Deep ultraviolet (UV) light sources are useful in a number of applications that include sterilization, medical diagnostics, as well as chemical and biological identification. However, state-of-the-art deep UV light-emitting diodes and lasers made from semiconductors still suffer from low external quantum efficiency and low output powers. These limitations make them costly and ineffective in a wide range of applications. Deep UV sources such as lasers that currently exist are prohibitively bulky, complicated, and expensive. This is typically because they are constituted of an assemblage of two to three other lasers in tandem to facilitate sequential harmonic generation that ultimately results in the desired deep UV wavelength. For semiconductor-based deep UV sources, the most challenging difficulty has been finding ways to optimally dope the (Al,Ga)N/GaN heterostructures essential for UV-C light sources. It has proven to be very difficult to achieve high free carrier concentrations and low resistivities in high-aluminum-containing III-nitrides. As a result, p-type doped aluminum-free III-nitrides are employed as the p-type contact layers in UV light-emitting diode structures. However, because of impedance-mismatch issues, light extraction from the device and consequently the overall external quantum efficiency is drastically reduced. This problem is compounded with high losses and low gain when one tries to make UV nitride lasers. In this thesis, we provide a robust and reproducible approach to resolving most of these challenges. By using a liquid-metal-enabled growth mode in a plasma-assisted molecular beam epitaxy process, we show that highly-doped aluminum containing III-nitride films can be achieved. This growth mode is driven by kinetics. Using this approach, we have been able to achieve extremely high p-type and n-type doping in (Al,Ga)N films with high aluminum content. By incorporating a very high density of Mg atoms in (Al,Ga)N films, we have been able to show, by temperature-dependent photoluminescence, that the activation energy of the acceptors is substantially lower, thus allowing a higher hole concentration than usual to be available for conduction. It is believed that the lower activation energy is a result of an impurity band tail induced by the high Mg concentration. The successful p-type doping of high aluminum-content (Al,Ga)N has allowed us to demonstrate operation of deep ultraviolet LEDs emitting at 274 nm. This achievement paves the way for making lasers that emit in the UV-C region of the spectrum. In this thesis, we performed preliminary work on using our structures to make UV-C lasers based on photonic crystal nanocavity structures. The nanocavity laser structures show that the threshold optical pumping power necessary to reach lasing is much lower than in conventional edge-emitting lasers. Furthermore, the photonic crystal nanocavity structure has a small mode volume and does not need mirrors for optical feedback. These advantages significantly reduce material loss and eliminate mirror loss. This structure therefore potentially opens the door to achieving efficient and compact lasers in the UV-C region of the spectrum.

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Over the past decade, intensive academic and commercial interests have been paid on compounds possessing photochemical properties, namely for their preparation, chemical properties, high efficiency and potential low-cost. Compounds having intense photochemical properties gained great interest due to wide range of potential applications. The sensitizers are one of the key components for high power-conversion efficiency in the dye sensitized solar cells (DSSCs). They are the core components in the organic light-emitting devices (OLEDs) due to their ability to emit light with the wavelengths largely red- shifted from their absorption wavelength. Ruthenium based sensitizers have been tagged “molecular light switches” because, although the fluorescence of these complexes in aqueous solutions is negligible, it increases of greater than 10000 fold in the presence of DNA. Many polypyridyl and dipyrido phenazine ruthenium complexes have achieved high power conversion efficiencies and therefore are of practical interest. Several research groups stated that the dipyrido phenazine ligand may be thought of as comprising two components: a bipyridyl unit and a phenazine unit. These two subunits behave essentially separately, with many molecular orbitals being localised over only one subunit and a redox properties of central phenazine moiety in the dipyrido phenazine ligand are important for the photochemical applications. Therefore a phenazine ligand was selected as a model for the present investigation. The chemistry of phenazine ligand is mostly limited to the late transition metal and f - element complexes. Our laboratory has a rich backgroung in the aluminum and early transition metal chemistry. The aluminum chemistry and early transition metal chemistry are of great interest since aluminum and early transition metal complexes are environmentally friendlier and cheaper than the late transition metal compounds. Another drawback of the ruthenium-based sensitizers is the lack of absorption in the red region of the visible spectrum, and also low molar extinction coefficients. An essential requirement for efficient conversion of solar energy is the good spectral match of the sensitizer absorption to the emission spectrum of solar radiation. In this regard, the ruthenium sensitizers’ spectral response in the lower energy regions is not sufficient. The current project has three parts. In the first part we collected and reviewed known literature regarding the certain classes of non-innocent ligands containing the six-membered carbon- nitrogen heterocycles and regarding the ligands potentially important for the photochemical applications. We also reviewed all available to the data information about the complexes supported by the phenazine ligand. In the second part we have investigated interaction of alkylaluminum compounds and phenazine and observed reduction of phenazine accompanied by formation of dialuminum cage type compounds containing two formally mononegative phenazine ligand. The derivatization of phenazine has been also observed. It resulted in formation of compounds having a stable organic radical. In a third part of our project we have explored interaction of phenazine or thiophenazine with the alkylaluminum compounds and chromium dichloride. The reaction in the three component system resulted in reduction of phenazine ligand and lead to the heterometallic Cr(II) - aluminum complexes containing a formally dinegative phenazine or thiophenazine ligands. When a large excess of triethylaluminum was taken, reduction of phenazine and chromium has been observed leading to the heterometallic multinuclear Cr(I) - aluminum complex containing a formally dinegative phenazine ligands and two chromium atoms in one complex in the rare oxidation state one.

Lighted push button switches and indicators serve many purposes in cockpits, shipboard applications and military ground vehicles. The quality of lighting produced by switches is vital to operators' understanding of the information displayed. Utilizing LED technology in lighted switches has challenges that can adversely affect lighting quality. Incomplete data exists to educate consumers about potential differences in LED switch performance between different manufacturers. LED switches from four different manufacturers were tested for six attributes of lighting quality: average luminance and power consumption at full voltage, sunlight readable contrast, luminance contrast under ambient sunlight, legend uniformity, and dual-color uniformity. Three of the four manufacturers have not developed LED push button switches that meet lighting quality standards established with incandescent technology.

Transient electroluminescence (EL) was used to measure the onset of emission delay in OLEDs based on transition metal, phosphorescent bis[3,5-bis(2-pyridyl)-1,2,4-triazolato] platinum(ΙΙ) and rare earth, phosphorescent Eu(hfa)3 with 4'-(p-tolyl)-2,2":6',2" terpyridine (ttrpy) doped into 4,4'-bis(carbazol-9-yl) triphenylamine (CBP), from which the carrier mobility was determined. For the Pt(ptp)2 doped CBP films in OLEDs with the structure: ITO/NPB (40nm)/mcp (10nm)/65% Pt(ptp)2:CBP (25nm)/TPBI (30nm)/Mg:Ag (100nm), where NPB=N, N'-bis(1-naphthyl)-N-N'-biphenyl-1, 1'-biphenyl-4, MCP= N, N'-dicarbazolyl-3,5-benzene, TPBI=1,3,5-tris(phenyl-2-benzimidazolyl)-benzene, delayed recombination was observed and based on its dependence on frequency and duty cycle, ascribed to trapping and de-trapping processes at the interface of the emissive layer and electron blocker. The result suggests that the exciton recombination zone is at, or close to the interface between the emissive layer and electron blocker. The lifetime of the thin films of phosphorescent emitter Pt(ptp)2 were studied for comparison with rare earth emitter Eu(hfa)3. The lifetime of 65% Pt(ptp)2:CBP co-film was around 638 nanoseconds at the emission peak of 572nm, and the lifetime of neat Eu(hfa)3 film was obtained around 1 millisecond at 616 nm, which supports the enhanced efficiency obtained from the Pt(ptp)2 devices. The long lifetime and narrow emission of the rare earth dopant Eu(hfa)3 is a fundamental factor limiting device performance. Red organic light emitting diodes (OLEDs) based on the rare earth emitter Eu(hfa)3 with 4'-(p-tolyl)-2,2":6',2" terpyridine (ttrpy) complex have been studied and improved with respect performance. The 4.5% Eu(hfa)3 doped into CBP device produced the best power efficiency of 0.53 lm/W, and current efficiency of 1.09 cd/A. The data suggests that the long lifetime of the f-f transition of the Eu ion is a principal limiting factor irrespective of how efficient the energy transfer from the host to the dopant and the antenna effect are.

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Defect passivation and surface modification of perovskite semiconductors play a key role in achieving highly efficient and stable perovskite solar cells (PSCs) and light-emitting diodes (LEDs). This dissertation describes three novel strategies for such defect passivation and surface modification. In the first strategy, we demonstrate a facile approach using inorganic perovskite quantum dots (QDs) to supply bulk- and surface-passivation agents to combine high power conversion efficiency (PCE) with high stability in CH3NH3PbI3 (MAPbI3) inverted PSCs. This strategy utilizes inorganic perovskite QDs to distribute elemental dopants uniformly across the MAPbI3 film and attach ligands to the film’s surface. Compared with pristine MAPbI3 films, MAPbI3 films processed with QDs show a reduction in tail states, smaller trap-state density, and an increase in carrier recombination lifetime. The strategy results in reduced voltage losses and an improvement in PCE from 18.3% to 21.5%, which is among the highest efficiencies for MAPbI3 devices. The devices maintain 80% of their initial PCE under 1-sun continuous illumination for 500 h and show improved thermal stability. In the second strategy, we reduce the efficiency gap between the inverted PSCs and regular PSCs using a trace amount of surface-anchoring, long-chain alkylamine ligands (AALs) as grain and interface modifiers. We show that long-chain AALs suppress nonradiative carrier recombination and improve the optoelectronic properties of mixed-cation mixed-halide perovskite films. These translate into a certified stabilized PCE of 22.3% (23.0% PCE for lab-measured champion devices). The devices operate for over 1000 hours at the maximum power point (MPP), under simulated AM1.5 illumination, without loss of efficiency. Finally, we report a strategy to passivate Cl vacancies in mixed halide perovskite (MHP) QDs using non-polar-solvent-soluble organic pseudohalide (n-dodecylammonium thiocyanate (DAT)), enabling blue MHP LEDs with enhanced efficiency. Density-function-theory calculations reveal that the thiocyanate (SCN-) groups fill in the Cl vacancies and remove deep electron traps within the bandgap. DAT-treated CsPb(BrxCl1-x)3 QDs exhibit near unity (~100%) photoluminescence quantum yields; and their blue (~470 nm) LEDs are spectrally stable with an external quantum efficiency (EQE) of 6.3% – a record for perovskite LEDs emitting at the 460-480 nm range relevant to Rec. 2020 display standards.

The aim of this work is to prepare white emitting electroluminescent device using printing techniques. Preparation options are discussed in order to minimise reabsorption in the phosphor layer and thus increase the overall radiation intensity. Model devices were prepared, the active layer of phosphor printed in a pattern of stripes and circles. The impact of the applied voltage and frequency was studied on these devices. It has been shown that, in terms of white emission, it is better to use the patterns compared to the phosphor mixture. The ratios of emission intensities of both phosphors are more even, therefor closer to the white light. The output of this work is model designed to determine the necessary frequency area for obtaining the white emission of ACEL device.