(Zn2Al-LDH/ZnTPPS)n composite films with notable third-order optical nonlinearities

Abstract

New inorganic-organic transparent composite films of the formula (Zn[Formula: see text]Al-LDH/ZnTPPS)[Formula: see text] were fabricated using exfoliated cationic Zn[Formula: see text]Al layered double hydroxide (Zn[Formula: see text]Al-LDH) nanosheets and anionic meso-tertra(4-sulfophenyl) zinc porphyrin (ZnTPPS) through an electrostatic layerbylayer self-assembly method. The resulting composite films were characterized by UV-vis spectroscopy (UV-vis) scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that the films have relatively smooth and orderly surfaces, with the large ring plane of the porphyrin molecules vertically aligned LDH nanosheets and can grow in a nearly linear fashion with increasing the deposition cycles. Z-scan measurements, which were conducted under laser irradiation at a wavelength of 532 nm pulse width of 6 ns, repetition rate of 10 Hz and light intensity at focus [Formula: see text] of 10 [Formula: see text]J, revealed that the composite films have notable saturation absorption (cf., ZnTPPS in solution shows reverse saturation) and optical nonlinear self-defocusing behavior with the nonlinear optical absorption coefficient [Formula: see text] refractive index [Formula: see text], and third-order NLO susceptibility [Formula: see text] of the films increasing with the increase in number of layers of films ([Formula: see text] value is up to 7.86 × 10[Formula: see text] esu when [Formula: see text] 40), implying the NLO responses could be modified by fine tuning the thickness of composite films.