Fig. 4: Static encoding based on PL intensity of SiV centers in diamond microparticles.

a Illustration of the readout process of the diamond-PUF label using a 532 nm green laser. b A confocal fluorescence image of the diamond-PUF label with an area of 100 µm × 100 µm. c The cumulative curve of the PL intensity (photon counts: counts per second, cps) in the measured area shown in (b). d The digitization of the quaternary encoding of the PL intensity levels at each pixel at a resolution of 25 pixels × 25 pixels and 50 pixels × 50 pixels. The digitization of e decimal encoding, and f hexadecimal encoding at a resolution of 50 pixels × 50 pixels. The pairwise match of 25 PUF labels with quaternary, decimal and hexadecimal encodings of PL intensity levels at each pixel are shown next to the corresponding encoding matrix. The x-axis and the y-axis represent the first and the second measurement of the labels, respectively, and the color bar shows the similarity index. g The corresponding Hamming inter- and intra-distance (normalized) of the quaternary, decimal and hexadecimal keys generated from 25 labels.