Phosphorescence of gadolinium(III) chelates under ambient conditions

The gadolinium(III) chelates Gd(dtpaH2), Gd(hfac)3, Gd(tta)3 and Gd(qu)3 with dtpa=1,1,4,7,7-diethylenetriaminepentaacetate, hfac=hexafluoroacetylacetonate, tta=thenoyltrifluoroacetonate and qu=8-quinolinolate (or oxinate) show a phosphorescence under ambient conditions. While the UV emission of Gd(dtpaH2) at λmax=312 nm comes from a metal-centered ff state, the bluish (λmax=462 nm), green (λmax=505 nm) and red (λmax=650 nm) luminescence of Gd(hfac)3, Gd(tta)3 and Gd(qu)3, respectively, originates from the lowest-energy intraligand triplets.