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Field-induced luminescence in organic and inorganic media, OLEDs, and LEDs

Luminescent films of Eu3+ dinuclear complex embedded in PMMA as candidates for application in PC-LED lighting devices

Ariane C. F. Beltrame1, Sergio A. M. de Lima1, Ana M. Pires1

1FCT-UNESP, Department of Chemistry and Biochemistry - Brazil

E-mail: ariane.beltrame@unesp.br

Luminescent materials based on phosphors or complexes containing rare earth ions are intensively explored by the scientific community due to their applicability as cell markers and biological thermometers, in solar concentrators, as anti-fraud reagents, in imaging devices, in screens and lighting devices, more recently, of the type of LEDs and OLEDs. Aiming the application in lighting devices, this study focuses on the synthesis and characterization of films produced by the drop-casting method containing the red-emitting [Eu(dbm)3-µ-(bpm)Eu(dbm)3] complex (Hdbm = dibenzoylmethanate; bpm=2,2'-bipyrimidine), using polymethyl-methacrylate (PMMA) as polymeric matrix. The [Eu(dbm)3-µ-(bpm)Eu(dbm)3] complex was synthesized without any coordinated water molecule and its structure and its features were elucidated by FTIR, TGA, UV-Vis, and photoluminescence spectroscopy. Focusing on the optical behavior, the synthetized Eu3+ dinuclear complex exhibited the expected narrow emission bands within the orange-red spectral region due to the Eu3+ 5D07FJ (J = 0-4) set of transitions. From the kinetic point of view, it was found that the lifetime of the 5D0 excited state of the Eu3+ complex via ligand excitation was 0.377 ms, exhibiting an intrinsic quantum yield of 29.6%. These values are higher than those of the mononuclear [Eu(dbm)3H2O] complex (0.05 ms and 3.3%). The gain in the dinuclear architecture is relevant, in addition to the fact that these data indicate the absence of coordinated water molecules, agreeing with the proposed structure. Furthermore, the band related to the 5D07F2 transition of the dinuclear complex exhibited a similar profile of the tris, in terms of position of the maximum and in the number of components, indicating a structure with low symmetry, as expected. Finally, to produce the luminescent films, the proportion of the complex [Eu(dbm)3-µ-(bpm)-Eu(dbm)3] in PMMA were varied as being 0.1, 0.25, 0.5, 0.75, 1 or 2 % by weight, yielding films completely transparent up to 1 wt%. They also exhibited the characteristic Eu3+ luminescence within the orange-red spectral region due to the 5D07FJ (J = 0-4) transitions. So, it is possible to conclude that the films produced based on the dinuclear complex express very promising characteristics to be used in the manufacture of red PC-LED prototypes or even as a red component in the PC-WLED architecture.

Keywords: Luminescence, Lanthanides, Solid State Lighting

Acknowledgments: The authors would like to thank the Brazilian agencies CNPq (grants nº 304003/2018-2 and 309448/2021-2), CAPES (grants nº 88887.672234/2022-00) for funding grants to support scientific research.

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