Controlling plasmon-enhanced luminescence
Abstract
Plasmons are collective oscillations of the free electrons in a metal or an ionized gas. Plasmons dominate the optical properties of noble-metal nanoparticles, which enables a variety of applications. This thesis focuses on plasmon-enhanced luminescence of silicon quantum dots (Si QDs) and optically active erbium ions. Both these emitters are compatible with silicon processing technology, and are therefore of great technological interest. In part I we describe three fabrication methods of Ag nanoparticles: electron beam lithography, a sequential Si/Ag/Si electron-beam evaporation process, and a sequence of Na+ ? Ag+ ion exchange and ion irradiation of Na+-containing glass. In part II we show that the photoluminescence intensity of Si QDs can be enhanced in a spectrally selective way by coupling to Ag nanoparticles. The observed luminescence enhancements range between a factor 2 and a factor 6. In addition, we demonstrate that the luminescence enhancement is polarized for elongated Ag nanoparticles. Based on both the spectral selectivity and the polarization selectivity, we conclude that the observed luminescence enhancement is due to coupling of the Si QD emission dipoles to plasmon modes, rather than due to an enhanced excitation rate. As a consequence, the concept of plasmon-enhanced luminescence could also be applied to enhance the luminescence intensity of electrically driven light sources. This possibility is explored by integrating Ag nanoparticles in prototype Si QD light-emitting devices fabricated using processing facilities at Intel Inc. The Si QD electroluminescence intensity of these devices has been enhanced by up to a factor 2.5. Mechanisms that could explain this enhancement are discussed. By engineering extremely anisotropic Ag nanoparticles, we demonstrate in part III that the photoluminescence intensity of optically active Er3+ ions positioned in close proximity to these nanoparticles is significantly enhanced if the nanoparticles support plasmon modes that are resonant with the erbium emission at 1.5 ?m. Also for these systems, the enhancement is polarized corresponding to the plasmon resonances of the nanoparticles. These results indicate the opportunities of Ag nanostructures for the reduction of quench processes of erbium in a wide range of materials. Plasmon-enhanced luminescence of erbium may for example enable the realization of efficient light sources based on erbium-doped silicon. The theoretical investigation of plasmon-enhanced luminescence described in part IV focuses on the modifications of the radiative and nonradiative decay rates of an optical emitter positioned in close proximity to a noble-metal nanoparticle. We analyze the influence of both spherical metal nanoparticles and anisotropic metal nanoparticles, and determine optimal geometries for plasmon-enhanced luminescence. Altogether, the thesis provides insight in the fundamental aspects of plasmon-enhanced luminescence, and correlates these to experiments on light emitters in practical geometries. Specific insights in possible applications are discussed in the corresponding chapters.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- April 2007
- Bibcode:
- 2007PhDT.......325M
- Keywords:
-
- Gersten and Nitzan model;
- LED;
- erbium;
- quantum dot;
- spontaneous emission;
- nano-antenna;
- plasmon