Optical Absorption and Luminescence of I‐Centers in KBr

Optical absorption and luminescence of interstitial ion centers, the I‐, I A (Na), and I A (Li) centers in KBr are studied. Two optical absorption bands associated with each center are identified around 230 nm and the separations of the two bands for the I‐, I A (Na), and I A (Li) centers are 0.31, 0.39, and 0.35 eV, respectively. These two bands are ascribed to the transition to the spin‐orbit doublet, E 5/2 and 6 3/2 , and the increase in the width of the lower energy band in the order of the I‐, I A (Na), and I A (Li) centers is ascribed to the removal of the degeneracy of G 3/2 in the C 3 v symmetry. On the basis of the similarity of the I‐center luminescence and recombination luminescence, it is suggested that the I‐center luminescence is essentially caused by the recombination of (Br   2 −+ e)*. The relaxation processes from the excited Br − at the interstitial site to the (Br   2 −+ e)* at either the singlet or triplet states are discussed.