CF schemes were also determined for Tm3+ in TmMn2Si2 and Er3+ in both ErCr2Si2 and ErMn2Si2. For the RNiAl4 series, TmNiAl4 was determined to be antiferromagnetic below TN = 4.7 K with the 169Tm-Mo??ssbauer spectra retaining a magnetic appearance up to 80 K due to the effect of slow spin-lattice relaxation. The relaxation data are consistent with a well-isolated ground state doublet (or pseudo-doublet) whose eigenfunctions have high components of mJ = ??6 states and with the relaxation proceeding via an excited state at 350 K. Because of the relaxation effect, the 169Tm-Mo??ssbauer data could not be interpreted in terms of CF parameters in the usual way. Instead, the INS spectra recorded for ErNiAl4 were analysed using a novel semi-empirical approach that coupled rank 2 CF parameters converted from the EFG tensor for isostructural GdCr2Si2 (determined elsewhere using 155Gd-Mo??ssbauer spectroscopy) with simple point-charge model calculations of the rank 4 and 6 within-rank CF parameter ratios. The first full set of CF parameters for this series was then determined for the Er3+ site in ErNiAl4.

Thesis (M.S.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 64-66).

Thesis (Ph. D.)--Michigan State University. Dept. of Chemistry, 2007. / Title from PDF t.p. (viewed on Apr. 16, 2009) Includes bibliographical references. Also issued in print.

Thesis (Ph.D.)--University of Texas at Dallas, 2005. / Includes vita. Includes bibliographical references.