Upconverting nanoparticles typically absorb low frequency radiation and emit at higher frequencies relying upon multiphoton processes. One such type of particle is NaYF4:Yb. Er. which absorbs at 975 nm while emitting in visible radiation. https://www.diegojavierfares.com/mega-offer-Classic-Premier-Navy-Drapery-Fabric-by-Premier-Prints-30-Yard-Bolt-super-offer/