Development of luminescent systems based on PHB and PMMA polymers doped with rare earth complexes / Desenvolvimento de sistemas luminescentes à base dos polímeros PHB e PMMA dopados com complexos de terras raras

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

This work presents the preparation, characterization and studies of photoluminescence properties based on trivalent rare earth coordination complexes of βdiketonates and salicylates (β-diketonates = acac- and tta-; salicylates = Hsal- and RE3+ = Sm3+, Eu3+, Gd3+ and Tb3+) doped into polymers PHB (poly3hydroxybutyrate) and PMMA (polymethylmethacrylate). The polymer systems were characterized using techniques of CHN microanalysis, complexometric titration with EDTA, infrared absorption spectroscopy, thermogravimetric analysis TGA/DTG and Xray powder diffraction. Data from the IR spectroscopy revealed the occurrence of interaction between the PHB and PMMA polymer matrix with the RE3+ complex of βdiketonates and salicylates. The thermogravimetric analysis TGA/DTG suggested anhydrous character in most doped polymer systems and showed a decrease of thermal stability with increasing doping content. The Xray diffraction study showed that the polymer films are semicrystalline and each series presents spectral profiles similar to each other. The crystallinity of the polymeric systems increased according to the doping percentage and, at the same time, maintained independent to the alteration of RE3+ ion or the coordinated ligand. It was observed in the excitation spectra of PHB and PMMA polymer systems doped with RE3+-complexes luminescence quenching of narrow bands arising from the 4f4f transitions of RE3+ ions. In the emission spectra of PHB and PMMA systems doped with Sm3+, Eu3+ and Tb3+ complexes, characteristic emission bands arising from intraconfigurational transitions were observed from the ions Sm3+ (4G5/2→6H5/2,-11/2), Eu3+ (5D0→7FJ, J = 0-6) and Tb3+ (5D4→7FJ, J = 6-0), exhibiting orangered, red and green colour emission, respectively. Most of the doped films displayed concentration quenching of luminescence. Photoluminescence properties were investigated based on the spectroscopic data obtained for systems of PHB and PMMA doped with hydrated complexes. Particularly, emission bands arising from the 5D0→7F0-4 transitions (Eu3+) were dominated by the hypersensitive 5D07F2 transition (~612 nm), indicating that the Eu3+ ion is found in a noncentrosymmetric chemical environment. PHB:Eu(tta)3 and PMMA:Eu(tta)3 films showed high Ω2 values, suggesting that the Eu3+ ion is located in a more polarizable chemical environment. The highest values of emission quantum efficiency (η) of the 5D0 emitting level were found with those polymer films doped with [Eu(tta)3(H2O)2] complex. The emission colours of polymer systems synthesized in this work enabled their potential applications in fullcolour displays, since their emissions are the primary colours: red (Eu3+), blue (Gd3+) and green (Tb3+). The PMMA:Gd(Hsal)3 films exhibits intense blue colour emission arising from the T1→S0 transition of the salicylate ligand at room temperature (298 K). The polymer matrix performs an essential role in the luminescent sensitization processes for systems containing Sm3+, Eu3+, Gd3+ and Tb3+, hence the overall systems act as Light Conversion Molecular Devices (LCMDs)

ASSUNTO(S)

trivalent rare earth pmma terras raras trivalentes coordination compounds pmma phb polymer matrix transferência de energia energy transfer compostos de coordenação photoluminescence spectroscopy phb matrizes poliméricas espectroscopia de fotoluminescência

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