Di-functional luminescent sensors based on Y3+ doped Eu3+ and Tb3+ coordination polymers: fast response and visible detection of Cr3+, Fe3+ ions in aqueous solutions and acetone

Abstract

With the careful modulation of the relative ratio of Y³⁺/Eu³⁺and Y³⁺/Tb³⁺, two series of bimetallic RE-CPs (Eu _x Y_{1- x} and Tb _x Y_{1- x} ) were successfully obtained through the isomorphous substitution method. Interestingly, the introduction of Y³⁺ ions does not change the fluorescence characteristic peak of 1-Eu and 1-Tb, but enhances its fluorescence lifetime and quantum yield. Experimental and theoretical simulation results show the co-doping process changes the intramolecular energy transfer process and reduces the non-radiative transition resulting from concentration quenching. Eu_0.1Y_0.9 and Tb_0.1Y_0.9 with the largest luminescence lifetime were selected as the representative research objects, their potential application for the detection of toxic metal ions and organic molecules was further investigated. Interestingly, Eu_0.1Y_0.9 and Tb_0.1Y_0.9 demonstrate high sensitivity and good selectivity towards Fe³⁺, Cr³⁺ and acetone. Besides, fine fluorescence visibility provides the necessary conditions for the preparation of simple and fast response fluorescent test papers in order to achieve real-time and convenient detection of these toxic materials.

Scheme 1. Schematic diagram of the synthetic strategy for RE-MOFs (the phosphorescence spectrum of 1-Gd was used to calculate the energy of triplet state (T₁) for H₄BPTC).

Scheme 2. Schematic diagram of the synthetic strategy for Eu_xY_1−x and Tb_xY_1−x.

Fig. 1. PXRD patterns of (a) Eu_0.1Y_0.9 and (b) Tb_0.1Y_0.9 immersed in different pH (2–12) solutions for 24 hours.

Fig. 2. (a) The solid-state luminescence of 1-Y, Eu_0.1Y_0.9 and Tb_0.1Y_0.9 (λ_ex = 275 nm). (b) CIE chromaticity diagram for 1-Y, Eu_0.1Y_0.9 and Tb_0.1Y_0.9. Inset: photographs of (1) 1-Y, (2) Eu_0.1Y_0.9 and (3) Tb_0.1Y_0.9 under ultraviolet light of 365 nm.

Fig. 3. The energy transfer process of Eu_0.1Y_0.9 and Tb_0.1Y_0.9.

Fig. 4. Luminescent spectra of (a) Eu_0.1Y_0.9 and (c) Tb_0.1Y_0.9 upon the addition of various metal ions in DMF (λ_ex = 275 nm); quenching efficiency values of (b) Eu_0.1Y_0.9 and (d) Tb_0.1Y_0.9 in DMF by different metal ions (1 × 10⁻² M).

Fig. 5. (a) Luminescent spectra of Eu_0.1Y_0.9 dissolved in different solvents (λ_ex = 275 nm). (b) Bar chart obtained for Eu_0.1Y_0.9 upon addition of different solvents. (c) Luminescent spectra of Eu_0.1Y_0.9 with the gradual addition of acetone (0–100 ppm).

Fig. 6. (a) Time-dependent emission spectra after exposure of Eu_0.1Y_0.9 to the Fe³⁺. (b) Fluorescence quenching percentage by Fe³⁺ (λ_ex = 275 nm). (b) Plots of ln(I₀/I_t) for the luminescent intensity of Eu_0.1Y_0.9 at 615 nm obtained from the spectra.

Fig. 7. Durability and stability of (a) Eu_0.1Y_0.9 and (b) Tb_0.1Y_0.9 dispersed in Fe³⁺ ions aqueous solution (the green bars represent the initial fluorescence intensity, and the red bars represent the intensity upon addition an aqueous solution of 1 mL of 1 × 10⁻² M Fe³⁺ ion).

Fig. 8. The XPS spectra of Eu_0.1Y_0.9 before and after the detection of Fe³⁺ and Cr³⁺.

Fig. 9. Optical images of Eu_0.1Y_0.9 test papers under UV light irradiation at 365 nm after immersion in various solutions.