Polarized IR and Raman spectra of zoisite: insights into OH-dipole orientation and the luminescence

The OH-dipole in the mineral zoisite has been a topic of discussion regarding its general orientation and vibrational modes. We present new polarized single-crystal Raman and infrared spectra and verify the orientation of the OH-dipole along the crystallographic c axis with a slight deviation towards the crystallographic a axis. Polarized Raman and FTIR spectra confirm that the OH band at 3150 cm(-1) corresponds to the O(10)-H center dot center dot center dot O(4) hydrogen bridge and exclude a previously suggested second hydrogen bridge O(10)-H center dot center dot center dot O(2). Further, Raman spectra provide insights on the luminescence of zoisite and the interference of luminescence peaks in the OH-region.