Amino acids (l-arginine and l-alanine) passivated CdS nanoparticles: Synthesis of spherical hierarchical structure and nonlinear optical properties

• Amino acids capped, spherical and hierarchical structured CdS NPs have been synthesized.
• Semiconducting NPs were characterized by UV–vis, FT-IR, TEM, XRD and PL.
• Colloidal suspension of CdS NPs in PVAc has been characterized by open aperture Z-scan.
• Thermally stimulated third order NLO properties under cw laser have been analysed.
• Enhanced value of β = 5.93 × 10−6 m/W obtained for l-alanine capped CdS-PVAc colloids.

CdS nanoparticles (NPs) passivated with amino acids (l-alanine and l-arginine) having spherical hierarchical morphology were synthesized by room temperature wet chemical method. Synthesized NPs were characterized by ultraviolet–visible (UV–vis) spectroscopy to study the variation of band gaps with concentration of surface modifying agents. Increase in band gap has been observed with the increase in concentration of surface modifying agents and was found more prominent for CdS NPs passivated with l-alanine. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis were carried out for the study of crystal structure and morphology of CdS NPs. The average particle size of CdS NPs calculated from Debye-Scherer formula was found to less than 5 nm and agrees well with those determined from UV–vis spectra and TEM data. Fourier transform infrared (FT-IR) spectroscopy was performed to know the functional groups of the grown NPs. Peaks in FT-IR spectra indicate the formation of CdS NPs and capping with l-alanine and l-arginine. Photoluminescence spectra of these NPs were also studied. Finally, colloidal solution of CdS-PVAc was subjected to Z-scan experiment under low power cw laser illumination to characterize them for third order nonlinear optical properties. CdS-PVAc colloidal solution shows enhanced nonlinear absorption due to RSA and weak FCA on account of two photon absorption processes triggered by thermal effect.

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