Development of Anti-counterfeiting ink  and  Hydrogel with red luminous Ca2+-doped Y2O3:Eu3+ 1 mol%) nanoparticles

A divalent calcium ion (1 mol %) co-doped with Y₂O₃:Eu³⁺ (1 mol %) nano-phosphors was successfully synthesized via the solution combustion method using urea as a fuel. The nanophosphor underwent structural and optical characterization via XRD, SEM, and PL techniques. X-ray diffraction confirmed a pure, highly crystalline cubic Y₂O₃ phase, while SEM revealed a spherical morphology with slight agglomeration. The PL data revealed that Ca²⁺ co-doping significantly enhanced the red 5D₀ → 7F₂ emission of Eu³⁺ at 613 nm, indicating improved energy transfer and local symmetry. The phosphor exhibited near-ideal red CIE coordinates making it a strong candidate for solid-state lighting and display technologies. Moreover, the prepared luminous material was used to develop an anti-counterfeiting (AC) invisible ink that emits a vivid red glow under UV light. The designs were treated with several solvents, including ethanol, acetone, HCl, NH3, and NaOH, which could destroy the design's foundation, in order to assess the ink's chemical stability. The digital images displayed in Fig. demonstrate the patterns' notable resistance to the solvent.