Synthesis, characterization and application of an orange-red-emitting InGaZnO4:Eu3+ phosphor in latent fingerprint and security ink

A series of orange-red InGaZnO₄:xEu³⁺ (0.2 mol% ≤ x ≤ 20 mol%) phosphors were successfully synthesized via high-temperature solid-state reaction. The structural characterization, morphology, elemental analysis, and optical properties of the prepared phosphors were extensively discussed. Under 468 nm excitation, the prepared phosphors emit orange-red light at 614 nm and 625 nm due to the electric dipole (ED) transition from the ⁵D₀ to ⁷F₂ level of Eu³⁺. The emission peak at 593 nm is attributed to the magnetic dipole (MD) transition. The optimal doping concentration of Eu³⁺ in the phosphor is 2 mol%, resulting in excellent color purity, with all samples exhibiting purity levels exceeding 99.9 %. Furthermore, the phosphors demonstrate remarkable thermal stability, retaining 73.5 % of their luminescent intensity at 420 K and surpassing a thermal quenching temperature of 480 K. The calculated activation energy (E_a) of InGaZnO₄:2 mol%Eu³⁺ (0.27 eV) further underscores its exceptional thermal stability. The internal quantum efficiency (IQE) of the InGaZnO₄:2 mol%Eu³⁺ phosphor is measured at 46.3 %, indicating a high level of photoelectric conversion efficiency. Latent fingerprints (LFPs) developed using the InGaZnO₄:2 mol%Eu³⁺ phosphor display outstanding selectivity and contrast, allowing for precise identification of Level I-III fingerprint details. Additionally, security ink formulated with InGaZnO₄:2 mol%Eu³⁺ shows potential applications in information encryption and anti-counterfeiting measures. Therefore, the investigated phosphors exhibit significant potential for further development due to their favorable optical properties.