ABSTRACT Optoelectronics of polymer light emitting diode (LED) depends significantly on polymer molecular structure and charge conjugation. This study focused on the optoelectronics of freestanding films and LEDs of a colinear, fully conjugated heterocyclic aromatic rigid-rod polymer (PBT) and its mixtures with a partially conjugated coil-like polymer (Pbi). A deuterated PBTd4 was also mixed with a fully conjugated coil-like polymer (ABPBI) for UV-Vis absorption spectrum, photoluminescence (PL), diodic current-voltage response, and electroluminescence (EL). Rigid-rod PBT was only soluble in strong protic acid. PBT films were processed using methanesulfonic acid. PBT free-standing films showed maximum absorptions at 468 nm and 640 nm; PBTd4 having all hydrogen atoms on the phenylene moiety substituted by deuterium retaining same electron orbitals thus showed same absorption and PL spectra. It was likewise for the PBTd4 and ABPBI mixtures at ABPBI concentrations of 1 % and 10 %. For mixtures of PBT and Pbi, the absorption spectra indicated super- position of individual optical absorption response and no energy transfer. However, PL spectra showed a blue shift with increasing Pbi content. This was attribed for PBT rod-like configuration, or PBT aggregation perturbed by mixing with Pbi. Monolayer LED of Al/PBT/ITO and Al/Pbi/ITO yielded a threshold voltage of 4 V. When PBT/Pbi mixtures of 75/25, 50/50, 25/75, were used as the light emitting layer, the threshold voltage altered to 10 V, 7 V and 17 V, respectively. This threshold voltage deviation from 4 V is due mainly to difference in layer thickness, or phase separation affecting the tunneling effect. To enhance LED stability, an Ag layer was evaporated onto the Al electron injection electrode. For Ag/Al/PBT/ITO devices and mixed PBT/Pbi (75/25,50/50,25/75) devices, the maximum EL wavelength exhibited no systematic change at 753 nm, 714 nm, 727 nm, and 697 nm, respectively, due to using different bias voltage.

This paper tries to explore the phosphor optical characteristics through reliability tests using white light emitting diodes (WLEDs) with a high color rendering index (CRI ,Ra¡Ö90). Based on light mixing principles and considering the high CRI, three color-coded powders were mixed separately with silicone into a phosphor, and then bottomed with blue chips into WLEDs. The three powders were oxide nitride (red), YAG (yellow), and silicate (green). Two kinds of samples were fabricated ¡V phosphor and emitters similar to commercial products. Both cool-white (CCT=5650~7000K, lumen efficiency¡Ö60 lum/w.) and warm-white (CCT=2850~3250K, lumen efficiency¡Ö50 lum/w.) samples passed the Bin Code distribution process and brightness measurement. The results indicate better lumen efficiency than previously published research. After the three kinds of mono-colored phosphors were created, .we implemented the reliability test in which three CREE standards were chosen. These standards were (1) high temperature with high humidity test (60¢J , 90% humidity) in operating and non-operating condition; (2) thermal shock test (-40¢J ~125¢J ); (3) life time test. The thermal shock test showed the decaying power of intensity for red, yellow, and green phosphors were 11.7%, 17.5%, and 19.3% respectively. These results demonstrate that the red phosphor has the best thermal resistance. However, after the high temperature with high humidity tests, the decaying power of intensity for red,yellow, and green phosphor were 15.7%, 10.1% and 6.4% correspondingly. These results show that the green phosphor has best aqua resistance. In the life time test of emitters, the decaying power of intensity for the cool-white emitter was 3.2%, while the warm-white emitter showed 4.2%. As such, cool-white emitters were concluded to have better reliability than warm-white emitters.

This thesis use laser diode, lens, grating, and mirrors to composite the external cavity system to retrieve the thickness of the liquid crystal and its characteristics. This way is different to the traditional way of measure. It has good accuracy on the vertical resolution and the vertical resolution can reach to 0.3£gm. At the same time, it can develop the high quality of horizontal resolution. On the basis of the correlation between the cavity length and the wavelength of the semiconductor laser, the system is capable of developing high horizontal resolution of accurate liquid crystal measurements. The horizontal resolution can reach to 40£gm. Furthermore, by adding bias on liquid crystal through this system, it expanded more understandings on the influences of bias and induced electric field of the electrodes to the tilting angle of the liquid crystal.

Electrowetting is an electromechanical response that can be used to change the equilibrium shape of droplets on a surface through the application of an electric potential. By applying this potential asymmetrically to a droplet, the droplet can be moved. Typical electrowetting devices use an electrode covered by a dielectric to reduce electrochemical interactions. Successful electrowetting requires electrodes and dielectric layers that can resist damage through many cycles of voltage. Continuous Electrowetting (CEW) is performed on high resistivity silicon wafers. In this process, when an electric potential difference is applied between the substrate ends, the droplet on the substrate moves towards the side with positive voltage. The diode behavior of consecutive metallic spots, placed in the oxide layer, is the root of the droplet movement. This thesis investigates electrode, dielectric, and electrolyte material combinations that can achieve long stable performance with a particular emphasis on continuous electrowetting. Incorporation of diodes can also improve standard EW conditions to achieve lower voltage operation. In passivating systems, a reverse biased electrode becomes electrochemically passive. This way we have performed low voltage and reliable Electrowetting on Dielectric (EWOD) for 5000 test cycles. This is while, in non-passivating systems, EWOD degrades significantly from the first cycles. In CEW devices, SiO2 can also serve as a steady dielectric. It is observed that, with larger electrolytes, contact angle change would remain consistent for 10000 cycles with less than 19% degradation, while would be as high as 47% with small electrolytes. In CEW device, consistent and ideal behavior of electrochemical diodes is expected. Even though diode pairs reduces current flow and the extend of electrochemical reactions, the diode behavior can degrade over test cycles due to electrochemical reactions. To evaluate the diode behavior of different electrodes, a coefficient (referred to as actuation coefficient) is introduced which varies between zero (the least favorable diode behavior) and one (the best diode behavior) It is shown that, with the use of titanium as the electrode, the diodes behave more ideally and they behave consistently over 2000 test cycles. The best diode performance was observed with Na2SO4 electrolyte solution, where actuation coefficient remains at around 0.8 for 10000 test cycles. Aluminum can perform well in the beginning of the test cycles, but its performance degrades significantly over the first cycles.

Mid-infrared lasers in the 3-5 µm range are important for wide variety of applications including trace gas sensing, infrared counter measures, free space optical communications, etc. GaSb-based type-I quantum well (QW) diode lasers are an attractive choice due to their relatively simple design and growth tolerances, as compared with quantum cascade lasers and interband cascade lasers. Excellent diode lasers have been demonstrated for wavelengths up to ~3.0 µm, employing GaInAsSb/AlGaAsSb QW active regions. But, device performance tends to degrade at longer wavelengths, due to Auger recombination and decreasing QW valence band offsets. In this work we look into the feasibility of using highly strained GaInAsSb/GaSb QWs as active regions for diode lasers operating at wavelengths beyond 3.0 µm. Heavy strain in the QW can improve valence band offset and also increase the splitting between the heavy and light hole bands which can help minimize Auger recombination. Through optimized molecular beam epitaxy (MBE) growth conditions we were able to incorporate up to 2.45 % compressive strain in these QWs enabling laser operation up to 3.4 µm at room temperature. An alternate path to extend the emission wavelength is to incorporate dilute quantities of nitrogen into the QW. Incorporating dilute quantities of substitutional nitrogen into traditional III-V’s strongly reduces the bandgap of the alloy. The advantage for the case of GaSb based dilute-nitrides is that the bandgap reduction is almost exclusively due to the lowering of the conduction band leaving the valence band offsets unaffected; thus providing a path to mitigating hole leakage while extending the emission wavelength. Although GaSb-based dilute-nitrides are a potentially elegant solution for extending the operating wavelength of GaSb-based type-I QW diode lasers, the luminescence efficiency of this material system has been relatively poor. This is most likely due to the presence of a high concentration of point defects, like nitrogen substitutional clusters. Through careful optimization of MBE growth conditions and post growth annealing, we demonstrate improved luminescence efficiency. With further optimization this material system can potentially extend the emission wavelength of GaSb-based type-I QW diode lasers even further into the mid-infrared spectrum. / text

The piezo-phototronics effect is the three way coupling of semiconductor properties, photonics and piezoelectricity in the same material. Research on piezo-phototronics effect has illustrated its application on various Zinc Oxide (ZnO) nanowire based devices, yet a systematical study with comprehensive theoretical model is still missing. Here we have designed experiments on wider variety of materials to investigate the mechanism of the piezo-phototronics effect, and then built up a theoretical model for more thorough understanding. Experimental results are shown for Cadmium Sulfide (CdS) photodetectors for visible light detection, inorganic/organic hybrid Light Emitting Diodes (LEDs) and LED arrays, and it is demonstrated that strain can significantly tune the performance of these optoelectronic devices. Theoretical methodologies are proposed for Metal-Semiconductor-Metal (MSM) structure and p-n junctions, including analytical solutions and Finite Element Method (FEM) simulations. For Schottky contacts in photodetectors, barrier height change is determined as the main reason for the effect, and an exponential relationship between applied external strain and the device current is discovered, and is qualitatively confirmed from experimental results. For p-n junctions in LEDs, change in size of depletion region under strain is credited for the current change, and a charge channel is predicted for large strain, which gives explanation for the observed gigantic enhancement of light emission efficiency in experiments.

Metal/organic/indium tin oxide (ITO) structures, including OLEDs, are demonstrated to contain multiple nonvolatile conductance states that can be programmed by the application of an external bias above a certain threshold voltage (Vth). These conductance states are stable and in turn can be probed by the use of a bias lower in value than Vth. The unbiased retention time of states is greater than several weeks, and more than 48,000 write-read-rewrite-read cycles have been performed with minimal degradation. It is found that the programming of a continuum of conductance states is possible, and techniques to do so are outlined. The electrical conductivity of the highest and lowest states can differ by six orders of magnitude. Switching speeds below 50 ns are shown, resulting in an energy requirement of about 100 pJ to switch from one conductance state to another. The memory phenomenon is shown to be influenced by the active layer thickness and anode/surface roughness while temperature dependence is limited. The electrical characteristics of these devices are consistent with metal diffusion or filament phenomena found in metal-insulator-metal structures, suggesting a possible mechanism by which the states are stored.Electroluminescent devices employing several new organic-inorganic lumophore-functionalized macromolecules are presented. In this study, macromolecules incorporating several lumophores covalently bonded to the vertices of a cubical core structure based on Polyhedral Oligomeric Silsesquioxane (POSS) in multiple configurations are implemented as light-emitting centers. The hole-transporting polymer poly(N-vinylcarbazole) (PVK) and electron-transporting additive 2-(4-biphenylyl)-5-(4-tert-butylphenyl)1,3,4-oxadiazole (PBD) are used as a two-part host to enhance the carrier transport in these simple solution-processed single-layer devices. A study of energy transfer in several systems is carried out to understand the requirements needed to create white-light emission from a single macromolecule. A single macromolecule incorporating twenty-one blue and one yellow lumophore is shown to exhibit field-independent stable white-light electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.31, 0.37). An external quantum efficiency of 0.55 percent and a maximum brightness of 1600 cd/m2 are attained with simple solution-processed single-layer devices. High solubility and ease of purification give these macromolecule white-light emitters advantages over their small molecule and polymeric type counterparts.

White LEDs (Light Emitting Diodes) in Visible Light Communication (VLC) is an emerging technology that is being researched so it can eventually be used for common communications systems. LEDs have a number of advantages, one of which is long life expectancy. However, like many emerging technologies, VLC has many technical issues that need to be addressed. We proposed an optical indoor wireless communication system that used white LEDs like plug-in devices. We developed a practical implementation of VLC and demonstrated it experimentally. In particular we focused on designing a prototype of VLC that can be used without having to make major changes to the present infrastructure with two types of protocol — namely RS-232 and USB — for data transmission.

Surface plasmon is a collective oscillation behavior of electrons in metal nanoparticle induced by the excitation of incident light, which can create an enhanced localized electric field near the surface of metal nanoparticle. To date, metal nanoparticle surface plasmon resonances have been extensively studied in the photoluminescence domain; little work however was devoted to electroluminescent and photovoltaic research. In this thesis, as a fundamental study we firstly investigated surface plasmon enhanced europium complex luminescence and obtained an improved understanding of the importance of optical spacer in metal enhanced fluorescence phenomenon. Under this guideline, we incorporated metal NPs into organic light emitting diodes (OLED) and organic solar cells, by means of thermal evaporation and wet chemistry. Metal nanoparticles are demonstrated to enhance the efficiency of both OLEDs and solar cells only under tailored device architecture. The surface plasmon enhanced local electric field plays an important and comprehensive role in enhancing device performance. In Alq3 based OLED we observed increased charge carrier injection by depositing Ag nanoparticles underneath the Al cathode; in Ir(ppy)3 based OLED we gained enhanced luminous efficiency via doping silica functionalized Ag nanoparticles into emitting layer; in P3HT based organic polymer solar cell we noticed an increased polymer absorption by incorporating Ag nanoparticles over the active layer. On the other hand, adverse effects such as metal nanoparticle induced charge carrier recombination and light extinction are also observed. The study of surface plasmon effects in organic optoelectronic devices reveals interesting surface plasmon features and permits to optimize optoelectronic devices from a novel point of view. / Thesis (Ph.D, Chemistry) -- Queen's University, 2012-01-05 17:22:40.074

High power diode-pumped solid state (DPSS) lasers are a rapidly growing technology that is attractive for various applications in scientific and industrial fields. DPSS lasers are highly efficient, reliable and durable with superior beam quality when compared to flash-lamp pumped lasers. Double-tungstate crystals such as potassium yttrium tungstate Yb:KY(WO₄)₂ (Yb:KYW) are one of the most popular active materials used in DPSS lasers for generation of continuous wave radiation and ultrashort (i.e. femtosecond, 10⁻¹⁵ s) pulses with high average output power. The high pump power of laser diodes results in considerable heat generation in a laser crystal that in turn causes thermal lensing effect. Thermal lensing affects the performance and stability of a resonator, and plays an important role in limiting the output power and degrading the beam quality of solid state lasers. Despite these facts, no detailed studies of thermal effects in Yb:KYW lasers were reported to date. In this work thermal lensing in a diode-pumped Ng-cut Yb:KYW laser operating at the wavelength of 1.04 μm was characterized. A maximum output power of 3.5 W with a nearly diffraction limited output beam (M₂ < 1.2) was achieved under the absorbed pump power of 13.8 W. The focal lengths of the induced thermal lenses were obtained from the laser output beam size measurements at various incident pump power levels and ABCD matrix analysis. At maximum output power the focal length of the induced thermal lens was found to be 814 mm for the Nm direction (horizontal) and 144 mm for the Np direction (vertical). Thermal lens sensitivity factors were 1.26 m⁻¹/W and 0.32 m⁻¹/W for the Np and Nm directions, respectively. This highly astigmatic thermal lensing can be explained by strong anisotropy of thermo-optical properties of the crystal and its cooling geometry. In addition, the finite element analysis (FEA) method was employed to obtain the focal lengths of the induced thermal lens inside the crystal. Simulation results obtained from the theoretical model were compared to experimental data, and the accuracy of the model was verified. The results of this work are critical for practical design of the efficient and reliable Yb:KYW lasers with multi-Watt average output power.