Two-step upconversion luminescence in Yb:Tb:YSGG crystal

Abstract

Multiline upconversion luminescence ranging from 375 to 635 nm was studied in Yb:Tb:YSGG crystal, a possible candidate for a tunable upconversion laser material. This luminescence was attributed to the transitions starting from the 5D3 and 5D4 excited levels of Tb. Two sequential steps in the upconversion were determined: at the first step Yb–Tb cooperative upconversion and cooperative absorption populate level 5D4, and at the second step interaction of excited Yb and Tb (in the 5D4 state) ions populates level 5D3. At 500-mW Ti:sapphire pumping, the excited-state concentration of Tb ions exceeded 2% of Yb excited-state concentration.