Quenching of luminescence by non-radiative tunnelling

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Abstract
In semiconductors at low temperatures, where thermal ionization is unlikely, the tunnelling of a carrier away from radiative centres (density p r) to non-radiative centres (density p n) provides an alternative luminescence quenching mechanism to thermal excitation into the band. It is argued that this may be a common quenching process in a variety of solid and liquid systems. When p r ≪ p n, an upper limit to the luminescence efficiency is given by a nearest-neighbour approximation. A lower limit is derived by a new many-neighbour approximation, and this is shown to be close to the exact value found by a Monte-Carlo simulation. The efficiency has also been calculated as p r approaches p n in the nearest-neighbour approximation, and it is shown to depend increasingly on tunnelling between nearest-neighbour radiative pairs.