DOI: https://doi.org/10.29363/nanoge.incnc.2021.025
Publication date: 8th June 2021
Materials displaying electron photoemission under visible-light excitation are of great interest for applications in advanced electron beam sources, free electron lasers, electron microscopy, and photochemistry. We demonstrate that using CdSe colloidal quantum dots (CQDs) heavily doped with manganese (Mn) [1], we can realize highly efficient electron photoemission under excitation with visible-light pulses. This effect is enabled by extremely fast (<300 femtoseconds) spin-exchange Auger energy transfer from excited Mn ions to an intrinsic CQD exciton [2]. Since the rate of this process outpaces that of intra-band cooling, the high-energy ‘hot’ electron produced by the first Auger-excitation step can be efficiently promoted further into the external ‘vacuum’ state via one more Mn-to-CQD energy-transfer step. This CQD ionization pathway exploits exceptionally large up-hill energy gain rates associated with the spin-exchange Auger process (>10 eV ps-1) and leads to photoemission efficiencies of more than 3%, orders of magnitude greater than in the case of undoped CQDs. High photoelectron yields along with extremely short timescales of spin-exchange Auger ionization could enable ultrabright sources of sub-picosecond electron pulses with unprecedented current densities of tens of kiloamperes per cm2. In addition to photocathodes, other prospective uses of this phenomenon include advanced hot-carrier photovoltaics, ‘high-energy’ photochemistry, and ultrafast photodetectors enabled by long-range hot-electron transport.
These studies were supported by the Solar Photochemistry Program of the Chemical Sciences, Biosciences and Geosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.
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