  Electron-hole generation and recombination rates for plasmon emission and
absorption in Graphene are presented. The recombination times of carriers due
to plasmon emission have been found to be in the tens of femtoseconds to
hundreds of picoseconds range. The recombination times depend sensitively on
the carrier energy, carrier density, temperature, and the plasmon dispersion.
Carriers near the Dirac point are found to have much longer lifetimes compared
to carriers at higher energies. Plasmons in a Graphene layer on a polar
substrate hybridize with the surface optical phonons and this hybridization
modifies the plasmon dispersion. We also present generation and recombination
rates of carriers due to plasmon emission and absorption in Graphene layers on
polar substrates.
