Yeah they absorb infrared from 710 - 880nm depending on the ink you get. My other question is why does a purple red filter for this as from my understanding purple is closer to the wavelength of UV.
I stumbled upon an old thread from 2014 about invisible IR ink and have been looking into the same thing very recently.
https://www.physicsforums.com/threads/does-infrared-ink-exist.744888/
So far on my research I have found an IR ink that absorbs Infrared...