Luminescence properties of materials consisting of Eu(III) or Tb(III) complexes with 2,2′-bipyridine N,N′-dioxide and coligands entrapped in xerogels

Abstract Ln(III) ions, where Ln(III) = Eu and Tb, were complexed with 2,2′-bipyridine N,N′-dioxide (bpyO2) as a ligand. To the coordination sphere were introduced coligands such as 1,10-phenanthroline (phen), triphenylphosphine oxide (TPPO), salicylic acid (SA) and phthalic acid (PA) to substitute water molecules (O–H quenching oscillators) from the nearest environment of the central ion. These Ln(III) complexes were encapsulated in silica or methylated silicate xerogels. Additionally, moderate thermal treatment or chemical drying reduced the concentration of O–H oscillators in the matrices and simultaneously improved the photophysical properties of the materials. The complex ions of the type [Ln(bpyO2)3]3+ with some free coordination places were prepared intentionally to study role of coligands in isolating the coordination sphere from the quenching water ligands. Coligands with O donor atoms (PA, SA and TPPO) improve the emission intensity of the ternary Ln(III) complexes entrapped in both the xerogel matrices in comparison with the binary complexes. On the other hand, phen with N donor atoms lengthens the luminescence lifetime in the Eu(III) bearing materials and Tb(III) immobilised in SiO2.