In this work we investigate some optical properties of semiconductor ZnO spherical quantum dot embedded in an amorphous SiO2 dielectric matrix. Using the framework of effective mass approximation, we have studied intraband S-P, and P-D transitions in a singly charged spherical ZnO quantum dot. The optical properties are investigated in terms of the linear and nonlinear photoabsorption coefficient, the change in refractive index, and the third order nonlinear susceptibility and oscillator strengths. Using the parabolic confinement potential of electron in the dot these parameters are studied with the variation of the dot size, and the energy and intensity of incident radiation. The photoionization cross sections are also obtained for the different dot radii from the initial ground state of the dot. It is found that dot size, confinement potential, and incident radiation intensity affects intraband optical properties of the dot significantly

The second harmonic generation (SHG) and the sum frequency generation (SFG) processes are investigated in the conduction band states of the singly charged ZnO quantum dot (QD) embedded in the HfO 2 , and the AlN matrices. With two optical fields of frequency ω p and ω q incident on the dot, we study the variation with frequency of the second order nonlinear polarization resulting in SHG and SFG, through the electric dipole and the electric quadrupole interactions of the pump fields with the electron in the dot. We obtain enhanced value of the second order nonlinear susceptibility in the dot compared to the bulk. The effective mass approximation with the finite confining barrier is used for obtaining the energy and wavefunctions of the quantized confined states of the electron in the conduction band of the dot. Our results show that both the SHG and SFG processes depend on the dot size, the surrounding matrix and the polarization states of the pump beams. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx

Electronic transitions in the quantum confined states in the conduction band of spherical ZnO semiconductor quantum dot are studied. Photoabsorption spectra and oscillator strengths have been obtained for various sizes of quantum dot using effective mass approximation. Electric quadrupole effect has been included in addition to the electric dipole effect. The nonlinear contribution to photoabsorption spectra has also been studied. Results for transition energies of the quantum confined states are found to be in good agreement with the available experimental data.

In the present study, we applied a sonication based method to achieve graphene oxide (GO) and reduced graphene oxide (r-GO) nano-structures. X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and x-ray absorption near edge structure (XANES) spectroscopy measurements were applied to characterize the samples. XRD, TEM and Raman results demonstrate significant crystalline nature of GO nano sheets. On the other hand, the r-GO sample shows poor crystallinity with a large number of lattice defects. The FTIR spectrum conveys the attachment of significant oxygen-containing functional groups in GO sample. The detachment of oxygen function groups from the r-GO sample, under the reduction process, is also confirmed by the FTIR spectra. Local electronic structure investigations, from the C K-edge XANES of GO and r-GO nano sheets, convey the lowering of 1s → π* and 1s → σ* transitions and lesser sp2 character of the carbon ring. The O K-edge XANES spectra have shown the accumulation of C = O σ*, C–O σ* and O–H σ* states at the basal plane of GO and elimination of such functional groups in the r-GO samples and convey controlled tailoring of the functionalities of GO and r-GO nano sheets.

In this paper, we investigate the linear and nonlinear photoabsorption processes in the conduction-band-confined levels of a singly charged ZnO quantum dot (QD) surrounded by HfO 2 and AlN matrices. We also investigate the photoelectric process in which the conduction band electron ejects from the dot to the vacuum. We use the effective mass approximation with a finite barrier height at the dot-matrix interface. We consider the self-energy of the electron in the dot and the local field effect. The electromagnetic interaction of the incident radiation with the electron in the dot is considered in the electric dipole plus quadrupole approximation. Results for the photoabsorption coefficient and the photoelectric process are presented for different dot sizes and different intensities of incident radiation. It is found that the inclusion of the quadrupole effect reveals new photoabsorption peaks in the absorption spectra. Both the photoabsorption and photoelectric processes significantly depend on the dot size and the surrounding matrix. The change in the intensity of the incident radiation significantly influences the nonlinear photoabsorption. The photoabsorption coefficient and the photoelectric cross sections are found to be relatively higher for the ZnO QD embedded in the high-dielectric constant matrix HfO 2 as compared with the lower-dielectric constant AlN matrix.