Luminescence of lanthanide-dimethyl sulfoxide compound solutions

Dimethyl sulfoxide (DMSO) has the ability to penetrate living tissues without causing significant damage. Of foremost importance to our understanding of the possible functions of DMSO in biological systems is its ability to replace some of the water molecules associated with the cellular constituents or to affect the structure of the omnipresent water. Luminescence probes have been widely used for biological studies such as labeling, imaging, and detection. Luminescence probes formed in DMSO may find new applications. Here luminescence compounds formed by refluxing lanthanide nitrates of Ce, La, Tb, Yb, Nd, Gd, and Eu in DMSO are reported and their luminescence properties investigated. On the basis of their luminescence spectral properties, the compounds can be classified into four classes. For compounds I with Yb, Ce, and La, the excitation and emission spectra are very broad and their excitation or emission peaks are shifted to longer wavelengths when the monitored emission or excitation wavelength is longer. For compounds II with Gd and Nd, both the excitation and emission spectra are very broad but their emission wavelengths change little at different excitation wavelengths. For Tb-DMSO as compound III, both the typical emissions from the f-f transitions of Tb³⁺ and a broad emission at 445 nm are observed. At low reaction temperatures, the f-f emissions are dominant, while at high reaction temperatures such as 180 °C, the broad emission at 445 nm is dominant. For compound IV, Eu-DMSO, the dominant emissions are from the f-f transitions of Eu³⁺ and only a weak broad emission is observed, which is likely from the d-f transition of Eu²⁺ rather than from metal-to-ligand charge transfer states.