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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

LEDs and Doped Polymer Light Guides for Efficient Illumination and Colour Engineering

January 2005 (has links)
This project involves the study of optical properties of polymers doped with TRIMM (transparent refractive index matched micro-particles), and their uses in light guides. The refractive index difference between dopant and host material is small (0.02), so forward transmittance is high, and losses due to backscattering are negligible. Flexible polymer optical fibre (POF) and polymethylmethacrylate (PMMA) rods are being incorporated into an increasing range of lighting and light mixing applications. For energy efficient mixing of red, green and blue (RGB) light-emitting diodes (LEDs) to produce white light and a range of other colours, light is transmitted from the end of a light guide ('endlight'). A major problem here is solved, namely the achievement of uniform illumination, simultaneously with low losses from scattering. Light output from RGB LEDs is shown to be completely mixed by short TRIMM-doped light guides. Alternatively, long lengths of TRIMM-doped POF can be used for 'side-light'. The concentration of TRIMM for these is chosen such that light is emitted from the side walls of the guide to give even illumination along its length. A geometrical method of ray tracing in particle-doped rectangular and cylindrical light guides is derived, and Monte Carlo ray tracing simulations performed for undoped and TRIMM-doped light guides. The evolution of the distribution of ray angles, internal and external to a light guide, with propagation distance are studied. Computer simulations of angular distribution of light emitted from the wall of POF agree with measurements performed using a photogoniometer. Simulations and measurements of light output intensity and colour from RGB LED arrays when projected from the end of a mixing rod, are also presented. Colour calculations agree with photometric measurements of RGB LED output from clear and TRIMM-doped PMMA mixing rods. Results of transmittance measurements and computer simulations show that light losses are almost entirely due to Fresnel reflectance from the entrance and exit surfaces of the rods. Photogoniometer measurements of the angular distribution of light from LEDs are used as a basis for LED source models used in ray tracing simulations. Results of an investigation comparing the effect of using a smoothed LED source model instead of measurement-based models on simulated light output distributions are presented. The light output from LEDs can have sudden peaks in intensity at certain angles, resulting in distinctive patterns with clear colour separation, after mixing in clear polymer mixing rods. These caustic patterns are eliminated by using TRIMM-doped mixing rods, with a transmittance of 90% after Fresnel losses, which can be readily reduced.
62

Nanostructured organic light-emitting diodes with electronic doping, transparent carbon nanotube charge injectors, and quantum dots /

Williams, Christopher D. January 2006 (has links)
Thesis (Ph. D.)--University of Texas at Dallas, 2006. / Includes bibliographical references (leaves 109-116).
63

Matrix-addressable III-nitride light emitting diode arrays on silicon substrates by flip-chip technology /

Keung, Chi Wing. January 2007 (has links)
Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 64-69). Also available in electronic version.
64

Molecular design of organic semiconductors for electronic devices and their application in flexible light emitting diodes

Pandya, Hermona K. January 2006 (has links)
Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Mary E. Galvin, Dept. of Materials Science & Engineering. Includes bibliographical references.
65

Device optimization studies of organic light emitting devices

Hui, Kwun-nam. January 2005 (has links)
Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.
66

Design of High Performance Organic Light Emitting Diodes

Wang, Zhibin 07 January 2013 (has links)
Organic light emitting diodes (OLEDs) are being commercialized in display applications, and will be potentially in lighting applications in the near future. This thesis is about the design of high performance OLEDs, which includes both the electrical and optical design of OLEDs. In particular, the following work is included in this thesis: i) Energy level alignment and charge injection at metal/organic interfaces have been systematically studied. ii) Transition metal oxide anodes have been developed to inject sufficient holes into the OLEDs due to their high work function. The oxide anodes have also been used to systematically study the transport properties in organic semiconductors. iii) Highly simplified OLED devices with unprecedentedly high efficiency have been realized using both fluorescent and phosphorescent emitters. The high performance was enabled by using a high work function metal oxide anode and a hole transport material with very a deep highest occupied molecular orbital (HOMO). iv) An optical model has been developed to describe the optical electric field across the OLED device. By using the model, a high performance flexible OLED using metal anode was designed and realized.
67

The Study of Highly Efficient Single Emitting Layer White Light Organic Light-Emitting Diodes on Tandem Structure

Lien, Kuan-Yi 27 July 2009 (has links)
We report that the tandem OLEDs made of two electroluminescent (EL) units connected by the interconnecting layer. If It is compared wih the traditional OLEDs. The tandem OLEDs have higher efficiency and well lifetime. We not only used the single emitting layer WOLEDs as EL unit but also studied the effect of the interconnecting layer for whole device. First, we designed the interconnecting layer with Alq3¡GLi (1%) (n-doping layer)/MoO3 (p-doping layer), and we optimized the thickness of the interconnecting layer by using green unit cell (Alq3 for EML), ITO/NPB(65 nm)/Alq3(30 nm)/Alq3(30 nm)/Alq3(x nm)¡GLi (1%)/MoO3(y nm)/NPB(65 nm)/Alq3(30 nm)/Alq3(30 nm)/LiF(0.8 nm)/Al(200 nm) x=10¡A20¡A30¡A40¡Fy=1¡A3¡A5¡A7¡A10 We found that the best thickness of Alq3¡GLi (1%) and MoO3 are 20 nm and 5 nm. In our study, we concluded that there are the best thickness to each interconnecting layer, and it keeps the charge balance between two units. Finally, we used our single emitting layer WOLEDs as unit cell, which used 1,3,5-Tri(1-pyrenyl)benzene (TPB3) as the host, and 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the guest, unit cell was ITO(130 nm)/NPB(65 nm)/ TPB3(30 nm)¡GDCJTB(0.05%)/ Alq3(30 nm)/LiF(8 nm)/Al(200 nm) Whole device was ITO(130 nm)/NPB(65 nm)/ TPB3(30 nm)¡GDCJTB(0.05%)/ Alq3(30 nm)/Alq3(20 nm)¡GLi(1%)/MoO3(5 nm)/NPB(65 nm)/TPB3(30 nm)¡GDCJTB(0.05%)/Alq3(30 nm)/ LiF(0.8 nm)/Al(200 nm) We got almost three times luminance from the tandem one at the same current density (670 cd/m2 for 2360 cd/m2 at 20 mA/cm2) and efficiency as high as 9.7 cd/A ( at 24 mA/cm2). It¡¦s a excellent contribution for device lifetime. But the operation voltage and the power efficiency didn¡¦t reach to our expectancy. In order to improve the disadvantage, we changed the concentration of n-doping layer Alq3¡GLi (z %)¡Az=1%¡A2%¡A3%. It was actually improved the turn-on voltage from 10 V to 7 V. But the luminescent characteristics also degenerated. Although we enhanced the charge mobility of the n-doping layer, it also caused the degeneration of luminescent characteristics because of the unbalance of the charge transference.We got the efficiency 8.1 cd/A ( at 14 V) and almost two times luminance from the tandem one at the same current density (670 cd/m2 for 1760 cd/m2 at 20 mA/cm2), most close to the white area of CIE coordinates was (0.30 , 0.37) at 15 V. Its range of CIE coordinates was (0.35 , 0.46)~(0.28 , 0.33) at 8 V~20 V. We have already developed the tandem WOLEDs using single white emitting layer as EL units that have never be reported. It not only maintained the advantages of the tandem structure, but also had excellent stability of luminescent characteristics at wide range operation voltage. We reached our goal to improve the WOLEDs and make it more suitable for commercial applications, especially for the development of light sources.
68

Reliability study of InGaN/GaN light-emitting diode

Li, Zonglin, January 2009 (has links)
Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 81-89). Also available in print.
69

Shipboard LED lighting a business case analysis /

Cizek, Christopher J. January 2009 (has links) (PDF)
Thesis (Master of Business Administration)--Naval Postgraduate School, December 2009. / Thesis Advisors: Dew, Nicholas ; Mutty, John. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: LED lighting, solid state lighting, business case analysis. Includes bibliographical references (p. 81-83). Also available in print.
70

LED shipboard lighting a comparative analysis /

Freymiller, Aaron Troy. January 2009 (has links) (PDF)
Thesis (Master of Business Administration)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Dew, Nicholas. Second Reader: Hudgens, Bryan. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Lighting, LEDs, shipboard lighting. Includes bibliographical references (p. 31-32). Also available in print.

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