Luminescent Erbium‐Doped Silicon Thin Films for Advanced Anti‐Counterfeit Labels

Abstract The never‐ending struggle against counterfeit demands the constant development of security labels and their fabrication methods. This study demonstrates a novel type of security label based on downconversion photoluminescence from erbium‐doped silicon. For fabrication of these labels, a femtosecond laser is applied to selectively irradiate a double‐layered Er/Si thin film, which is accomplished by Er incorporation into a silicon matrix and silicon‐layer crystallization. The study of laser‐induced heating demonstrates that it creates optically active erbium centers in silicon, providing stable and enhanced photoluminescence at 1530 nm. Such a technique is utilized to create two types of anti‐counterfeiting labels. The first type is realized by the single‐step direct laser writing of luminescent areas and detected by optical microscopy as holes in the film forming the desired image. The second type, with a higher degree of security, is realized by adding other fabrication steps, including the chemical etching of the Er layer and laser writing of additional non‐luminescent holes over an initially recorded image. During laser excitation at 525 nm of luminescent holes of the labels, a photoluminescent picture repeating desired data can be seen. The proposed labels are easily scalable and perspective for labeling of goods, securities, and luxury items.