Gd³⁺-Doped NaYF₄:Yb,Er Upconversion Nanoparticles: Synthesis, Luminescence Enhancement, and Anti-Counterfeiting...

Precise control over the optical properties of lanthanide-doped upconversion nanomaterials is of fundamental importance for their wide-ranging applications. In this study, Gd³⁺-doped nanoparticles with enhanced upconversion luminescence were prepared. The influence of Gd³⁺ doping on luminescence was systematically investigated. This method significantly improves the uniformity of particle size and enhances the luminescence intensity of NaYF₄:Yb/Er nanoparticles. Doping with Gd³⁺ replaces Y³⁺ ions and induces local lattice distortion, which modifies the crystal field symmetry around the rare-earth ions, increases their transition probability, and thereby directly enhances the luminescence intensity. Additionally, Excitation-power-dependent log-log analysis reveals that Gd³⁺ incorporation modifies the effective photon numbers of the upconversion channels. Importantly, this material enables the generation of high-resolution anti-counterfeiting patterns through inkjet printing. The proposed method to enhance upconversion emission is meaningful for designing novel luminescent materials and expanding their optical applications.