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Ge J.,Key Laboratory of Weak Light Nonlinear Photonics | Zhao L.,Key Laboratory of Weak Light Nonlinear Photonics | Zhao L.,Nankai University | Guo H.,Key Laboratory of Weak Light Nonlinear Photonics | And 4 more authors.
Physical Chemistry Chemical Physics | Year: 2013

A series of rare earth (RE) doped oxyfluoride glasses with the composition of (45-x) SiO2-5Al2O3-40PbF2- 10CdF2-xRe2O3 (x = 1, 5, 10, 15) (mol%) were prepared by a traditional melt-quenching method. Glass ceramics (GCs) were obtained after thermal treatment and characterized by X-ray diffraction (XRD) to investigate the nanocrystal structure and distortion. Both the dopant type and the doping level play an important role in the distortion of the PbF 2-RE lattice. It is found that a cubic Pb3REF9 phase forms in low doping GCs, a tetragonal PbREF5 phase forms in middle doping GCs and cubic PbRE3F11 forms in high doping GCs. Accordingly, the site symmetry of RE3+ dopants in β-PbF2 nanocrystal undergoes a transition of O h⋯D4h⋯Oh with the increase of doping level. The change in the ligands coordinating the RE3+ ions was further illustrated by the optical changes in Yb-doped GCs. This paper provides insights on the nanocrystal structure of RE at the atomic level and tries to make a complete description of the nanocrystal structure and distortion in these glass-ceramic materials, which will benefit the optimization of optical properties. © 2013 the Owner Societies.

Liu Z.-B.,Key Laboratory of Weak Light Nonlinear Photonics | Zhao X.,Key Laboratory of Weak Light Nonlinear Photonics | Zhang X.-L.,Key Laboratory of Weak Light Nonlinear Photonics | Yan X.-Q.,Key Laboratory of Weak Light Nonlinear Photonics | And 3 more authors.
Journal of Physical Chemistry Letters | Year: 2011

The ultrafast relaxation dynamics and nonlinear optical response in single- and few-layered graphene oxide (GO) were studied by ultrafast optical differential transmission spectroscopy and Z-scan technique using various pump intensities. It was found that charge carriers with subpicosecond-to-picosecond dynamics from sp2-hybridized domains dominate the ultrafast response at low pump intensities, like graphene. Surprisingly, the influence of two-photon absorption from sp3-hybridized domains on the transient absorption signal becomes increasingly strong with pump intensities. On the basis of heterogeneous ultrafast dynamics of GO with saturable absorption in sp2 domains and two-photon absorption in sp3 domains, the nonlinear optical response can be tailored by manipulation of the degree and location of oxidation on GO sheets; this unravels the important role of sp 3 domains in graphene optics and will facilitate the potential applications of GO in optoelectronics. © 2011 American Chemical Society.

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