Eu³⁺ -tetrakis β-diketonate complexes for solid-state lighting application

Eu³⁺ -β-diketonate complexes are used, for example, in solid-state lighting (SSL) or light-converting molecular devices. However, their low emission quantum efficiency due to water molecules coordinated to Eu³⁺ and low photostability are still problems to be addressed. To overcome such challenges, we synthesized Eu³⁺ tetrakis complexes based on [Q][Eu(tfaa)₄ ] and [Q][Eu(dbm)₄ ] (Q1 = C₂₆ H₅₆ N⁺ , Q2 = C₁₉ H₄₂ N⁺ , and Q3 = C₁₇ H₃₈ N⁺ ), replacing the water molecules in the tris stoichiometry. The tetrakis β-diketonates showed desirable thermal stability for SSL and, under excitation at 390 nm, they displayed the characteristic Eu³⁺ emission in the red spectral region. The quantum efficiencies of the dbm complexes achieved values as high as 51%, while the tfaa complexes exhibited lower quantum efficiencies (28-33%), but which were superior to those reported for the tris complexes. The structures were evaluated using the Sparkle/PM7 model and comparing the theoretical and the experimental Judd-Ofelt parameters. [Q1][Eu(dbm)₄ ] was used to coat a near-UV light-emitting diode (LED), producing a red-emitting LED prototype that featured the characteristic emission spectrum of [Q1][Eu(dbm)₄ ]. The emission intensity of this prototype decreased only 7% after 30 h, confirming its high photostability, which is a notable result considering Eu³⁺ complexes, making it a potential candidate for SSL.