This thesis is concerned with the preparation of organic light-emitting diodes (LEDs) by using different thin film technologies: the Langmuir-Blodgett (LB) technique; spin-coating and thermal evaporation. The π-conjugated polymer, poly(2-methoxy-5-(5'-ethylhexyloxy)-p-phenylenevinylene) (MEH-PPV), was used as the emissive layer and was deposited onto patterned indium-tin oxide (ITO) glass using the LB technique or spin-coating. Y-type LB films of MEH-PPV were deposited at a surface pressure of 17 mN m(^-1) with a transfer ratio of 0.95 ± 0.03. Many efforts were made to improve the LB film device performance parameters, such as external quantum efficiency and operating lifetime, by inserting an electron transporting or insulating layer between the emissive layer and top cathode. Annealing the LB films was found to result in an improved operating lifetime. LEDs based on spun films possessed higher external quantum efficiencies than devices made from LB films. The more ordered LB films had a higher probability of intra- and intermolecular interactions and formed more excimer states within the structure. This led to a lower quantum efficiency compared to devices incorporating spun films. The operating lifetime of the LEDs was highly dependent on the morphology of the film surface. A smoother film surface is required for a longer device operating lifetime. A new electron transporting material, 2,5-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]pyridine (PDPyDP), was deposited on top of the MEH-PPV spun film. Despite a high external quantum efficiency of 0.7 %, this device suffered from dark regions in the electroluminescence output resulting in degradation of the device. The dark area formation was attributed to delamination of the aluminium electrode from the PDPyDP layer, which was lessened by: (a) annealing the degraded devices; (b) evaporating a thicker aluminium layer at a high rate and (c) inserting a buffer layer (Alq(_3)) between the PDPyDP and the Al top electrode.

ABSTRACT Organic light emitting diode (OLED) has significant scientific implication and technological potential. Using organic materials for tailored emitting color, threshold voltage reduction, and emission efficiency gain are the key points for the commercialization of OLED. An UV-Vis spectrophotometer was applied to obtain the absorption spectra of PVK, C6, and PRL, as well as their respective band gap (Eg) values of 3.49 eV, 2.32 eV, and 2.55 eV. The turn-on oxidation potential of cyclic voltammograms was reduced for HOMO energy at 5.64 eV, 5.21 eV, and 5.16 eV, respectively. The Eg subtracted from HOMO energy yielded the respective LUMO values of 2.15 eV, 2.89 eV and 2.61 eV. Excitation at 457 nm or 325 nm was applied to the freestanding films of PVK, PVK doped with C6 (10/1), and PVK doped with PRL (10/1). From the UV-Vis absorption spectra and Egs, we knew that 457 nm excitation did not generate photoluminescence (PL) of PVK. The PL spectra of the doped freestanding films were mostly attributed to the dye molecules of C6 or PRL. The PL spectra of doped freestanding films were insensitive to the excitation sources at 325 nm and 457 nm. There was a blue shift at the PL emission peak indicative of energy transfer from PVK to C6 or PRL for the doped films. Using spin-coating or vacuum deposition to fabricate PVK, C6, and PRL films onto an ITO substrate followed by evaporating Al (Ag) as the electron injector to form OLED devices. Because of the energy transfer between PVK and C6 or PRL, ITO/PVK:C6/Al homojunction OLED showed a smaller threshold voltage than that of ITO/C6/Al, from 9 V to 3.5 V. Likewise, ITO/PVK:PRL/Al homojunction OLED had a smaller threshold voltage than that of ITO/PRL/Al, from 8 V to 4.5 V. PVK was also used as the hole blocking layer to construct heterojunction OLED to balance electron-hole numbers in the emitting layer. The threshold voltage of ITO/C6/Al reduced from 9 V to 7 V with a heterojunction of ITO/PVK/C6/Al. A device of ITO/PRL/Al having a threshold voltage of 8V reduced to 6V with an ITO/PVK/PRL/Al heterojunction OLED. Coating a protective layer (Ag) on the metallic electron injector, or packaging the device in N2 could both decrease the decay and increase the life time of OLED.

Organic light-emitting diode has several advantages using in the flat penal display, but it is still needed to improve the disadvantages. The charge-carriers of the organic layers are one of the dominant factors to influence the performance of OLED. Hence, it is worth to study and understand the charge transporting behaviors by the theoretical simulation in the organic layers of OLED, and that is helpful for the OLED in future. In this study, three kinds of models are used to simulate the characteristics of several different organic light-emitting devices, and it also try to compare the relationship between the current density and voltage. Three kinds of models are described as (1) The field-dependent carrier mobility model (FDM model), (2) An exponential distribution of traps model (EDT model), and (3) The field dependent trap occupancy model (FDTO model). For the simulation of three models, the characteristics of several hole-only devices and electron-only devices were analyzed to investigate and discuss the organic layer of the devices with different materials. In addition, by varying the parameters such as the thickness and temperature, a comparison was made between the results simulated from models with the values obtained from experimental works. Finally, based on above results, the characteristics of OLED could be improved for future applications.

The purpose of this thesis is to fabricate an LED module with low half intensity angle(HIA) ,and to use this module to form a line source with optical performance comparable to that of a CCFL .In addition ,heat dissipation of the LED module on different sub-mounts is also investigated . The LED modules were formed by first etching a through si via on silicon substrate using wet etching technology for light confining .Then a thin layer of metal was deposited on to the via to reflect the lights emitted from the LED .The LED die was attached to the Si sub-mount with electrodes ,and the connections between the LED and the Si sub-mount were completed by wire bonding .Finally ,the LED modules were obtained by positioning the Si substrates onto the Si sub-mounts using UV epoxy . The optical performance of the LED module was simulated by Lighttools .For the si substrate with a thickness of 400 £gm ,a simulated HIA of 36 o was obtained .Using six-LED package ,a 3-cm line source with 84.8% output uniformity was simulated .On the other hand ,the measured HIA of a LED module ,and the uniformity of 3-cm line source are 38 o and 84.8% ,respectively. The thermal resistance of the si sub-mounts were also investigated .The different structures of the sub-mount were proposed ,namely ,LED to Copper case ,LED to Si sub-mount to Copper case ,and LED to Si sub-mount with Copper filled via to Copper case .The estimated thermal resistance of the sub-mounts are 13 W/mk¡B19.4 W/mk and 34.7 W/mk .We believe that the large thermal resistance of the Si sub-mount with Copper filled via is primarily caused by 800 £gm thick substrate .

Silicon-based lighting show promise for display and solid state lighting use. Here we demonstrate a novel thin film light emitting diode device using nanocrystalline silicon quantum dots as an emission layer, and metal oxides as charge transport layers. Sputtering deposition conditions for the nickel and zinc oxides were explored in order to balance deposition rate with minimal roughness, optical absorption, and electrical resistivity. Devices displaying characteristic diode current-voltage behavior were routinely produced, although most showed significant reverse saturation current due to the presence of shunts. Current-voltage behavior of devices made in the same batch showed high repeatability, however variations in device performance was observed between batches while the parameters of synthesis were kept constant. Some devices were observed to emit orange-colored light, consistent with photoluminescence behavior of the silicon quantum dots. Photomultiplier tube measurements shows a turn-on voltage of 5V and an exponential increase in light emission with voltage increase.

Silicon-based lighting show promise for display and solid state lighting use. Here we demonstrate a novel thin film light emitting diode device using nanocrystalline silicon quantum dots as an emission layer, and metal oxides as charge transport layers. Sputtering deposition conditions for the nickel and zinc oxides were explored in order to balance deposition rate with minimal roughness, optical absorption, and electrical resistivity. Devices displaying characteristic diode current-voltage behavior were routinely produced, although most showed significant reverse saturation current due to the presence of shunts. Current-voltage behavior of devices made in the same batch showed high repeatability, however variations in device performance was observed between batches while the parameters of synthesis were kept constant. Some devices were observed to emit orange-colored light, consistent with photoluminescence behavior of the silicon quantum dots. Photomultiplier tube measurements shows a turn-on voltage of 5V and an exponential increase in light emission with voltage increase.

Solar radiation influences virtually all biological process on earth. Yeasts, the microbial driver of ethanol fermentation, evolved on the surface of vegetation and had to adapt to survive photonic assault. Past research has demonstrated that white light affects yeast metabolism along with the ability to entrain circadian rhythms, although no known genetic mechanism accounts for this. High intensity narrow wavelength light-emitting diodes were employed to illuminate synthetic cultures under fermentation. Multiple colors along the visible spectrum were used, corresponding to the peak absorbance wavelengths of Saccharomyces sp. yeast. Impacts in primary metabolite evolution were found, dependent on wavelength. Longer wavelengths produced higher amounts of acetic acid and glycerol; shorter wavelengths produced more ethanol. Because past research showed light timing had pronounced effects, illumination schemes on the scale of milliseconds to hours were tested for ethanol production. Light schemes on the scale of enzymatic reactions, yeast generation times, and circadian rhythms produced the most ethanol. Discrete blocks and duration of illumination were used to elucidate where light had the most influence over yeast metabolism and fermentation. Late lag phase and mid log phase illumination impacted ethanol fermentation more than any other period of time. Light effects were tested on apple juice to see if they extended from synthetic media to natural products. Significant impacts on ethanol production were discovered and flavor/aroma impacts were noted. Light, color, intensity, and timing have all been shown to control and affect fermentation with both positive and negative effects established. / Doctor of Philosophy / Sun light influences virtually all biological process on earth. Yeasts, the microbial drivers of ethanol fermentation, evolved on the surface of vegetation and had to adapt to survive destructive effects of the sun. Past research has demonstrated that white light affects yeast metabolism along with the ability to develop growth cycles similar to day / night patterns, although it is currently not believed this possible due to the biology of yeast. High intensity single color light-emitting diodes were employed to illuminate laboratory formulated cultures under fermentation. Multiple colors along the visible spectrum were used, corresponding to the peak absorbance wavelengths of Saccharomyces sp. yeast. Green/yellow/red wavelengths produced higher amounts of acetic acid (vinegar) and glycerol; blue and ultraviolet wavelengths produced more ethanol. Because past research showed light timing could change how yeast grow and consumed carbohydrates, light timing on the scale of milliseconds to hours were tested for ethanol production. Light timing on the scale of milliseconds, hours, and daylight cycles produces the most ethanol. Discrete blocks and duration of illumination were used to find where during fermentation light had the most impact. It was found that from immediately after the beginning of fermentation to the middle of fermentation is where yeast responded the most strongly. Light effects were tested on apple juice to see if they extended laboratory cultures to natural products. Significant changes in the amount of ethanol produced were discovered and changes in the taste and smell of fermented apple juice were noted. Light, color, intensity, and timing have all been shown to control and affect fermentation with both positive and negative effects established.

A series of rapid, high sensitivity capillary electrophoresis (CE) separation systems have been developed for the analysis of biological analytes and systems. A majority of the work has focused on development of novel instrumentation, in which new injection and detection strategies were investigated to improve the sensitivity of fast CE. A novel optical injection interface for capillary zone electrophoresis based upon the photophysical activation of caged dye attached to the target analyte was developed. The primary advantage of this approach is the lower background and background-associated noise resulting from reduced caged-fluorescein emission in conjunction with the high quantum yield of the resulting fluorescein. Improved detection limits were obtained compared to those observed in photobleaching-based optical gating. A primary drawback of photolytic optical gating CE is the lack of available caged-dye analogs with sufficiently fast reaction kinetics for online derivatization. To overcome this limitation, we have developed a chemical derivatization scheme for primary amines that couples the fast kinetic properties of o-phthaldialdehyde (OPA) with the photophysical properties of visible, high quantum yield, fluorescent dyes. The feasibility of this approach was evaluated by using an OPA/fluorescent thiol reaction, which was used to monitor neurotransmitter mixtures and proteins. The utilization of a high power ultraviolet light emitting diode for fluorescence detection in CE separations has been introduced to analyze a range of environmentally and biologically important compounds, including polyaromatic hydrocarbons and biogenic amines, such as neurotransmitters, amino acids and proteins, that have been derivatized with UV-excited fluorogenic labels. To understand cellular chemistry, it is imperative that single cells should be studied. This work was focused on developing CE based method to characterize the cellular uptake of TAT-EGFP. We demonstrated TAT mediated delivery of EGFP protein into HeLa cells and TAT-EGFP loaded single cell was analyzed by CE-LIF to determine the intracellular EGFP content. An application of CE-LIF for the determination of biogenic amine levels in the antennal lobes of the Manduca sexta is also explored and methods were developed to analyze a single antennal lobe dissected from moths. The lobe was digested and contents were labeled with the fluorogenic dye prior to CZE analysis.

This project involved designing and building a radiochromic film (RCF) densitometer using a still digital camera as the light detector and light emitting diode, LED, as the light source. The behaviour of the LED and charged coupled device (CCD) in the still digital camera, under different light exposure settings (by changing LED current and camera shutter speed) were measured and an optimal setting was determined. Additionally, methods were devised and tests were carried out in order to spread the illumination area of the single light source. Uniform spreading of the LED illumination area was possible by the use of two diffusers placed at an optimum separation distance that was determined in this work. The usefulness of this custom-made RCF densitometer was demonstrated by using this device to image exposed RCF and using the film analysis software, Image J, to determine the film absorbed dose. Two clinical situations were examined: open and virtual wedge radiation beams. It was concluded that still digital cameras can be used in RCF densitometers provided they can capture and store raw images, a single diffused LED can illumination an area large enough for RCF densitometry and appropriate film analysis software is needed to extract and handle the large volume of greyscale data from the RCF.

Recently, the high-power light-emitting diodes (LEDs) have been used from the traditional indicator purpose to general illumination purpose. The operating environment and requirement has been more severe. The long operating life high efficiency and high reliability are its main feature attracting the lighting community to this technology. The effect of operating temperature on the degradations of high-power blue LEDs is studied in this thesis. The experiment, measurements, and finite element simulations were conducted to investigate the possible causes of LED degradation. The influence of LED material degeneration on the radiometric pattern was analyzed by tracing rays simulation. Different groups of sample LEDs produced by Lumileds, Unity opto technology Co., and Everlight electronics Co. were studied. Different operating ambient temperatures, e.g. 80oC, 100 oC, and 120 oC, were considered in the accelerated aging test. Experimental results indicated that yellowing, carbonization, gel degeneration, lens chapping and deformation were observed during the test. Results also indicated that the operating temperature is the key factor for LED failure mechanism, that is, different operating ambient temperature may lead to different degradation phenomenon. Numerical simulation results shown that the creep caused by high temperature and thermal stress would cause solder takeoff. This takeoff defects were observed in experimental results. Through ray tracing simulation, it is assured that gel degeneration would change the radiometric pattern of the LED significantly.