Eu3+ complex/polymer films for light-emitting diode applications

Abstract

Eu3+ complexes exhibit potential to be applied as the red emitter component of white-light-emitting LEDs due to their intense absorption in the near-UV spectral region and intense red-light emission. However, the main problem concerning this application is the poor photostability usually displayed by Eu3+ complexes. To overcome such issue, in this study, transparent films of [C26H56N]+[Eu(dbm)4]- (C26H56N+ is the didodecyldimethylammonium cation and dbm− is 1,3-diphenyl-1,3-propanedione anion) dispersed in poly (methyl methacrylate) (PMMA) were used to coat commercial near-UV emitting LEDs in order to fabricate red-light-emitting LED prototypes. This Eu3+ complex was selected due to its high 5D0 state quantum efficiency (51 %) and absence of water molecules in its structure; the polymer, in its turn, had the purpose to protect the complex from photodegradation. Several PMMA films were produced by the addition of different amounts of complex, i.e., 0.1%, 0.25%, 0.5%, and 1% (w/w). All the films feature the usual Eu3+ emission in the red spectral region and the 5D0 state quantum efficiency enhances as the complex amount increases from 0.1% to 0.5%, while for the 1%, a decrease was observed. Thus, the 0.5% film was adhered with a cyanoacrylate glue on the top of a near-UV LED chip and the prototype exhibited the typical Eu3+ red emission with lower blue contribution coming from the UV LED chip, indicating that UV photons are efficiently converted by the film. Finally, the LED prototype performance was monitored over 26 h, and the emission intensity decreased 35% after 17 h, and from then on, it kept constant. A second LED prototype was manufactured using 5% (w/w) of the complex blended only with the cyanoacrylate glue and it displayed an intensity decrease of 50% after 26 h, confirming the role of PMMA in protecting the Eu3+ complex from photodegradation.