This thesis consists of two parts. The first part deals with the visible emission of ZnO Nanocrystals and its possible application in Resonance Energy Transfer (RET) studies. The second part of the thesis is on the magnetic properties of the layered transition metal Thiophosphates MPS3 (M = Mn, Fe), their solid solutions and intercalation compounds. Recent advances in semiconductor nanocrystals or quantum dots (QDs) as inorganic fluorophores have pioneered a new direction in the fluorescent based techniques to investigate fundamental processes in lifesciences. Their broad absorption spectra with narrow, Size-tunable emissions with high quantum e±ciency and stability under relative harsh environments have made inorganic QD's the fluorophores of choice in many applications. Among inorganic fluorophores the II-VI semiconductors based on cadmium chalcogenides are the front-runners. The cytotoxicity associated with these QDs is, however, a major drawback and has lead to the search for new nanocrystalline fluorophores that are non-toxic and possess the same favorable fluorescence properties as the Cd based QDs, viz, tunability and narrow spectral profile. ZnO Nano particles are known to exhibit two emission bands; a narrow emission band in UV around 380 nm (3.25 eV) at a wavelength just below the onset of the band gap excitation in the absorption spectra and a broad emission band in the blue-green part of the visible spectrum, with a maximum between 500 and 550 nm (2.5-2.2 eV). The UV Emission originates from the recombination of bound excitons - excited electrons in the Conduction band with holes in the valence band. The visible emission of ZnO nanocrystals is known to involve deep trap states that lie approximately midway between the Conduction and valence bands and surface defects that exist as shallow traps. In principle, visible-light-emitting ZnO nanocrystals would be ideal candidates as replacement for Cd-based fluorescent labels since they are nontoxic, less expensive, and chemically stable in air. Nanoscale ZnO, however, tends to aggregate and/or undergo Ostwald ripening be-Cause of high surface free energy resulting in an increase in crystallite size and consequent Disappearance of the visible emission. Most attempts to stabilize the ZnO nanocrystals by Capping has usually resulted in the quenching of the visible trap emission. The objective of the present study was to stabilize the visible light emission of ZnO nanocrystals, to Understand the origin and mechanism of the visible emission and to explore the possibility Of using the visible emission of ZnO in RET studies. The stabilization of visible light emission in ZnO nanocrystals was achieved by forming ZnO:MgO core-shell nanocrystals. The nanocrystals were synthesized by a sequential preparative procedure that involved formation of a ZnO core followed by an MgO shell. The Nanocrystals were characterized by using XRD, TEM, optical absorption and photoluminescence spectroscopy. These are described in Chapter 2 of the thesis. The ZnO: MgO Core-shell nanostructures exhibit stable emission in the visible for extended periods. Application of the ZnO: MgO nanocrystals either as fluorescent probes or RET studies require that they be dispersible in both polar and non-polar solvents. This as realized by appropriate choice of the capping agents (Chapter 3). ZnO: MgO nanocrystals with hydrophobic surface were obtained by capping the nanocrystals with oleic acid. The oleate capped ZnO: MgO nanocrystals are soluble in a variety of non-polar organic solvents with no change in their emission properties. Water-soluble ZnO: MgO nanocrystals were obtained by capping the ZnO:MgO nanocrystals with carboxymethyl-β-cyclodextrin (CMCD). The hydroxyl groups located at the rim of the cyclodextrin cavity renders the surface hydrophilic. The integrity of the CMCD molecules are preserved on capping and their by hydrophobic cavities available for host-guest chemistry. The visible emission of The ZnO: MgO nanocrystals are unaltered by the nature of the capping agent. The origin and mechanism of the visible emission from ZnO: MgO nanocrystals has been Investigated using time-resolved emission spectroscopy technique (Chapter 4). The time-evolution of the photoluminescence spectra show that there are, in fact, two features in the visible emission whose relative importance and efficiencies vary with time. These features originate from recombination involving trapped electrons and holes, respectively, And with efficiencies that depend on the occupancy of the trap density of states. The application of the visible emission of ZnO: MgO nanocrystals as resonance energy transfer (RET) donors in water and hydrophobic media are demonstrated. In aqueous media, the carboxymethyl β-cyclodextrin (CMCD) capped ZnO: MgO nanocrystals is able to accommodate the organic dye Nile Red by an inclusion in the anchored hydrophobic cyclodextrin cavity forming a 1:1 complex. Nile Red was chosen as the guest molecule because its absorption has appreciable overlap with ZnO: MgO visible emission, a prerequisite for RET to occur. The resonance energy transfer on the band gap excitation of The ZnO core to included Red molecules in the CMCD-ZnO: MgO-Nile Red supramolecular assembly is demonstrated in aqueous media. A similar RET process is shown to occur in the non-polar media in the oleate capped ZnO: MgO nanocrystals when Nile Red is partitioned from the solvent into hydrophobic anchored oleate chains. The wavelength dependent energy transfer in the system has been studied using time-resolved emission spectroscopic technique. The importance of trap states in giving rise to non-Forster distance dependence for the RET is highlighted. The second part of the thesis deals with magnetism in low dimensional layered transition metal thiophophates, MPS3 (M = Mn, Fe). Low dimensional magnetic systems continue to be a fertile ground for discovering new phenomena and properties. Among two-dimensional magnetic systems the insulating transition metal thiophosphates are one of the few known layered systems, in which both magnetic and crystallographic lattices are two dimensional (2D). In the metal chalcogenophosphates, the magnetic MPX3 layers are separated by a van der Waals gap that effectively rules out interlayer exchange and hence these systems are nearly perfect 2D magnetic systems, with the magnetic ions forming a honeycomb arrangement within the layer. Due to the crystallographic two-dimensional nature these materials may be intercalated by variety of molecules or ions leading to change in magnetic properties. The objective of this thesis work is to try and modify the magnetic properties of the transition metal thiophosphates either by forming solid solutions of the type, M1-xMxPS3, (M, M = Mn, Fe) or by intercalating hydrated metal ions within the layers. The structure, Bonding, reactivity and magnetic properties are briefly introduced in Chapter 7. The Scope and nature of the present work in presented towards the end of the chapter. MnPS3 and FePS3 have identical crystal structures and both order antiferromagnetically at low temperatures, TN. The in-plane magnetic structures of the antiferromagnetically ordered the Neel state in the two compounds are, however, different. In MnPS3 the spins Alternate up-down whereas in FePS3 the spins are arranged as ferromagnetic chains with Alternate chains coupled antiferromagnetically. Since the crystal structures are identical, These two compounds can form solid solutions, Mn1-xFexPS3(0≤x≥1) over the entire concentration range. The magnetic properties of the single crystals of the solid solutions was measured by using a SQUID magnetometer. This system is of interest since the contrasting Neel states of the end-members may give rise to new magnetic phenomena at intermediate composition. It is shown that the magnetic behavior falls into three distinct categories. The Mn-rich compositions behave like a dilute MnPS3 lattice, the Fe-rich compositions behave like dilute FePS3 and in the intermediate compositions a spin-glass like phase appears. The phase boundaries for these regime in Mn1-xFexPS3, 0≤x≥1 is shown to be related to the percolation threshold for a honeycomb lattice. MnPS3 is known to undergo a unusual ion-exchange intercalation reaction. Intercalation occurs by the inclusion of hydrated metal ions in the galleries of MnPS3 with charge neutrality maintained by loss of the Mn2+ ions from the layer (Equation). MnPS3 + 2xG+ (aq) → Mn1-xPS3 [G (H2O) y] 2x + xMn2+ (aq) Where G is a neutral guest species. This chemistry has been exploited to intercalate hydrated Mn2+ ions in the interlamellar space to give Mn1-xPS3[Mn(H2O)6]x. the magnetic properties of this 3D analogue of MnPS3 has been investigated in Chapter 9.

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In dieser Arbeit wurden die beiden Membranen Schweinekornea und Rindernasenmukosa hinsichtlich ihrer Permeabilität für den lipophilen Arzneistoff Androstendion (AD), der sowohl zur ophthalmologischen Anwendung als auch für die nasale Applikation mit systemischer Wirkung von Interesse ist, verglichen. Zusätzlich wurden identische Versuche mit der synthetischen Membran, Nephrophan(r), durchgeführt. Neben der gepufferten Arzneistofflösung, für die aufgrund des differenzierten Membranaufbaus Permeationskoeffizienten (Peff) für AD im Verhältnis von 3:1:4 (Mukosa : Kornea : Nephrophan(r)) resultierten, standen zwei entwickelte wasserkontinuierliche, nicht-ionische Mikroemulsionen (ME) und ihre Einzelkomponenten als Trägerformulierungen bei den Permeationsstudien im Vordergrund. Darüber hinaus wurde ein ME-System mit einem kationischen Kotensid entwickelt, charakterisiert und in die Untersuchungen einbezogen. Die getesteten Trägerformulierungen führten an den einzelnen Membranen zu unterschiedlichen Ergebnissen. Um auch den "hydrophilen Permeationsweg" einzuschließen, wurde parallel Fluorescein-Na (FSC) als hydrophile Modellsubstanz getestet. Als mögliche Ursache für diese differenzierten Ergebnisse wurde ein Einfluss der Additiva und Formulierungen auf das Verteilungsverhalten des lipophilen AD zwischen Donatorlösung und Membran in Betracht gezogen und daher in einem weiteren Versuchsblock die Penetrationsrate untersucht. Darüber hinaus wurde parallel dazu der metabolische Abbau, den AD während des Membrandurchtritts durch die vorhandenen Enzyme erfahren kann, berücksichtigt. Die Resultate zeigten Übereinstimmung mit den Permeationsergebnissen indem die Additiva und Formulierungen die Penetration in das Gewebe und den Metabolismus mehr oder weniger herabsetzten. Zur Charakterisierung der systemischen Verfügbarkeit von AD nach nasaler Applikation wurden im Anschluss an die Permeations- und Penetrationsversuche In-vivo-Studien an Kaninchen durchgeführt, die hier allerdings lediglich mit orientierendem Charakter einbezogen werden konnten. Um schließlich die Verhältnisse am Auge bzw. den mehrschichtigen Tränenfilm hinsichtlich einer Applikation der ME-Systeme modellhaft zu simulieren, wurden biophysikalische Untersuchungen in einem Langmuir-Trog mit Meibom''schen Drüsensekret als Oberflächenfilm durchgeführt, die über mögliche Interaktionen der Formulierungen bzw. ihrer Bestandteile mit der Tränenlipidschicht des Auges Auskunft geben sollten. Hier zeigten sich günstige Einflüsse der ME auf die Tränenlipidschicht, die vor allem bei einer Anwendung der ME bei Trockenem Auge von Vorteil sein können. / In these studies in vitro permeability of porcine cornea and bovine nasal mucosa was investigated and compared to each other using the lipophilic drug androstenedione (AD), which is of interest for ocular use as well as nasal, systemical administration. Additionally, the artificial membrane, Nephrophan(r), was used for identical investigations. Because of the differentiated membrane structure AD-permeation behaviour out of buffer solution resulted in a ratio of permeability coefficients (Peff) of 3:1:4 (nasal mucosa : cornea : Nephrophan(r)). Furthermore, two water-continuous, non-ionic microemulsions (ME) and their isolated components were investigated as carrier formulations. Additionally, a new ME containing a cationic co-surfactant was developed, characterized and included in the permeability studies as well. Permeation out of these carrier formulations also resulted in different Peff in case of all tissues. For including studies of the hydrophilic transport way flourescein-sodium (FSC) was investigated as well representing a hydrophilic model substance. Influence of the additives and formulations on the partition behaviour of AD between membrane and donor solution was considered to partially cause these results. Therefore, penetration of AD was investigated together with the metabolic conversion of AD caused by enzymes located in the biological membranes. The additives and formulations decreased penetration into the tissue as well as metabolism of the drug. These findings corresponded with and could therefore explain the results of the permeability studies to some extend. For characterizing systemical availability of AD after nasal administration and improving the results of the permeability and penetration investigations in vivo studies using rabbits were carried out. However, these studies could give but marginal information and therefore be incorporated for orientation only. Furthermore, biophysical investigations were carried out using a Langmuir trough with Meibomian gland secrete (MGS) as the surface layer in order to simulate the multiple layer tear film. These studies were supposed to give some information about interactions between the ME or their isolated components, respectively, and the lipid layer of the tear film, regarding ocular administration of these formulations. The results showed suitable influence of the ME on the MGS, which can especially be advantageous for a use in Dry eye syndrome.