Optical Limiting of Carbon Nanohorn-Based Aqueous Nanofluids: A Systematic Study

Abstract

Nowadays, the use of lasers has become commonplace in everyday life, and laser protection has become an important field of scientific investigation, as well as a security issue. In this context, optical limiters are receiving increasing attention. This work focuses on the identification of the significant parameters affecting optical limiting properties of aqueous suspensions of pristine single-wall carbon nanohorns. The study is carried out on the spectral range, spanning from ultraviolet to near-infrared (355, 532 and 1064 nm). Optical nonlinear properties are systematically investigated as a function of nanohorn morphology, concentration, dimensions of aggregates, sample preparation procedure, nanostructure oxidation and the presence and concentration of surfactants to identify the role of each parameter in the nonlinear optical behavior of colloids. The size and morphology of individual nanoparticles were identified to primarily determine optical limiting. A cluster size effect was also demonstrated, showing more effective optical limiting in larger aggregates. Most importantly, we describe an original approach to identify the dominant nonlinear mechanism. This method requires simple transmittance measurements and a fitting procedure. In our suspensions, nonlinearity was identified to be of electronic origin at a 532 nm wavelength, while at 355 nm, it was found in the generation of bubbles.

Efficient Optical Limiting in Carbon-Nanohorn Suspensions

“…For the lowest concentration sample at 532 nm and for the highest concentration suspension at 1064 nm wavelength, the fitting with both models was possible. In this case, the NL-LB threshold is higher than the MMJ one at 532 nm, while at 1064 nm the reverse is true, suggesting that the dynamic interplay of electronic and interaction effects is strongly wavelength dependent, in agreement with previous findings [21]. When the sample is subjected to irradiation by 355 nm light, no models fit.…”

“…The optical properties of the nanofluid were characterized in terms of transmittance and optical limiting behavior. We demonstrated broadband optical limiting properties of both concentrations of ultrasonicated suspensions of SWCNH at three different wavelengths (355, 532 and 1064 nm), with bubble production being the dominant nonlinearity mechanism involved, in particular at 355 and 1064 nm wavelengths, in agreement with previous findings [21]. The lack of wavelength selectivity of the evidenced nonlinear behavior (at least from UV-355 nm-to near-infrared-1064 nm-, in the whole range experimentally available in the present work) is a major force point of these investigated materials, proving a flexibility able to increase their possible applications both in the field of laser safety for science and defense and in the field of energy.…”

“…Comparing the samples described in the present work to the SWCNH suspensions previously investigated [21], we obtained in the present case a stronger optical limiting and a higher bubble production. In agreement with the optical limiting trend previously evidenced as a function of the size of nanoparticle clusters, we could attribute the stronger OL properties of the present samples to the larger dimensions of their aggregates (336 nm versus the 202 nm, which was the largest size investigated in Reference [21]), thus confirming the dominant role of aggregates size in comparison to other sample parameters.…”

“…This behavior is likely due to a heavy nonlinear scattering due to a significant bubble production in the sample, stronger than the case described by the MMJ equation. Bubbles production in nanofluids containing carbon nanoadditives has been often theorized in literature but not documented except very recent cases, investigated by our group [21,25]. A video recording of the remarkable bubble formation in the 0.025 g/L sample under 355 nm incident radiation can be found in the additional material which accompanies the present work.…”

“…The appealing characteristics of SWCNHs lies in their non-toxic or non-carcinogenic characteristics [17], unlike other carbon nanoparticles like, e.g., nanotubes, opening many possible applications for these nanomaterials, such as biosensing, drug delivering, gas storage and direct sunlight absorbers in thermal solar collectors [18][19][20]. Very recently, we studied optical limiting in SWCNHS as a function of the sample morphology, surfactant use and concentration [21], identifying correlations among OL characteristics, dominant OL mechanisms (reverse saturable absorption and nonlinear refraction) and parameters of the samples. The present work reports on the optical limiting obtained in SWCNH aqueous suspensions prepared by simple sonication.…”