Optical and Electro-Optic Properties of Transition Metal Dichalcogenide and Inorganic Perovskite Nanomaterials
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The study of semiconductor nanocrystals and quantum dots with controlled size and shape offers a unique platform to study the effects of morphological and structural asymmetries, as well as quantum confinement on the optical properties of semiconductors. In the first part of this work we will study the asymmetric optical, vibrational, and electro-optic properties in transition metal dichalcogenide (TMDC) nanodiscs, resulting from the strong asymmetry in the crystal structure. The second part of this work will focus on the carrier dynamics in perovskite quantum dots and doped nanoparticles, materials currently being investigated for next generation optical and opto-electronic devices. In both material systems we will rely on the use of steady state and time resolved absorption spectroscopy to study carrier dynamics and vibrational properties, as well as electro-optic studies to probe the electronic properties in these novel semiconductor systems. The effects of anisotropy are observed in the optical and electronic properties in the TMDC nanodiscs. In laterally confined TMDC nanodiscs, photoexcited charge carriers couple preferentially to the anisotropic in-plain phonons, and the carrier relaxation, band transport, and charge transfer properties are affected by the anisotropy of the material. The effect of anisotropy can also be observed in the macroscopic properties, including the electronic coupling between nanodiscs in stacked assemblies, and the anisotropy of electronic properties such as the induced dipole moment. The carrier dynamics in perovskite quantum dots and doped nanoparticles were studied via time resolved absorption and photoluminescence. In the Mn^2+ doped CsPbClv3 nanoparticles, the exciton-Mn energy transfer time was extracted (~300ps), roughly twice as long compared with Mn^2+ doped CdSe suggesting weaker exciton-Mn exchange coupling. Taking advantage of recently developed synthetic protocol for the preparation of highly monodispersed CsPbBrv3 quantum dots, we studied confinement induced carrier dynamics. The turning on of formally forbidden transitions due to broken optical selection rules after photo excitation was observed in confined CsPbBrv3 quantum dots, resulting from the formation of a dipole moment in the presence of electron-hole pairs.
Rossi, Daniel Peyton (2018). Optical and Electro-Optic Properties of Transition Metal Dichalcogenide and Inorganic Perovskite Nanomaterials. Doctoral dissertation, Texas A & M University. Available electronically from