Powerful optical spectroscopic and imaging tools have revolutionized many areas of science and technology. The detection sensitivity and chemical specificity are two major considerations when characterizing an optical technique. The fluorescence spectroscopy and microscopy provide excellent sensitivity down to single molecules. However, its reliance on probing the electronic transition limits the obtainable chemical information. In contrast, vibrational spectroscopy such as Raman scattering provides exquisite chemical specificity about the molecular structure, dynamics, and coupling with the environment. However, Raman scattering is intrinsically weak, and its cross sections are many orders of magnitudes smaller than those of fluorescence. The efforts that trying to bridge these two powerful methods can be traced back to the 1980s. But it was until our attempt in 2019, by carefully tuning the electronic pre-resonance and optimizing the excitation duration, the first successful Raman-featured fluorescence spectroscopy was demonstrated. This hybrid technique was named as stimulated Raman excited fluorescence (SREF). As expected, SREF combines both high sensitivity and exquisite chemical specificity, which enables the first all-far-field single-molecule Raman spectroscopy and imaging. This thesis is trying to provide a comprehensive interpretation of SREF, and at the same time serves as a practical guide for experiments and instrumentation. In chapter 1, the early (unsuccessful) attempts for SREF spectroscopy are reviewed. Additionally, I briefly summarize the basic theory for single- and multi-photon excitation process of a single fluorophore, from which the feasibility of SREF spectroscopy is explained. Chapter 2 is mainly focused on the instrumental details of the first successful SREF spectroscopy, and the basic spectroscopic features of SREF are summarized. The generality of SREF spectroscopy is systematically discussed in Chapter 3, and a rule-of-thumb criterion for successful SREF excitation based on the simple two-beam excitation strategy is proposed. Aimed at background-free SREF microscopy, a three-beam system based on nonlinear fiber optics and lock-in detection is illustrated in Chapter 4. In chapter 5, the first attempt to combine SREF and the stimulated emission depletion (STED) for an all-far-field super-resolution vibrational imaging is proposed. At last, as a simple application of SREF microscopy, SREF-based vibrational Stark spectroscopy on visualizing the electrostatic field at the water-oil interface of microdroplets is discussed(Chapter 6).

Traps are ubiquitously present in semiconductors. Their presence results in ineffective charge transport and thus limited the device performance. For organic semiconductors, traps can present intrinsically via structural disorder or extrinsically during synthesis or device fabrication. A thorough understanding of traps is important to optimize the device performance and material design. This thesis employs two trap measurement techniques, photothermal deflection spectroscopy (PDS) and thermal admittance spectroscopy (TAS), to investigate the trap density in the materials. The subgap optical absorptions of several high performance bulk-heterojunction (BHJ) systems for organic solar cells have been studied by PDS. The charge transfer (CT) states are, in particular, looked into detail. CT states are intermediate bound electron-hole pairs at the donor/acceptor (D/A) interface of an organic solar cell. The dynamics and energetics of CT states are crucial to free charge generation and recombination processes. With the help of PDS and external quantum efficiency (EQE) measurements, the CT states the delocalized CT states (hot) from the localized CT states (cold) are observed and differentiated directly. It is discovered that the localized CT states are more pronounced when the acceptor concentration reaches its percolation limit. As the acceptor concentration reaches its optimized composition, the intensity of these CT states is significantly reduced due to the reduced recombination. Using the CT energies measured from PDS, the open-circuit voltage losses from the BHJs are determined. Besides PDS, thermal admittance spectroscopy (TAS) is employed as an alternative method to measure the trap densities. TAS measures the frequency dependent capacitance response of a semiconductor under a small ac signal excitation. This technique is useful to measure the trap depth and trap density of a semiconductor. The defect profiles in two classes of materials are investigated, they are perovskite compounds and an organic hole transporter with an intentional dopant. The trap density are determined by TAS is compared with that obtained by PDS.

No description available.

A magnetic resonance imaging (MRI) compatible near infrared spectrometer (NIRS) system was developed and evaluated for continuous-wave diffuse optical spectroscopy (DOS) and concurrent functional MRI measurements of human muscle. Phantom and in-vivo experiments using the system’s fiber bundle suggested that an isolation distance greater than 8 mm needs to exist between adjacent illumination-detection channels. Using single and probe-pair arrangements (inter-fiber separations of 80 µm and 5 mm, respectively), in-vivo DOS point-measurements (total=20 images) were performed on 1) the antecubital vein and a reference tissue area and 2) the lower leg at the medial (MG) and lateral gastrocnemius (LG) under isokinetic exercise. Mean spectral morphological differences and relative mean intensity changes at Hemoglobin key wavelengths were found, namely reduced mean pixel intensity (~30%) for the vessel-area and a signal change of ~1-4% between the rest and the recovery condition at both muscle locations for the single-probe configuration. Subsequent work is necessary to evaluate the oxygenation assessment capabilities of this system. Lastly, experiments were performed in which two volunteers had concurrent measurement of optical and blood oxygen level dependent (BOLD) MRI, before and following exercise. The same probe arrangement was used for DOS measurements for this experiment. The BOLD signal was studied for manually-derived ROIs. BOLD recovery curves corresponding to the LG followed routine temporal progression where immediate post-exercise signal is hypointense, followed with a sigmoidal-shaped recovery. A decrease ranging between ~0.1-20% was found in the normalized mean spectral signal (20 images) for recovery with reference to the rest condition at both muscle locations for single-probe measurements and for one probe-pair measurement (for 800,808 and 850 nm). The specific trend of the measured decrease in the mean spectral curves during recovery was not consistent among these trials. Future steps include repeatable phantom experiments, increased optical power delivery, enhanced skin contact and improved reflectance measurements / Thesis / Master of Applied Science (MASc)

Analytical as well as fundamental measurements were performed with an inductively coupled plasma (ICP) using the novel technique of cavity ringdown spectroscopy. A newly designed ICP torch was presented. Limits of detection were measured for elemental mercury, both in an ICP as well as in a cold mercury chemical generator. The efficiency of the technique was compared with laser-induced fluorescence (LIF) in the ICP. Isotopically resolved spectra of uranium were collected with this technique and results were compared to previous studies using LIF. Gas temperature and electron density estimations were done by lineshape measurements on lead atoms in the ICP. Abel inversion technique was used to extract absolute atom densities and ringdown proved to be an excellent candidate for trace detection when coupled with an atomization source. Spectra of hydroxyl radical coming from dissociation of water molecules in air were recorded and OH density was estimated. The plasma was found to be in local thermal equilibrium by comparing simulated and measured OH emission spectra. Future developments of cavity ringdown with ICP using continuous-wave lasers are discussed.

No description available.

No / Spectroscopic techniques have the potential to provide powerful, molecular-specific, non-invasive measurements on polymers during melt processing operations. An exploration is reported of the application and assessment of sensitivity of in-process vibrational spectroscopy¿on-line mid-infrared (MIR), on-line near-infrared (NIR), in-line NIR and in-line Raman¿for monitoring of single screw extrusion of high-density polyethylene and polypropylene blends. These vibrational spectroscopic techniques are compared with novel in-line ultrasound velocity measurements, which were acquired simultaneously, to assess the sensitivity of each method to changes in blend composition and to explore the suitability for their use in real time process monitoring and control.

Doctor of Philosophy / Department of Chemistry / Viktor Chikan / Ever depleting sources of fossil fuel has triggered more research in the field of alternate sources of energy. Over the past few years, CdSe nanoparticles have emerged as a material with a great potential for optoelectronic applications because of its easy exciton generation and charge separation. Electronic properties of CdSe nanoparticles are highly dependent on their size, shape and electronic environment. The main focus of this research is to explore the effect of different electronic environments on various spectroscopic properties of CdSe nanoparticles and link this to solar cell performance. To attain that goal, CdSe quantum dots (QDs) and nanorods (NRs) have been synthesized and either doped with metal dopants or embedded in polymer matrices. Electronic properties of these nanocomposites have been studied using several spectroscopic techniques such as absorption, photoluminescence, time-resolved photoluminescence, confocal microscopy and wide field microscopy. Indium and tin are the two metal dopants that have been used in the past to study the effect of doping on conductivity of CdSe QDs. Based on the photoluminescence quenching experiments, photoluminescence of both indium and tin doped samples suggest that they behave as n-type semiconductors. A comparison between theoretical and experimental data suggests that energy levels of indium doped and tin doped QDs are 280 meV and 100 meV lower than that of the lowest level of conduction band respectively. CdSe nanorods embedded in two different polymer matrices have been investigated using wide field fluorescence microscopy and confocal microscopy. The data reveals significant enhancement in bandedge luminescence of NRs in the vicinity of a conjugated polymer such as P3HT. Photoactive charge transfer from polymers to the surface traps of NRs may account for the observed behavior. Further study shows anti-correlation between bandedge and trap state emission of CdSe NRs. A recombination model has been proposed to explain the results. The origin of traps is also investigated and plausible explanations are drawn from the acquired data.

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LD2668 .T4 1948 C65 / Master of Science