  We study the double occupancy in a fermionic Mott insulator at half-filling
generated via a dynamical periodic modulation of the hopping amplitude. Tuning
the modulation amplitude, we describe a crossover in the nature of
doublon-holon excitations from a Fermi Golden Rule regime to damped Rabi
oscillations. The decay time of excited states diverges at a critical
modulation strength, signaling the transition to a dynamically bound
non-equilibrium state of doublon-holon pairs. A setup using a fermionic quantum
gas should allow to study the critical exponents.
