Luminescent Properties of Lanthanoid-Poly(Sodium Acrylate) Composites: Insights on the Interaction Mechanism

Abstract

The interaction between polyelectrolytes and metal ions is governed by different types of interactions, leading to the formation of different phases, from liquid state to weak gels, through an appropriate choice of metal ion/polyelectrolyte molar ratio. We have found that lanthanide ions, europium(III) and terbium(III), are able to form polymer composites with poly(sodium acrylate). That interaction enhances the luminescent properties of europium(III) and terbium(III), showing that Eu3+/poly(sodium acrylate) (PSA) and Tb3+/PSA composites have a highly intense red and green emission, respectively. The effect of cations with different valences on the luminescent properties of the polymer composites is analyzed. The presence of metal ions tends to quench the composite emission intensity and the quenching process depends on the cation, with copper(II) being by far the most efficient quencher. The interaction mechanism between lanthanoid ions and PSA is also discussed. The composites and their interactions with a wide range of cations and anions are fully characterized through stationary and non-stationary fluorescence, high resolution scanning electronic microscopy and X-ray diffraction.

Luminescent Papers with Asymmetric Complexes of Eu(III) and Tb(III) in Polymeric Matrices and Suggested Combinations for Color Tuning

“…It is well-known that certain metal ions quench the luminescence of lanthanide ions in polymeric matrices. Studies with Eu(III)/PSA and Tb(III)/PSA have already been reported [ 5 ], and Cu(II) was the cation accounting for the highest suppression of luminescence in both cases.…”

“…336 nm and 348 nm, owing to Phen-to-metal energy transfer, along with some characteristic absorption bands that allow us to distinguish Eu(III)-based from Tb(III)-based complexes ( Figure S1 ). Excitation spectra of Eu(III)/PSA and Tb(III)/PSA can be found elsewhere [ 5 ].…”

“…Hard Lewis bases, including organic ligands with carboxylate groups [ 4 ], are generally favored over soft donors. When these carboxylate groups belong to a polymer such as poly(sodium acrylate) (PSA), this polymer can simultaneously work as a binder, thickener, and support matrix [ 5 ]. Still, owing to the low molar extinction coefficients of Ln(III), a second condition is that at least one of those ligands can act as a light harvester, absorbing photons and transferring energy to the metal ion.…”

“…On the one hand, the emission of Ln(III) complexes is often quenched by electron acceptors that have been postulated to compete with Ln(III) ions for organic ligands [ 18 , 19 ]. However, given the high availability of carboxylate groups, a previous work has discarded the competition for PSA as the quenching mechanism [ 5 ]. On the other hand, polyfluorenes undergo fluorescence quenching by mechanisms such as Förster resonance energy transfer or photoinduced electron transfer [ 20 ].…”

Reusable and pH-Stable Luminescent Sensors for Highly Selective Detection of Phosphate

“…The broad band in the range of 230–300 nm in the excitation spectrum results from the O 2− → Eu 3+ charge transfer and π–π* electronic transition in coordinated organic ligands [ 30 , 31 , 32 ]. As shown in Figure 3 a and Supplementary Figure S3 , the emission spectra exhibit five characteristic transitions of Eu 3+ centered at 579, 591, 615, 651, and 699 nm, corresponding to the 5 D 0 → 7 F J transitions ( J = 0, 1, 2, 3, and 4), respectively [ 33 ].…”