Tunable optical activities in chiral transition metal oxide nanoparticles

• Published in: Nanoscale 2022-10, Vol.14 (41), p.15414-15421
• Main Authors: Xiao, Shuyu, Liang, Jiechun, Li, Junzi, Cheng, Jiaji, Zhu, Xi, He, Tingchao
• Format: Article
• Language: English
• Subjects: Broadband; Capping; Cobalt oxides; Cysteine; Dipole moments; Electric dipoles; Histidine; Nanoparticles; Nonlinear optics; Optical activity; Optoelectronic devices; Second harmonic generation; Transition metal oxides
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/d2nr02555h

Chiral transition metal oxides (TMOs) are widely used in various optoelectronic devices. However, the currently poor understanding of how the optical activities of TMOs can be regulated considerably hinders their applications. We have synthesized a series of chiral TMO nanoparticles (NPs), i.e. , MoO x ( x = 2, 2.4 and 2.5) and Co 3 O 4 . Compared with TMO NPs with l -/ d -cysteine molecules as the capping ligand, l -/ d -histidine-capped TMO NPs possess larger anisotropic factors ( g abs ), which are as high as ∼0.01 and ∼0.02 for l -/ d -histidine-capped MoO 2.5 and Co 3 O 4 NPs, respectively. A nondegenerate coupled oscillator (NDCO) theoretical calculation confirms that l -/ d -histidine molecules can generate a smaller electric dipole moment and thus induce higher optical activity than l -/ d -cysteine molecules. Impressively, the chiral NPs exhibit broadband second harmonic generation. This work indicates that chiral TMO NPs have potential for application in nonlinear optical devices. The optical activities of chiral transition metal oxide nanoparticles are regulated, achieving a maximum anisotropic factor of approximately 0.02. Impressively, the chiral nanoparticles demonstrate broadband second harmonic generation.