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

ABSTRACT We report a stepwise strategy for synthesizing a multifunctional Fe 3 O 4 /Y 1.76 Yb 0.2 Er 0.04 O 3 @SiO 2 -[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 Fe 3 O 4 co-precipitation, homogeneous precipitation of the Y 2 O 3 :Yb 3+ /Er 3+ shell, silica coating, and surface functionalization with isocyanate groups followed by carboxylic acid grafting. Carboxylate groups were coordinated to Eu 3+ , while dbm - ligands occupied the remaining sites, promoting efficient antenna-mediated sensitization of Eu 3+ luminescence. The final hybrid retained soft-magnetic behavior (Ms = 0.89 emu g -1 ; negligible coercivity), exhibited strong orange upconversion under 980 nm excitation from Yb 3+ /Er 3+ centers and intense Eu 3+ downshifting emission under 340 nm excitation (intrinsic quantum yield = 52%), and yielded a PVA-based multifunctional ink preserving luminescent duality and magnetic response after incorporation into polyvinyl alcohol matrices, demonstrating the versatility of multifunctional magnetic nanoparticle/lanthanide hybrid platforms for next-generation security ink systems and devices in advanced anti-counterfeiting applications.