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

Abstract.

Nonlinear optical properties of surface-oxidized CuFe_xS_y (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.