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ZnO nanoflowers were synthesized by the hydrothermal process at an optimized growth temperature of 200 • C and a growth/reaction time of 3 h. As-prepared ZnO nanoflowers were characterized by x-ray diffraction, scanning electron microscopy, UV-visible and Raman spectroscopy. X-ray diffraction and Raman studies reveal that the as-synthesized flower-like ZnO nanostructures are highly crystalline with a hexagonal wurtzite phase preferentially oriented along the (1 0 1 1) plane. The average length (234-347 nm) and diameter (77-106 nm) of the nanorods constituting the flower-like structure are estimated using scanning electron microscopy studies. The band gap of ZnO nanoflowers is estimated as 3.23 eV, the lowering of band gap is attributed to the flower-like surface morphology and microstructure of ZnO. Room temperature photoluminescence spectrum shows a strong UV emission peak at 392 nm, with a suppressed visible emission related to the defect states, indicating the defect free formation of ZnO nanoflowers that can be potentially used for UV light-emitting devices. The suppressed Raman bands at 541 and 583 cm −1 related to defect states in ZnO confirms that the ZnO nanoflowers here obtained have a reduced presence of defects.

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We report above-bandgap ordinary optical properties of -phase GaSe single crystal. Reference-quality pseudodielectric function ͗͑E͒͘ = ͗ 1 ͑E͒͘ + i͗ 2 ͑E͒͘ and pseudorefractive index ͗N͑E͒͘ = ͗n͑E͒͘ + i͗k͑E͒͘ spectra were measured by spectroscopic ellipsometry from 0.73 to 6.45 eV at room temperature for the light polarization perpendicular to the optic axis ͑E ៝ Ќ ĉ͒. The ͗͘ spectrum exhibited several interband-transition critical-point structures. Analysis of second-energy derivatives calculated numerically from the measured data yielded the critical-point energy values.