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 Al³⁺

Abstract

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 = Tb3+, Y3+) 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 x OS1–x -LTbH (x = 0.10, 0.15, 0.20 , 0.25) and HNA y OS1–y -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, HNA0.25OS0.75-1:1-LYH, HNA0.25OS0.75-1:2-LYH, and HNA0.05OS0.95-1:1-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 (HNA0.25OS0.75-1:1-LTbH) has also a relatively higher quantum yield of 12.46%. The HNA0.25OS0.75-1:1-LYH colloid exhibits excellent recognition selectivity for Al3+ over other metal ions (Mg2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+, and Hg2+) with distinct fluorescence sensitization. It shows an intense change in its fluorescence emission when it is bound to Al3+ ions, giving a lower detection limit of 6.32 × 10–6 M. This is novel research on the fluorescence chemosensing of LRH composites.

A ratiometric luminescence nanoprobe based on layered terbium hydroxide nanosheets for quantitative detection of an anthrax biomarker

“…It can also be seen that the composites are composed of microcrystalline particles. 33 Cl-LTbH (Fig. 2(a)) mainly crystallizes into elongated hexahedral platelets, and some grow into columnar or flower-like aggregates, which are observed in previous studies.…”

“…2(a)) mainly crystallizes into elongated hexahedral platelets, and some grow into columnar or flower-like aggregates, which are observed in previous studies. 24,28,33 SDS-LTbH (Fig. 2(b)) keeps the morphology of the Cl-LTbH precursor.…”

“…32 The sharp and symmetric diffractions suggest the formation of well-crystallized layered compounds. 24,33 For SDS-LTbH (Fig. 1(A)-b), a series of sharp and symmetric basal (00l) reflections are observed at 2.78, 1.39, 0.92, 0.69 and 0.56 nm with a basal spacing (d basal ) of 2.78 nm, indicating the well-ordered hydroxide layers.…”

“…Normally, the sensitization luminescence effect needs an effective energy transfer from the activators to the acceptors, 33,34 which means a perfect fit of the energy gap between the excited state energy levels of Tb 3+ and the triplet state energy levels of the organics. If the energy difference is too large, then the probability of electron conversion will be little, thus decreasing the chance of transition.…”

“…If the energy difference is too small, inverse or mutual transition may occur, while most of the energy would be inactivated by vibration rather than luminescence. 33 An energy gap of 3500 cm −1 or higher is necessary to facilitate efficient and irreversible energy transfer. 23,33 As shown in Scheme 1, the mechanism of the energy transfer can be ascribed to the antenna effect: DPA is excited by energy (usually the ultraviolet light) and electrons generate the π-π transition.…”