Exciton emission in PTCDA films andPTCDA∕Alq3multilayers

Abstract

We investigate the exciton emission in 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) thin films and PTCDA/aluminium-tris-hydroxyqinoline ͑Alq 3 ͒ multilayers by photoluminescence spectroscopy in the temperature range from 10 to 300 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 eV in PTCDA/ Alq 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.

Modified charge-transfer emission in perylene tetracarboxylic dianhydride-aluminum quinoline layer structures

“…These band assignments have been supported in recent straindependent PL studies on ␣-PTCDA single crystals 23 and on crystalline PTCDA films. 24 In this work, we extend our studies to PTCDA/ Alq 3 multilayers and to codeposited films using temperaturedependent PL spectroscopy, x-ray diffraction, and Fourier transform infrared ͑FTIR͒ spectroscopy. Since our investiga-tions are focused on intrinsic film properties, the films are prepared on weakly interacting Si substrate with natural oxide surface.…”

“…The deposition rate was measured using a calibrated quartz crystal thickness monitor. 24 Typical deposition rates from the effusion cells are 0.01 nm/ s at temperatures of 320 and 230°C for the PTCDA and Alq 3 , respectively. For the codeposition sample at a PTCDA: Alq 3 ratio of 10: 1 ͑sample: Co-10͒, the deposition rate for Alq 3 was reduced by a factor of 10 by decreasing the evaporation cell temperature.…”

Effects of high pressure on the photoluminescence transitions of excitons in α‐PTCDA (perylene tetracarboxylic dianhydride) crystals

“…The low energy band at 1.68 eV, labeled CT2, corresponds to a relaxed charge transfer exciton transition between stacked molecules in different unit cells. Finally, the high energy band at 1.95 eV was recently assigned to CT2-nr, the transition of an analogous non-relaxed state of the CT2 charge transfer exciton [14].…”

“…At 8.2 kbar a high energy shoulder becomes visible, emerging in the 2.0 -2.1 eV region as the main peak shifts more rapidly out of this region. The most likely assignment for this shoulder is the isolated monomer transition observed as a fast decaying (~3 ns) component contributing to the high-energy wing of the 1 atm emission spectrum [7,8,14]. The monomer transition originates mainly from a PTCDA molecule within a randomized surroundings as e.g.…”

Vibronic spectra of charge transfer excitons and of mixed charge transfer and Frenkel excitons

“…The lowest electronic excitations of both crystals exhibit the mixed nature of FEs and CTEs states [6,9]. Thus their excitonic and vibronic spectra investigated in absorption, photoluminescence, and electronic energy-loss spectroscopy have been extensively studied [10][11][12][13][14]. Our theoretical treatment is directed to establish connections between absorption spectra and exciton-phonon coupling in charge transfer crystals.…”