Exploration of Excitonic States in Dilute Magnetic Organic Semiconductors

The electronic and excitonic properties of mixed dilute metal/metal-free phthalocyanine crystalline thin films are explored. The immediate focus is on molecular systems containing Cobalt and Copper phthalocyanines in ratios to the metal-free phthalocyanines ranging from 1:1 to 1:10. The molecular thin films samples are deposited using a novel hollow pen-writing technique\footnote{R. Headrick et al, APL 92 063302 (2008)} that produce millimeter sized grains with long range macroscopic order. Electronic and excitonic states are investigated using temperature dependent absorption/transmission and photoluminescence spectroscopy. All optical characterization indicates a very uniform mixing of the species is achieved in films without loss of long range order previously observed in individual species. At low temperatures, a novel high energy state is observed. Its intensity is directly related to the ratio of metal to metal-free Phthalocyanine. In addition, a unique linear dichroism mapping is performed on these thin film samples, giving insight into electronic states both close to and far from grain boundaries.