Abstract: The ultraviolet upconversion luminescence from 1 I6 state of Tm3 + at room temperature observed in Tm∶ YAG crystal by femtosecond laser irradiation. The dependence of the intensity of the Tm3+ emission on the pump power reveals that the three-photon excitation is dominant in the upconversion process.It is suggested that one-photon excitation to 3H4 level followed by a two-photon absorption produces,the population of upper laser level in which the characteristic luminescence occurs.

Key words: The ultraviolet upconversion luminescence from 1 I6 state of Tm3 + at room temperature observed in Tm∶ YAG crystal by femtosecond laser irradiation. The dependence of the intensity of the Tm3+ emission on the pump power reveals that the three-photon excitation is dominant in the upconversion process.It is suggested that one-photon excitation to 3H4 level followed by a two-photon absorption produces,the population of upper laser level in which the characteristic luminescence occurs.