Abstract: The photooxidation of Tb³⁺ in KIO₄-KOH solution is reported in this paper.The soluble complex formed in this system was irradiated by high pressure mercury lamp (366nm). The influences of the concentration of KIO₄,KOH and Tb³⁺,the time and area of exposure and the light intensity on the amount of Tb⁴⁺ formed were investigated. The preferable concentration of KOH is >0.3M,and that of KIO₄ is two orders higher than the initial concentration of Tb³⁺. The soluble complex ion of Tb⁴⁺ formed is red-brown and fairly stable. The maximum of its absorption band is at about 420nm.

Key words: Terbium ion, Photooxidation, Photochemistry of rare-earth elements