Analysis on fluorescence of dual excitable Eu(TTA)3DPBT in toluene solution and PMMA

Photoluminescence of Eu(TTA)3DPBT (TTA=thenoyltrifluoro-acetonate DPBT=2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine) in toluene and PMMA thin film are measured with excitation at 350 and 404 nm, respectively, and analyzed using Judd–Ofelt theory. Under excitation at 350 nm, it is found that Eu(TTA)3DPBT in toluene has a larger Ω2 value (14.33×10−20 cm2) than that (12.70×10−20 cm2) of Eu(TTA)3Phen (Phen=1,10-phenanthroline) in the same solvent, and has a smaller Ω2 value (12.70×10−20 cm2) in PMMA than that (Ω2=14.09×10−20 cm2) of Eu(TTA)3Phen in PMMA. At the same time, it can be seen that under excitation at 350 nm Ω2 value of Eu(TTA)3DPBT in toluene is larger than that in PMMA. Excited by 404 nm, Ω2 of Eu(TTA)3DPBT obtained in toluene and in PMMA are the same as that excited at 350 nm. The transition probability (A), emission cross-section (σ) and the fluorescence branching ratio (β) are also evaluated. The lifetime of 5D0 metastable state is measured on 350 and 404 nm excitation, respectively. For the former situation, it is 455 μs in toluene and 640 μs in PMMA, for the latter it is 460 μs in toluene and 664 μs in PMMA. By comparing absorptions with excitations, it can be found that DPBT is more efficient than TTA as an energy donor. Phosphorescence spectra are also measured to estimate the lowest triplet level and analyze the energy transfer for DPBT and TTA, from which it is found that the energy transfer from TTA to DPBT occurs in the luminescent process.