The paper discussed the preparation of rare earth europium complexes ultraviolet rays (UV) photochromic ink and the influences of factors, such as europium complexes using a rare earth ternary complex of Eu ion with 3-benzoylbenzoic acid and phenathrolinephen [Eu(BA)3Phen] content upon printing ink formula. In the experiment, we utilized fluorescence spectrophotometer to make quantitative deter...