NMR Studies of Optically Active Impurities under In Situ Illumination

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This is a renewal award to a senior professor at Oregon State University for a project that will exploit the local, chemically specific properties of nuclear magnetic resonance (NMR) to investigate the microscopic properties of optically active impurities in semiconductors and insulators. Solid-state NMR techniques will be combined with in situ illumination to examine the effects of optical excitation on the electronic structure and local atomic arrangements associated with specific impurities. Particular attention will be given to bistable impurities such as Ga or In in CdTe and other II-VI compounds as well as CdF2. Optically enhanced host (113Cd, 125Te, and 19F) nuclear spin-lattice relaxation will be used as an indicator of conversion of the bistable impurities to conventional effective mass donors. Impurity species NMR, especially 69Ga, will be used in combination with in situ illumination to search for direct evidence of structural rearrangements in the impurity ground state. Impurity species NMR (69Ga and 63Cu) will also be used to study the local environments of active centers in phosphors such as SrS(Cu,M) and ZnS(Mn, Ga). The goal is to elucidate a microscopic understanding of these impurities that will facilitate the engineering of this class of material for specific electronic and optical applications. The proposed experiments will provide a venue for Ph.D. and M.S. graduate education and undergraduate research opportunities; they will also be exploited for enrichment of undergraduate courses in Modern Physics and Solid State Physics in the form of projects and demonstrations.%%%The controlled introduction of specific impurities is critical in determining the properties of technologically important electronic and optical materials. This renewal award to a senior professor at Oregon State University is for research that will focus on a class of impurities that are optically-active. Such impurities change their atomic-scale properties when illuminated or emit light when subject to illumination or electric currents in the host material. The applications of these materials include light emitting elements for flat panel displays and optical data storage. Nuclear magnetic resonance (NMR) is a spectroscopy that reveals atomic-scale details of the environments of specific chemical elements in a material. In this research, NMR will be used to probe the effects of illumination on host atom environments, say Cd in CdTe or CdF2, or impurities such as Ga in these materials and in phosphors being developed for flat panel displays. The goal of this and related research is to reach a level of microscopic understanding that will facilitate the engineering of this class of material for specific electronic and optical applications. The proposed research will be integrated into undergraduate and graduate education. Ph.D. and thesis research will train graduates for entry into U.S. high technology industry. Undergraduates will participate in undergraduate research and through enrichment (projects and demonstrations) of formal courses in Modern Physics and Solid State Physics at Oregon State University.***