Hypersensitive luminescence of Eu3+ in dimethyl sulfoxide as a new probing for water measurement.

Dimethyl sulfoxide (DMSO) is a well-known organic solvent that can be used for biological applications. DMSO is miscible with water, and it is very common that the two solvents are mixed for some applications. It is important to detect water in DMSO, and this has been done using the luminescence decay lifetimes from Eu(3+) ions. We observed that the emissions of Eu(3+) in DMSO are very strong and very sensitive to water. The emission band from the (5)D(0) → (7)F(2) transition has two peaks at 613 and 617 nm, respectively, and these two peaks change in the opposite ways when water is added into DMSO. The intensity ratio of the two peaks follows nearly perfect linear dependence on the water concentration added in DMSO. This linear relationship provides a new and convenient method for water measurement in DMSO.