Avalanche up-conversion processes in Pr, Yb-doped materials

The general characteristics of the 'photon-avalanche' up-conversion process are presented. The Pr;Yb system was spectroscopically investigated in Pr;Yb:YLiF4 and Pr,Yb:YAlO3 with respect to the realization and understanding of this process. Whereas Pr,Yb:YLiF4 exhibits an avalanche-type excitation mechanism under infrared pumping, no such behavior is observed for Pr;Yb:YAlO3. A time dependent rate equation model was developed to describe these different behaviors using experimentally determined parameters. The absence of an avalanche-type excitation mechanism in Pr;Yb:YAlO3 is mainly caused by (i) a better spectral overlap between the excited state absorption in the Pr and the ground state absorption of Yb, (ii) higher transfer rates between Yb and Pr and within the Pr, and (iii) lower intrinsic decay rates from the participating excited energy levels (P-3(0.12) and (1)G(4)). (C) 2000 Elsevier Science S.A. All rights reserved.