Abstract
We investigate the exciton emission in 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) thin films and PTCDA/aluminium-tris-hydroxyqinoline $(\mathrm{Al}{\mathrm{q}}_{3})$ multilayers by photoluminescence spectroscopy in the temperature range from $10\phantom{\rule{0.5em}{0ex}}\text{to}\phantom{\rule{0.5em}{0ex}}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The films are grown by organic molecular beam deposition on Si(001) and Pyrex™ substrates at high vacuum. The obtained temperature dependence of the different recombination channels arising from indirect Frenkel excitons, charge transfer excitons, excimers, and relaxed excited monomers is compared to the recombination channels in single PTCDA crystals. A strong recombination band is observed at $1.63\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in $\mathrm{PTCDA}∕\mathrm{Al}{\mathrm{q}}_{3}$ multilayers. This emission band is attributed to charge transfer transitions between stacked PTCDA molecules that are compressed by strain fields within the PTCDA layers. This assignment is supported by strain-dependent photoluminescence measurements on pure PTCDA films.
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