DEVELOPMENT OF ENERGY DOWN CONVERSION (QUANTUM CUTTING) MATERIALS

Abstract

This research aims to develop lanthanide-based metal-organic frameworks (MOFs) with aggregation-induced emission (AIE) ligands to achieve direct sensitization from the ligand to the lanthanide ion. AIE ligands composed of AIE active cores and multiple carboxylic acid groups form a contiguous structure with Ln ions and AIE luminophores to obtain direct sensitization in zerodistance. The quantum cutting (QC) process is considered using Tb3+ as the sensitizer ion and Yb3+ as the activator ion. A solid-fluorescent ligand, dihydroxyterephthalic acid (DHTA), is used to improve UV light absorption and transfer energy via coordination bonds to solve the concentration quenching issue that reduces quantum cutting efficiency. The energy conversion efficiency of the prepared MOFs is evaluated using intensive optical measurements. This study is novel as it employs AIE or low concentration quenching fluorescent ligands, which is different from the conventional fluorescent ligands for Ln-MOF, and addresses the concentration quenching issue. The research contributes to the development of energy downconversion materials made of lanthanide metalorganic frameworks with AIE ligands, with potential applications in solar energy conversion. The results of photoluminescence (PL) spectroscopy analysis of Ln-AIE MOFs with the DHTA and TPA ligands at different Tb concentrations (8%, 12%, and 15%) show that the AIE ligand sensitization is successfully demonstrated. The emission peaks of Yb3+ in the near-infrared range correspond to the transitions 2F5/2 → 2F7/2 as a result of QC. Quantum resonance energy transfer from Tb3+ to Yb3+ is observed only when the AIE ligand is incorporated in the MOF structure, which is a characteristic of quantum cutting. The AIE ligand sensitized Ln-MOF have a strong potential to improve solar energy conversion efficiency of single hetero-junction solar cell.