A novel luminescent center in LiNbO3 : Cr : Mg crystals

We report on the observation of a novel luminescent center in LiNbO3 : Cr : Mg. This center is characterized by a set of narrow emission lines located in the 770 - 850 nm region which occur in addition to the well-known broad T-4(2) emission of the major low-field Cr3+ site. The set of narrow emissi on lines can be readily observed in samples containing more than 4% Mg. All lines exhibit the same relaxation time and are strongly rc polarized. Subs titution of Mg by Zn produces the same set of lines, indicating that the Mg ions are not directly incorporated in the novel center, but play an essent ial charge compensating role. Based on our absorption, excitation, luminesc ence, and fluorescent line-narrowing experiments, we associate the novel ce nter with an exchange coupled Cr-center. (C) 1999 Elsevier Science B.V. All rights reserved.