Enhancement of the Anti-Stokes Fluorescence of Hollow Spherical Carbon Nitride Nanostructures by High Intensity Green Laser

Fluorescence spectra of graphitic (g-C3N4) and spherical (s-C3N4) modifications of carbon nitride were measured as a function of green pulsed (6 ns-pulse) laser intensity. It was found that the intensity of the laser increases the maximum of the fluorescence shifts towards the anti-Stokes side of the fluorescence for s-C3N4 spherical nanoparticles. This phenomenon was not observed for g-C3N4 particles. The maximum of the anti-Stokes fluorescence in s-C3N4 nanoparticles was observed at 480 nm. The ratio of the intensity of the anti-Stokes peak (centered at 480 nm) to that of the Stokes peak (centered at 582 nm) was measured to be I484/582 = 6.4 × 10−3 at a low level of intensity (5 mW) of a green pulsed laser, whereas it rose to I484/582 = 2.27 with a high level of laser intensity (1500 mW)

Synthesis of Star-Shaped Boron Carbide Micro-Crystallites under High Pressure and High Temperatures

We synthesized star-shaped pentagonal microcrystals of boron carbide with an extremely low carbon content (~5%), from m-carborane under high pressure (7 GPa) and high temperature (1370⁻1670 K). These crystals have five-fold symmetry and grow in the shape of stars. A 5-fold symmetry in large micron-sized crystals is extremely rare making this a striking observation

Elastic and inelastic behavior of graphitic C₃N₄ under high pressure

We conducted high pressure measurements on the graphitic C₃N₄ (g-C₃N₄) phase using Brillouin light scattering (BLS) up to 41.5 GPa and X-ray Raman scattering (XRS) up to 26 GPa to probe the behavior of sp² bonds. Analysis of the BLS and XRS measurements of g-C₃N₄ reveals no structural phase transition and, unlike graphite, no sp² to sp³ rehybridization in this pressure range. From the BLS results we estimate the ambient condition longitudinal velocity (VL = 6.27 ± 0.12 km/s), aggregate shear wave velocity (VS = 3.04 ± 0.2 km/s), and the shear (μ = 21.6 GPa) and bulk elastic moduli (KV = 63.1 GPa) of the g-C₃N₄.4 page(s

Near-Ir Raman Spectroscopy of Graphitic B–C–N Materials

Raman scattering (RS) by graphitic phases BCxN (g-BCxN), obtained by different methods, was studied using an excitation laser operating in the near-IR (NIR) range. With such excitation the most characteristic peaks for g-BCxN are 1300 cm–1 (D-peak) and 1505 cm–1 (G-peak). It is shown that the D- and G-peaks are associated with disordered graphite: the D-peak is observed because the selection rules change, and its intensity is correlated with the size of the graphite cluster sp2 in a polycrystalline graphite; the G-band is associated with thegraphite mode that is RS-active in the E2g plane. The shift of the D-peak in g-BCxN (1300 cm–1 ) as compared with its position in graphite (1355 cm–1 ) can be explained by the positional dispersion of the D-peak with excitation wavelength. The RS line centered at 1260 cm–1, which could be associated with a RS-active mode, is observed only for samples with high crystallinity and for RS spectra obtained at high pressures and high temperatures