Tb3+ Photophysics: Mapping the radiative and non-radiative transition probabilities of [Tb(H2O)9]3+ using molecular photophysics

The study of optical transitions in lanthanides has evolved separately from molecular photophysics. However, the forbidden transitions can be accurately described using the framework developed in molecular photophysics. 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 (τ), radiative (kr ≡ A) and non-radiative (knr) rate constant and oscillator strength (f) was determined for Tb(CF3SO3)3 in H2O/D2O mixtures in order to map the radiative and non-radiative transition probabilities. It was shown that the intense luminescence observed from Tb3+ compared to other Ln3+ is not due to a higher radiative transition probability but rather due to a lack of quenching, quantified by a contribution to knr from O-H oscillators in the aqua ion of kq(OH) = 2090 s-1 for terbium and kq(OH) = 8840 s-1 for europium. Further, the Horrocks method of determining inner-sphere solvent molecules has been revisited, and it was concluded that the coordination number of Tb3+ in aqueous solution is 9.