Related question: what is the blacklight-fluorescingest blacklight-fluorescent material? Hippies and partygoers, please advise?
Caveat: this information is intended for a Halloween decoration project, so any recommended material or product should ideally NOT be dangerously radioactive, insanely toxic, prohibitively expensive such that it is typically sold in microgram units, or purchasable solely through government contract or the East Asian black market.