Existence of cooperative absorption lines for Yb–(OH,OD) pairs: Absolute oscillator strengths

Due to its energy scheme simplicity, Yb3+ has been chosen in order to investigate the (Ln3+OH−) cooperative pair lines predicted by Dexter. For the first time by direct absorption such pair lines have been shown to exist in Yb(OH3),Yb(OOH) microcrystals and in [Yb(C2H5SO4),9H2O],[YbCl3,6H2O] crystals and in their aqueous solutions, either with light or heavy water. Absolute oscillator strengths of pairs at sum frequencies of the Yb electronic line (2F7/2−2F5/2) and of the ν1 stretching (OH)−, (OD)− vibrations have been found to be respectively (3.5±0.5)×10−9 and (2.6±0.3)×10−9. Results are discussed in terms of the cooperative model of Stavola–Dexter and of the vibronic sideband description, showing what is common to both models and what is different.