Upconversion emissions from high energy levels of Tb3+ under near-infrared laser excitation at 976 nm

Ultraviolet upconversion emissions from high energy levels (D-5(1), L-5(8), L-5(9), (5)G(5), and L-5(10)) of Tb3+ were observed in the NaYF4:Tb3+, Yb3+ microcrystals under excitation of a 976 nm laser diode at room temperature. These energy levels were populated by energy transfer and excited state absorption processes. Power dependence measurements confirmed it was caused by a three-photon upconversion process. Concentration quenching did not strongly affect the population of these levels. (C) 2015 Optical Society of America