Method for labeling products with a transparent photoluminescent label, and transparent photoluminescent label

A method for marking a product (1) with a photoluminescent mark, said mark comprising a photoluminescent portion (10) which is transparent under normal light conditions and revealed by photoluminescence under UV illumination, said mark further comprising a non photoluminescent portion (9) which is transparent under normal light conditions as well as under UV illumination, said method comprising: deposing on said product a stack, said stack comprising alternatively layers (2, 4), such as AlN, with a thickness of less than 1 micron and layers (3) of a second material, such as GaN, with a thickness of less than 10nm; raising the transparency of said non photoluminescent portion (10) with a deposition of transparent material (6) or incorporation of ions into said non photoluminescent portions.