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D R Gamelin

Publications and source records attributed to D R Gamelin.

5 recordsLinked to original sources
PubMed2005

Negligible magnetism in excellent structural quality Cr(x)Ti(1-x)O(2) anatase: contrast with high-T(C) ferromagnetism in structurally defective Cr(x)Ti(1-x)O(2).

We reexamine the mechanism of ferromagnetism in doped TiO(2) anatase, using epitaxial Cr:TiO(2) with excellent structural quality as a model system. In contrast to highly oriented but defective Cr:TiO(2) (approximately 0.5 micro(b)/Cr), these structurally superior single crystal films exhibit negligible ferromagnetism. Similar results were obtained for Co:TiO(2). We show for the first time that charge-compensating oxygen vacancies alone, as predicted by F-center mediated exchange, are not sufficient to activate ferromagnetism. Instead, the onset of ferromagnetism correlates with the presence of structural defects.

Journal Article↗
PubMed2001

Electronic absorption spectroscopy of cobalt ions in diluted magnetic semiconductor quantum dots: demonstration of an isocrystalline core/shell synthetic method.

This paper reports the application of ligand-field electronic absorption spectroscopy to probe Co(2+) dopant ions in diluted magnetic semiconductor quantum dots. It is found that standard inverted micelle coprecipitation methods for preparing Co(2+)-doped CdS (Co(2+):CdS) quantum dots yield dopant ions predominantly bound to the nanocrystal surfaces. These Co(2+):CdS nanocrystals are unstable with respect to solvation of surface-bound Co(2+), and time-dependent absorption measurements allow identification of two transient surface-bound intermediates involving solvent-cobalt coordination. Comparison with Co(2+):ZnS quantum dots prepared by the same methods, which show nearly isotropic dopant distribution, indicates that the large mismatch between the ionic radii of Co(2+) (0.74 A) and Cd(2+) (0.97 A) is responsible for exclusion of Co(2+) ions during CdS nanocrystal growth. An isocrystalline core/shell preparative method is developed that allows synthesis of internally doped Co(2+):CdS quantum dots through encapsulation of surface-bound ions beneath additional layers of CdS.

Journal Article↗
PubMed2000

Electronic structure contributions to electron transfer in blue Cu and Cu(A).

The experimentally determined electronic structures of mononuclear blue Cu and binuclear Cu(A) centers are summarized and their relation to intra- and inter-protein electron transfer (ET) kinetics are described. Specific contributions of the electronic structures of these two broad classes of Cu ET proteins to H(AB), lambda, and deltaE degrees are discussed. Also, the role of the protein structure in determining key geometric features which define the electronic structures of the metal sites in these proteins is considered.

Bacterial Proteins↗
PubMed2000

Design of luminescent inorganic materials: new photophysical processes studied by optical spectroscopy.

Recent spectroscopic results in the emerging area of transition-metal NIR-to-visible upconversion are related. The examples of Ti(2+)-, Re(4+)-, and Os(4+)-doped materials showing upconversion illustrate GSA/ESA, GSA/ETU, and photon avalanche multiphoton excitation mechanisms, respectively. Strategies for manipulation of such upconversion processes using the spectroscopic or magnetic properties of the host material are described. High-resolution low-temperature continuous-wave absorption and emission and time-resolved emission experiments combine to yield information about energy splittings, intensities, and excited-state dynamics, and assist in the design and development of luminescent materials showing novel multiphoton excitation properties.

Inorganic Chemicals↗