Third-order nonlinear optical property of poly(2,5-dihexyloxy)-p-phenylene vinylene modified by N+ ion implantation

A soluble poly(2,5-dihexyloxy)-p-phenylene vinylene (PDHOPV) was prepared via dehydrochlorination reaction from hydroquinone and n-hexyl bromide as raw materials. The PDHOPV films implanted by 20 keV nitrogen ions (N+) in the dose range of 3.8 × 1015-9.6 × 1016 ions/cm2 were characterized by UV-vis absorption spectra, which showed the optical absorption was raised gradually in the visible region followed by a red shift of optical absorption threshold and the band gap (Eg) was reduced from 2.12 eV to 1.71 eV with the increase of ion dose. The third-order nonlinear optical (NLO) susceptibilities (χ(3)) were measured by degenerate four-wave mixing (DFWM) technique at 532 nm. The results demonstrated that the χ(3) value of PDHOPV film could be enhanced effectively by means of N+ ion implantation. When the ion dose was 3.8 × 1016 ions/cm2, the χ(3) value of PDHOPV film was maximized to 1.06 × 10−8 esu which was almost eleven times larger than that of the pristine film. Moreover, the mechanism responsible for the variation of χ(3) value of PDHOPV film with N+ ion dose was also discussed tentatively.