Tb <sup>3+</sup> Photophysics: Mapping Excited State Dynamics of [Tb(H <sub>2</sub> O) <sub>9</sub> ] <sup>3+</sup> Using Molecular Photophysics
Nicolaj Kofod, Thomas Just Sørensen
Abstract
The study of optical transitions in lanthanide(III) ions has evolved separately from molecular photophysics, but the framework still applies to these forbidden transitions. In this study, a detailed photophysical characterization of the [Tb(H2O)9]3+ aqua ion was performed. The luminescence quantum yield (Φlum), excited state lifetime (τobs), radiative (kr ≡ A) and nonradiative (knr) rate constants, and oscillator strength (f) were determined for Tb(CF3SO3)3 in H2O/D2O mixtures in order to map the radiative and nonradiative transition probabilities. It was shown that the intense luminescence observed from Tb3+ compared to other Ln3+ ions is not due to a higher transition probability of emission but rather due to a lack of quenching, quantified by quenching to O–H oscillators in the aqua ion of kq(OH) = 2090 s–1 for terbium and kq(OH) = 8840 s–1 for europium. In addition, the Horrocks method of determining inner-sphere solvent molecules has been revisited, and it was concluded that the Tb3+ is 9-coordinated in aqueous solution.