Bradshaw, Hauser, McLaurin , Gamelin J . Phys. Chem. C 2012 , 116 , 9300

1. Luminescence Saturation via Mn2+−Exciton Cross Relaxation in Colloidal Doped Semiconductor NanocrystalsDaniel R. Gamelin, University of Washington, DMR 0906814 Mn2+ doped wide-gap semiconductors are the extremely efficient phosphors used in the first thin-film electroluminescent devices. Their nanoscale counterparts have attracted recent attention related to modern photonic devices. Our research into doped semiconductor nanocrystals has revealed new properties having no counterpart in the corresponding bulk materials. One effect that becomes prominent at the nanoscale is rapid (picosecond) cross-relaxation between excited-state Mn2+ ions and semiconductor excitons. Our time-resolved photoluminescence measurements and kinetic modeling indicate that this effect completely overwhelms the slower (microsecond) processes responsible for luminescence saturation in bulk materials, likely due to longer exciton lifetimes and increased Mn2+-semiconductor exchange coupling in nanocrystals. Detailed understanding of such processes is crucial to implementing nanophotonics applications (including imaging) involving even modest-power excitation schemes. A C B (A) Power saturation of Mn2+ photoluminescence. (B) Mn2+:ZnSe quantum dots under UV irradiation. (C) A schematic of the cross-relaxation mechanism responsible for luminescence saturation in nanocrystals. Bradshaw, Hauser, McLaurin, Gamelin J. Phys. Chem. C 2012, 116, 9300

2. Luminescence Saturation via Mn2+−Exciton Cross Relaxation in Colloidal Doped Semiconductor NanocrystalsDaniel R. Gamelin, University of Washington, DMR 0906814 The discovery and understanding of low-power luminescence saturation in Mn2+-doped semiconductor nanocrystals has drawn attention to the exceptional suitability of these materials for application in new super-resolution optical imaging technologies based on nonlinear response to excitation modulation. These results also directly impact the continuing interest in these materials for solar, display, or lighting applications. This work is the product of international collaboration, including hosting Prof. Andreas Hauser on sabbatical leave from the University of Geneva, Switzerland. This work has been presented at numerous national and international conferences. Locally, researchers on this project were active in Seattle-area high-school outreach programs that demonstrated the roles of chemistry in new energy technologies.