Enhancing luminescence in lanthanide coordination polymers through dilution of emissive centers

A Ln-adipate metal-organic framework templated with 4,4′-bipyridine (GWMOF-6) was synthesized with Eu(III) or Tb(III) ions with various concentrations of optically inert Gd(III) ion in order to evaluate the effects of diluting the emissive metal center on the efficiency of luminescence. The doping ratios of Ln:Gd (Ln = Eu or Tb) showed that of the ratios studied, the 50:50 system had among the highest quantum yields (Eu = 3.9%, Tb = 7.6%) with increasing lifetimes as Gd(III) concentration increased. A 50:50 Eu:Tb system was also synthesized and showed to be more efficient than the Eu:Gd systems (Φ = 15.3%), with an exceptionally high energy transfer efficiency (80%) from the ⁵D₄ state of the Tb(III) ion to the ⁵D₁ and ⁵D₀ energy levels of the Eu(III) ion.