Role of OH- ions on the optical absorption spectra of pure and doped KMgF3 fluoroperovskite

VUV and high resolution (0.04 cm(-1)) FTIR absorption spectroscopies, in the temperature range 9-300K, are used to study OH- centers and OH--impurity complexes in KMgF3 single crystals. Go-doping with either Ag or Pb favours the OH- inclusion into the crystal. Proper thermal treatments, isotopic substitution of OD- for OH- allowed to assign the i.r. line at 3733.7 cm(-1) to the OH--stretching mode and the lines at 3550.9 and 3567.7 cm(-1) to the stretching of an OH- ion in Pb-related defects. Possible defect models are discussed. Anharmonicity effects of the OH--stretching mode were monitored by weak overtone Lines and analyzed in the framework of the Morse model. The anharmonicity parameters (similar to 2 x 10(-2)) are along with those found for OH--defects in LiF and NaF. The temperature dependence of the line position allowed to determine the frequencies of the phonons coupled to the OH--stretching modes.