Dual emission in doped core-shell nanocrystals

Daniel R. Gamelin, University of Washington, DMR 0906814

We are developing new intermediate-gap doped semiconductor nanocrystals with unique electronic, magnetic, and magneto-optical properties. Recently, we discovered a new effect ("exciton storage by Mn2+"):• In wide-gap ZnMnSe quantum

dots, excitonic emission is quenched by fast energy transfer to excited dopant states.

• Narrowing the energy gap between excitonic and excited dopant states by growth of narrower-gap ZnCdSe shells allows thermally assisted back energy transfer, producing excitonic emission again. The ratio of the two emission peaks is highly temperature dependent, making these nanocrystals sensitive optical probes of temperature.

TEM image and schematic illustration of a core-shell QD

Temperature-dependent emission of core/shell QDs. The photographs show these QDs under UV irradiation at two different temperatures.

Schematic of the electronic structure leading to exciton storage. After excitation (hn), the excited state population evolves via various kinetic processes, denoted by their rate constants, k. Tthe Boltzmann population distribution is depicted to the right.

Article DOI: 10.1021/nl102135k

This research is being conducted by University of Washington graduate and undergraduate students collaborating with researchers from Germany, Canada, and the Netherlands. Participating students are learing skills that transcend the traditional borders of chemistry, physics, and materials science.

The picture at left shows undergraduate Rob Johns and graduate student Vlad Vlaskin preparing to analyze the temperature dependence of recently synthesized dual-emitting nanoparticles by luminescence spectroscopy.

Dual emission in doped core-shell nanocrystals

Daniel R. Gamelin, University of Washington, DMR 0906814