We report the first systematic study of the frequency dependence of optical nonlinearities of bulk GaAs at room temperature. In contrast to the previous understanding, band filling and plasma screening of Coulomb enhancement of continuum states are found to be the dominant contributions to the dispersive optical nonlinearities under quasi steady-state excitations. The partly phenomenological semiconductor plasma theory is in good agreement with the experimental data.

A novel material, namely, Fe-containing lithium-metal triphosphate (LiM2P3O10; MFe), has been synthesized by wet-chemical method. The phase shows the monoclinic structure (P21/m≡C 2 2 h ). The crystal chemistry and chemical structural characteristics have been analyzed by X-ray-diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Surface chemical composition, valence state, and chemical bonding and local structure analysis have been performed by X-ray photoelectron (XPS) and Raman scattering (RS) spectroscopy. EDS and HAADF-STEM indicate the chemical homogeneity and purity of LiFe2P3O10 samples. Both XPS and RS experiments show the existence of an amorphous carbon deposit at the surface of the LiFe2P3O10 particles. Comparison between XPS results for LiFePO4 olivine and LiFe2P3O10 revealed the change in the binding energy of Fe(II) ions. Studies of the local structure characterized by Raman scattering show the evolution of the chemical bonding with the increased number of interconnected PO4 oxo-anionic groups. The electrochemical characteristics of LiFe2P3O10 demonstrate their applicability in lithium batteries.