Excitation dynamics of cerium in niobate crystals

Transient gratings have been observed in Ce³⁺-doped SBN(Sr_xBa_1−xNb₂O₆) and KNSBN (potassium–sodium SBN) niobate crystals by picosecond-pulse, two-photon excitation using degenerate four-wave-mixing (DFWM) in the case where the C-axis is perpendicular to the grating vector. The charge-carriers produced in the conduction band are responsible for the observed coherent signal associated with the third-order nonlinearity, while a post-coherent, slow signal is due to the temporal lattice distortion associated with formation of Nb⁴⁺-hole polarons. Following excitation of the niobate host, energy transfer between host and rare-earth ions occurred, resulting in the excited state of cerium ions being populated and cross-luminescence from host to Ce³⁺ being observed. This excitation mechanism was also verified by a fluorescence study.