Pr(III) luminescence enhancement by chelation in solution and in sol–gel glass

• Two Pr(III) complexes were synthesized.
• The complexes were encapsulated in sol–gel glass.
• Visible luminescence of the composite materials were diagnosed in solution and in sol–gel.
• The goal was to demonstrate the effect of chelation and host matrix on emission.
• Our purpose was to end up with highly luminescent solid state materials.

Due to the weak emission of lanthanide ions in solution, it is common practice to form complexes of the lanthanide ions with organic ligands that strongly absorbs light and transfers the energy to the lanthanide ion center via the antenna effect. The organic ligands 2-6-pyridinedicarboxylate (L1) and the polytonic diazine (N–N) ligand L2 (C22H16N12O2) were used to synthesize two Pr(III) complexes, namely: Pr-L1 (Na3[Pr(C7H3NO4)3]) and Pr-L2. The prepared complexes were further encapsulated in an optically transparent sol–gel glass. The synthesized ligands and complexes were characterized by FTIR and 1H NMR. Room temperature luminescence of Pr-L1 and Pr-L2 complexes in solution and in sol–gel glass were investigated using a spectrofluorometer. Excitation at the maximum absorption wavelength of the ligands (280 nm) resulted in the typical visible luminescence (centered at around 600 nm) resulting from the 1D2 → 3H4 transition of the Pr(III) ion, which contributes to the efficient energy transfer from the absorbing ligand L1 to the chelated Pr(III) ion (an antenna effect) while the Pr(III) luminescence is not efficiently sensitized by ligand L2. The obtained emission spectra indicated that the excitation energy level for the central Pr(III) is in a slightly lower location than ligand L1 excitation triplet (T1) level and can accept the energy transfer from T1 efficiently.

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