Luminescence Tuning of Layered Rare-Earth Hydroxides (LRHs, R = Tb, Y) Composites with 3-Hydroxy-2-naphthoic Acid and Application to the Fluorescent Detection of Al.

Tunable luminescence (quenching or blue shift) of HNA/OS-LRH composites (HNA is 3-hydroxy-2-naphthoic acid; OS is the anionic surfactant of 1-octanesulfonic acid sodium; LRHs are layered rare-earth hydroxides, R = Tb, Y) in the solid state and delaminated state is reported, which is utilized as an effective fluorescent probe for detecting metal ions. HNA/OS species are intercalated into LRH layers to generate composites of HNA OS-LTbH ( x = 0.10, 0.15, 0.20 , 0.25) and HNA OS-LYH ( y = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30). In the solid state, LYH composites exhibit green emissions (from 493 to 504 nm) with a large blue shift in comparison to the 542 nm emission of free HNA anions, while in the delaminated state in formamide (FM), the composites display blue emission (480 nm) relative to the green emission (512 nm) of an HNA soltuion in FM. However, LTbH composites display coquenched luminescence in both the solid state and delaminated state. Also, HNAOS-1:1-LYH, HNAOS-1:2-LYH, and HNAOS-1:1-LYH (1:1 and 1:2 are HNA:NaOH molar ratios) show significantly elongated fluorescence lifetimes of 15.35, 14.37, and 12.72 ns, respectively, in comparison with free HNA-Na (6.44 ns), and their quantum yields of 23.40%, 21.97%, and 22.31%, respectively, are much larger than that of free HNA-Na (4.86%). The LTbH composite (HNAOS-1:1-LTbH) has also a relatively higher quantum yield of 12.46%. The HNAOS-1:1-LYH colloid exhibits excellent recognition selectivity for Al over other metal ions (Mg, Co, Ni, Cu, Zn, Pb, Cd, and Hg) with distinct fluorescence sensitization. It shows an intense change in its fluorescence emission when it is bound to Al ions, giving a lower detection limit of 6.32 × 10 M. This is novel research on the fluorescence chemosensing of LRH composites.