The role of defects in the nonlinear optical absorption behavior of pristine and Co-doped V2O5 layered 2D nanostructures

Abstract

V2O5 nanostructures doped with 1% Co have been successfully synthesized by simple hydrothermal method. Structural and morphological aspects, vibrational spectra and optical properties (linear and nonlinear) of pristine as well as Co-doped V2O5 (V2O5:Co) nanoparticles are investigated. X-ray diffraction patterns indicate that both V2O5 and Co doped V2O5 are stabilized in an orthorhombic structure. Energy band gaps measured using the Tauc plot give 2.24 eV for V2O5 and 2.16 eV for Co doped V2O5. When excited using 5 ns laser pulses at 532 nm in the open aperture Z-scan configuration, pristine as well as Co-doped V2O5 nanoparticles are found to show excellent nonlinear absorption, which arises from strong reverse saturable absorption occurring in the sample at this wavelength. The corresponding effective two-photon absorption coefficients are in the range of 10−11 to 10−12 m/W, and effective three-photon absorption coefficients are in the range of 10−22 to 10−23 m3/W2. When excited at the same wavelength using a continuous wave laser beam, the effective two-photon absorption coefficient gets enhanced to 10−6 m/W. These results confirm the suitability of V2O5 and Co-doped V2O5 nanoparticles for the fabrication of optical limiter devices for the protection of human eyes and sensitive optical detectors from hazardous laser radiation.