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;Y b:YLiF4 and Pr,Yb:YAlO3 with respect to the realization and understanding o f this process. Whereas Pr,Yb:YLiF4 exhibits an avalanche-type excitation m echanism under infrared pumping, no such behavior is observed for Pr;Yb:YAl O3. A time dependent rate equation model was developed to describe these di fferent behaviors using experimentally determined parameters. The absence o f 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 betwee n Yb and Pr and within the Pr, and (iii) lower intrinsic decay rates from t he participating excited energy levels (P-3(0.12) and (1)G(4)). (C) 2000 El sevier Science S.A. All rights reserved.