The increasing prevalence of glass windows in modern buildings has raised the demand for solar control windows that possess climate-appropriate properties. Glass windows made of abundant and low-cost materials which can both decrease the heating energy consumption as well as enhance the light climate indoors would sufficiently meet the goals of economical yet uplifting buildings. The main objective of this thesis was to examine whether a plasmonic hybrid interface, comprising three layers of thin films (gold nanoparticles of approximately 10 nm, ZrO2 with a thickness range of 20-35 nm, and ZnO with a thickness of approximately 20 nm), could achieve the upconversion of infrared light to visible light through a multiphoton absorption process in the ZnO layer. If successful, this configuration, in conjunction with an established layer capable of downconverting ultraviolet light to visible light, would be applied to commercially available glass windows to enhance the solar utilization and improve indoor lighting conditions. ZnO was selected as the upconversion material due to its wide emission range in the visible spectrum, indicative of intermediate electron states between the valence and conduction bands suitable for excitation. The objective of the plasmonic material, the gold nanoparticles, was to increase the probability of the upconversion process by utilizing the enhanced electric field resulting from plasmons localized at the surface of the gold nanoparticles. ZrO2 served as a separator layer between the plasmonic material and the ZnO, to effectively preventing charge transfer and ensuring that any upconversion or other photoluminescence processes were purely photonic. Various optical experimental techniques were employed in this study to assess any upconversion, plasmon enhancement, and map the intermediate electron states of the ZnO. The ZrO2 layer successfully prevented charge transfer between the layers. However, the influence ofthe gold’s surface plasmons and it’s enhanced electric field on ZnO emission varied among the samples, likely due to the synthesis processes. Ultimately, the plasmonic hybrid interface investigated in this thesis did not exhibit detectable upconversion when illuminated with either 600 or 750 nm light. Further research is necessary to increase the density of intermediate electron states in ZnO, along with optimization of the thin film synthesis to enhance plasmon effects. These advancements would augment the probability of detectable upconversion.

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In this thesis, Density Functional Theory and Time-Dependent Density-Functional Theory approaches are applied to study the optical and magnetic properties of several types of nanostructures. In studies of the optical properties we mainly focused on the plasmonic and excitonic effects in pure and transition metal-doped noble metal nanochains and their conglomerates. In the case of pure noble metal chains, it was found that the (collective) plasmon mode is pronounceable when the number of atoms in the chain is larger than 5. The plasmon energy decreases with further with increasing number of atoms (N) and is almost N-independent when N is larger than 20. In the case of coupled pure chains it was found that the plasmon energy grows as square root of the number of chains, and reaches the visible light energy 1.8eV for the case of three parallel chains. Doping of pure Au chains with transition-metal atoms leads in many cases to formation of additional plasmon peaks close in energy to the undoped chain peak. This peak comes from the local charge oscillations around the potential minima created by the impurity atom. The effect is especially pronounced for Ni-doped chains. In the multiple-chain case, we find an unusual hybridization of the two different (local and collective) plasmon modes. Changing the chain size and chemical composition in the array can be used to tune the absorption properties of nanochains. The case of coupled finite (plasmonic) and infinite (semiconductor, excitonic) chains was also analyzed. We find that one can get significant exciton-plasmon coupling, including hybridized modes and energy transfer between these excitations, in the case of doped chains. The impurity atoms are found to work as attraction centers for excitons. This can be used to transform the exciton energy into local plasmon oscillations with consequent emission at desired point (at which the impurity is located). In a related study the optical properties of single layer MoS2 was analyzed with a focus on the possibility of ultrafast emission, In particular, it was found that the system can emit in femto-second regime under ultrafast laser pulse excitations. Finally, we have studied the magnetic properties of FeRh nanostructures to probe whether there is an antiferromagnetic to ferromagnetic transition as a function of the ratio of Fe and Rh atoms, as in the bulk alloy.. Surprisingly, the ferromagnetic phase is found to be much more stable for these nanostructures as compared to the bulk, which suggests that band-type effects may be responsible for this transition in the bulk, i.e. the transition cannot be described in terms of modification of the Heisenberg model parameters.

The continued size reduction in electronic integrated circuits has lead to a demand for on-chip high-bandwidth and low loss communication channels. Optical interconnects are considered an essential addition to the silicon electronics platform. A major challenge in the field of integrated Si photonics is the development of cost effective silicon compatible light sources. This thesis investigates the sensitization of group IV doped silica films emitting at 1.535μm for applications as silicon compatible light sources. Thin erbium-doped silica films containing excess silicon and germanium were deposited using a multi-gun sputter system. The composition of the deposited materials was verified by Rutherford Backscattering Spectrometry. Samples from each deposition were annealed in a controlled atmosphere tube furnace at temperatures between 500ºC and 1100ºC for 30 minutes. The photoluminescence spectra from the visible to the near-infrared region were acquired while pumping either near or far from the Er3+ absorption lines. Under both excitation conditions all samples annealed at temperatures below 1000ºC show clear emission at 1.535μm from Er3+ ions in the host material. In the current literature this is attributed to exciton mediated excitation of the Er3+. By contrast, in these studies indirect excitation was observed for samples annealed at temperatures well below the onset of nanocrystal nucleation and growth (between 500ºC and 1000ºC), suggesting excitation via small clusters or lattice defects. These findings could have significant implications in the further development of group IV sensitized silicon compatible gain media.

In this dissertation, I report the results of my research on twisted moiré photonic crystals which can be formed through multi-beam holographic interference without a physical rotation and later fabricated by electron-beam lithography. Their optical properties, such as photonic bandgaps, multiple resonance modes, and quality factor are presented. Randomized moire photonic crystals in lattice are also studied. The applications of moire photonic crystals in improving light extraction efficiency are simulated and verified in light emitting devices. Furthermore, I simulated the light extraction efficiency in OLED when the Al layer is patterned with a triangular GPSC, square moiré PhC with defects in the uniform area, and random locations of the photonic lattice, and obtain light extraction efficiency of 78.9%, 79.9%, 81.7%, respectively. Also, the ratios of photoluminescence intensity of LED integrated with twisted moiré PhCs and random moiré PhCs over that without moiré PhCs are measured to be (1.3-1.9) and 1.74, respectively, in a good agreement with simulated ratios of 1.69 and 1.8.

Direct heteroepitaxy of III-Vs on silicon (Si) has always been a challenge and there are various strategies to integrate these materials. This thesis deals with one such strategy known as Epitaxial lateral overgrowth (ELOG) which is extensively supported by experiments. For an application such as a multijunction solar cell, with silicon as a bottom cell, the highest efficiency can be achieved with a top cell having a bandgap of 1.7 eV and hence GaAsP as a material suits the profile. The ELOG GaAsP and GaAs samples were grown using the epitaxial growth technique known as hydride vapor phase epitaxy (HVPE). With its near equilibrium operation capacity, high quality layers were grown. To specifically focus on the crystal defects and dislocations of the atoms, GaAsP was grown on GaAs substrate. Samples with varying growth parameters are investigated using several characterization techniques such as scanning electron microscopy (SEM), Photoluminescence (PL) spectroscopy and Raman spectroscopy. Composition variations (group V elemental incorporation in GaAsP) and crystalline quality are the two major factors that are analyzed. Additionally, ELOG GaAs samples grown on GaAs substrate using HVPE are studied as a reference to observe any strain effects due to the ELOG profile and compare with the GaAsP samples. The ideal goal of this thesis is to optimize the crystalline quality of the ELOG GaAsP samples and to verify that GaAsP grown using ELOG technique has a better crystallinity than the planar growth (direct epitaxy of GaAsP on GaAs substrate) using two major optical characterization tools - PL and Raman spectroscopy. This work is a step towards the development of high efficiency multi-junction solar cells with GaAsP and Si as the respective top and bottom cells. / Direkt heteroepitaxi av III-V på kisel (Si) har alltid varit en utmaning och det finns olika strategier för att integrera dessa material. Den här avhandlingen behandlar en sådan strategi som kallas Epitaxial lateral overgrowth (ELOG) som stöds externt av experiment. För en applikation som en multi junction solcell, med kisel som bottencell, kan den högsta effektiviteten uppnås med en toppcell med ett bandgap på 1,7 eV och därmed GaAsP som ett material som passar profilen. ELOG GaAsP- och GaAs-proverna odlades med användning av den epitaxiella tillväxttekniken känd som hydriddampfasepitaxi (HVPE). Med dess nära kapacitet för jämviktsdrift odlades lager av hög kvalitet. För att specifikt fokusera på kristalldefekter och dislokationer av atomerna odlades GaAsP på GaAs substrat. Prover med varierande tillväxtparametrar undersöks med användning av flera karakteriseringstekniker såsom skanningselektronmikroskopi (SEM), Photoluminescence (PL) -spektroskopi och Raman-spektroskopi. Kompositionvariationer (grupp V elemental inkorporering i GaAsP) och kristallin kvalitet är de två huvudfaktorerna som analyseras. Dessutom studeras ELOG GaA-prover odlade på GaAs-substrat med användning av HVPE som en referens för att observera eventuella belastningseffekter på grund av ELOG-profilen och jämföra med GaAsP-proverna. Det ideala målet med denna avhandling är att optimera den kristallina kvaliteten på ELOG GaAsP-proverna och att verifiera att GaAsP som odlas med ELOG-teknik har en bättre kristallinitet än den plana tillväxten (direkt epitaxi av GaAsP på GaAs underlag) med två huvudsakliga optiska karaktäriseringar verktyg - PL- och Raman-spektroskopi. Detta arbete är ett steg mot utvecklingen av högeffektiva multi junction solceller med GaAsP och Si som respektive topp- och bottenceller.

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