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Previous issue date: 2017-08-25 === Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) === Neste trabalho, foi sintetizada uma s?rie de redes metalorg?nicas mistas a base de ?ons lantan?deos (MLOFs) pelo m?todo solvot?rmico, utilizando como componente org?nico o ?cido tereft?lico (1,4-H2BDC). Inicialmente foram preparadas tr?s matrizes contendo gadol?nio dopadas com 5% molar de ?ons Eu3+ (Eu/Gd-1,4-BDC). Esta etapa teve como foco o estudo dos efeitos do tempo de s?ntese (3, 5 e 7 dias) sobre as propriedades morfol?gicas e luminescentes das MLOFs. Tal estudo se torna essencial, j? que com o aumento da cristalinidade da rede, normalmente verifica-se uma diminui??o dos canais de relaxa??o n?o radioativos. Posteriormente, foram sintetizadas matrizes com diferentes percentuais molares de Eu3+ (1, 3, 5, 7 e 9%) com o intuito de determinar a concentra??o limite do dopante, assim como investigar o efeito de tal varia??o percentual, no crescimento das redes e propriedades fotof?sicas. Por fim, uma amostra co-dopada com 2,5% molar de Tb3+ e Eu3+ (Gd/Tb/Eu-1,4-BDC) foi preparada e suas propriedades luminescentes sintoniz?veis estudadas. Os materiais sintetizados na forma de p?, foram caracterizadas por Difra??o de raios-X (DRX), Espectroscopia na regi?o do Infravermelho com Transformada de Fourier por Reflet?ncia Total Atenuada (FTIR-ATR), Microscopia Eletr?nica de Varredura (MEV), An?lise termogravim?trica (TGA) e Fotoluminesc?ncia (PL). Todas as amostras apresentaram elevada estabilidade t?rmica, e o aumento do tempo de s?ntese teve significativa influ?ncia sobre a morfologia dos cristais. Com base nas an?lises de DRX, FTIR e PL, identificou-se que a partir de 7% molar de ?ons eur?pio uma segunda fase cristalina come?a a se formar. Al?m disso, observou-se a partir dos espectros de excita??o e emiss?o que ocorreu uma efetiva transfer?ncia de energia intramolecular entre o ligante e os n?veis do Eu3+, gerando luminesc?ncia vermelha caracter?stica deste ?on. Estas amostras apresentaram linhas de emiss?o caracter?sticas do Eu3+ atribu?das as transi??es 5D0 ? 7F0, 7F1, 7F2, 7F3 e 7F4. A amostra co-dopada apresentou eficiente sintoniza??o de cor oriunda da transfer?ncia de energia entre Tb3+ ? Eu3+. Nenhum mecanismo de transfer?ncia de energia no sentido inverso foi identificado. Portanto, os materiais descritos s?o promissores para diversas aplica??es ?pticas. === In this work a series of new metal-organic frameworks containing lanthanide ions (LOFs) was synthesized by a solvothermal method at 180 0C, using terephthalic acid (1,4-H2BDC) as an organic component. Initially, three samples containing gadolinium doped with 5 mol% Eu3+ ions were prepared (Eu/Gd-1,4-BDC-MOFs). The objective of this part of the work was to study the effect of synthesis time (3, 5 and 7 days) on the morphological and luminescent properties of these materials. This study is essential because it is well known that the increase in crystallinity may lead to the decrease in reticular vibrations and, consequently, a decrease of nonradioactive relaxation channels. Subsequently, samples with different Eu3+ molar percentages (1, 3, 5, 7 and 9%) were synthesized to investigate the effect of the dopant content on the structure and photophysical properties of the LOFs. Finally, a sample co-doped with 2.5 mol% of Tb3+ and Eu3+ (Gd/Tb/Eu-1,4-BDC-MOF) was prepared and its tunable luminescent properties studied. The samples in powder form, were characterized by X-ray Diffraction (PXRD), Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR), Scanning Electronic Microscopy (SEM), Thermogravimetric Analysis (TGA) and Photoluminescence (PL). Based on the analyzes of DXRP, FTIR and PL, it was identified that materials containing up to 7 mol% of europium ions presented a single-phase. In addition, it was observed from the excitation and emission spectra that an effective intramolecular energy transfer occurred between the ligand and the Eu3+ levels, generating characteristic red luminescence of this ion. These samples emission spectra exhibited characteristic emission lines of the Eu3+ ion ascribed to the 5D0 ? 7F0, 7F1, 7F2, 7F3 and 7F4 transitions. The co-doped sample presented efficient luminescent tuning resulting from the transfer of energy between Tb3+ ? Eu3+. Therefore, the described materials are promising for various optical applications.
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