Optical properties and intensity parameters of UV excited efficient red emitting europium complexes containing fluorinated 1, 3-dione as primary sensitizer in solution, solid and PMMA thin films

The two adducts of tris(fluorinated β-diketonate)Eu (III) with 4,4ʹ-bpy (1) and tppo (2) were synthesized and characterized by spectroscopic techniques. The thermal stability, 1H NMR and IR studies of these complexes were discussed. The steady state and time resolved PL of the complexes were studied in chloroform, solid state and their 5% PMMA based hybrid thin films. The PL spectra of the complexes in different phases don't have characteristic emission from organic ligands (fluorescence and phosphorescence) which suggests that the energy transfer from the chosen organic sensitizers in this study to europium (III) is efficient. From the corresponding emission spectra, the photophysical parameters (e.g., radiative rate constant (Arad), non-radiative rate constant (Anrad), natural lifetime (τrad), intrinsic quantum yield (φEuEu), colour coordinate values and Judd-Ofelt intensity parameters were calculated in different phases. The φEuEu of [Eu(fod)3(tppo)2] (2) in solid state is 79% which is very high. It is worth to mention that the φEuEu of low asymmetric eight-coordinate [Eu(fod)3(tppo)2] (2) complex is higher (by 33.64% in chloroform, 15.30% in solid state and 59.198% in hybrid thin film) than low symmetric seven-coordinate [Eu(fod)3(4,4ʹ-bpy)] (1) complex. Moreover, the quantum efficiency of [Eu(fod)3(4,4ʹ-bpy)] (1) and [Eu(fod)3(tppo)2] (2) increased by 33.64 and 15.30% in solid state than their chloroform solution respectively. The φEuEu of both complexes decrease drastically when embedded in PMMA by 49.87% (1) and 40.29% (2) compared to their chloroform solutions. The colour coordinate values of both complexes depicts orange red to pure red emission.