A Brandner, T Kitahara, N Beare, C Lin, MT Berry, and P. Stanley May – Inorganic Chemistry, ACS publications.
The emission properties, including luminescence lifetimes, of the lanthanide complexes Ln(Tf2N)3 (Tf2N = bis(trifluoromethanesulfonyl)amide); Ln3+ = Eu3+, Tm3+, Dy3+, Sm3+, Pr3+, Nd3+, Er3+) in the ionic liquid bmpyr Tf2N (bmpyr = 1-n-butyl-1-methylpyrrolidinium) are presented. The luminescence quantum efficiencies, η, and radiative lifetimes, τR, are determined for Eu3+(5D0), Tm3+(1D2), Dy3+(4F9/2), Sm3+(4G5/2), and Pr3+(3P0) emission. The luminescence lifetimes in these systems are remarkably long compared to values typically reported for Ln3+ complexes in solution, reflecting weak vibrational quenching. The 1.5 μm emission corresponding to the Er3+ (4I13/2→4I15/2) transition, for example, exhibits a lifetime of 77 μs. The multiphonon relaxation rate constants are determined for 10 different Ln3+emitting states, and the trend in multiphonon relaxation is analyzed in terms of the energy gap law. The energy gap law does describe the general trend in multiphonon relaxation, but deviations from the trend are much larger than those normally observed for crystal systems. The parameters determined from the energy gap law analysis are consistent with those reported for crystalline hosts. Because Ln3+ emission is known to be particularly sensitive to quenching by water in bmpyr Tf2N, the binding properties of water to Eu3+ in solutions of Eu(Tf2N)3 in bmpyr Tf2N have been quantified. It is observed that water introduced into these systems binds quantitatively to Ln3+. It is demonstrated that Eu(Tf2N)3 can be used as a reasonable internal standard, both for monitoring the dryness of the solutions and for estimating the quantum efficiencies and radiative lifetimes for visible-emitting [Ln(Tf2N)x]3–xcomplexes in bmpyr Tf2N… resolved photon counting. The detection system was calibrated for relative wavelength response using a standard Tungsten lamp with extended calibration out to 1700 nm. (Stellar Net, SL1-CAL). Luminescence lifetimes visible.
