Vacuum ultra-violet and high-resolution FTIR absorption spectroscopy, at temperatures ranging from 9 to 300K, were used to study OH- centers and OH- impurity complexes in single crystals. It was noted that co-doping with Ag or Pb favored the incorporation of OH- into the crystal. Careful heat-treatment, and the substitution of OD- for OH-, permitted an infra-red line at 3733.7/cm to be attributed to the OH- stretching mode. Lines at 3550.9 and 3567.7/cm were attributed to the stretching of an OH- ion in Pb-related defects. Anharmonicity of the OH- stretching mode was monitored via weak overtone lines, and was analyzed within the framework of the Morse model. The anharmonicity parameters (about 0.02) were similar to those for OH- defects in LiF and NaF.

P.Beneventi, P.Bertoli, R.Capelletti, R.Francini, U.M.Grassano, A.Ruffini, A.Scacco: Materials Science Forum, 1997, 239-241, 449-52