Light Emission from Nanostructures

PROGRESS IN LIGHT EMISSION FROM SILICON NANOSTRUCTURES... 

Romero, D. B., Schaer, M., Staehli, J. L., and Zuppiroli, L., Blue light-emission from a nanostructured organic polymer semiconductor. Solid State Commun., 95, 185-189... 

Figure 9.1 Four major mechanisms for light emission in a scanning tunneling microscope. (a) Injection of minority carriers from the tip into an unoccupied band of a doped semiconductor leading to carrier diffusion and radiative recombination, (b) Surface plasmon mediated emission. Hot carrier injection into a metal leads to radiative decay of a tip-induced surface plasmon. (c) Direct dipole radiation. The transition from tip to substrate results in a direct dipole that can emit light, (d) An absorbed molecule or nanostructure accepts opposite carriers into its states leading to radiative recombination on the molecule.

The last section revealed that semiconductor band gaps for nanostructures vary with the size of the structure. The wavelength of light emitted when an electron in the conductance band returns to the valence band will therefore also vary. Thus, different colour fluorescence emission can be obtained from different-sized particles of the same substance (e.g., different sized quantum dots of CdSe irradiated with UV emit different colours of light). To produce fluorescence, light of greater photon energy than the band gap is shone onto the nanocrystal. An electron is excited to a... 

Metal nanostructures can act as small antennas that aid in the reception and broadcasting (absorption and emission) of light from nearby fluorophores. Whether fluorescence enhancement or quenching is observed in a given system is determined by the relative extent of excitation enhancement (increased light absorption), emission enhancement (increased radiative decay), and quenching (increased non-... 

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