PICOSECOND ABSORPTION-SPECTROSCOPY OF SURFACE-MODIFIED COPPER SULFIDENANOCRYSTALS IN POLYMERIC FILM

The transient induced absorption and bleaching are examined in 10 nm s ize CuS nanocrystals embedded in polyvinylalcohol film. Partial surfac e oxidation of CuS nanocrystals produces a new near-IR-absorption band peaked at 1100 nm. The surface oxidized shell is supposed to form a m idgap electron acceptor level and the near-IR band relates to the elec tron transfer from the CuS valence band. The near-IR band is bleached easily by 15 ps pump pulse from YAG:Nd laser (1.08 mu m). The bleachin g is accompanied by the induced absorption at the red side of CuS fund amental edge. Both signals induced decay quickly with the time constan t 65-70 ps. The model is proposed where the electron-hole pair excited by near-IR photon (electron in surface shell and hole inside CuS core ) creates strong internal electric field, which induces the Stark red shift of CuS fundamental edge. (C) 1996 American Institute of Physics.