Revisiting fluorescein and layered double hydroxide using a synergistic approach: A complete optical study

Abstract

The luminescence of Fluorescein, an inexpensive dye, ought to be interesting for lighting application devices such as commercial LEDs. However, the molecule suffers from severe instability, making it inappropriate for such applications. As previously studied, fluorescein molecules may be hosted in a layered double hydroxide (LDH), and the role of such an inorganic material in stabilizing the dye has been underlined. However, a deep understanding of the resulting optical properties is still required. Using extremely small amounts of fluorescein, it is demonstrated here that Zn 2 Al cation-based LDH tethering acts as a «solid solvent» for the dye, enabling its luminescence even in powder form, whereas fluorescein molecules on their own emit no luminescence at all in the solid state. However, aggregations of the dye occur in the interlamellar space, leading to non-radiative emission. Emission and excitation spectra, as well as fluorescence decays, are studied to explain the difference between the hybrid LDH-Fluorescein material and an aqueous solution of fluorescein. Additionally, LDH platelets are found to help the dispersion of the intercalated fluorescein in silicone to obtain a homogeneous composite film, which exhibits luminescent properties. Finally, an accelerated photoaging study demonstrates that the LDH-fluorescein filler has a pro-degradant effect on polymer aging under UV radiation.

Sulforhodamine B-LDH composite as a rare-earth-free red-emitting phosphor for LED lighting

“…Concentration screening of SRB in LDH matrix XRD pattern As mentioned in the introduction, this kind of photoactive molecule is known for its efficient incorporation into LDH matrices. 3,11 The dispersion provided by hosting photoactive molecules in LDH has already been demonstrated 10 to improve the luminescent properties of dyes such as fluorescein. In the same vein, the hosting of SRB molecules in Zn 2 Al is expected to lead to a luminescent hybrid powder.…”

“…The same behaviour was evinced in the case of fluorescein molecules incorporated into LDH galleries. 10 Indeed, when intercalated SRB molecules are sufficiently close to each other in such a restricted space, they are prone to aggregation by π-stacking (parallel stacking) due to conjugated xanthene rings or by hydrogen bonding (head-to-tail). Xanthene dyes such as SRB or fluorescein are well-known 30 to interact mutually, resulting in luminescence quenching when the concentration reaches a critical value to form dimers, trimers, etc.…”

“…Indeed, SRB exhibits interesting luminescence characteristics but only in diluted solutions, 8, 9 as most organic dyes, and is optically inactive in its solid state. Furthermore, it has already been reported that the straightforward dispersion of dye molecules into a polymer can cause them to aggregate, thus forming heterogeneous composite films presenting a tiny absolute photoluminescence quantum yield (PL QY abs ), 10 underlining the need to maintain the dye molecules apart from each other to avoid their optical quenching. An elegant solution consists in immobilizing the SRB molecules in a host lattice like a layered double hydroxide (LDH) as previously reported.…”

Luminescent N-heterocycles based molecular backbone interleaved within LDH host structure and dispersed into polymer

“…Expectedly, the dispersion of the dye into LDH matrix would allow to reproduce a solid state mixed into a solvated system as in a liquid solution to increase the absolute PLQY. However, the desired effect is not occurring as for the fluorescein (Legentil et al, 2019). The absolute PLQY of the LDH-PTPH paste is higher than the absolute PLQY of the powder, the absolute PLQY max is 11.9 % for λ exc = 320 nm.…”

Reliability study under thermal and photonic stresses of sulforhodamine B (SRB) confined in layered double hydroxide (LDH)

“…As mentioned before, to further address a practical application in commercial lighting devices, a major specification required of the fluorophore and its associated system is to present long-term stability with respect to various types of stress in real operating conditions. Several published works mentioned the use of fluorophore with a potential application for replacing traditional phosphors with rare earth elements in commercial WLED, such as fluorescein, pyranine, rhodamine or triphenylamine derivatives for instance (Das and Manam, 2018;Legentil et al, 2019;Nyalosaso et al, 2019;Zhang et al, 2008). However, the authors do not usually pay attention to the reliability of the dyes in stressful conditions.…”