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 (²F_7/2−²F_5/2) 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.