Lanthanide upconverting luminescence in molecular complexes and metal–organic frameworks

Abstract

Lanthanide-based upconverting luminescence (UCL) has emerged as a promising strategy for converting low-energy light into higher-energy emission, enabling wide-ranging applications in bioimaging, sensing, anti-counterfeiting, and photonic technologies, among others. While traditional inorganic nanocrystals have dominated UCL research, recent progress in lanthanide complexes and lanthanide-based metal–organic frameworks (Ln-MOFs) has introduced new opportunities for designing tunable and structurally versatile UCL materials. This review focuses on recent progress in the rational design and photophysical engineering of UCL-active lanthanide complexes and Ln-MOFs, highlighting how molecular coordination environments, ligand structures, and framework topology influence upconverting performance. We discuss strategies that control energy transfer pathways, enhance emission efficiency, and improve stability under excitation. Comparative insights between lanthanide complexes and MOFs are provided, emphasizing differences in emission behaviour, structural rigidity, and functional tunability. Despite existing challenges such as low quantum yields, emerging design strategies including hybrid architectures and stimuli-responsive systems show promise for next-generation upconversion platforms.