Tunable Fluorescein-Encapsulated Zeolitic Imidazolate Framework‑8 Nanoparticles for Solid-State Lighting

A series
of fluorescein-encapsulated zeolitic imidazolate framework-8
(fluorescein@ZIF-8) luminescent nanoparticles with a scalable guest
loading has been fabricated and characterized. The successful encapsulation
of the organic dye (fluorescein) is supported by both experimental
evidence and theoretical simulations. The measured optical band gap
is found to be comparable with the computed values of a hypothetical
guest–host system. Isolated monomers and aggregate species
of fluorescein confined in ZIF-8 nanocrystals have been systematically
investigated through fluorescence lifetime spectroscopy. The quantum
yield (QY) of the obtained solid-state materials is particularly high
(QY ∼ 98%), especially when the concentration of the fluorescein
guest is low. Combining a blue LED chip and a thin photoactive film
of fluorescein@ZIF-8, we demonstrate a device with good optical tunability
for multicolor and white light emissions. Additionally, we show that
the fluorescein@ZIF-8 nanoparticles exhibit an improved photostability
due to the shielding effect conferred by the nanoconfinement of the
host framework, making them promising candidates for practical applications
such as solid-state lighting, photonics, and optical communications.