Control of the radiative properties of functional molecules near metals is a key issue in nano-optics, and is particularly important in the fields of energy transfer and light manipulation at the nanoscale1,2 and the development of plasmonic devices3,4,5. Despite the various vibronic transitions (S1(v′) → S0(v)) available for frequency tuning of fluorescence, the molecular emissions near metals reported to date have been subject to Kasha's rule, with radiative decay from the lowest excited state (S1(0)) (refs 6–10). Here, we show resonant hot electroluminescence arising directly from higher vibronic levels of the singlet excited state (S1(v′ > 0)) for porphyrin molecules confined inside a nanocavity in a scanning tunnelling microscope, by spectrally tuning the frequency of plasmons. We also demonstrate the generation of unexpected upconversion electroluminescence. These observations suggest that the local nanocavity plasmons behave like a strong coherent optical source with tunable energy, and can be used to actively control the radiative channels of molecular emitters by means of intense resonance enhancement of both excitation and emission.
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The authors acknowledge discussions with B. Wang and X.P. Wang, and support from the National Basic Research Program of China (grant nos 2006CB922003 and 2010CB923300), the Chinese Academy of Sciences (grant no. KJCX2.YW.H06) and the Natural Science Foundation of China (grant nos 10574117 and 10974186).
The authors declare no competing financial interests.
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Dong, Z., Zhang, X., Gao, H. et al. Generation of molecular hot electroluminescence by resonant nanocavity plasmons. Nature Photon 4, 50–54 (2010) doi:10.1038/nphoton.2009.257
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