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Dynamics of Singlet Excitons in Alq3 and Magnetic Mode Switching in Index Matched Organic Waveguides

Thompson, Jonathan R.

Abstract Details

2018, PhD, University of Cincinnati, Arts and Sciences: Physics.
Organic materials have proved very useful for many devices, ranging from organic light emitting diodes (OLED) to waveguiding structures. One such organic material is tris(8-hydroxyquinoline)aluminum (Alq3), whose high emission efficiency and electron mobility make it ideal for efficient high-quality OLED displays. However, a complete picture of the exciton dynamics responsible for Alq3 fluorescence is still up for debate. With a better understanding of these dynamics we will have the potential to make OLEDs even more efficient than those capable today. For this reason, the singlet exciton lifetime of Alq3 films is investigated using time-integrated (TI-) and time-resolved photoluminescence (TR-PL) measurements for temperatures between 20 and 300 K. By adjusting the laser excitation pulse repetition and energy fluence, the dynamics of bimolecular quenching processes between singlets and triplets can be observed. Furthermore, the quasi-amorphous structure of Alq3 creates local traps, which not only account for an increase in singlet and triplet annihilation rates, but also explains the decrease in PL efficiency above 180 K, where singlets can be thermally freed from their traps and recaptured by non-radiative centers. In addition to their emission properties, organic materials make ideal waveguides insofar that they can be better integrated into opto-electronic computing devices because of their ability to be deposited on various substrates without the need of lattice matching, unlike traditional crystalline semiconductors. As will be shown, the inclusion of magnetic layers within an organic waveguide allows the structure to act as an optical mode switch. In order to create such a device with efficient mode conversion, there must be perfect index matching (PIM) between transverse electric (TE) and transverse magnetic (TM) waveguide polarizations. Thus, several Alq3 – perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) multilayer waveguides are fabricated and investigated. It is found that some of these waveguides exhibit long-range index matching over the wavelengths 620 – 920 nm. Effective refractive index measurements are made using the m-line prism coupling technique and modelled using the transfer matrix method (TMM). Furthermore, a copper phthalocyanine (CuPc) – cobalt ferrite (CFO) waveguide index matched at the wavelength 850 nm is investigated. Through the application of an external magnetic field oriented in the direction of wave propagation within the film, there is an observed Faraday rotation between the two index matched polarizations TE0 and TM0. The conversion efficiency, as well as waveguide propagation length, is calculated by using coupled mode theory (CMT). A decrease in conversion efficiency is observed at wavelengths that did not satisfy perfect index matching. Finally, theoretical investigations into hybrid organic-plasmonic multilayer waveguides are made, where a thin ferromagnetic nickel (Ni) layer is added into Alq3-PTCDA multilayers. It is found that the thin metal film creates symmetric and antisymmetric surface plasmon polaritons (SPP) at the dielectric-metal interface for the TM0 mode. The symmetric SPP exhibited long-range propagation, transverse field confinement, and perfect index matching with the TE0 mode between the wavelengths 815 – 875 nm. Calculations are made to estimate the effectiveness of using a plasmonic waveguide as an optical switch.
Hans Peter Wagner, Ph.D. (Committee Chair)
Philip Argyres, Ph.D. (Committee Member)
Carlos Bolech, Ph.D. (Committee Member)
Leigh Smith, Ph.D. (Committee Member)
192 p.

Recommended Citations

Citations

  • Thompson, J. R. (2018). Dynamics of Singlet Excitons in Alq3 and Magnetic Mode Switching in Index Matched Organic Waveguides [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535459125887475

    APA Style (7th edition)

  • Thompson, Jonathan. Dynamics of Singlet Excitons in Alq3 and Magnetic Mode Switching in Index Matched Organic Waveguides. 2018. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535459125887475.

    MLA Style (8th edition)

  • Thompson, Jonathan. "Dynamics of Singlet Excitons in Alq3 and Magnetic Mode Switching in Index Matched Organic Waveguides." Doctoral dissertation, University of Cincinnati, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535459125887475

    Chicago Manual of Style (17th edition)