Preparation of Eu2+, Dy3+, Zr4+ ions co-doped strontium aluminate/molybdate multi-optical functional hybrid pigments for anti-counterfeiting

Eu2+, Dy3+ and Zr4+ ions co-doped strontium aluminate (i.e., SrAl2O4:Eu2+,Dy3+,Zr4+)/molybdate (i.e., Ho2MoO6 or Nd2MoO6) with photo-/mechano-luminescence and allochroic effect as multi-optical functional hybrid pigments were prepared via solid state reactions and subsequent mixing. The phosphor and hybrid pigments were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, ultraviolet–visible spectroscopy, L∗a∗b∗ color scale analysis, spectrophotometry and mechanoluminescent measurement. The results show that the optimum luminescent emission intensity of SrAl2O4:Eu2+,Dy3+,Zr4+ phosphor can be obtained when 5 mol% Zr4+ ions is doped into the lattice. Under the excitation of 365 nm wavelength, the hybrid pigments prepared with the phosphor and molybdate at a mass ratio of 1:1 present a green broad band emission located at 460–650 nm due to 4f65d1→4f7 transitions of Eu2+ ions. The hybrid pigments have the superior mechanoluminescent property and emit light after being exerted by mechanical stresses. Besides, the hybrid pigments also exhibit an allochroic effect under different illuminants. In addition, the anti-counterfeiting of the hybrid pigments as a promising application was also presented.