Highly Fluorescent Metal-Organic-Framework Nanocomposites for Photonic Applications

Area of Science:

• Materials Science
• Nanotechnology
• Photochemistry

Background:

• Metal-organic frameworks (MOFs) are tunable porous hybrid materials with potential as next-generation luminescent materials, analogous to semiconductor quantum dots.
• The luminescence in fluorescent nano-MOFs arises from ligand molecular excitons, with unique packing allowing exciton diffusion while preventing aggregation-induced quenching.
• Despite their promise, nano-MOFs suffer from very low fluorescence quantum yields (QY).

Purpose of the Study:

• To analyze the fluorescence process in blue-emitting nano-MOFs.
• To model exciton diffusion and quenching mechanisms in nano-MOFs.
• To identify strategies for enhancing the low fluorescence QY of nano-MOFs.

Main Methods:

• Photoluminescence spectroscopy was used to study blue-emitting nano-MOFs.
• Exciton diffusion and quenching mechanisms were modeled.
• Nano-MOF surfaces were passivated by embedding them in an inert polymeric host.

Main Results:

• Exciton quenching in nano-MOFs is primarily caused by surface nonradiative recombination centers.
• Passivation of nano-MOF surfaces effectively enhances emission efficiency.
• Embedding nano-MOFs in a polymer host resulted in a >200% increase in fluorescence QY, restoring isolated ligand emission properties.

Conclusions:

• Surface passivation is a key strategy to improve the luminescence of nano-MOFs.
• Nano-MOFs can achieve high fluorescence QY comparable to isolated molecules through surface treatment.
• This work paves the way for developing highly efficient luminescent nano-MOF materials.