What is it about?
Broadband optical limiting and wavelength-dependent nonlinear absorption studies of Au-Fe2O3-(15, 25, 40 wt %)rGO (reduced graphene oxide) nanocomposites were investigated using the Z-scan technique and excited with femtosecond (700−900 nm, 80 MHz, 150 fs) laser pulses. A reduction in the graphene perfect (La) domain and ID/IG ratio observed in the Raman data and the appearance of a Au 4f and Fe 2p singlet along with a shift in the C 1s state toward higher energy in the XPS data, peak broadening in the XRD data, and different mass residues left out with respect to content of rGO in the TG-DTA data strongly indicated the incorporation of Au-Fe2O3 nanostructures on solar exfoliated reduced graphene oxide. Selected aread electron diffraction data ascertained the presence of Au and Fe2O3 as a composite, and transmission electron microscopy (TEM) data revealed that the nanooctahedra Au-Fe2O3 turned themselves into nanospindles during incorporation of rGO. Ground state absorption spectra illustrated a pure and composite system possessing a broad absorption in the UV−visible spectral region which suffered band structure alteration with respect to its morphology. All the samples exhibited reverse saturable absorption (RSA) and broadband optical limiting action. The RSA has been attributed to the presence of a two-photon absorption (2PA) process. As wavelength increased, the 2PA coefficient also increased and was found to be varying in the order of Au-Fe2O3-rGO > Au-Fe2O3 > rGO. The higher 2PA coefficient (16.0 × 10−10 m/W) and lower onset-optical limiting threshold (22.01 μJ/cm2) of Au-Fe2O3-(15 wt %)rGO is attributed to the higher loading content of Au-Fe2O3, extent of conjugation due to reduction, higher ID/IG ratio and 1D (nanospindle) structure. Our results suggest that the Au-Fe2O3-(15 wt %)rGO nanocomposite is promising for broadband optical limiting applications to protect sensitive detectors (including human eyes) from high-power, near-infrared, ultrafast, laser-pulse-induced damage.
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Why is it important?
Broadband optical limiting studies in nanocomposites is important to identify their true potential.
Perspectives
In summary, Au-Fe2O3-rGO nanocomposites with superior NLO properties have been directly synthesized from rGO through a simplistic, effectual, and hydrothermal method that is scalable. We have demonstrated wavelength dependent tunable NLA and broadband OL activity related with n−π* transition of graphene and surface plasmon state of Au NPs of Au-Fe2O3-rGO nanocomposite. The NLA coefficient increased with increase in the excitation wavelength, and the higher NLO coefficients obtained at 900 nm are not only due to involved longer wavelength exposure but also because of the contribution arising from the SPR of Au metal nanoparticles. The tunability of NLO properties was achieved by varying the content of rGO, and the Au-Fe2O3-(15 wt %)rGO nanocomposite possesses a stronger nonlinear absorption coefficient and low onset optical limiting threshold under the chosen NIR (700−900 nm) wavelength. This arises from the contribution from densely decorated Au-Fe2O3, increase in the number of defects due to Au-Fe2O3 functionalization, and onedimensional nanospindle morphology of Au-Fe2O3. Accordingly, Au-Fe2O3-(15 wt %)rGO nanocomposites have been demonstrated as promising candidates for broadband ultrafast optical limiters.
Professor Venugopal Rao Soma
University of Hyderabad
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This page is a summary of: Wavelength-Dependent Nonlinear Optical Absorption and Broadband Optical Limiting in Au-Fe2O3-rGO Nanocomposites, ACS Applied Nano Materials, October 2018, American Chemical Society (ACS),
DOI: 10.1021/acsanm.8b01544.
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