Femtosecond-Laser-Induced Saturable Absorption and Optical Limiting of Hollow Silver Nanocubes: Implications for Optical Switching and Bioimaging

Abstract

The effects of shape, size, and surface plasmon resonance (SPR) peak position (λ SPR ) on nonlinear absorption (NLA) were investigated at 808 nm, using a femtosecond laser. We found that NLA behavior is the result of competition between saturable absorption (SA) and reverse saturable absorption (RSA). SA behavior, i.e., optical transparency in silver nanocrystals, is introduced by the change in shape and structure from solid nanospheres to hollow nanocubes. For the latter, SA behavior dominates at low input irradiance, while RSA dominates at higher laser powers. A series of hollow silver nanocubes (HAgNCs) was synthesized that exhibit SPR peaks at 510, 550, 590, and 630 nm, hence named as HAgNC-510, HAgNC-550, HAgNC-590, and HAgNC-630, respectively. The edge lengths (l) of HAgNC-510, HAgNC-550, HAgNC-590, and HAgNC-630 were determined to be 33 ± 4, 45 ± 8, 70 ± 10, and 100 ± 15 nm. The switching of SA to RSA occurred at lower laser power for larger HAgNCs as compared to the smaller ones. The saturation intensity (I sat ) was found to vary linearly with the size of HAgNCs. Moreover, for a four-times rise in input pulse intensity (63 → 252 GW/cm 2 ), a huge increase of 3650% in the NLA coefficient, β eff , was observed for HAgNC-590, whereas merely 19% increase was found for the solid silver nanoparticles (SAgNP-400). The extraordinary enhancement in β eff is attributed to the enhanced electric field at the sharp edges and corners of the nanocubes. The red-tailing of SPR peaks also had a significant effect on the values of β eff . The outcomes, i.e., optical transparency and SA−RSA switching, will open vistas for a variety of diverse applications such as optical switching, limiting, and bioimaging.

Antimony Sulfide Nanosheets with Size-Dependent Nonlinear Optical Properties for Q-Switched Pulse Applications

“…As depicted in Figure b, characteristic Raman modes are located at 187, 251, and 81 cm –1 along with a weak broad peak at 449 cm –1 , which are ascribed to the B 1g mode, antisymmetric and symmetric bending of S–Sb–S bonds, in-plane vibrations, and symmetric Sb–S–S–Sb stretching. − The linear optical absorption spectra of suspensions of Sb 2 S 3 nanosheets of different sizes are shown in Figure c, which suggest that the Sb 2 S 3 nanosheets possess broadband absorption and that the absorption correlates well with their sizes, making it possible for an NLO material under laser illumination at 532 and 1064 nm. Meanwhile, this result suggests that the NLO properties may also exhibit size dependence. − …”

Multi‐Functional Applications of H‐Glass Embedded with Stable Plasmonic Gold Nanoislands

“…[75] This non-radiative decay process occurs through intra-band and/or inter-band transitions, generating charge carriers, that is, electron-hole pairs. [74,76,77] The intra-band excitation takes place between the filled ground state (sp-band) below the fermi level and the excited state conduction band (sp-band), while the inter-band excitation occurs be-tween the d-band, which exists below the fermi level, and the excited conduction band (sp-band) (Figure 5f). Figure 2a shows that the SPR peak in the visible region ranges from 490 to 1000 nm, with a peak maximum located around 580 nm.…”

No-Stirring Synthesis of sub-50 nm Hollow Silver Nanoshells with Dimethylglyoxime-Induced Plasmons in Visible and Second NIR Windows for Biomedical Applications

“…The hollow nanoshells of silver or gold exhibit an exciting phenomenon of “plasmon hybridization” arising on account of dipolar oscillations occurring on two surfaces, inner and outer ones . In most of these nanoshells, a single, intense surface plasmon resonance (SPR) peak has been observed by previous workers. − These nanoshells have found their way into a wide range of applications such as catalysis, bioimaging, , and photothermal therapy . Especially for biomedical applications, the plasmon peak should lie in the biologically transparent window (650 → 1350 nm) .…”