Interface excitons inKrmNeNclusters: The role of electron affinity in the formation of electronic structure

Abstract

The formation of the electronic structure of small ${\mathrm{Kr}}_{m}$ clusters $(m<~150)$ embedded inside ${\mathrm{Ne}}_{N}$ clusters $(1200<~N<~7500)$ has been investigated with the help of fluorescence excitation spectroscopy using synchrotron radiation. Electronically excited states, assigned to excitons at the Ne/Kr interface, $1i$ and ${1}^{\ensuremath{'}}i$ were observed. The absorption bands, which are related to the lowest spin-orbit split atomic Kr ${}^{3}{P}_{1}$ and ${}^{1}{P}_{1}$ states, initially appear and shift towards lower energy when the krypton cluster size $m$ increases. The characteristic bulk $1t$ and ${1}^{\ensuremath{'}}t$ excitons appear in the spectra when the cluster radius exceeds some critical value ${R}_{\mathrm{cl}}>{\ensuremath{\delta}}_{1i}.$ The ${\mathrm{Kr}}_{m}$ clusters comprising up to 70 atoms do not exhibit bulk absorption bands. We suggest that this is due to the penetration of the interface excitons into the krypton cluster volume, because of the negative electron affinity of surrounding Ne atoms. From the energy shift of the interface absorption bands with cluster size an unexpectedly large penetration depth of ${\ensuremath{\delta}}_{1i}=7.0\ifmmode\pm\else\textpm\fi{}0.1\AA{}$ is estimated, which can be explained by the interplay between the electron affinities of the guest and the host cluster.