Optical transient bleaching and induced absorption of surface-oxidized CuFeS nanoparticles

Nonlinear optical properties of surface-oxidized CuFexSy (x=1, 2, y=2, 3) nanoparticles incorporated in polymeric film are studied. Surface oxidation of CuFeS2 and CuFe2S3 nanoparticles results in appearance of the additional absorption band with maximum at 1.03 and 1.15 μm, respectively. Bleaching of this additional absorption band in CuFe2S3 particles and the induced absorption in all studied samples after picosecond laser excitation take place. An energy level scheme for CuFeS2 and CuFe2S3 nanoparticles with long-lived trap levels in the band gap is proposed and the origin of additional absorption is discussed. Characteristic times for career relaxation from conduction band to these trap levels are ≈25±5 ps for CuFe2S3 and ≈70±10 ps for CuFeS2 oxidized nanoparticles. The relaxation of electrons from trap levels has a characteristic time of more than 500 ps.