Commercial success had been achieved with electroluminescent phosphor
powders, particularly zinc sulfide activated with copper. The applications of AC
Powder EL (ACPEL) are mainly limited to backlighting and lamp applications that require low brightness. This includes low illumination environments, such as nightlights and backlighting for LCDs and keypads in portable electronics and home electronics. By using nanowires as nanoelectrodes, a novel and self-supported nanostructured powder EL device has been developed in this thesis. The novel structure contains a single layer of ZnS:Cu powder phosphor which is embedded in a polymer matrix with one surface exposed. A dilute layer of conductive nanowires directly contacts the phosphor layer and works as rear electrodes. A highly intensified electric field can be induced in the phosphor region by the metal nanowires if a specific voltage is applied
to the device. Simulations of the electric field by using commercial software show that the localized electric field can be at least one order of magnitude higher than the average field depending on the dimensions of the nanowires. As a result, electrons can be injected into the phosphor lattice by high-field-assisted tunneling, hence inducing electron avalanching. The electrons finally are trapped at the donors. When the external field is reversed, the electrons recombine with the holes that are previously injected by the same process and trapped at the acceptors. Therefore, visible light is produced by the recombination of the electron-hole pairs through the donor-acceptor pairs.
The indium nanowires, with diameters of 300 nm and lengths of several microns, have been fabricated by using anodic aluminum oxide (AAO) templates which are known as self-organized porous structures formed by anodization of aluminum in an appropriate acid solution. A hydraulic pressure injection method has been applied to inject molten indium metal into the nanopores of the AAO template and form nanowires. By dissolution of the template, a large number of free indium nanowires is obtained. The nanowires are transferred onto a ZnS-embedded substrate by a wet-coating method. Finally, the entire device is completed by deposition of Au rectangular electrodes on the top of the indium nanowires. The indium nanowires have been characterized by using SEM and XRD. The tests of the dependence of luminance on voltage at various frequencies for a nanowire contact EL device sample are performed. A peak luminance of 25 cd/m2 has
been achieved for the device driven at frequency of 8.2 kHz and a voltage of 425 V. The EL performance of the nanowire contact EL device is not as good as traditional powder EL devices so far, however, the novel structures have the potential for a lower operating voltage with simultaneous long lifetime and high luminance to overcome limitations of traditional powder EL. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/16580 |
| Date | January 2008 |
| Creators | Chen, Feng |
| Contributors | Kitai, A. H., Materials Science |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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