Multifunctional magnetic–luminescent hybrid ink with dual upconversion and downshifting lanthanide(III) emissions for anti-counterfeiting technologies

We report a stepwise strategy for synthesizing a multifunctional Fe3O4/Y1.76Yb0.2Er0.04O3@SiO2-[Eu(dbm)3(pamba)] hybrid (dbm: 1,3-diphenyl-1,3-propanedione, pamba: 4-(aminomethyl)benzoic acid-derived ligand) combining magnetic responsiveness with dual downshifting/upconversion luminescence for security ink applications. The architecture was assembled through Fe3O4 co-precipitation, homogeneous precipitation of the Y2O3:Yb3+/Er3+ shell, silica coating, and surface functionalization with isocyanate groups followed by carboxylic acid grafting. Carboxylate groups were coordinated to Eu3+, while dbm- ligands occupied the remaining coordination positions, promoting efficient sensitization of Eu3+ luminescence. The final hybrid retained soft-magnetic behavior (Ms = 0.89 g−1; negligible coercivity), exhibited strong orange upconversion under 980 nm excitation from Yb3+/Er3+ centers and intense Eu3+ downshifting emission under 340 nm excitation (intrinsic quantum yield = 52%), and yielded a PVA-based multifunctional ink preserving luminescent duality and magnetic response. This system demonstrates the versatility of multifunctional magnetic nanoparticle/lanthanide hybrid platforms for next-generation security ink systems and devices in advanced anti-counterfeiting applications.