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Fluorescence quenching and excitation transfer between semiconducting and metallic organic layers

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By modeling diffusion-controlled exciton energy transfer to atoms at the interface or surface of rare gas films it is shown that about 10% of the available light flux can be funneled to a coverage of the order of 1/100 of a monolayer. Analytical expressions for the transfer efficiency with respect to absorption coefficient, diffusion length, boundary condition, and the linear range of detection probability are presented and applied to F atoms in a Kr/Ar interface. Transfer efficiencies, exciton diffusion lengths and densities are derived from the measured spectral and thickness dependences of the Kr2* and Kr2F fluorescence. This system provides nearly optimal parameters, and the potential for penetration depth measurements of atoms is illustrated.

Penetration depths of atoms with kinetic energy provided by photodissociation of parent molecules in the top layer of a multilayer sample are determined from the probability to cross a spacer layer of thickness d and to arrive at the interface to a substrate. Top layer growth up to a final thickness s corresponds to a continuous increase of the effective spacer layer thickness. Modeling of growth and comparison with sample-to-sample variation of d allows us to determine separately and in a consistent way the precursors’ dissociation cross section q⋅σ and the mean penetration depth d0 of the fragments together with elimination of contaminated samples. For F atoms with 4.3 eV kinetic energy from F2 dissociation values of q⋅σ=3×10−17 cm2 and d0=2.1 nm (8 to 9 monolayers) are derived for Ar spacers. A strong increase of d0 in the case of unintentional multistep excitation of F fragments is demonstrated.