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Item type:Publication, Fabrication and luminescence properties in Yb–Tb co-doped a-SiCO thin films(VBRI Press, 2020-07-24)Amorphous silicon oxycarbide (a-SiCxOy) single doped with Yb3+ and co-doped with the couple Tb3+ - Yb3+ thin films were grown on crystalline silicon substrates by rf magnetron sputtering. The elemental composition in at. % is determined by energy dispersive spectroscopy and fourier transform infrared spectroscopy allows to investigate the chemical properties of the host. The concentration of Yb in the single doped sample was 3.5% and for the codoped samples (Yb, Tb) were (3%, 0.9%), (3.5%, 0.6%) and (4%, 0.6%), respectively. Post-deposition annealing treatments were made in order to induce optical activation of the rare earths. Conversion or absorption of high energy photons were analyzed by photoluminescence spectroscopy. The photoluminescence spectra show that for a given temperature range in the thermal annealing process, as well as for the appropriate rare earth concentrations the activation of Yb3+ and Tb3+ is enhanced. A strong reduction of the Tb3+ emission in contrast to the Yb3+ emission in the a-SiCxOy,:Tb:Yb samples at annealing temperature at 500°C suggests a energy transfer from Tb3+ to Yb3+ ions. Copyright © 2018 VBRI Press. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Molecular α-relaxation process of exopolysaccharides extracted from Nostoc commune cyanobacteria(Elsevier, 2020-10-15)Broadband dielectric spectroscopy was used to investigate the molecular α-relaxation of the exopolysaccharides (EPS) extracted from Nostoc commune cyanobacteria. The EPS were modified in different ways. EPS were carboxymethylated to obtain carboxymethyl-exopolysaccharides (CEPS). EPS and CEPS were doped with ammonium iodide and 1-butyl-3-methylimidazolium chloride. An α relaxation process was observed for all specimens. The temperature dependence of the relaxation times for pure and doped, EPS and CEPS polymers exhibited non-Arrhenius behavior. This relaxation process was associated with the glass transition of the complex heteropolysaccharides produced by the cyanobacteria. The molecular mobility at the glass transition, Tg, was affected by both the carboxymethylation treatment and the doping. The fragility index also decreased for the doped specimens, which may be attributed to an increase in the mobility of the polymer chains due to the plasticizing effect of the doping agents. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Revisiting the optoelectronic properties of sputtered aluminium-doped zinc oxide: a study combining advanced optical dispersion models(Institute of Physics, 2025)Aluminium-doped zinc oxide (AZO) thin films with different aluminium (Al) concentrations were grown by RF-magnetron sputtering with substrate active cooling. Sputtering induced sample heating was aimed to be mitigated by the applied cooling, achieving films with electrical resistivities as low as 3.3 × 10 − 3 Ω ⋅ cm , in the as-deposited state. Subsequently, an annealing treatment was performed to enhance the electrical properties and assess the effect of the Al concentration. The absorption coefficient spectra of zinc oxide (ZnO) exhibits an excitonic absorption contribution to the fundamental absorption that is typically not considered in AZO when determining the optical bandgap. Nevertheless, here we show that this free exciton band remains visible in AZO even at Al concentrations greater than 4 at.%. Additionally, the doping-induced defect states increases the width of tail states. These two factors have a substantial effect on the absorption edge, and thus must be considered with adequate models when attempting to determine the optical bandgap. In this work, we use a recently developed Elliot-based optical dispersion model to accurately determine the optical bandgap, exciton binding energy and Urbach energy of AZO thin films. On the other hand, we assess the infrared free carrier absorption, typically modeled by the Drude dispersion formula, by considering a complex frequency-dependent dynamical resistivity and the polar nature of the ZnO lattice. Normally, the real part of the dynamical resistivity follows a power law dependence and the exponent is assumed to be −1.5 for highly-doped semiconductors. Notwithstanding, here we let this exponent as a free fitting parameter to assess the effect of distinct scattering mechanisms present in sputtered AZO thin films and its dependence with the Al doping concentration. We believe these results can be extended to other degenerated semiconductors and are relevant for the understanding and tailoring of their fundamental optoelectronic properties.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Significant Luminescence Enhancement of Ga-Doped WS₂ Monolayers Grown by CVD(American Chemical Society, 2025)Monolayer tungsten disulfide (WS₂) is a direct-band-gap semiconductor that has excellent luminescence properties, which are of great interest for optoelectronic applications. In this study, we investigated the effect of gallium (Ga) on WS₂ monolayers grown by chemical vapor deposition. Our results indicate that Ga-doped WS₂ exhibits a 3.6-fold increase in photoluminescence intensity for doped samples compared to pristine WS₂. To confirm the existence of Ga in the WS₂ structures, resonance Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were utilized as characterization methods. A redshift of the XPS spectrum was observed as well as an increase in the disorder-related Raman modes, which were attributed to the influence of Ga. XPS analysis and ab initio electronic structure calculations reveal the presence of substitutional Ga atoms as well as Ga atoms adsorbed on WS₂ surfaces.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Triboelectric Nanogenerators Based on Ulvan Biopolymer: Impact of Lithium Sulfate Doping on Electrical Output(John Wiley and Sons, 2025)The increasing demand for sustainable energy solutions has driven extensive research into energy harvesting devices, such as triboelectric nanogenerators (TENGs). Although various additives, including nanowires and salts, have been investigated to enhance the performance of biopolymer-based TENGs, the use of lithium salts in green algae-based TENGs remains unexplored. Herein, a series of TENGs are fabricated using ulvan, a biopolymer derived from the green algae Ulva nematoidea. To improve the output performance of these TENGs, the ulvan matrix is doped with lithium sulfate (Li2SO4) at concentrations of 0%, 10%, 20%, 30%, 40%, and 50% by weight. Dielectric permittivity measurements are conducted to calculate the surface charge density. The results show an increase from 0.94 nC cm−2 for the pristine film to 1.14 nC cm−2 at 30 wt% Li2SO4, beyond which further increases in salt concentration lead to a decrease in charge density. The incorporation of salts significantly enhances the electrical performance, with the 20% Li2SO4/ulvan device achieving a maximum power density of 0.156 W m−2, representing an 85.7% improvement compared to the pristine ulvan TENG. The open-circuit voltage (Voc) and short-circuit current also increase with salt concentration, with Voc reaching 87.71 V at 30% Li2SO4.1