Synthesis, characterisation and luminescence properties of MCM-41 impregnated with an Eu3+ β-diketonate complex

A luminescent material has been prepared by formation of the Eu3+ beta-diketonate complex Eu(NTA)(3)L '' {NTA = 1-(2-naphthoyl)-3,3,3-trifluoroacetonate; L '' = ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate} within the channels of MCM-41-type ordered mesoporous silica. Using simple wet impregnation methods, the ligand L '' was first encapsulated followed by treatment with the complex Eu(NTA)(3)(H2O)(2). An analogous Gd3+ supported material was also prepared, as well as the model complexes Ln(NTA)(3)L ' {Ln = Eu, Gd; L ' = 2-[3(5)-pyrazolyl]pyridine}. The materials were characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), FTIR and FT Raman spectroscopies, C-13 and Si-29 MAS NMR, and photoluminescence spectroscopy. The spectroscopic studies showed that exchange of the H2O ligands for the bidentate ligand L '' occurred to give the desired 8-coordinate species Ln(NTA)(3)L '', with a local Ln(3+) coordination environment similar to that for the model complexes. The low (-259 circle C) and room temperature emission spectra of the Eu-modified mesoporous material displayed the typical Eu3+ intra-4f(6) lines ascribed to transitions between the D-5(0.1) excited states and the ground multiplet (F-7(0-4)). Negligible emission from the organic part of the encapsulated species was observed, indicating that energy transfer from the ligands to the Eu3+ ion was quite efficient. The D-5(0) quantum efficiency was estimated to be 21.1%, compared with 46.1% for for the model complex Eu(NTA)(3)L '. This difference is attributed to the presence of an excited state of the organic ligands in the supported material that lies approximately resonant with the D-5(1) intra-4f(6) level, opening up an additional non-radiative channel that is not present in the corresponding model complexes. (C) 2007 Elsevier Inc. All rights reserved.