Optoelectronic Materials Based on Gaq3@ZIF-8 Metal-Organic Framework Composites for Solid-State Lighting

Light-emitting diodes (LEDs) are an efficient source of lighting, with many commercial applications like general illumination, camera flashes, phone or laptop displays, and TV screens. However, they present some limitations, including low-quality colour rendition, and the use of expensive/toxic rare-earth elements. Therefore there is an urgent need for the development of improved luminescent materials free of rare earths. Luminescent metal-organic framework (LMOF) materials have emerged as promising candidates for photonics devices. Most of the MOF-LEDs reported hitherto are of the down-converter type, where UV or blue LED are coated with LMOFs, however there is very limited progress in the development of LED using LMOFs as the electroluminescent layer. Herein, we report a novel Guest@MOF composite synthesized by encapsulating a semiconducting Gaq3 metal complex [gallium(III) tris(8-hydroxyquinolinato)], into the ZIF-8 pore [Zn (2-methylimidazolate)₂], yielding a green-yellowish luminescent material exhibiting a relatively high quantum yield (15%) upon photo-excitation. Subsequently, we show a down-converter LED made from 405-nm violet LED coated with Gaq3@ZIF-8, yielding a white MOF-LED. Then we demonstrate the use of Gaq3@ZIF-8 as an electroluminescent layer in a hybrid-LED, achieving an orange-yellowish emitting device. This work reveals the potential of LMOFs for next-generation LED technology, by exploiting the Guest@MOF concept to enable electroluminescent applications.