Nanocomposites and nanomaterials

Nonlinear optics of nanocomposites with bimetallic nanoparticles Ag/Au at different laser wavelengths
Klumusheva G.1 , Tolochko A.1 , Rudenko V.1 , Zhulai D.1 , Bugaychuk S.1 ,   Yaremchuk G.2, Mirnaya T.2
1 Institute of Physics of the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03028, Ukraine. E-mail: klimush@iop.kiev.ua
2 V. I. Vernadsky Institute of General and Inorganic Chemistry, NAS of Ukraine, Prospect Palladin., 32/34, Kyiv-03142 Ukraine.

The results of study of nonlinear optical properties of mesomorphic composites based on a liquid-crystalline cadmium alkanoate matrix with bimetallic nanoparticles (NPs) Ag/Au are presented. Synthesis of bimetallic NPs was carried out directly in the thermotropic liquid-crystalline phase of cadmium octanoate (CdC8) by the simultaneous chemical method [1]. The total concentration of NPs was 4% mol. or varied according to the formula x Ag + (4-x) Au % mol. Structural characterization of NPs was obtained by the method of small-angle X-ray scattering. Bimetallic NPs actively absorb light in both the visible and infrared regions of the spectrum due to surface plasma resonance. The position of the maximum of the surface plasma resonance band in a wide optical range is changed depending of the ratio of silver and gold in the nanocomposites.  Nonlinear optical properties nanocomposites CdC8+Ag/Au (3:1); CdC8+Ag/Au (1:1); CdC8+Ag/Au (1:3) were studied by z-scan method. The nonlinear optical measurements were performed by using Nd:YAG pulsed laser, generating 9 ns pulses, with wavelength 532 nm or 1064 nm. At lower input intensities there is competition of mechanisms the saturation absorption (SA) and the reverse saturation absorption (RSA). We also obtained a change in the sign of nonlinear refraction index (n2) from negative to positive, i.e. the effect of self-focusing. The excitation an optical wavelength of 1064 nm has great interest for photoacoustic research due to low intrinsic absorption [2]. So, our multifunctional nanocomposites with bimetallic homogeneous or gradient alloys Ag/Au NPs may be considered promising candidates for use in optoelectronic, photonic applications and photoacoustic.

1.	Mirnaya T., Yaremchuk G. Obtaining and optical properties of nanocomposites based on liquid crystals with bimetallic Au + Ag nanoparticles of the alloy type // Ukr. Chim. Jour. -2019.- 85 (5).
2.	Sara Park, Gyeongbae Park, Jeesu Kim, Wonseok Choi, Unyong Jeong, and Chulhong Kim. Bi2Se3 Nanoplates for Contrast-enhanced Photoacoustic Imaging at 1064 nm // Nanoscale. -2018. -10. 20548-20558