Terbium(III) lyoluminescence induced by the dissolution of UV-irradiated potassium peroxodisulfate in aqueous solutions

Abstract

The OO bond of solid potassium peroxodisulfate can be ruptured by UV irradiation, which results in a solid solution of sulfate radicals in potassium peroxodisulfate. The dissolution of this irradiated solid in water produces a solid/solution interface rich in hydrated sulfate radicals, which can either recombine to form peroxodisulfate ions, or react with solvent or solutes in a sample solution. In terbium(III)-containing aqueous solutions, this dissolution produces the characteristic radiative 5D 4→ 7F-multiplet transitions of terbium(III). This study points out that the light-emitting pathway of this terbium(III) lyoluminescence consists of the following steps: (i) hydrated sulfate radical oxidizes terbium(III) to terbium(IV), (ii) terbium(IV) is immediately reduced by water via a process that is sufficiently energetic to leave the resulting terbium(III) in its lowest excited state 5D 4 and finally, (iii) the relaxation of this excited 5D 4 state of terbium(III) induces the aforementioned transitions. Thus, this terbium(III) lyoluminescence can be also classified as chemiluminescence. In addition, x-ray irradiated potassium peroxodisulfate is capable of generating an analogous terbium(III) lyoluminescence, which is, however, investigated only on qualitative basis. Lyoluminescence generation of both irradiated materials can be used to determine hydrated Tb(III) down to the micromolar level in aqueous solutions.