Layered Niobates: Synthesis, characterization, reactivity and luminescenece properties study / Niobatos lamelares: síntese, caracterização, reatividade e estudo das propriedades luminescentes

AUTOR(ES)

Marcos Augusto Bizeto

DATA DE PUBLICAÇÃO

2003

RESUMO

The study described in this Thesis is related to the synthesis and evaluation of some chemical properties of layered niobates with formulas K4Nb6O17 (hexaniobate), KNb3O8 (triniobate) and K1-xLnxCa2-xNb3O10 (layered perovskites - Ln = La, Eu and x = 0.02; 0.25; 0.50; 0.75 and 1.00). These niobates are constituted of negative layers and an interlayer region filled with potassium ions that maintain the system charge neutrality. The reactivity of these niobates was evaluated through intercalation reactions of simple species such as butylamine and bulky species such as porphyrin, aluminum polyoxocation and organosilanes. The high charge density of the niobate layer makes the direct intercalation of bulky guest species more difficult. Therefore, to overcome this situation, new synthetic routes were developed. The intercalation of bulky species was achieved by using colloidal dispersions of exfoliated niobates that, upon restaking, incorporate the guest species into the interlayer region. The luminescent properties of the lamellar niobates are very dependent on the structure. Niobates that present a perovskite structure do not show emission even at liquid helium temperature. The hexaniobate presents emission at nitrogen liquid temperature and triniobate at both room and 77 K temperatures. In this study the luminescent properties of EuxK4-3xNb6O17, EuxK1-3xNb3O8 e KCa2Nb3O10 (intercalated with Eu3+ and doped with 1 % of Eu3+ or La3+) were evaluated. Charge transfers processes were observed in both intercalated and doped niobates with Eu3+ ion. The lanthanide doping also promoted changes in the photophysical properties of niobates with perovskite structure, which become to show emission of the niobate group even at room temperature.

ASSUNTO(S)

pilarização layered oxide luminescence niobatos lamelares pilaring nióbio luminescência niobium oxide niobium sólidos lamelares layered niobates Óxido de nióbio

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