2-STEP UP-CONVERSION LUMINESCENCE IN YB-TB-YSGG CRYSTAL

Multiline upconversion luminescence ranging from 375 to 635 nm was stu died in Yb:Tb:YSGG crystal, a possible candidate for a tunable upconve rsion laser material. This luminescence was attributed to the transiti ons starting from the D-5(3) and D-5(4) excited levels of Tb. Two sequ ential steps in the upconversion were determined: at the first step Yb -Tb cooperative upconversion and cooperative absorption populate level D-5(4), and at the second step interaction of excited Yb and Tb (in t he D-5(4) state) ions populates level D-5(3). At 500-mW Ti:sapphire pu mping, the excited-state concentration of Tb ions exceeded 2% of Yb ex cited-state concentration. (C) 1996 Optical Society of America