Influência de incorporação de >i<nanoclusters>/i< de prata nas propriedades ópticas de vidros germanato dopados com íons de Yb>sup<3+>/sup< para aplicações em fotônica.

Abstract

The purpose of this work is to produce and characterize GeO2-PbO (GP) glass samples codoped with Yb 3+ ions and silver nanoclusters (silver NCs), and to study the mechanisms of energy transfer between them. The glass samples were produced by the melt-quenching technique followed by rapid cooling to relieve internal stress; additional treatments were performed to promote the growth of silver NCs. The silver NCs and Yb 3+ ions emissions were analyzed with excitation at different wavelengths. The silver NCs emission showed tunable light emission in the visible region of the electromagnetic spectrum for different concentrations of Yb 3+ and also for excitations in the range of 355-410 nm. The dependence of emission tuning on the concentration of Yb 3+ is due to the fact that they normally restrict the size of silver NCs. By analyzing the silver NCs and Yb 3+ ions lifetime, and measuring luminescence, energy transfer mechanisms between them were studied and confirmed. Energy transfer between silver NCs and Yb 3+ ions at 980 nm was observed for excitations at 355 and 410 nm. In the first case, an increase of over 100% in the emission of Yb 3+ ions was observed for the sample 4.5% AgNO3/4.5% Yb2O3, and in the second case, an increase of over 1000% was observed for the sample 4.5% AgNO3/2% Yb2O3 (weight total %). Larger silver NCs are more adequately excited at longer wavelengths, which explains the efficient energy transfer mechanisms for the 4.5% AgNO3/2% Yb2O3 sample when excited at 410 nm. Energy transfer occurs through the S1→T1 decays (spin-forbidden electronic transition between singlet-triplet states) of the silver NCs to the Yb 3+ ions. A decrease in the short and long lifetimes of the silver NCs at 550 nm (for excitations at 355, 380 and 405 nm) and 800 nm (for excitation at 405 nm) was observed in samples co-doped with Yb 3+ ions, compared to the sample doped only with AgNO3, supporting the mentioned energy transfer mechanism. To verify the influence of Yb 3+ ions on the formation of silver NCs, transmission electron microscopy (TEM) measurements were performed, which showed a change in the average size when added Yb 3+ ions (the average size changes from 4.7 to 3.0 and 2.2 nm). These results confirm for the first time the possibility of producing GP glasses with silver NCs and Yb 3+ ions, and the energy transfer mechanism between them, with applications for photonic devices such as devices with tunable light emission, solar cells, and broadband visible light sources.