This thesis contains optical investigations on 3,4,9,10 perylene tetracarboxylic dianhydride (PTCDA) and tris (8-hydroxy) quinoline aluminum (Alq3) films as well as on PTCDA/Alq3 multilayers and co-deposited films. The organic layers are grown on Si and Pyrex substrates using the technique of organic molecular beam deposition (OMBD). In temperature dependent (10 - 300 K) transmission measurements the exciton absorption in PTCDA⁄Alq3 multilayers and co-deposited films is shifted to higher energies with respect to the pure PTCDA films. In comparison with a recently developed theoretical model for α PTCDA the observed energy shift is explained by Coulomb screening.
In strain dependent photoluminescence (PL) measurements of PTCDA film uniaxial pressure is applied along the molecular stacking direction using a specially designed pressure cell. With increasing pressure exciton emission channels are shifted to lower energy and the integrated PL intensity is quenched. When the pressure is released, the PL spectrum and the total PL intensity partially recover, indicating a reversibility of the strain effects to a large extent. The experimental results are compared with recent total energy calculations.
The assignment of different emission channels in PTCDA single crystals and polycrystalline films is validated by photoluminescence excitation studies. From the excitation energy dependence of the spectral position of different emission bands the transition energies of free and self trapped excitons are deduced. The obtained transition energies are compared with theoretically predicted values.
The anisotropy of the refractive index in PTCDA waveguides is investigated using the m-line technique. The observed effective refractive index values of TE and TM modes are used to determine the waveguide thickness as well as the inplane and perpendicular bulk refractive index values.
The recombination dynamics of excitonic states in thin Alq3 films is studied using temperature and time resolved PL measurements. The experimental results indicate that the PL emission originates from two different trapped states and from thermally activated self trapped exciton states. The density of self trapped exciton states increases with rising temperature explaining the observed PL efficiency increase at temperatures ranging from 10 - 190 K. These interpretations are supported by a simplified coupled rate equation model.