Optical transient bleaching and induced absorption of surface-oxidized Cu-Fe-S nanoparticles

Nonlinear optical properties of surface-oxidized CuFexSy (x = 1, 2, y = 2, 3) nanoparticles incorporated in polymeric film are studied. Surface oxidat ion of CuFeS2 and CuFe2S3 nanoparticles results in appearance of the additi onal absorption band with maximum at 1.03 and 1.15 mu m, respectively. Blea ching of this additional absorption band in CuFe2S3 particles and the induc ed absorption in all studied samples after picosecond laser excitation take place. An energy level scheme for CuFeS2 and CuFe2S3 nanoparticles with lo ng-lived trap levels in the band gap is proposed and the origin of addition al absorption is discussed. Characteristic times for career relaxation from conduction band to these trap levels are approximate to 25 +/- 5 ps for Cu Fe2S3 and approximate to 70 +/- 10 ps for CuFeS2 oxidized nanoparticles. Th e relaxation of electrons from trap levels has a characteristic time of mor e than 500 ps.