Spatial Organization of GaSe Quantum Dots: Organic/Semiconductor Liquid Crystals

Mixed liquid crystals consisting of the smectic-A phase of 8CB and 8 nm GaSe nanoparticles have been formed and studied using static and time-resolved optical polarization spectroscopy. The mixtures consist mostly of 8CB, with a small volume fraction of the nanoparticles. Polarized absorption spectra indicate that the nanoparticles are highly aligned in the liquid crystal environment. The absorption and fluorescence spectra suggest that GaSe nanoparticles in 8CB form aggregates having two distinct types of domains. Most of the nanoparticles are in domains in which there are weak interactions between adjacent nanoparticles. A small fraction are in strongly coupled domains in which adjacent nanoparticles have about 1600 cm -1 interaction energies. Because of facile energy transfer, the fluorescence spectrum is dominated by the strongly coupled domains. Energy transfer from the weakly to the strongly interacting domains occurs within about 30 ps. Subsequent relaxation within the strongly interacting domains occurs on the 3 ns time scale.