Cinnamate intercalated-layered yttrium hydroxide: A potential hybrid UV filter

Cinnamate-Intercalated Layered Yttrium Hydroxide: UV Light-Responsive Switchable Material

In recent years, there has been an increasing interest in stimuli-responsive host-guest materials due to the high potential for their application in switchable devices. Light is the most convenient stimulus for operating these materials; a light-responsive guest affects the host structure and the functional characteristics of the entire material. UV-transparent layered rare earth hydroxides intercalated with UV-switchable anions are promising candidates as stimuli-responsive host-guest materials. The interlayer distance in the layered rare earth hydroxides depends on the size of the intercalated anions, which could be changed in situ, e.g., via anion isomerisation. Nevertheless, for layered rare earth hydroxides, the possibility of such changes has not been reported yet. A good candidate anion that is capable of intercalating into the interlayer space is the cinnamate anion, which undergoes UV-assisted irreversible trans-cis isomerisation. In this work, both trans- and cis-cinnamate anions were intercalated in layered yttrium hydroxide (LYH). Upon UV-irradiation, the interlayer distance of trans-cinnamate-intercalated layered yttrium hydroxide suspended in isopropanol changed from 21.9 to 20.6 Å. For the first time, the results obtained demonstrate the possibility of using layered rare earth hydroxides as stimuli-responsive materials.

Superlattice films of semiconducting oxide and rare-earth hydroxide nanosheets for tunable and efficient photoluminescent energy transfer

Europium and terbium doped layered gadolinium hydroxides were prepared by microwave assisted hydrothermal precipitation. They were subsequently exfoliated into nanosheets by sonication treatment in formamide. The thickness of the nanosheets (LGdH:Eu and LGdH:Tb) was found to be approximately 1 nm, exemplifying a single-layer feature. Multilayer and superlattice films were prepared through layer-by-layer (LbL) deposition of exfoliated hydroxide nanosheets with a polyanionic electrolyte (polystyrene sulfonate, PSS) and heteroassembly with semiconducting oxide nanosheets (Ti0.87O20.52- and TaO3-), respectively. Compared to the multilayers of (LGdH:Eu/PSS)n and (LGdH:Tb/PSS)n, the superlattices of (LGdH:Eu/Ti0.87O20.52-)n and (LGdH:Tb/TaO3-)n exhibited significantly enhanced photoluminescence intensity, ∼14 times and ∼5 times, respectively. The photoenergy absorbed by the semiconducting nanosheets can be transferred to the excited states of rare-earth hydroxide nanosheets for enhanced photoluminescence emission. Further investigation on the stacking sequence of the nanosheets revealed that direct neighboring and energy level matching with semiconducting nanosheets was essential for realizing efficient energy transfer across the nanosheet interface. Annealing at 600 °C could further enhance the emission intensity of the superlattice structured films. The current work demonstrates an important strategy for hetero-assembling nanosheets at the molecular level with a carefully designed interface for tunable and enhanced functionalities.