Two-Photon Absorption Properties of Eu3+-DPA-Triazolyl Complexes and the Derived Silica Nanoparticles Embedding These Complexes.

Several complexes and silica-based nanohybrids of rare-earth ions (Eu³⁺, Gd³⁺) have been synthesized from dimethyl 4-azidopyridine-2,6-dicarboxylate ( 4) following the Click chemistry approach. A complete spectroscopic study indicates that such compounds exhibit strong sensitization by the antenna effect from both UV and NIR excitations. The Gd³⁺-based materials show phosphorescence under ambient conditions, which originates from the lowest-energy intra-ligand triplets. Fine analysis of the NIR excitation spectra using time resolved photoluminescence spectroscopy (TRS) indicates that the spectral repartition of the triplet T₁ state differs notably between the complexes and the NPs embedding the complexes. Moreover the dependence of Eu³⁺ luminescence vs. incident beam power in the NIR region diverges from pure quadratic dependence expected in the framework of the two-photon absorption process. The results are discussed considering the occurrence of a direct singlet-to-triplet optical absorption transition (S₀→T₁) upon NIR excitation. [ABSTRACT FROM AUTHOR]