S. R. Lüthi, M. P. Hehlen, T. Riedener and H. U. Güdel
Excited state dynamics and optical bistability in the dimer system Cs₃Lu₂Br₉:Yb³⁺
J. Lumin. 76-77, 447-450 (1998)                 

Abstract: Cooperative visible upconversion is reported in crystals of Cs₃Lu₂Br₉ : 1% Yb³⁺, Cs₃Lu₂Br₉ : 10% Yb³⁺, and Cs₃Yb₂Br₉. The near-infrared emission decays twice as fast as the visible emission as expected from theory. Both, the 10% and the 100% crystals exhibit bistability of the luminescenee intensity as a function of the excitation intensity at temperatures below 30 K. The bistable region gets narrower and moves to lower excitation intensities with increasing temperature and concentration. Both trends are in accordance with theoretical models.