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<p>Eu<sup>3+</sup>-doped hydroxyapatite nanoparticles were synthesized and integrated into plasma electrolytic oxidation (PEO) coatings on magnesium alloys to develop a multifunctional system with corrosion protection, self-healing capability, and optical degradability monitoring. Structural analyses confirmed successful Eu<sup>3+</sup> incorporation into the hydroxyapatite lattice without secondary phases, with Eu<sup>3+</sup> ions preferentially occupying low-symmetry Ca<sub>2</sub> sites. The photoluminescence behavior exhibited an optimal emission at 12 at.% Eu<sup>3+</sup>, while sintering at 500 °C maximized photoluminescence through enhanced crystallinity. When incorporated into PEO coatings, the HAp:Eu<sup>3+</sup> nanomaterials underwent gradual dissolution and reprecipitation in Hanks’ solution, accompanied by morphological changes and the formation of Mg(OH)<sub>2</sub> and Mg<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> phases. Photoluminescence intensity decreased following apparent first-order kinetics, indicating preferential leaching of Eu<sup>3+</sup>, particularly from the less stable Ca<sub>2</sub> sites. Electrochemical measurements revealed a three-stage corrosion evolution, transitioning from initial passivation to active corrosion and subsequent re-passivation through redeposition. To correlate optical responses with corrosion behavior during the early degradation stage, a simplified multivariate regression model was established. Using <i>I</i><sub>ED</sub>/<i>I</i><sub>MD</sub>, I<sub>616</sub>, and immersion time as predictors, the fitted coefficients demonstrated that stronger Eu<sup>3+</sup>emission and higher spectral ratios correspond to lower corrosion activity, while the positive <i>γ</i> term captured the time-dependent acceleration of dissolution. This optical–electrochemical coupling confirms that Eu<sup>3+</sup> luminescence encodes structural and kinetic information associated with coating degradation. This result provides a possibility for tracking the degradation of coatings using Eu<sup>3+</sup>-based optical signals. The synergistic use of optical and electrochemical signals provides a novel non-destructive strategy for assessing the stability of functional coatings, with promising implications for the design of smart biodegradable implants with tunable corrosion and bioactive properties.</p>

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Photoluminescence and Electrochemical Investigations on the Degradation Mechanism of PEO@HAp:Eu3+ Coatings on Magnesium Alloy in Hanks’ Solution

  • 期刊论文

  • 发表日期：

    2026年3月2日

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  • Zhaozhong Qiu,
  • Ke Liu,
  • Zhaoyan Liu,
  • Xincheng Zhang,
  • Wenkai Lan,
  • Jia Sun,
  • Yao Zhang,
  • Jiawen Xu,
  • Ailian Liu,
  • Gang Liang,
  • Sun Limei

摘要

Eu3+-doped hydroxyapatite nanoparticles were synthesized and integrated into plasma electrolytic oxidation (PEO) coatings on magnesium alloys to develop a multifunctional system with corrosion protection, self-healing capability, and optical degradability monitoring. Structural analyses confirmed successful Eu3+ incorporation into the hydroxyapatite lattice without secondary phases, with Eu3+ ions preferentially occupying low-symmetry Ca2 sites. The photoluminescence behavior exhibited an optimal emission at 12 at.% Eu3+, while sintering at 500 °C maximized photoluminescence through enhanced crystallinity. When incorporated into PEO coatings, the HAp:Eu3+ nanomaterials underwent gradual dissolution and reprecipitation in Hanks’ solution, accompanied by morphological changes and the formation of Mg(OH)2 and Mg3(PO4)2 phases. Photoluminescence intensity decreased following apparent first-order kinetics, indicating preferential leaching of Eu3+, particularly from the less stable Ca2 sites. Electrochemical measurements revealed a three-stage corrosion evolution, transitioning from initial passivation to active corrosion and subsequent re-passivation through redeposition. To correlate optical responses with corrosion behavior during the early degradation stage, a simplified multivariate regression model was established. Using IED/IMD, I616, and immersion time as predictors, the fitted coefficients demonstrated that stronger Eu3+emission and higher spectral ratios correspond to lower corrosion activity, while the positive γ term captured the time-dependent acceleration of dissolution. This optical–electrochemical coupling confirms that Eu3+ luminescence encodes structural and kinetic information associated with coating degradation. This result provides a possibility for tracking the degradation of coatings using Eu3+-based optical signals. The synergistic use of optical and electrochemical signals provides a novel non-destructive strategy for assessing the stability of functional coatings, with promising implications for the design of smart biodegradable implants with tunable corrosion and bioactive properties.