Effect of pressure on the optical absorption of REF centers in Ce and Tb doped CaF2

Abstract

The effect of pressure to 80 kbar has been measured on the absorption peaks associated with REF centers in Ce and Tb doped CaF2. The results are compared with previous data for Gd doped CaF2. The lowest and highest energy excitations [α(1E) and γ(2E)] are associated with an excited state largely of metal 5d(eg) character. The intermediate peak has predominantly color center character. The results are qualitatively similar and consistent with Alig's assignments for all three rare earths. However, the mixing of rare earth and color center orbitals is markedly less for the Ce doped crystal than for the other two. A peak in the spectrum of the Ce doped CaF2 assigned to a 4f → 5d transition in trivalent cerium shifted to lower energy with pressure by an amount essentially identical with the shifts observed for similar transitions on a series of divalent rare earth ions in CaF2.