Why is filter paper fluorescent?
In the production of white paper, the bleached pulp is often treated with optical brightening additives (OBA), that absorb in the uv and emit in the blue range. If I remember correctly, a typical example is 4,4'-diaminostilbene-2,2'-disulfonic acid.



Here's an article from The Open Textile journal (OA) in which the compound mentioned above is used as a starting material in the synthesis of another optical brightener for textiles.