Date of Award

12-2019

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Dr. Asghar N. Kayani

Second Advisor

Dr. Sung Chung

Third Advisor

Dr. Ramakrishna Guda

Fourth Advisor

Dr. John Tanis

Keywords

Ion implantation, silver nanoparticles, Rutherford backscattering spectrometry, localized surface plasmon, metal enhanced photoluminescence, optical spectroscopy

Abstract

Imaging of biologically significant molecules using plasmons of Metal Nanoparticles (MNPs) is gaining attention in the research community. Localized Surface Plasmon Resonance (LSPR) is the coherent oscillation of conduction electrons of MNPs. The biologically significant molecule is labeled with the fluorophore molecule to get the image. This approach is widely used in clinical practices, however, low intensity light emission from the labeled molecule makes it difficult to image the biologically significant material. One way to improve the weak intensities of fluorophore is to enhance the brightness using a process called Metal Enhanced Photoluminescence (MEP). This phenomenon occurs in the close vicinity of MNPs. Most of the studies in this regard have been carried out using chemically synthesized MNPs of different crystallinity, sizes and shapes. One problem with this approach is the possibility of direct chemical interaction between the fluorophore and MNPs that results in quenching of the Photoluminescence (PL) intensity.

In this dissertation we adopted the approach to enhance the PL of different fluorophore molecules/materials by exploiting the LSPR of embedded noble MNPs. Noble MNPs (Au, Ag, Cu) are widely used because the LSPR resonant frequency falls in the visible region of the electromagnetic spectrum that closely overlaps with the excitation frequency of the fluorophore that are used for biological imaging. We tested our approach using Coumarin (C 515) dye and lead halide perovskites, CsPbX3 (X = Cl, Br, and I) and successfully enhanced PL intensity. Moreover, lead halide perovskites have several optoelectronics applications that make them fluorophore of interest.

In this dissertation, embedded Silver Nanoparticles (Ag NPs) were synthesized via low energy ion implantation within a few nanometers below the surface of quartz substrates. Ion implantation was carried out with different ion beam fluences and 70 keV ion beam energy. Rutherford Backscattering Spectrometry (RBS) measurements were used to obtain the depth profile and concentration of silver within the quartz substrate. The formation of Ag NPs is characterized by UV/Visible spectroscopy measurements. LSPR peaks of Ag NPs were observed with respect to different fluences that confirmed the formation of embedded Ag NPs. An increase in the size distribution of Ag NPs was observed as the fluence of Ag within the substrate increased. Size increase of Ag NPs was confirmed by the broadening as well as the red-shift of LSPR peaks.

Steady-state excitation and emission measurements of C 515, CsPbI3, CsPbBrI2, and CsPbBr3 were carried out to see the effect of embedded Ag NPs on the PL properties of fluorophores. An increase in the PL intensity of C 515, CsPbI3, and CsPbBrI2 was observed with the increase in fluences, giving maxima of 2.1, 3.6, and 5.9 times the PL intensity enhancement. The observed PL enhancement was attributed to a combination of plasmon enhancement with larger Ag NPs and increased plasmonic hot spots. In addition, PL quenching was also observed in case of the CsPbBr3 perovskite nanocomposites with the quenching corresponding to the non-radiative energy transfer from CsPbBr3 perovskite to silver nanoparticles.

Access Setting

Dissertation-Open Access

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Physics Commons

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