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Study On The Light Emission Properties And Design Of Organic Light Emitting Diodes (OLED) And Other Layered Nanostructures

Posted on:2009-06-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:X W ChenFull Text:PDF
GTID:1118360242492021Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Light emission from various nanostructures has been under intensive research due to their foreseeable great applications in advanced display, lighting, imaging, biological labeling, environmental monitoring and ultra-high resolution near-field microscopy. In this thesis, we study comprehensively the light emission properties of emitters from three kinds of layered nanostructures, including thin-film organic light-emitting diodes (OLEDs), nanowires/ nanotubes / nanocables and nanoparticles with core-shell structures. In addition, we investigate and design these nanostructures to manipulate the light emission, for example to enhance or suppress or redistribute the emission through microcavity effect or (and) surface plasmon effect in the devices.At first, we propose an accurate and efficient optical model for OLEDs with arbitrary number of films and emitting elements and discuss comprehensively the microcavity effect and the Purcell effect in the device. Then we study both experimentally and theoretically the modifications of internal quantum efficiency and the exciton lifetime with the change of the device structures and show that the internal quantum efficiency of an OLED can be indirectly obtained by measuring the exciton lifetime. Regarding top-emitting OLEDs, we optimally design the device structure to achieve high efficiency, large viewing angle and low angular color distortion through the Purcell enhancement of the internal quantum efficiency and the microcavity effect. Moreover, we demonstrate voltage-controlled color-tunable OLEDs based on m-ADN (blue emitter) and m-ADN:DCM(2% wt) (red emitter) and study the carrier barrier effect on the color-tuning range of the device.As for light emission from semiconductor NWs or NTs or NCs, an accurate and efficient method is proposed to simulate light emission of an emitter in a general cylindrically multilayered nanostructure. By using the model, we comprehensively study the emission properties of the emitter, including quantum efficiency and the distribution of the emission to the lateral farfield and waveguided modes of the nanostructure. We find theoretically that the photoluminescence of one-dimensional nanostructures is strongly excitation polarization dependent, in accordance with the experimental results reported.Fluorescences from core-shelled nanoparticles are important for biological applications. We study theoretically the light emission properties of an emitter in a spherically multilayered nanoparticle and discuss the effect of plasmonic resonance for the nanoparticle with a metallic shell. In addition, we propose and design a dual-shell structure consisting of a silica buffer shell and a metallic outer shell for highly efficient and tunable fluorescence. With the present dual-shell structure a fivefold enhancement of the fluorescence efficiency can be achieved for a nanofluorophore comprised of multiple tetramethylrhodamine isothiocyanate (TRITC) dye molecules, as compared to the nanofluorophore within a single silica shell. Furthermore, the fluorescence spectrum in the present dual-shell structure is sensitive to the refractive index of the ambient environment due to the surface plasmon resonance effect.
Keywords/Search Tags:OLED, fluorescence, microcavity, surface plasmon, color voltage-tunable, quantum efficiency, Purcell effect, nanowire, nanotube, nanocable, core-shell structure, nanoparticle
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