Dual-barrier interface engineering enabling long-term sub-detection-limit release of lanthanide ions and surface...

The environmental persistence and ecological risks of lanthanide ions make leakage from doped functional materials a critical bottleneck for their safe application. This study employs poly(butylene succinate)-CaF₂:Yb,Eu/mesoporous silica glass-CaF₂:Yb,Tm (PETM) composite microspheres with a surface-enriched gradient architecture to investigate long-term stability and lanthanide ion release. Microspheres were immersed in a deposition solution for 28 days, monitoring degradation, pH, ion release, and fluorescence retention. Results show slow, controllable degradation (apparent mass loss 9.9%) and stable pH (7.40-7.60). Yb^3 + release remained below the ICP-OES detection limit (0.01 ppm) throughout, achieving sub-detection-limit release; the estimated cumulative release fraction over 28 days was < 0.13%. After baseline correction, net peak height retention rates of Tm³⁺ and Eu³⁺ emission peaks were 53.1% and 55.5%, with peak shapes and positions stable. An in-situ-formed dense hydroxyapatite layer provided a self-reinforcing protection mechanism. Four controlled experiments revealed synergistic confinement by KH-550 chemical anchoring and MSG mesoporous physical isolation: normalized reductions were ∼73% and ∼87%, respectively; their combination suppressed release below the detection limit. This work proposes a dual-barrier interface strategy based on the safety-by-design concept, providing a quantifiable control scheme for the environmental safety of lanthanide-doped functional materials during long-term service.