I came across https://www.nano-resonance.com/ which appears to be the promotional page for the technique, it has a nice diagram which appears to show how the size of the silicon nanoparticle enhances certain wavelengths of light.

Very cool how they can use an inkjet printer for their approach.

Also see https://en.wikipedia.org/wiki/Lippmann_plate for a photographic process that creates colours using diffraction patterns.

https://www.youtube.com/watch?v=-DyrBDsKA5s is a fun video on lippmann plates.

"...smart displays and vibrant art pieces (that won’t fade over time)... However, when the display is turned off, the images become visible, which allows for information display without using any energy."

Nowhere does it say that the coloration can be changed, once applied. The different-sized particles are embedded in acrylic. So how does this enable a "smart display?" I guess you can say that a turned-off monitor can now show "information," but that information printed on the screen would be static for all time... wouldn't it?

No doubt a potential worry for currency producers. Inkjets that have control over the physical build up of ink structure would pose an even greater threat of counterfeiting.

No doubt mints can introduce countermeasures to detect such threats but I'd suggest this tech (if perfected) will likely be too good for humans to detect a forgery at a glance. Reckon machine readers will become the order of the day, that's if physical paper/plastic currency continues to exist.

Probably a foolish question, but wouldn't there be some unavoidable loss of brightness to the transmitted light, unless the structured color somehow "knows" to transmit light in one direction and reflect it in the other direction (which seems impossible given that it is printed by an inkjet)?

Doesn't the pigment act as ("natural") nanoscale structure as well?