Confidential document reproduction prevention method

Claim 1

A confidential document reproduction prevention method for use in a reproduction machine, comprising the steps of: attaching a fluorescent material to at least one portion of an original confidential document, said fluorescent material, when exposed to infrared radiation, being capable of emitting visible light, said fluorescent material being selected from the group consisting of YF 3 , LaF 3 , GdF 3 , LuF 3 , BaYF 5 , BaLuF 5 , BaY 2 F 3 , BaF 2 , LiYF 4 , Y 2 O 2 S, La 2 O 2 S, LaGaO 3 , Gd 2 O 2 S, Y 2 O 3 , Gd 2 O 3 , Y 3 OCl 7 , YOCl, YbOCl, YCl 3 , YbNa(WO 4 ) 2 , LaGaO 3 and YbOCl-MRX 4 , wherein M represents an alkaline metal, X represents halogen, and R represents Y, La, Gd or Lu, said fluorescent material being doped with a combination of rare earth elements wherein said combination of rare earth elements is a combination of Ce or Yb, and at least one element selected from the group consisting of Er, Ho and Tm; in said reproduction machine, exposing said original document which bears said fluorescent material to infrared radiation so that visible light is emitted by said fluorescent material; detecting said emitted visible light by a detector element which is capable of generating a detection signal upon detecting said emitted visible light; and stopping or cancelling at least one of the steps indispensable for reproduction of said original document in said reproduction machine in response to said detection signal from said detector element.