Investigation progresses of rare earth complexes as emitters or sensitizers in organic light-emitting diodes

Due to unique photo-physical characteristics, rare earth (RE) complexes play important roles in many fields, for example, telecommunications, life science, and organic light-emitting diodes (OLEDs). Especially, thanks to narrow emission bandwidth and 100% theoretical internal quantum efficiency (IQE), the study of RE complexes in the electroluminescence field has been a hot research topic in recent 30 years. As a leading technology in solid-state light source fields, OLEDs have attracted great interest from academic researchers and commercial endeavors. In the last decades, OLED-based products have trickled into the commercial market and developed quickly into portable display devices. Here, we briefly introduce the luminescent characteristics and electroluminescent (EL) study of RE complexes in material synthesis and device design. Moreover, we emphatically reveal the innovative application of RE complexes as sensitizers in OLEDs. Through experimental validation, the application of RE complexes as sensitizers can realize the complementary advantages of RE complexes and transition metal complexes, leading to significantly improved performances of OLEDs. The application of RE complexes as sensitizers provides a new strategy for designing and developing novel high performances OLEDs.