Upconversion luminescence of Ce3+ doped scintillator crystals by femtosecond laser irradiation

Ultraviolet and visible upconversion luminescence was demonstrated in trivalent cerium doped YAlO3 crystal (Ce:YAP) and Lu2SiO5 crystal (Ce3+:LSO) under focused infrared femtosecond laser irradiation. The fluorescence spectra show that the upconverted luminescences come from the 5d-4f transitions of the electrons in trivalent cerium ions. The dependence of luminescence intensity of trivalent cerium on infrared pumping power reveals that the conversions of infrared radiation are dominated by three-photon excitation process. It is suggested that the simultaneous absorption of three infrared photons pumps the Ce3+ ion into upper 5 d level, which quickly nonradiatively relax to lowest 5 d level. Thereafter, the ions radiatively return to the ground states, leading to the characteristic emission of Ce3+.