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<p>When studying the structure formation and fragmentation of complex atomic and nuclear systems it is preferable to start with simple systems where all details can be explored. Some of the knowledge gained from studies of atomic dimers can be generalised to more complex systems. Adding a third atom to an atomic dimer gives a first chance to study how the binding between two atoms is affected by a third. Few-body physics is an intermediate area which helps us to understand some but not all phenomena in many-body physics.</p><p>Very weakly bound, spatially very extended quantum systems with a wave function reaching far beyond the classical forbidden region and with low angular momentum are characterized as halo systems. These unusual quantum systems, first discovered in nuclear physics may also exist in systems of neutral atoms.</p><p>Since the first clear theoretical prediction in 1977, of a halo system possessing an Efimov state, manifested in the excited state of the bosonic van der Waals helium trimer ⁴₂He₃, small helium and different spin-polarised halo hydrogen clusters and their corresponding isotopologues have been intensively studied the last three decades.</p><p>In the work presented here, the existence of the spin-polarized tritium trimer ground state, ³₁H₃, is demonstrated, verifying earlier predictions, and the system's properties elucidated. Detailed analysis has found no found evidence for other bound states and shape resonances in this system. The properties of the halo helium trimers, ⁴₂He₃ and ⁴₂He₂-³₂He have been investigated. Earlier predictions concerning the ground state energies and structural properties of these systems are validated using our three-dimensional finite element method. In the last part of this work we present results on the bound states and structural properties of the van der Waals bosonic atomic trimers Ne₃ and Ar₃. We believe to be the first to find evidence of a possible shape resonance just above the three-body dissociation limit of the neon trimer.</p>

When studying the structure formation and fragmentation of complex atomic and nuclear systems it is preferable to start with simple systems where all details can be explored. Some of the knowledge gained from studies of atomic dimers can be generalised to more complex systems. Adding a third atom to an atomic dimer gives a first chance to study how the binding between two atoms is affected by a third. Few-body physics is an intermediate area which helps us to understand some but not all phenomena in many-body physics. Very weakly bound, spatially very extended quantum systems with a wave function reaching far beyond the classical forbidden region and with low angular momentum are characterized as halo systems. These unusual quantum systems, first discovered in nuclear physics may also exist in systems of neutral atoms. Since the first clear theoretical prediction in 1977, of a halo system possessing an Efimov state, manifested in the excited state of the bosonic van der Waals helium trimer 42He3, small helium and different spin-polarised halo hydrogen clusters and their corresponding isotopologues have been intensively studied the last three decades. In the work presented here, the existence of the spin-polarized tritium trimer ground state, 31H3, is demonstrated, verifying earlier predictions, and the system's properties elucidated. Detailed analysis has found no found evidence for other bound states and shape resonances in this system. The properties of the halo helium trimers, 42He3 and 42He2-32He have been investigated. Earlier predictions concerning the ground state energies and structural properties of these systems are validated using our three-dimensional finite element method. In the last part of this work we present results on the bound states and structural properties of the van der Waals bosonic atomic trimers Ne3 and Ar3. We believe to be the first to find evidence of a possible shape resonance just above the three-body dissociation limit of the neon trimer.

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Global energy demands have escalated over the past few decades, creating a necessity for alternative energy sources. Solar technologies inspired by the primary solar energy storing process known on earth, photosynthesis, have subsequently gained popularity. The natural photosynthetic apparatus comprises a network of membrane-bound pigment-protein complexes, with the main plant light-harvesting complex (LHCII) consisting of chlorophyll (Chl) and carotenoid (Car) pigments. Electronic excitation energy transfer (ET) of the harvested energy takes place amongst these pigments on ultrafast timescales. This energy is funnelled towards a photosynthetic reaction centre where charge separation is achieved, creating a Biobattery, which powers the subsequent manufacture of energy-rich chemical compounds for photosynthetic activity. Transient absorption pump-probe spectroscopy has proven to be a useful technique for monitoring the evolution of the excited state dynamics, such as electronic transitions and excitation ET amongst Car and Chl pigments of LHCII trimers isolated from spinach leaves. This method was utilized to probe samples excited under four different conditions: at pump excitation wavelengths (𝜆𝑒𝑥) of 489 nm (preferentially exciting Cars Lutein1 and Neoxanthin) and 506 nm (targeting Cars Lutein2 and Violaxanthin), each with an intensity of either 800 nJ/pulse (relatively high) or 500 nJ/pulse (comparatively low). A global analysis was applied to each dataset using the robust, open-source Glotaran software, from which three kinetic decay lifetimes for the various processes were extracted. General spectral observations encompassed a negative pump ground state bleach (GSB) at each 𝜆𝑒𝑥; negative Chl b and Chl a GSBs, superimposed with negative stimulated emission (SE) signals; and a positive excited state absorption (ESA) band. The first lifetime of a few picoseconds corresponded mainly to Car-S2 depopulation, resulting either from energy relaxation towards Car-S1, or ET to Chls. Small, but distinct Chl b signals of less than 3 mOD were also detected on this timescale. The second lifetime, which is between 10 and 12 ps, was characteristic to the Lutein Car-S1 lifetime, mainly depicting Car-S1 ET to Chl a. The third lifetime, which extended from ~200 ps to the nanosecond timescale, was attributed to Chl a fluorescence. The 𝜆𝑒𝑥 of 489 nm directly excites the Chl Soret region, whilst excitation at 506 nm shows a pump intensity-dependence. Laser pulse photon density values were ~1014 photons·cm-2·pulse-1 for these datasets. Singlet-singlet annihilation calculations performed on the samples excited at 506 nm provided low annihilation probabilities of 9.0% and 11.5% for a low and high pump intensity, respectively, limiting the possibility of sample photobleaching. Optimization and redevelopment of the experimental setup significantly improved both the data quality and various recorded parameters, concluding that pump-probe spectroscopy was successful on the prepared LHCII trimers. Results acquired and calculations performed correlated with literature, where minimal changes were noticed in the timescales and ET pathways. The robustness of plant systems was confirmed through both excitation-wavelength and intensity dependence. This work paves the way for advanced studies on the role Cars play in non-photochemical quenching (NPQ), a self-protection mechanism of plants against over-illumination; and for the tailoring of artificial light-harvesting antennas based on research conducted on their natural counterparts. / Globale energievereistes het oor die afgelope paar dekades toegeneem, wat die ontwikkeling van alternatiewe energiebronne noodsaaklik maak. Sontegnologieë, geïnspireer deur die primêre sonenergiebergingsproses op aarde, fotosintese, het daarom gewild geword. Die natuurlike fotosintetiese apparaat bestaan uit 'n netwerk van membraangebonde pigment-proteïenkomplekse, met die hoof ligversamelingskompleks in plante (LHCII) wat bestaan uit chlorofil- (Chl) en karotenoïed- (Car) pigmente. Die energie wat deur die pigmente geabsorbeer word, word tussen elektroniese opgewekte toestande op verskillende pigmente op ultravinnige tydskale oorgedra. Hierdie energie word na ʼn fotosintetiese reaksiesentrum gekanaliseer, waar 'n ladingskeiding geïnduseer word en 'n Biobattery sodoende geskep word. Die energie wat in dié battery gestoor is, word gebruik om energieryke chemiese verbindings te vervaardig — wat as brandstof vir die plant dien om sy lewensfunksies te verrig. Tydopgeloste-absorpsie-pomp-tasting-spektroskopie is 'n nuttige tegniek om die dinamika tussen opgewekte toestande te volg. ‘n Voorbeeld van sulke dinamika is die elektroniese opwekking en energie-oordrag tussen die Car- en Chl-pigmente van geïsoleerde LHCII-trimere in spinasieblare. Hierdie metode is gebruik om monsters onder vier verskillende toestande te ondersoek by pompgolflengtes (𝜆𝑒𝑥) van 489 nm (waar hoofsaaklik die Cars Luteïne1 en Neoksantine opgewek word) en 506 nm (vir Cars Luteïne2 en Violaksantine), en pompenergieë van ‘n relatief hoë 800 nJ/puls, of 500 nJ/puls vir elke golflengte. / Dissertation (MSc)--University of Pretoria, 2017. / National Research Foundation (NRF) / Physics / MSc / Unrestricted

This dissertation focuses on the development, characterization, and analysis of luminescent materials and coatings for sensing applications, including CO2, heavy metals, and silver. Chapter 2 involves the use of a gold(I) pyrazolate trimer that is able to detect silver ions with an AgNP medium. Detection of silver is vital, because there is an influx of silver into our environment caused by the increased use of AgNP. Therefore, having a sensor that is able to differentiate between and detect only Ag ions is an important first step to solving the toxicity mystery of AgNPs. Chapter 3 focuses on the development of sensor coatings containing a Eu(III) based luminescent system for sensing dissolved CO2 without the aid of an absorption-based dye. It is well-known that monitoring CO2 levels in our environment is important since even at low concentrations it can cause adverse health effects to the human body. This work demonstrates a pH-sensitive Eu complex being used directly as a CO2 sensor without the aid of any other absorption-based dye. Chapter 4 explores the idea of developing a heavy metal sensor for lead and its ability to detect lead in wide concentration range upon changing the pH of the medium and the polymer matrix. Different heavy metals have toxicity at different concentrations, therefore, being able to change the dynamic range of the sensor is advantageous. This research is the first step towards developing a luminescent Pb sensor with a tunable dynamic range.

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The two major topics studied in this dissertation are the gold(I) pyrazolate trimer {[Au(3-R,5-R’)Pz]3} complexes in aqueous chitosan polymer and phosphorescent polymeric nanoparticles based on platinum(II) based complex. The first topic is the synthesis, characterization and optical sensing application of gold(I) pyrazolate trimer complexes within aqueous chitosan polymer. A gold(I) pyrazolate trimer complex, {[Au(3-CH3,5-COOH)Pz]3}, shows high sensitivity and selectivity for silver ions in aqueous media, is discussed for optical sensing and solution-processed organic light emitting diodes (OLEDs) applications. Gold(I) pyrazolate trimer complexes are bright red emissive in polymeric solution and their emission color changes with respect to heavy metal ions, pH and dissolved carbon dioxide. These photophysical properties are very useful for designing the optical sensors. The phosphorescent polymeric nanoparticles are prepared with Pt-POP complex and polyacrylonitrile polymer. These particles show excellent photophysical properties and stable up to >3 years at room temperature. Such nanomaterials have potential applications in biomedical and polymeric OLEDs. The phosphorescent hybrid composites are also prepared with Pt-POP and biocompatible polymers, such as chitosan, poly-l-lysine, BSA, pnipam, and pdadmac. Photoluminescent enhancement of Pt-POP with such polymers is also involved in this study. These hybrid composites are promising materials for biomedical applications such as protein labeling and bioimaging.