Single emitter cryo-micro-spectroscopy of pyramidal quantum dots, fluorescent proteins, and light-harvesting complexes

Singh, Vikramdeep 2023. Single emitter cryo-micro-spectroscopy of pyramidal quantum dots, fluorescent proteins, and light-harvesting complexes. PhD Thesis, Cradiff University. Item availability restricted.

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Abstract

In this thesis, I present experiments involving low-temperature single emitter optical spectroscopy of pyramidal quantum dots, light harvesting complexes, and fluorescent proteins. Additionally, ensemble optical spectroscopy studies on fluorescent proteins are included. I investigate indium gallium arsenide pyramidal quantum dots with a double quantum dot system, having two different interdot separations. Micro-photoluminescence spectroscopy at cryogenic temperature is employed to study the spontaneous emission lineshape, characterised by the spectrally sharp zero-phonon line emission superimposed on a broad emission due to phonon-assisted transitions. Excitation power dependence and polarisation resolved photoluminescence measurements are conducted to identify the exciton, biexciton and trions emission lines. Further, using two-dimensional four-wave mixing measurements, coherent coupling of the excitons between two distant quantum dots is investigated. For the double quantum dot system with 10 nm interdot separation, coherent coupling between exciton due to static dipole-dipole interactions is revealed with a coupling strength of 150 micro-eV. I develop a sample design and preparation protocol for plasmonically enhanced low-temperature single emitter micro-photoluminescence measurements. A slow evaporation drop-casting method is developed to form monolayers of a polymer film containing the emitter around plasmonic nanoparticles to have efficient coupling. The choice of shape and size of plasmonic nanoparticles is discussed, and the optical scattering cross section of silica-coated plasmonic gold nanorods is calculated using the boundary element method. The Purcell factor and fluorescence enhancement of an emitter near plasmonic gold nanorods are estimated. I study plasmonically enhanced emission from individual light harvesting complexes LH2 at a temperature of 5 K. Plasmonically enhanced emitter positions show spectrally sharp zero-phonon emission lines that undergo spectral diffusion, contrasting with the broader emission observed from the unenhanced emitters. From the statistics of the different measured positions, an emission linewidth of 0.5 milli-eV is observed. I also analysed experimental data for LH2 emission at low temperatures without plasmonic enhancement from the literature to extract intrinsic lineshapes using a novel method separating the jitter, yielding a linewidth, and providing an alternative interpretation of the data. I study low-temperature photoluminescence and surface enhanced Raman scattering on mRhubarb720 fluorescent protein complex using plasmonic gold nanorods using a variant of the sample design used for LH2. The plasmonic properties of the gold nanorods are estimated using the boundary element method. The emission spectrum is characterised by spectrally sharp resonant Raman emission lines from individual fluorescent proteins. I measured power dependence, and polarisation resolved time traces of emission lines. From a fitting procedure of emission lines, I calculated the correlation between different emission lines. I also used non-negative matrix factorisation to explain observed time traces of emission lines by a combination of different spectral components. Finally, I study the ultrafast spectroscopy of three different fluorescent proteins at room temperature in an ensemble. Pump-probe spectroscopy measurements are conducted on the thin film of fluorescent proteins. From a Fourier transform analysis of the transient absorption spectrum, low-frequency vibrational beating at 250 per cm is observed for different fluorescent proteins. Two dimensional electronic spectroscopy measurements are also conducted to reveal the ultrafast relaxation within the molecules. I conducted an ensemble study of different fluorescent proteins using fluorescence line narrowing emission at low temperatures. These fluorescent proteins, variants of the same type but featuring distinct functional groups attached to them, exhibit different absorption and emission lineshapes. From the excitation power dependence of the emission spectra, I analyse the change in the emission lineshapes for different variants.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Optical spectroscopy, non-linear optics, coherent ultrafast spectroscopy, pyramidal quantum dots, coherent coupling, single molecule spectroscopy, SERS, plasmonic nanoparticles, cryogenic micro-spectroscopy
Date of First Compliant Deposit:	5 September 2024
Last Modified:	05 Sep 2024 14:13
URI:	https://orca.cardiff.ac.uk/id/eprint/171839

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