VIBRATION PLUS LIBRATION ABSORPTION-BANDS OF OH CENTERS IN LINBO3

Hydrogen centres in the bulk of stoichiometric (VTE) LiNbO3 exhibit a sharp absorption band of the OH(OD) stretching vibration near 3466 (25 62) cm(-1). In congruent LiNbO3 the OH band (<(v)over bar (max)> = 348 4cm(-1)) is rather broad (FWHM similar to 30 cm(-1)) and for the high proton concentration layers in proton exchanged LiNbO3:PE the broad ab sorption band (FWHM similar to 30 cm(-1)) is shifted to about 3507 cm( -1). For all the above bands which are completely polarized perpendicu lar (z) over right arrow weak high energy sidebands have been found, s hifted by about 950 cm(-1) for OH and 700 cm(-1) for OD with respect t o the position of the stretching vibration. The intensity of these sid ebands and their spectral form is found to be proportional to the stre tching vibration, respectively to the concentration of the H(D) centre s. These sidebands are identified as libration + vibration combination bands and display the polarization dependence (I-parallel to/I-perpen dicular to approximate to 0.5 for OH with respect to (z) over right ar row) of a three-dimensional oscillator. The libration + vibration comb ination bands have also been detected as sidebands to higher vibration al transitions in proton (deuteron) exchanged LiNbO3:PE(DE).