Cooperative vibronic spectra involving rare earth ions and water molecules in hydrated salts and dilute aqueous solutions

Several cooperative vibronic bands have been observed in the excitation and emission spectra of polycrystalline hydrates and dilute aqueous solutions of TbCl3. A radiative transition involving the simultaneous electronic transition of a Tb3+ ion and vibrational transition of a nearby water molecule gives rise to these bands. Theoretical calculations, based on an electrostatic coupling model, explain the intensities of the cooperative vibronic transitions. Selection rules are derived and quantitative estimates of intensities are made.