Multi-Level Anti-Counterfeiting Glasses Using Chinese Blue Ancient Pigments

A multi-level luminescent, transparent and permanent glass ceramic system for anti-counterfeiting systems and security was developed. The glass emits a radiation of different wavelength depending on the radiation used to illuminate them, possessing multiple levels of safety. The red persistent phosphor Y 2 O 2 S:Eu 3+ , Mg 2+ , Ti 4+ (YOS) was mixed with the Han Blue (HB), the oldest Chinese synthetic pigment, and the glasses were synthesized by sol-gel method. HB is constituted by two different crystalline phases, the effenbergerite and the colinowensite. Imaging techniques, excitation and emission spectra, and the time-resolved photoluminescence measurements were used to verify that the obtained systems showed the desired optical characteristic both in the infrared and in the visible spectral ranges. The two components act synergistically: upon UV illumination, YOS emits red photons over time, while HB absorbs this energy and re-emits it as infrared photons. The resulting dual emission, combined with the specific luminescence lifetime of each emission component and the time-dependent afterglow behaviour, provides a unique and non-trivial optical fingerprint. These four independent authentication parameters — (i) visible dual emission, (ii) NIR emission response, (iii) characteristic luminescence lifetime, and (iv) persistent afterglow duration and evolution — can be regarded as four distinct levels of security, significantly enhancing the reliability and robustness of the proposed anticounterfeiting glass system.