Next‐Generation Multilevel Anti‐Counterfeiting Technologies: Deciphering the UV/Violet Luminescence of Bi‐Doped Yttrium Germanates

Counterfeiting is a global issue with severe economic, security, and health impacts, requiring advanced anti‐counterfeiting solutions. Luminescent materials offer unique, hard‐to‐replicate identification features. To this purpose, Y 2 GeO 5 and LiYGeO 4 samples doped with 0.5 mol% of bismuth (Bi) are synthesized by a solid‐state reaction. X‐ray diffraction and Raman spectroscopy revealed their polyphasic nature, with the samples mainly consisting of the desired crystalline phases. Photoluminescence measurements indicated that all samples exhibit a strong emission band in the ultraviolet A spectral region (355–365 nm), attributed to Bi 3+ intraionic transitions. Despite their similarities, lifetime measurements under 300 nm excitation revealed that the LiYGeO 4 sample had a lifetime nearly 100 times longer than the Y 2 GeO 5 sample. Furthermore, afterglow decay profiles demonstrated that persistent luminescence (PersL) is only observed in the LiYGeO 4 sample, detectable for over 7 h after 10 min of stimulation with 250 nm light. Longer wavelengths failed to induce PersL. This finding highlights the importance of the host material and its associated defects as trap centres that contribute to PersL. By combining these materials, multi‐level anti‐counterfeiting codes can be designed based on the differences in lifetime, PersL, and excitation energy, making them extremely difficult to replicate without specific knowledge of the materials involved.