Luminescence and quenching kinetics of lanthanide(bis(trifluoromethylsulfonyl)imide)3 salts in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide

Trivalent lanthanides (Ln3+) solutions offer more physical flexibility and are easier to process for various applications than solid lanthanide matrices. However, conventional solvents inhibit luminescence due to quenching. Ionic liquids (IL) appear to be more efficient hosts than conventional solvents. We are investigating the IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (bmpyrTf2N) as a solvent host for luminescent lanthanides. We have characterized and compared the luminescence quenching kinetics of a series of lanthanide ions in the ionic liquid bmpyr Tf2N in order to understand the properties that govern quenching. This allowed us to determine whether the trend of the luminescence lifetime followed the energy gap law. Since water acts as a quencher, we need to understand the binding properties of water to Ln3+ in the IL solution. By adding controlled increments of water to our Eu(Tf2N)3 in bmpyr Tf2N sample and measuring the lifetime, we were able to see the effect water had on the luminescence of Eu(Tf2N) 3 in bmpyr Tf2N due to multiphonon relaxation. Luminescence was used as a probe to allow us to know quantitatively how many water molecules were directly bound to each Eu3+ molecule. Eu3+ can then be used as a probe to determine water content of IL samples. The luminescence quantum efficiency of Eu(Tf2N)3 in bmpyr Tf2N was calculated using the measured luminescence decay rate constant and corrected emission spectrum. This allowed us to calculate the quantum efficiency of Tm(Tf2N)3 in bmpyr Tf2N using Eu(Tf2N)3 in bmpyr Tf2N as a secondary standard. The quantum efficiency of Tm(Tf2N)3 was then used in conjunction with the total luminescence decay constant to calculate the radiative and non-radiative rate constants.