E.O. Serqueira

Energy transfer between CdS nanocrystals and neodymium ions embedded in vitreous substrates

Experimental evidence has been observed for energy transfer from CdS nanocrystals, synthesized by the fusion method, to Nd(3+) ions embedded in vitreous substrates. These dot samples doped with neodymium have been investigated by combined optical absorption (OA), photoluminescence (PL), and time-resolved photoluminescence (PLRT) techniques. Radiative and nonradiative energy transfers between CdS dot and Nd(3+) ion levels, to our knowledge not reported before, can be clearly observed in the PL spectra where the emission band valleys correspond exactly to the energy absorption peaks of the doping ion. The PLRT data reinforce these energy transfer mechanisms in which the increasing overlap between the CdS PL band and the OA to the Nd(3+) levels decreases stimulated emissions from the doping ions.

Effect of Na2O concentration on the lifetime of Er3+-doped sodium silicate glass

A set of sodium silicate glass matrices with different Na2O concentrations and doped with constant Er3+ content were synthesized by fusion. The influence of Na2O on the luminescence of Er3+ ions in the region of 1.53 μm was studied. Samples were characterized by optical absorption (OA), time and energy resolved photoluminescence and Fourier Transform Infrared (FTIR). Sodium oxide concentration controls the absorption of OH radicals. FTIR showed a decrease in OH radicals, which is correlated with an increase in the lifetime of the transition at approximately 1.53 μm. However, a decrease in sodium concentration implies increasing interaction between the silicon network and Er3+ ions, thereby increasing non-radiative energy transfer from Er3+ ions to SiO4 structures. The gain in the lifetime of this transition (∼6.9 ms) was obtained for the sample with the highest silicon concentration and is comparable with the well-known YAG system. Molecular dynamic results show that a reduction in non-bridging oxygen species occurs as Na2O concentration decreases, which explains the reduction in OH radical absorption obtained in the experimental results.

Effects of OH radicals and the silicon network on the lifetime of Eu 3+ -doped sodium silicate glasses

A set of sodium silicate glass matrices were synthesized to study the influence of Na2O concentration on the optical properties of Eu3+. The samples were characterized by optical absorption (OA), time and energy resolved photoluminescence and Fourier Transform Infrared (FTIR). We observed that decreasing sodium oxide concentration affects the absorption of OH radicals in the host matrix. Adjusting the obtained FTIR spectra by Gaussian functions, we observed the existence of two possible non-radiative transfer channels with the transition from the 5D0 to the 7F2 state of the Eu3+ ions. The first was produced by resonance with the 5th harmonic vibration of OH bonded radicals and the second by resonance with the 14th harmonic vibration of the silicon network. A decrease in OH radicals observed by FTIR was followed by an increase in the lifetime of the 5D0 state of the Eu3+ ions. However, resonance with higher harmonic orders did not affect the optical properties of the Eu3+ ions. Increases in the lifetime of this transition (~3.3 ms) were obtained from the synthesized sample with the lowest sodium oxide concentration. This lifetime is comparable with the well-known YAG system. Molecular dynamic results show that decreasing sodium oxide content in the host matrix produces structural changes such as decreases in non-bridge oxygen species, which may explain the decreases in OH radical absorption seen in the experimental results.