Correlation between composition, microstructure, and emission properties in Nd-doped Si-rich Si oxynitride films: investigation into the nature of the sensitizer.

Rare earth (RE) ions doped in Si-based materials, compatible with Si technology, are promising compounds with regards to optical communication and energy conversion. In this article, we show the emission properties of Nd-doped Si-rich Si oxynitride (Nd-SRSON) films, and their dependence on the dangling bond density and the nature of the sensitizer. These films were prepared by reactive magnetron sputtering and post-annealing. The film composition, microstructure, and emission properties were investigated as a function of deposition parameters and annealing temperatures. Both Fourier transform infrared (FTIR) and ellipsometry spectroscopy measurements have confirmed that the sample composition (Si/N ratio) can be carefully tuned by varying the ratio of reactive nitrogen to argon in the sputtering plasma. Moreover, FTIR and x-ray photoelectron spectroscopy measurements demonstrate the existence of both nitrogen and oxygen dangling bonds (N· and O·) in as-deposited samples. These dangling bonds were passivated during annealing. Under non-resonant excitation at 488 nm, the films exhibit a significant photoluminescence (PL) signal from Nd3+ ions demonstrating the occurrence of an effective sensitization of Nd3+ ions in the host matrix. Both PL excitation and ellipsometry results (the energy band gap from new amorphous model) exclude the sensitization by an exciton with energy over the band gap, whereas the presence of Si agglomerates, at the atomic scale, have been identified as effective sensitizers towards Nd3+ ions. This work not only provides knowledge to optimize Si-based materials for favorable emission properties, but also, presents a universal methodology to investigate the nature of sensitizers for RE emitters. This allows one to find correlations between composition, microstructure, and emission properties.

Structural and emission properties of Tb3+-doped nitrogen-rich silicon oxynitride films.

Terbium doped silicon oxynitride host matrix is suitable for various applications such as light emitters compatible with CMOS technology or frequency converter systems for photovoltaic cells. In this study, amorphous Tb3+ ion doped nitrogen-rich silicon oxynitride (NRSON) thin films were fabricated using a reactive magnetron co-sputtering method, with various N2 flows and annealing conditions, in order to study their structural and emission properties. Rutherford backscattering (RBS) measurements and refractive index values confirmed the silicon oxynitride nature of the films. An electron microscopy analysis conducted for different annealing temperatures (T A) was also performed up to 1200 °C. Transmission electron microscopy (TEM) images revealed two different sublayers. The top layer showed porosities coming from a degassing of oxygen during deposition and annealing, while in the region close to the substrate, a multilayer-like structure of SiO2 and Si3N4 phases appeared, involving a spinodal decomposition. Upon a 1200 °C annealing treatment, a significant density of Tb clusters was detected, indicating a higher thermal threshold of rare earth (RE) clusterization in comparison to the silicon oxide matrix. With an opposite variation of the N2 flow during the deposition, the nitrogen excess parameter (Nex) estimated by RBS measurements was introduced to investigate the Fourier transform infrared (FTIR) spectrum behavior and emission properties. Different vibration modes of the Si-N and Si-O bonds have been carefully identified from the FTIR spectra characterizing such host matrices, especially the 'out-of-phase' stretching vibration mode of the Si-O bond. The highest Tb3+ photoluminescence (PL) intensity was obtained by optimizing the N incorporation and the annealing conditions. In addition, according to these conditions, the integrated PL intensity variation confirmed that the silicon nitride-based host matrix had a higher thermal threshold of rare earth clusterization than its silicon oxide counterpart. Analysis of time-resolved PL intensity versus T A showed the impact of Tb clustering on decay times, in agreement with the TEM observations. Finally, PL and PL excitation (PLE) experiments and comparison of the related spectra between undoped and Tb-doped samples were carried out to investigate the impact of the band tails on the excitation mechanism of Tb3+ ions.

Therapeutic time window of YGY-E neuroprotection of cerebral ischemic injury in rats.

YGY-E is an active ingredient in traditional Chinese medical herbs which have anti-ischemic activity. The present work was designed to study its therapeutic time window in cerebral ischemic injury as well as its effect on neuronal apoptosis. Animals received an intravenous injection of YGY-E at 1, 3, and 6 h, respectively, after permanent focal cerebral ischemia induced by electrocoagulation of the middle cerebral artery. Infarct ratio and neurological function were employed to assess the effects of YGY-E on the therapeutic time window in this animal model. Furthermore, we evaluated effects of this compound on neuronal apoptosis and synthesis of Bcl-2 and Bax in ischemic brain tissue with in situ DNA end labeling (TUNEL), immunohistochemistry assay, and Western blot analysis. YGY-E (2-8 mg/kg) delivered at all the three time points dosedependently decreased infarct ratio, neurological deficits, percentage of TUNEL-positive cells (p < 0.01) and Bax-positive cells (p < 0.01 or p < 0.05). In contrast, it increased the percentage of Bcl-2 positive cells (p < 0.01 or p < 0.05). These data demonstrated that YGY-E had protective effects against cerebral ischemia injuries in rats. But more importantly, they indicate that YGY-E has an unusually long (up to 6 h) therapeutic time window relative to classical drugs in treating cerebral ischemia. In addition, our results suggest that the anti-apoptotic effects of YGY-E are due to its regulation of the balance between Bcl-2 and Bax protein levels.