Deactivation effects of the lowest excited state of Ho3+ at 2.9 μm emission introduced by Pr3+ ions in LiLuF4 crystal.

The use of Pr3+ codoping for enhancement of the Ho3+:5I6 →5I7 mid-IR emissions were investigated in the LiLuF4 crystal for the first time. It was found that Pr3+ greatly increased Ho3+ 2.9 μm emission by depopulating the Ho3+:5I7 level while having little influence on the Ho3+:5I6 level, leading to greater population inversion. The energy transfer efficiency from Ho3+:5I7 to Pr3+:3F2 is calculated to be 88%. Based on Judd-Ofelt theory, the 2.9 μm emission cross section is calculated to be 1.91×10(-20)   cm2, and the gain property of the Ho3+:5I6 →5I7 transition is discussed. We propose that the Ho, Pr:LiLuF4 crystal may be a promising material for 2.9 μm laser applications.