Two- and three-photon absorption in bulk CuI

We report on photoluminescence emission in copper iodide bulk single crystals induced by two- and three-photon absorption around 1.525 eV. These non-linear optical processes are investigated utilizing density-dependent, steady-state, as well as time-resolved photoluminescence spectroscopy as a function of the excitation energy. Using an excitation energy that corresponds to half of the bandgap energy, the observed photoluminescence intensity dependence on the excitation power shows an almost parabolic behavior. By further reduction of the photon energy, a cubic contribution is observable, which increases with decreasing excitation energy. The experimentally observed behavior can be well described by taking into account two- and three-photon absorption. By a simultaneous analysis of the intensity behavior for all used excitation energies, we determined a ratio between the two- and three-photon absorption cross section on the order of σ0(3)/σ0(2)≈10−28 cm2s.