OPTICAL TRANSIENT BLEACHING AND INDUCED ABSORPTION OF SURFACE-MODIFIED COPPER SULFIDE NANOCRYSTALS

Surface oxidation of CuS nanocrystals leads to the appearance of an ad ditional absorption band in the near infrared. This is attributed to a n energy level in the band gap, 1 eV below the conduction band, with t he character of an electron donor. Bleaching of this additional absorp tion band and induced absorption in both oxidized and unmodified sampl es take place. An energy level scheme for CuS and CuS(ox) nanocrystals with long-lived trap levels in the band gap is proposed. The relaxati on time from the conduction band to these trap levels is similar to 80 ps. The relaxation of electrons from trap levels has characteristic t imes of more than 1 ns.