Nonlinear photoluminescence imaging of isotropic and liquid crystalline dispersions of graphene oxide

TL;DR

This study demonstrates visible-range nonlinear photoluminescence from graphene oxide flakes excited by near-infrared femtosecond laser light, enabling 3D label-free imaging of liquid crystalline dispersions.

Contribution

It introduces a new nonlinear PL technique for imaging graphene oxide dispersions, revealing polarization dependence and multiphoton excitation mechanisms.

Findings

PL intensity depends nonlinearly on laser power

PL is maximized when excitation polarization is parallel to flakes

Enables 3D label-free imaging of liquid crystalline GO dispersions

Abstract

We report a visible-range nonlinear photoluminescence (PL) from graphene oxide (GO) flakes excited by near-infrared femtosecond laser light. PL intensity has nonlinear dependence on the laser power, implying a multiphoton excitation process, and also strongly depends on a linear polarization orientation of excitation light, being at maximum when it is parallel to flakes. We show that PL can be used for a fully three-dimensional label-free imaging of isotropic, nematic, and lamellar liquid crystalline dispersions of GO flakes in water. This nonlinear PL is of interest for applications in direct label-free imaging of composite materials and study of orientational ordering in mesomorphic phases formed by these flakes, as well as in biomedical and sensing applications utilizing GO.