Ultrafast Photoluminescence from Graphene

TL;DR

This paper reports the observation of ultrafast, broadband photoluminescence from graphene excited by femtosecond laser pulses, revealing nonlinear emission behavior and rapid electron-phonon relaxation dynamics.

Contribution

It demonstrates significant visible-range light emission from graphene under ultrashort pulse excitation, supported by a two-temperature model explaining the fast relaxation processes.

Findings

Light emission across 1.7 - 3.5 eV range

Photon energies exceeding excitation energy

Relaxation time of tens of femtoseconds

Abstract

Since graphene has no band gap, photoluminescence is not expected from relaxed charge carriers. We have, however, observed significant light emission from graphene under excitation by ultrashort (30-fs) laser pulses. Light emission was found to occur across the visible spectral range (1.7 - 3.5 eV), with emitted photon energies exceeding that of the excitation laser (1.5 eV). The emission exhibits a nonlinear dependence on the laser fluence. In two-pulse correlation measurements of the time-domain response, a dominant relaxation time of tens of femtoseconds is observed. A two-temperature model describing the electrons and their interaction with strongly coupled optical phonons can account for the experimental observations.