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This dissertation studies the size- and site-dependent optical and magnetic properties of II-VI quantum dots (QDs). The first chapter provides a theoretical background used to analyze the data and the properties expected for diluted magnetic semiconductor materials at the nanoscale. The second chapter probes the size-dependent magnetic properties for Mn doped CdSe QDs. The Curie-Weiss law plots show significant size-dependent carrier concentration in the QDs. The carriers inside the small QDs can mediate the Mn(II)-Mn(II) ferromagnetic interaction by the RKKY model, which helps explain reasons for the observation of a superparamagnetism (SPM) in small Mn:CdSe QDs. The third chapter involves high frequency EPR analysis of possible dopant (Mn(II) ions) sites in CdSe lattice. Surface doped Mn:CdSe QDs and stochastically doped Mn:CdSe QDs were successfully made by traditional thermal decomposition of cluster and microwave irradiation. Two sets of hyperfine splitting were observed for stochastically doped Mn:CdSe QDs from EPR spectra and the ratio of the signal has liner relationship with the surface to volume ratio of QDs. One set of hyperfine splitting can be removed by surface acid treatment enabled us to identify the Mn(II) sites on the surface or core position of Mn:CdSe QDs. The fourth chapter is a study of chromium incorporation in ZnSe QDs by single cubic source precursor method. The formation of ZnCr2Se4 spinel structure was approved by XANES, and 4A2g to 4T2g transition of Cr (III) ion in absorption spectra.
A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
Geoffrey F. Strouse, Professor Directing Dissertation; Peng Xiong, University Representative; Naresh Dalal, Committee Member; Albert E. Stiegman, Committee Member.
Florida State University
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