Picosecond near-field microspectroscopic study of a single anthracene microcrystal in evaporated anthracene-tetracene film: Inhomogeneous inner structure and growth mechanism

Topographies, fluorescence images, fluorescence spectra, and fluorescence decay curves of anthracene-tetracene two-component evaporated films were observed by ps near-field fluorescence microspectroscopy. Individual anthracene microcrystals were formed on tetracene microcrystalline films, although layer-on-layer film was expected. It is interesting to note that the central part of individual anthracene microcrystals shows intense tetracene monomer fluorescence, while edge parts give relatively weak fluorescence. This means that energy transfer from anthracene to tetracene took place more preferably in the central part of the anthracene crystal than in the surrounding area. This inhomogeneity cannot be simply explained as an energy transfer at interface between anthracene and tetracene crystals. The characteristic position dependence of energy transfer dynamics implied special crystal growth and molecular diffusion mechanisms under the present sample preparation.