Multistage sensitization of 4F9/2→4I11/2 and 4F9/2→4I13/2 lasing transitions in Er3+ ions in a BaYb2F8 crystal
A new method was developed for determining the mechanism of anti-Stokes filling of luminescent levels of an activator in a rare-earth crystal. An investigation was made of the dependences of the absolute populations of the 4I13/2, 4I11/2, 4F9/2, 4S3/2, H9/2, 4G11/2, and 2P3/2 levels of Er3+ in a BaYb2F8 crystal on the energy absorbed within the Yb3+ sensitizer band. The mechanisms of anti-Stokes filling of the 4I13/2, 4F9/2, 4S3/2, and 2H9/2 levels of Er3+ were determined under conditions of weak (1 mJ/cm3) and strong (~10 J/cm3) pumping.