A variety of florescent particulate can be combined with Up Conversion IR inks in order to take a otherwise invisible bar code or QR code into a visible glowing readable beacon of light for robotics navigation and programming. In my case my application is both unique and useful. I regularly search for similar information about invisible marking methods like those in anti counterfeit measures.

https://phys.org/news/2012-09-upconverting-nanoparticle-inks-invisible-qr.html

Here is the first time I have seen this used specifically in the way that I have, but the specifics are kept secret, the postal service sometimes has UV reactive codes come through that use information to track mail outside just the address info.