Trapping and plasmon-enhanced emission from a single upconverting nanocrystal




Alizadehkhaledi, Amirhossein

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Plasmonics has been used to increase the interaction of an emitter and light. This enhancement can be achieved by using plasmonic resonators at the emission and/or absorption wavelengths of the emitter. This dissertation is based on four projects which are mainly about the interaction of light and upconversion nanocrystals (UCNCs) using plasmonic resonators. In the first project, rectangular apertures on a gold film are fabricated and used to trap and study single UCNC. These apertures are finely tuned to find the highest upconversion emission enhancement. Results show significant up to 400X enhancement along with many other interesting observations for trapped UCNCs. Finite-difference time-domain (FDTD) simulations show multiple plasmonic resonances at emissions and absorption UCNC wavelengths, which justify the experimental results. These results could pave the way for understanding the interaction of light and UCNC at very subwavelength scales and can find the applications of UCNCs in photovoltaics, single-photon sources, and bio-imaging. Single-photon sources are emission sources that can emit a single photon as demanded. One way to achieve a single-photon source at telecommunication wavelengths at 1550nm is by using a single lanthanide ion inside a cavity with a huge emission enhancement factor. In the second project, using the already designed plasmonic resonator in the first project, the upconversion emission of very low erbium (Er) concentration is investigated. Results show discrete levels of emissions depending on the number of Er inside the UCNC. These results would be a great way to design a single-photon source working at 1550nm wavelength using Er. Because it can solve two major problems of previous works in this field; First, increasing the low emission rate of Er and second, solving random distribution of ion emitters inside the cavity by trapping and isolating a particle contains a single Er emitter. In the third project, the different upconverted lights from samples with gold nanoparticles on mono dielectric layers on top of the gold samples are investigated. Under 1550nm pulsed laser illumination, we observe second and third harmonic generations, two-photon photoluminescence, and bright broadband upconverted emission, which we believe is due to light-induced inelastic tunnelling emission. In the last project, we show dual-wavelength (1210nm and 1520nm) excitation upconversion with plasmonic enhancement, which can increase the efficiency of solar cells by upconverting near-infrared wavelengths to shorter wavelengths.



Plasmonic, Upconversion, lanthanide, single-photon, tunneling, erbium