Millisecond‐Timescale, High‐Efficiency Modulation of Upconversion Luminescence by Photochemically Derived Graphene.

The millisecond‐timescale, high‐efficiency modulation of upconversion luminescence via ultraviolet laser‐induced photochemical reduction of graphene oxide is reported. The luminescence tuning is achieved by combining a thin film of graphene oxide with lanthanide‐doped upconversion nanoparticles. The recovery of the graphene‐like structure through the photochemical reduction of graphene oxide is accompanied by a variation in the absorption coefficient of the as‐synthesized nanocomposite, which enables super‐quenching of the luminescence emission from the upconversion nanoparticles under near‐infrared laser excitation with values of up to ≈90%. Further, the instantaneous reduction in the emission intensity upon ultraviolet laser irradiation allows a 106‐fold decrease of the time for fast modulation of upconversion luminescence from up to tens of minutes down to milliseconds at microwatt‐level laser power. Optical patterning is successfully produced in the nanocomposite and individual pixels are retrieved distinctly with high spatial resolution through upconversion luminescence emission quenching by reduced graphene oxide. This method offers a superior avenue for controlling upconversion luminescence with high contrast, fast reaction speed, and low power consumption. [ABSTRACT FROM AUTHOR]