  We present a joint theory-experiment study on ultrafast photoluminescence
from photoexcited graphene. Based on a microscopic theory, we reveal two
distinct mechanisms behind the occurring photoluminescence: Besides the
well-known incoherent contribution driven by non-equilibrium carrier
occupations, we found a coherent part that spectrally shifts with the
excitation energy. In our experiments, we demonstrate for the first time the
predicted appearance and spectral shift of the coherent photoluminescence.
