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Scheme of luminescence surface quenching experiment
- Direct comparison of a single layer and a double layer
- Primary processes in single layer:
- Excitation by light into absorbing state a
- Ultrafast relaxation into emitting state e
- Luminescence from e into ground state
- Additional processes in double layer:
- Transfer from a to quencher leads to reduction of initial
luminescence intensity
- Transfer from e to quencher leads to reduction of luminescence life-time
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Streak camera measurements for surface quenching
- Time resolved luminescence spectra can be directly measured
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Decay dynamics for surface quenching
- Decay traces of double layer PTCDA/TiOPc in comparison to single layer PTCDA directly show:
- Reduction of initial luminescence intensity due to quenching of a
- Reduction of life time due to quenching of e
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Luminescence decay of PTCDA in single layer PTCDA and double layer PTCDA/TiOPc.
From [Schüppel et al. 2004], Fig. 2.
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Exciton-exciton annihilation
- At high exciton densities, excitons can diffuse to each other and annihilate. This leads to non-exponential decay
of the exciton population.
- Creation of high exciton densities in pump-probe setup
- Time resolved detection of exciton density by transient absorption in
pump-probe setup
- Experimental decay traces for various initial densities: s. Figure right
- Evaluation by several microscopic annihilation models (3D-diffusion, 1D-diffusion along the stacks,
direct single step Forster-transfer), see [Engel et al. 2006]
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Decay of transient absorption in polycrystalline PTCDA layer for various initial exciton densities.
At high densities, the exciton population decays non-exponentially.
From [Engel et al. 2006], Fig. 3a.
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