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

Abstract

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 solidstate lighting, photonics, and optical communications.

A Luminescent Guest@MOF Nanoconfined Composite System for Solid-State Lighting

“…Encouragingly, we established a clear correlation between the amount of RhB guests applied at HCR synthesis stage (denoted as 0.01−1 mM) to the precise number of guest molecules detected from NMR. Of note, the number of cages per RhB guest determined here (7246, 1008, 186 for 0.01, 0.1, 1 mM, respectively) is appreciably lower than those established for the reported fluorescein@ZIF-8 samples (3703, 244, 30 for 0.01, 0.1, 1 mM, respectively [23]) employing an identical NMR method. The NMR results reveal the lower efficacy for the confinement of RhB within ZIF-8 compared with its fluorescein counterpart, which might be attributed to the bulkier RhB guest and its cation charge instead of anion for the latter.…”

“…However, this approach requires special attention to controlling the precise ratio and topological distribution of the component dyes during the synthesis stage in order to achieve good lighting performance and the dyes@MOF is excited by UV instead of blue light, i.e., the full phosphor-conversion approach is adopted. In this study, we will show that by combining RhB@ZIF-8 with a low RhB guest loading (this work) and Fluo@ZIF-8 (previously reported system [23]) with a low fluorescein loading in a simple post-synthetic mixing step, both a high QY and good quality in the emitted white color can be achieved via the partial phosphor-conversion approach, therefore providing an alternative facile strategy to fabricate an efficient hybrid dye@MOF photoluminescent material for various lighting applications.…”

“…A pink to red color solid product (whose color varies depending on the concentration of the RhB used) was formed instantaneously. Fluo@ZIF-8 corresponding to a fluorescein concentration of 0.01 mM was synthesized by employing a similar methodology (in accordance with [23]).…”

“…MOFs are nanoporous framework materials with potential applications in such diverse areas as dielectrics and optoelectronics [24,25], sensors [26][27][28], gas storage [29], catalysis [30,31], and biomedicine [32,33]. By nanoconfinement of fluorescein guest in the ZIF-8 host, we found the quantum yield (QY) of fluorescein is increased up to 98%, due to the reduction of intermolecular interactions between the fluorescein molecules that result in aggregation-induced quenching in the solid state (NMR established a loading concentration of 1 fluorescein guest per ~3700 cages [23]). We implemented a few WLED prototype devices using these fluorescein@ZIF-8 materials, and demonstrated their tunability of color temperature.…”

“…In our previous work [23], we encapsulated an organic dye molecule, fluorescein, into a sodalite cage-type metal-organic framework (MOF), Zeolitic Imidazolate Framework-8 (ZIF-8), to fabricate a composite fluorescein@ZIF-8 (Fluo@ZIF-8 for short) material. MOFs are nanoporous framework materials with potential applications in such diverse areas as dielectrics and optoelectronics [24,25], sensors [26][27][28], gas storage [29], catalysis [30,31], and biomedicine [32,33].…”