Stability to the radiation gamma of doped luminescent Poly(methyl methacrylate) films of methyl with complex tri(acetylacetonate) tetrahydrate [Tb(acac)3(H2O)4]

Polymeric luminescent devices are useful for many high technology applications and polymers doped with luminescent complexes are having an increasing development in the recent years. PMMA (Poly(methyl methacrylate)) doped with terbium coordinated with beta-diketonate ligands leads to a new luminescent polymeric material. Once these materials are excited by ultraviolet light of adequate wave length, they emit radiation in the visible region of spectra. The luminescent properties in the solid state, also the resistance to the thermal oxidation, had been analyzed in luminescent films before and after exposition to the gamma-irradiation of Co60. The characteristics of the excitation and emission spectra demonstrated that the radiation influences the luminescence properties of the system, showing dependence of the presence of the ligands groups. The thermal stability was determined by thermogravimetric analysis (TGA/DTG) in system TGA/SDTA-851e Metter- Toledo under the conditions: 25 deg C→500 deg C, with 10 deg C/min, in atmosphere of N2. The physical properties of the material were evaluated by differential scanning calorimetry (DSC) in system DSC-822e Metter - Toledo, under the conditions: -100 deg C→500 deg C, two scans with 10 deg C/min, in atmosphere of N2. The photoluminescence properties had been obtained through electronic spectroscopy with spectrofluorometry of system SPEX Fluorolog, model FL212, with double monochromators 0.22 mSPEX 1680 and continuous xenon light bulb of 450W. The Tb3+ ion (configuration 4f8) has been less investigated due to the complexity of its energy level structure, for instance, the 5D4 level contends nine degenerated levels which make it difficult for the spectral attributions. The complexes of Tb3+ show a series of bands derived from transitions 5D4→7FJ (where J = 6-0), with the hyper sensitive transition, 5D4→7F5, around of 540 nm, being the dominant transition. Consequently, the complexes of Tb3+ show green color under UV radiation. The excitation spectra of the doped polymer thin films, registered under excitation at 543 nm, present broad bands which can be attributed to the absorption of the acetylacetonate ligand group in the range of 250 the 350 nm. The broad bands of the 4f-4f transitions of the Tb3+ ion are attributed to the overlapping transitions of 7F6→5D1 (323 nm), 7F6→5L6 (337 nm), 7F6→5L9 (349 nm), 7F6→5L10 (366 nm), 7F6→5D3 (382 nm); and the sharp peaks, 7F6→5G6 (376 nm) and 7F6→5D4 (484 nm). In the case of the emission spectra of Tb3+ registered under excitation at 323 nm, it is observed characteristic lines of the following transitions: 5D4→7F6 (490 nm), 5D4→7F5 (545 nm), 5D4→7F4 (587 nm), 5D4→7F3 (621 nm), 5D4→7F2 (653 nm), 5D4→7F1 (669 nm) and 5D4→7F0 (682 nm). The doped films exposed to the gamma-irradiation of different dosage varying from 10 to 50 kGy resulted alterations of the bands in the emission spectra. This decay is proportional to the dosage of radiation, which makes this type of film possible for applications such as highly-sensitive dosemeter. (author)