Stoichiometrically controlled synthesis and comparative study of photoluminescence of seven and eight coordinate complexes of Sm3+, Eu3+ and Tb3+ based on 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod) and imidazole

Abstract

Taking the advantage of the unsaturation in the coordination of lanthanides, stoichiometrically controlled synthesis of seven– and eight–coordinate complexes of type [Ln(fod)3(im)] and [Ln(fod)3(im)2] was accomplished (Ln = La, Sm, Eu and Tb, fod is the anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione and im is imidazole). To study the effect of coordination geometry on the luminescence properties of a lanthanide ion, the steady state and time resolved spectra of the complexes are investigated in solutions, solid state and of doped PMMA thin hybrid films. A prominent distinction of the luminescent properties is observed between the two types of the complexes. The emission transitions of seven–coordinate complexes display extensive stark splitting compared to their eight–coordinate analogues. The seven–coordinate complexes (Eu = 985.18 μs and Tb = 402.88 μs) show longer lifetime of the excited states and higher intensity of hypersensitive transitions than their eight–coordinate analogues (Eu = 692.92 μs and Tb = 69.21 μs). It has been shown that the site symmetry could have profound effects on the luminescence properties (emission intensity, radiative lifetime, quantum yield and stark splitting of the emission transitions) of a lanthanide complex.