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NNSE618-L17-emission

NNSE618-L17-emission - 1 Lecture contents Emission and...

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NNSE 618 Lecture #17 1 Lecture contents Emission and luminescence Band-to-band Recombination processes Exciton Donor-acceptor
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NNSE 618 Lecture #17 2 For two non-degenerate levels Emission and absorption We have seen previously the relationship between absorption and stimulated emission : Matrix elements for these transitions are exactly the same Both processes are proportional to the strength of the optical field Both treat radiation classically Spontaneous emission requires quantum mechanical treatment of e-m waves (photons) Einstein coefficients A and B describe spontaneous emission and absorption/stimulated emission: Total emission rate With photon energy density [Js/cm 3 ] And total emission rate (sum of spontaneous and stimulated emission: A and B coefficients are related: 21 3 3 2 21 8 B h c n A r  12 21 B B Density of electromagnetic modes [s/cm 3 ] 21 21 21 B A R N A A B A R 1 1 21 21 21 21 21 Energy density of electromagnetic modes [Js/cm 3 ] Photon occupation number [dimensionless]
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NNSE 618 Lecture #17 3 Imaginary part of refractive index and the emission rate R cv of pure Ge at 300 K (intraband process can change the spectra) Emission and absorption Low electromagnetic field no stimulated emission.
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