Minyung Lee

Low-lying electronically excited states of C60 and C70 and measurement of their picosecond transient absorption in solution

Abstract Low-lying electronically excited states of C60 and C70 were identified in picosecond transient absorption measurements extending in wavelength down to 1000 nm. Spectral features in the near-infrared region were found to be significantly different from the results of previous studies. The lifetimes for S1 states of C60 and C70 were determined to be 1.3±0.2 ns and 0.7±0.05 ns, respectively. A simple energy diagram for electronic states of C60 and C70 is presented.

Temperature-dependent photoluminescence study of C60 and C70

Abstract The photoluminescence (PL) spectra of C60 and C70 in toluene, as films on silicon and as KBr pellet, were obtained as a function of temperature. Different emission profiles are observed between the fullerenes in solution and in the solid form. The PL spectra of the C60 solids are similar regardless of their substrates, while those of C70 show different emission profiles between the films on silicon and the pellet, which is believed to be due to the substrate-dependent stacking disorder resulting from the nonspherical shape of the molecule. The changes in emission intensity and profile upon temperature are observed in the PL spectra of solid C60 and C70, suggesting the strong influence of rotational diffusion. The vibrational mode progressions are identified from the low-temperature photoluminescence spectra of C60 and C70.

Temperature and size dependent excitonic relaxation process in GaAs/AlGaAs quantum wells

Abstract Temperature dependent risetimes of exciton luminescence in different size quantum wells are obtained by using time correlated single phonon counting technique. The decreasing rate of risetimes with increasing temperature, the photoluminescence spectra, and the temperature dependent decay times consistently show that excitons are likely to be localized on interface defects as the well size decreases.