The excitation of the adsorbed vanadate group led to the red emission arising from the efficient energy transfer to Eu-doped layered gadolinium hydroxide (LGdH:Eu). This light-harvesting antenna effect allowed LGdH:Eu to detect selectively a vanadate in aqueous solution at different pHs. Because vanadate exists in various forms by extensive oligomerization and protonation reactions in aqueous solution depending on pH, it is important to detect a vanadate regardless of its form over a wide pH range. In particular, spacer molecules with long alkyl chains greatly facilitated access of a vanadate antenna into the interlayer surface of LGdH:Eu. The concomitant increase in adsorption capacity of LGdH:Eu achieved a strong antenna effect of vanadate on the red emission from Eu(3+). When a suspension containing LGdH:Eu nanosheets (1.0 g/L) was used, the vanadate concentration down to 1 × 10(-5) M could even be visually monitored, and the detection limit based on the (5)D0 → (7)F2 emission intensity could reach 4.5 × 10(-8) M.

The effect of interlayer anions on the photoluminescence of layered rare earth hydroxides was investigated with the rare earth (RE)-doped layered gadolinium hydroxynitrate as a representative base matrix for efficient and stable anion-exchange reactions. Eu 3+ , Tb 3+ , and Ce 3+ were employed as RE activator ions for red, green, and blue emissions, respectively. The excitation and emission behaviors of Gd 1.80 RE 0.20 (OH) 5 XÁnH 2 O (LGdH:RE) were systematically compared for various interlayer inorganic and organic anions, where X = F À , Cl À , I À , OH À , ClO 3 À , S 2À , CO 3 2À , SO 4 2À , terephthalate, 2-naphthoate, and dodecylsulfate members were obtained by the exchange reaction of corresponding X = NO 3 À members.Interestingly, a close relationship was found between the UV-Vis absorption spectra of aqueous solutions containing X anions and the excitation behavior of LGdH:RE. Thus, NO 3 À , I À , and S 2À anions showing high absorbance in aqueous solution consistently shielded the excitation light for the 8 S 7/2 -6 I J transition of Gd 3+ and the 4f -5d interconfigurational transitions of Tb 3+ and Ce 3+ to turn off the corresponding emissions from LGdH:Eu, LGdH:Tb, and LGdH:Ce. In contrast, the effect of terephthalate and 2-naphthoate, despite high absorbance in aqueous solutions, was significantly different depending on the RE activator ion. It is proposed that an identical interlayer anion in the gallery of LRHs can filter or sensitize the UV energy for excitation of RE 3+ -doped LRHs and its role (whether as a filter, a sensitizer, or just a spacer) is determined by the nature of activator ions. 201-2457 † Electronic supplementary information (ESI) available: Additional XRD patterns and FT-IR spectra of Gd 1.80 RE 0.20 (OH) 5 XÁnH 2 O (LGdH:RE) where RE = Eu, Tb, and Ce and X = NO 3 À , F À , Cl À , I À , OH À , ClO 3 À , S 2À , CO 3 2À , SO 4 2À , terephthalate, 2-naphthoate, and dodecylsulfate. XRD patterns measured as a function of reaction time during the exchange reaction of Gd 1.80 Ce 0.20 (OH) 5 NO 3 ÁnH 2 O with Cl À and vice versa. See

A new composite film based on calcined layered rare earth hydroxides and poly(vinyl alcohol) shows a visible light transmittance comparable to that of the pure matrix, highly reinforced mechanical strength as well as tunable photoluminescence in rolled and folded shapes.