A process for forming a phosphor screen of a color picture tube comprising forming a thin layer using a photosensitive composition which contains an aromatic diazonium salt as a photosensitive component and produces tackiness by exposure to actinic light on the surface of the substrate and contacting the tackified thin layer after exposure to light with phosphor particles to form each phosphor layer for emitting color is improved by using as the phosphor particles those coated with at least one surface coating material selected from the group consisting of Zn(OH).sub.2, Zn.sub.3 (PO.sub.4).sub.2 and AlPO.sub.4 in shortening the contact time between the thin layer and the phosphor particles.