Synthesis and Characterization of Erbium-Doped Silica Films Obtained by an Acid-Base-Catalyzed Sol-Gel Process.

Erbium-doped silica films were synthesized using a two-step sol-gel methodology that involved acid and base catalysts, with erbium concentration ranging from 0.2% to 6% and annealing temperatures varying from 500 °C to 900 °C. The photoluminescence spectra showed that the samples exhibiting efficient emission were annealed at 800 °C and 900 °C and doped with 3% and 6% erbium. The X-ray diffraction analysis revealed that the internal structure of the films was influenced by the different annealing temperatures and the doping concentrations. Samples with dominant 4f transitions were modelled. The results suggest that the proposed method is a promising approach for the synthesis of erbium-doped silica films with potential applications in optical devices.

A polymeric nitrogen N[Formula: see text]-N[Formula: see text] system with enhanced stability at low pressure.

Postulated in 1992 and synthesized in 2004 above 2000 K and 110 GPa, the singly-bonded nitrogen cubic gauche crystal (cg-PN) is still considered to be the ultimate high energy density material (HEDM). The search however has continued for a method to synthesize cg-PN at more ambient conditions or find HEDMs which can be synthesized at lower pressure and temperature. Here, using ab initio evolutionary crystal prediction techniques, a simpler nitrogen-based molecular crystal consisting of N[Formula: see text] and N[Formula: see text] molecules is revealed to be a more favorable polynitrogen at lower pressures. The energetic gain of  534 meV/atom over cg-PN and  138 meV/atom over the N[Formula: see text] molecular crystal at zero pressure makes the N[Formula: see text]-N[Formula: see text] system more appealing. Dynamical and mechanical stabilities are investigated at 5 and 0 GPa, and vibrational frequencies are assessed for its Raman and IR spectra. The prospects of an experimental synthesis of the N[Formula: see text]-N[Formula: see text] polymeric system compared to cg-PN is higher because the C[Formula: see text] symmetry of N[Formula: see text] within this crystal would be easier to target from the readily available N[Formula: see text] azides and the observed N[Formula: see text] and N[Formula: see text] radicals.

A practical way to enhance the synthesis of N8- from an N3- precursor, studied by both computational and experimental methods.

Polymeric nitrogen (PN) belongs to a general family of materials containing all-nitrogen molecules or clusters. Although it is rare and challenging to synthesize PN members, they are attracting increasing scientific attention due to their high energy storage capacity and possible use as a green catalyst. A few theoretical calculations predicted the possible PN phases from N2 gas, but they all require extremely high pressures and temperatures to synthesize. In this work, a practical way to synthesize N8 polymeric nitrogen from an N3- precursor is elucidated using density functional theory calculations. The detailed mechanism, , is determined. The calculated energy barriers indicate that the first step is the rate-limiting step. This result guides us to rationally synthesize N8 under UV (254 nm) irradiation, chosen based on the calculated absorption spectrum for the azide anion. As expected, UV irradiation enhances N8 yields by nearly four times. This provides an interesting route to the scalable synthesis of high energy density N8 compounds.

Predicting the crystal structure of [Formula: see text] high energy density material using ab initio evolutionary algorithms.

[Formula: see text] is the first successfully synthesized salt that has a polymeric nitrogen moeity ([Formula: see text]). Although 12 other [Formula: see text] salts followed, with [Formula: see text] and [Formula: see text] being the most stable, the crystal structure of [Formula: see text] remains unknown. Currently, it is impossible to experimentally determine the structures of [Formula: see text] due to its marginal stability and explosive nature. Here, following an ab initio evolutionary prediction and using only the stoichiometry of [Formula: see text] as a starting point, we were able to reveal the crystal structure of this high energy density material (HEDM). The [Formula: see text] symmetry of the [Formula: see text] cation, as suggested from earlier investigations, is confirmed to be the symmetry adopted by this polymeric nitrogen within the crystal. This result gave full confidence in the validity of this crystal prediction approach. While stability of the [Formula: see text] within the crystal is found to be driven by electronic considerations, the marginal stability of this HEDM is found to be related to a partial softening of its phonon modes.

Cubic gauche polymeric nitrogen under ambient conditions.

The long-sought cubic gauche phase of polymeric nitrogen (cg-PN) with nitrogen-nitrogen single bonds has been synthesized together with a related phase by a radio-frequency plasma reaction under near-ambient conditions. Here, we report the synthesis of polymeric nitrogen using a mixture of nitrogen and argon flowing over bulk ß-sodium azide or ß-sodium azide dispersed on 100 nm long multiwall carbon nanotubes. The cg-PN phase is identified by Raman and attenuated total reflection-Fourier transform infrared spectroscopy, and powder X-ray diffraction. The synthesis of the cubic gauche allotrope of high energy density polymeric nitrogen under near-ambient conditions should therefore enable its optimized production and applications as a "green" energetic material and a potential catalyst for different chemical reactions.Polymeric phases of nitrogen are promising as environmentally-friendly, high energy-density materials, but are inherently unstable. Here, the authors report the synthesis and stabilization of polymeric nitrogen in its cubic gauche phase under near-ambient conditions, via plasma-enhanced chemical vapour deposition.

N8 (-) polynitrogen stabilized on multi-wall carbon nanotubes for oxygen-reduction reactions at ambient conditions.

Polynitrogen (PN) species (Nn , n from 3 to 8) as highly energetic materials have attracted many theoretical calculations and predictions. N3 , N4 , N5 or their ions were experimentally detected under high-pressure and high-temperature conditions. Herein, a N8 (-) PN stabilized on the positively charged sidewalls of multi-walled carbon nanotubes (MWNTs) has been synthesized using cyclic voltammetry (CV) under ambient conditions. ATR-FTIR and Raman spectroscopic data assigned on the basis of density functional theory (DFT) calculations support the successful synthesis of a C2h symmetry chain structure of the N8 anion stabilized as MWNT(+) N8 (-) . Temperature programmed desorption (TPD) data show that MWNT(+) N8 (-) is thermally stable up to 400 °C. Oxygen-reduction reaction (ORR) experiments carried out using MWNT(+) N8 (-) as the cathodic catalyst shows that it is very active for ORR with an even higher current density than that of a commercial Pt/carbon catalyst.