Visible-light sensitized sol–gel-based lanthanide complexes (Sm, Yb, Nd, Er, Pr, Ho, Tm): microstructure, photoluminescence study, and thermostability

The homogeneously transparent hybrid gels (Ln–N–P-gel, Ln = Sm, Yb, Nd, Er, Pr, Ho, Tm) containing lanthanide complexes (by using dinaphthoylmethane (dnm) as the primary ligand and 1,10-phenanthroline (phen) as the synergic ligand) via the in situ approach have been prepared. The dnm ligand was synthesized and adopted with the aim to sensitize the lanthanide ions with visible light. The properties of Ln–N–P-gels were investigated by Fourier-transform infrared (FT-IR), diffuse reflectance (DR), scanning electron micrographs (SEM), fluorescence spectra and thermogravimetric analyses. The results reveal that the lanthanide complexes are successfully in situ synthesized in the corresponding Ln–N–P-gels. Under the excitation of visible-light, the Ln–N–P-gels showed the respective visible (Sm3+) and near-infrared (Sm3+, Yb3+, Nd3+, Er3+, Pr3+, Ho3+, Tm3+) luminescence. The near-infrared (NIR) luminescence of Sm3+, Pr3+, Ho3+, and Tm3+ complexes sensitized by visible-light had been rarely reported previously, which is highly desired for biomedical and photonics applications. Based on the relevant energy levels, a model was proposed to explain the visible-NIR luminescence of the Ln–N–P-gels based on the visible-light excitation.