Picosecond induced absorption in ultradisperse amorphous selenium particles

A study was made of the induced absorption in amorphous selenium particles (average radius ~20 nm) embedded in a polymer. A picosecond pump and probe technique was used. The change in the absorption was measured in the spectral range 550–750 nm when the pump radiation was in the form of pulses of 15 ps duration and 2.3 eV photon energy. The induced-absorption spectra were attributed to optical exciton–biexciton transitions. The exciton lifetime was estimated to be 424 ± 32 ps.