Fabrication, spectroscopic and photofunctional studies of layered lutetium-dysprosium hydroxides

The spectroscopic studies of layered rare-earth hydroxides (LRHs) have aroused great interests owing to the unique features of combing rare-earth ions with diverse anions. In this work, some anions were incorporated into layered lutetium-dysprosium hydroxides (LLuH:Dy) by the hydrothermal and ion exchange process, in which Dy3+ ion acted as the emission center. The results manifest that the assemblies possess clearly lamellar structure and flake shape, and emit the characteristic yellow and blue light of Dy3+ under ultraviolet excitation. The inorganic WO42- intercalated LLuH:Dy shows enhanced luminescence under the excitation with 280 nm which originates from the O-W charge transfer band. The more fantastic is that the assembly produces bright cyan light due to the appropriate yellow/blue light intensity ratio, and can transform into transparent and flexible film by mixing with certain polymer. Moreover, the intercalation of organic chromophore benzenetetracarboxylic anion into LLuH:Dy also greatly promotes the Dy3+ luminescence, and can easily form the nanosheet colloid through combining with surfactant dodecyl sulfonate. The colloid is very stable at ambient temperature and displays excellent selectivity, sensitivity and accuracy for detecting metal Co2+ in aqueous media, constructing a superior fluorescence sensor for Co2+ with a detection limit of 2.65 × 10-7 mol/L. This work expands the photofunctional performances of LRHs in the form of transparent film and colloidal state.

Spectroscopic properties and fluorescent recognition of dye sensitized layered lutetium-terbium hydroxides

The layered rare earth hydroxides have attracted increasing interests due to their diverse chemical composition and tunable spectroscopic properties. In this paper, a novel Tb³⁺ activated layered lutetium hydroxide (LLuH:Tb) was fabricated, in which the inorganic NO₃^- ions were ion-exchanged with organic (ibuprofen or dodecylsulfonate) anions. After the ion-exchange reaction, the organic anions intercalated LLuH:Tb showed the distinct lamellar structure with the interlayer distance of about 2.56 nm, confirming the formation of inorganic/organic hybrid assembly. The dye ibuprofen-intercalated hybrid effectively promoted the characteristic ⁵D₄ → ⁷F₅ green emission of Tb³⁺ in the host but failed to be exfoliated into nanosheet colloid. On the contrary, the dodecylsulfonate-intercalated hybrid was readily to be exfoliated into nanosheet colloid by dissolving in formamide solvent, but the green emission of Tb³⁺ was too weak to be observed. To take advantage of their respective merits and explore the practical uses, certain amounts of dye ibuprofen were directly added to the dodecylsulfonate-intercalated hybrid colloid. Excited with the ultraviolet light, the characteristic green fluorescence of Tb³⁺ was dramatically enhanced, indicating that the dye was a superior light-harvesting antenna to sensitize the activator Tb³⁺. The dye sensitized hybrid colloid was very stable at ambient temperature and exhibited excellent fluorescent recognition for Cu²⁺ ions over other metal ions in aqueous solution due to the large fluorescence quenching. The detection limit for Cu²⁺ ion reaches 7.63 × 10^-7 mol/L, which is far lower than the limitation of Cu²⁺ in drinking water recommended by the World Health Organization (1.57 × 10^-5 mol/L). The fluorescence enhanced/quenched sensor with excellent stability exhibits a high potential for the detection of Cu²⁺ in routine environmental water.

3,5-Dihydroxy Benzoic Acid-Capped CaF2:Tb3+ Nanocrystals as Luminescent Probes for the WO4 2- Ion in Aqueous Solution

We report a facile and effective luminescence method for the determination of the WO4 2- ion in aqueous medium at initial pH = 6.3. This is achieved using 3,5-dihydroxybenzoic acid-capped CaF2:Tb3+ (5%) nanocrystals (NCs) as a luminescent probe. This is accomplished based on the energy transfer luminescence from the WO4 2- ion to the Tb3+ ion in small-size CaF2:Tb3+ NCs. Hydroxyl groups on the surface ligand helps in binding the tungstate ion to the surface of the NCs. With the gradual addition of the WO4 2- ion, the intensity of the Tb3+ excitation and emission spectra significantly increased. The linear range of the detection was from 1 to 10 μM for the WO4 2- ion (R 2 = 0.99). The calculated detection limit was 0.4 μM (by applying the 3σ/K criterion).

A unique delaminated MoS4/OS-LEuH composite exhibiting turn-on luminescence sensing for detection of water in formamide

A delaminated MoS₄/OS-LEuH composite showed quenched luminescence in pure formamide while highly enhanced emission in the water-present case.

Antenna Effect on the Organic Spacer-Modified Eu-Doped Layered Gadolinium Hydroxide for the Detection of Vanadate Ions over a Wide pH Range

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 inner filter effect of Cr(vi) on Tb-doped layered rare earth hydroxychlorides: new fluorescent adsorbents for the simple detection of Cr(vi)

The effective overlap of excitation bands of Tb-doped layered yttrium hydroxychlorides with absorption bands of Cr(vi) (both HCrO₄⁻ and CrO₄²⁻ forms) constructs a new inner filter effect system resulting in fluorescence quenching.