Advanced Materials for Organic Photonics

V oblasti nových nízkomolekulárních organických materiálů patří deriváty difenyldiketopyrrolopyrrolu (DPP), používané dříve jako barviva a pigmenty, k objektům vysokého zájmu pro jejich potencionální aplikace v moderních technologiích. Studium jejich optických vlastností ve vztahu k jejich chemické struktuře umožní využití jejich vysokého potenciálu ve vývoji pokročilých inteligentních materiálů. Přehled chemických a fyzikálních vlastností DPP derivátů a zhodnocení současného stavu řešené problematiky jsou uvedeny v teoretické části této práce. Tři hlavní procesy studované v této práci jsou: klasická absorpce a emise, dvoufotonová absorpce (TPA) a zesílená spontánní emise (ASE). Výsledky budou diskutovány a shrnuty ve dvou částech: první zahrnuje první dvě výše zmíněné oblasti a druhá problematiku zesílené spontánní emise.Among low molecular organic materials, diphenyl-diketo-pyrrolopyrrole (DPP) derivatives used earlier as dyes are of high interest in modern technologies. The study of their optical properties related to their chemical structure will provide more information on the later relationship and comfort the high potential of DPP derivatives in the making of more performant smart materials. An overview of their chemical and physical properties is described in the theoretical part and followed by the state of the art in the field of interest concerning this thesis. The three main processes studied in this work are: The classic absorption and emission, the two photon absorption (TPA) and the amplified spontaneous emission (ASE). The results will be discussed and summarized in two parts: The first concerning the one and the two photon absorption and the second the amplified spontaneous emission.

The Role Of Photonics In Energy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)In celebration of the 2015 International Year of Light, we highlight major breakthroughs in photonics for energy conversion and conservation. The section on energy conversion discusses the role of light in solar light harvesting for electrical and thermal power generation; chemical energy conversion and fuel generation; as well as photonic sensors for energy applications. The section on energy conservation focuses on solid-state lighting, flat-panel displays, and optical communications and interconnects. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.5Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)U.S. National Science Foundation [DMR-1309459, ECCS 1408051, DMR 1505122]U.S. Office of Naval ResearchEngineering and Physical Sciences Research Council of the UK [EP/K00042X, EP/L012294]European Research Council of the European Union [321305]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Spontaneous fluctuations of transition dipole moment orientation in OLED triplet emitters

The efficiency of an organic light-emitting diode (OLED) depends on the microscopic orientation of transition dipole moments of the molecular emitters. The most effective materials used for light generation have threefold symmetry, which prohibit a priori determination of dipole orientation due to the degeneracy of the fundamental transition. Single-molecule spectroscopy reveals that the model triplet emitter tris(2-phenylisoquinoline)iridium(III) (Ir(piq)3) does not behave as a linear dipole, radiating with lower polarization anisotropy than expected. Spontaneous symmetry breaking occurs in the excited state, leading to a random selection of one of the three ligands to form a charge transfer state with the metal. This non-deterministic localization is revealed in switching of the degree of linear polarization of phosphorescence. Polarization scrambling likely raises out-coupling efficiency and should be taken into account when deriving molecular orientation of the guest emitter within the OLED host from ensemble angular emission profiles

Recent advances in solid-state organic lasers

Organic solid-state lasers are reviewed, with a special emphasis on works published during the last decade. Referring originally to dyes in solid-state polymeric matrices, organic lasers also include the rich family of organic semiconductors, paced by the rapid development of organic light emitting diodes. Organic lasers are broadly tunable coherent sources are potentially compact, convenient and manufactured at low-costs. In this review, we describe the basic photophysics of the materials used as gain media in organic lasers with a specific look at the distinctive feature of dyes and semiconductors. We also outline the laser architectures used in state-of-the-art organic lasers and the performances of these devices with regard to output power, lifetime, and beam quality. A survey of the recent trends in the field is given, highlighting the latest developments in terms of wavelength coverage, wavelength agility, efficiency and compactness, or towards integrated low-cost sources, with a special focus on the great challenges remaining for achieving direct electrical pumping. Finally, we discuss the very recent demonstration of new kinds of organic lasers based on polaritons or surface plasmons, which open new and very promising routes in the field of organic nanophotonics

Smart Thermostat using FPGA

This project developed a smart thermostat that automatically adjusts desired indoor temperatures based on human detection results. The system was implemented on the Zybo, a development board with a Xilinx Zynq All Programmable System-on-Chip, which integrates a dual-core ARM Cortex-A9 processor with a Xilinx 7-series Field Programmable Gate Array (FPGA) logic. The completed design was able to receive desired temperature values from users and automatically control the heating, ventilating and air conditioning system to maintain the comfort zone and maximize energy saving. The smart thermostat was supplied by real-time embedded software running on the ARM microprocessor. All communications between peripherals and the smart thermostat were designed and implemented on programmable logic

Attitude determination for small satellites using gps signal-to-noise ratio

Thesis (M.S.) University of Alaska Fairbanks, 2014An embedded system for GPS-based attitude determination (AD) using signal-to-noise (SNR) measurements was developed for CubeSat applications. The design serves as an evaluation testbed for conducting ground based experiments using various computational methods and antenna types to determine the optimum AD accuracy. Raw GPS data is also stored to non-volatile memory for downloading and post analysis. Two low-power microcontrollers are used for processing and to display information on a graphic screen for real-time performance evaluations. A new parallel inter-processor communication protocol was developed that is faster and uses less power than existing standard protocols. A shorted annular patch (SAP) antenna was fabricated for the initial ground-based AD experiments with the testbed. Static AD estimations with RMS errors in the range of 2.5° to 4.8° were achieved over a range of off-zenith attitudes

Design and modelling of anisotropic thin film light-emitting devices with the plane wave expansion method

In most emitting materials the dipole moments are distributed in an isotropic way, and light is emitted in all directions (modified by interference in the OLED layers). But the radiation of each individual dipole is directed around the equatorial plane of the dipole moment. By analyzing the photoluminescent decay times in different microcavities, a phosphorescent emitter with an anisotropic distribution of 80% in-plane dipoles is demonstrated. Simulations show that if all dipoles are arranged in-plane with the OLED layers the outcoupling efficiency to air would improve from 20% to 30%. Anisotropic emitters can be combined with known outcoupling techniques like microlens foils to provide even higher outcoupling efficiencies. With a fully oriented emitter nearly 70% of the light is reaches the OLED substrate where it is available for extraction by outcoupling foils. When organic laser dye molecules are dissolved into the CLC, a laser can be made. A CLC film supports a resonant standing wave for wavelengths at the edge of the bandgap. When the dye molecules are pumped above the lasing threshold by a pulsed shorter wavelength pump laser, longer wavelength laser light is emitted perpendicular to the CLC film. The thickness of the CLC film is around 10μm. Laser emission has been shown across the entire visible spectrum employing different dye molecules. The emission wavelength can also be tuned across ranges of about 50nm in different ways. However CLC lasers are still hindered by high lasing thresholds and low output power, as well as bleaching of the dye molecules. In this work the light emitting properties of CLC films are simulated with the anisotropic plane wave expansion method both for spontaneous and stimulated emission. The measured emitted spectrum at different angles and polarization are accurately modelled by the plane wave expansion. A model for estimating the gain threshold and laser wavelength of CLC films was developed and verified by experiment. Optical amplification is treated by introducing gain terms to the refractive index. This model may prove a valuable tool to design more advanced liquid crystal lasers

Doctor of Philosophy

dissertationIn Part 1, we demonstrate the fabrication of organic light-emitting devices (OLEDs) with precisely patterned pixels by the spin-casting of Alq3 and rubrene thin films with dimensions as small as 10　μm. The solution-based patterning technique produces pixels via the segregation of organic molecules into microfabricated channels or wells. Segregation is controlled by a combination of weak adsorbing characteristics of aliphatic terminated self-assembled monolayers (SAMs) and by centrifugal force, which directs the organic solution into the channel or well. This novel patterning technique may resolve the limitations of pixel resolution in the method of thermal evaporation using shadow masks, and is applicable to the fabrication of large area displays. Furthermore, the patterning technique has the potential to produce pixel sizes down to the limitation of photolithography and micromachining techniques, thereby enabling the fabrication of high-resolution microdisplays. The patterned OLEDs, based upon a confined structure with low refractive index of SiO2, exhibited higher current density than an unpatterned OLED, which results in higher electroluminescence intensity and eventually more efficient device operation at low applied voltages. We discuss the patterning method and device fabrication, and characterize the morphological, optical, and electrical properties of the organic pixels. In part 2, we demonstrate a new growth technique for organic single crystals based on solvent vapor assisted recrystallization. We show that, by controlling the polarity of the solvent vapor and the exposure time in a closed system, we obtain rubrene in orthorhombic to monoclinic crystal structures. This novel technique for growing single crystals can induce phase shifting and alteration of crystal structure and lattice parameters. The organic molecules showed structural change from orthorhombic to monoclinic, which also provided additional optical transition of hypsochromic shift from that of the orthorhombic form. An intermediate form of the crystal exhibits an optical transition to the lowest vibrational energy level that is otherwise disallowed in the single-crystal orthorhombic form. The monoclinic form exhibits entirely new optical transitions and showed a possible structural rearrangement for increasing charge carrier mobility, making it promising for organic devices. These phenomena can be explained and proved by the chemical structure and molecular packing of the monoclinic form, transformed from orthorhombic crystalline structure