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.
Keywords: erbium-doped silicon; laser-assisted fabrication; optical security labels; photoluminescence.
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