The Electroluminescent Decay Mechanism of Rare-Earth Ions in OLEDs Based on a Terbium Complex

The organic light-emitting diodes (OLEDs) based on terbium (Tb) complexes show sharp green emission spectrum with excellent color purity. However, the brightness of Tb-OLEDs is generally weak. Here, the electroluminescent (EL) decay mechanism of TB-OLEDs is studied by arbitrarily using tris-(1-phenyl-3-methyl-4-isobutyryl-5-pyrozolone)-bis(triphenyl phosphine oxide) terbium as the emitting layer. The device shows high EL efficiency at low current density but rapid reduction of device efficiency at higher current density. The transient EL is investigated for understanding the decay process of excited Tb³⁺ ions. Together with theoretical studies, exciton quenching is proposed to explain the decay of the Tb-OLEDs which is important for optimizing and engineering the material and device structures. The EL from the mixed layer of the Tb and europium (Eu) complexes is also studied. We find that the EL performance and transient decay of the excited Tb ions are modified by energy transfer from Tb to Eu in the OLEDs.