4,4'-Bipyridyl functionalized Eu³⁺-activated gadolinium nanophosphors for reversible Cr³⁺ OFF-ON luminescent sensing and photocatalytic dye degradation.

Authors

Nidhi Bhagat, Niharika, Richa Singhaal, Waseem Ahmed, Vikram Jeet, Rohit Singh, Haq Nawaz Sheikh

Published in

Dalton transactions (Cambridge, England : 2003). Jul 12, 2026. Epub Jul 12, 2026.

Abstract

The development of multifunctional luminescent nanomaterials for environmental monitoring and wastewater remediation has attracted considerable research interest. In this work, Eu³⁺-activated NaGd(MoO₄)₂, NaGd(WO₄)₂, and Na₃Gd(VO₄)₂ nanophosphors were hydrothermally synthesised and subsequently functionalized with 4,4'-bipyridyl (4,4'-bipy) to establish dual-mode photoluminescent sensing and photocatalytic platforms. Structural and morphological analyses confirmed the formation of highly crystalline rod-like nanostructures with successful surface functionalization. Among the synthesised materials, Na₃Gd(VO₄)₂:Eu³⁺@4,4'-bipy exhibited the highest emission intensity and longest decay lifetime (3.16 ms), indicating efficient energy transfer and suppressed non-radiative relaxation pathways. The functionalized nanophosphors demonstrated concentration-dependent turn-off photoluminescence sensing behaviour toward Cr³⁺ ions. Notably, Na₃Gd(VO₄)₂:Eu³⁺@4,4'-bipy showed superior sensing performance with a Stern-Volmer constant of 8.2 × 10⁴ M^-1 and a detection limit of 0.017 ppm. Furthermore, the quenched emission was effectively restored using chelating agents, particularly trisodium citrate, establishing a reversible dual-mode OFF-ON photoluminescent sensing system with a recovery efficiency of ∼92.6%. Mechanistic investigations suggested that the turn-off sensing process is primarily governed by photoinduced electron transfer (PET) and luminescence resonance energy transfer (LRET) interactions, whereas the turn-on emission recovery process is associated with trisodium citrate-assisted chelation of Cr³⁺ ions. In addition, NaGd(WO₄)₂:Eu³⁺@4,4'-bipy exhibited superior photocatalytic activity toward Rhodamine B degradation under UV irradiation owing to its lower bandgap energy and enhanced light absorption capability. These findings highlight the potential of rare-earth-functionalized nanophosphors for selective ion sensing, emission recovery, and environmental remediation applications.

PMID:
42437490
Bibliographic data and abstract were imported from PubMed on 13 Jul 2026.

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