Yuanyuan Hou

Synthesis of ZnS nanocrystals with controllable structure and morphology and their photoluminescence property

The controllable synthesis of ZnS nanocrystals with desirable morphology and correlative structure has been carried out via the solvothermal method by simply changing the molar ratio of the reactants. The hexagonal-shaped ZnS nanosheets with a zinc-blende structure were synthesized in one step for the first time. ZnS nanorods with wurtzite structure and large ratio of length to diameter were also fabricated. We found that phase transformation is easily induced and there is a strong correlation between the morphology and structure of the ZnS nanocrystals by changing the ratio of the reactants. The photoluminescence spectra of the ZnS nanosheets and nanorods exhibit different emission bands. ZnS nanosheets show a strong emission at 534 nm while the nanorods have two emissions located at 520 and 578 nm.

Synthesis and high pressure induced amorphization of C60 nanosheets

C60 nanosheets with thicknesses in the nanometer range were synthesized by a simple method. Compared to bulk C60, the lattice of the nanosheets is expanded by about 0.4%. In situ Raman spectroscopy and energy-dispersive x-ray diffraction under high pressures have been employed to study the structure of the nanosheets. The studies indicate that the bulk modulus of the C60 nanosheets is significantly larger than that of bulk C60. The C60 cages in nanosheets can persist at pressures over 30GPa, 3GPa higher than for bulk C60. These results suggest that C60 crystals in even small size will be a potential candidate of superhard materials.

Pressure-induced crystallization and phase transformation of amorphous selenium: Raman spectroscopy and x-ray diffraction studies

High-pressure Raman spectroscopy studies have been carried out on amorphous Se (a-Se) at room temperature in a diamond anvil cell with an 830 nm exciting line. Raman evidence for the pressure-induced crystallization of a-Se and the coexistence of the unknown high-pressure phase with the hexagonal phase is presented for the first time. Further experimental proof of high-pressure angle-dispersive x-ray diffraction studies for a-Se indicates that the unknown high-pressure phase is also a mixture phase of the tetragonal I41/acd and Se IV structure. Our Raman and x-ray diffraction results suggest that hexagonal Se I undergoes a direct transition to triclinic Se III at about 19 GPa, which is in good agreement with the theoretical prediction.

Solvothermal synthesis of ZnS nanorods and their pressure modulated photoluminescence spectra

ZnS nanorods in a wurtzite structure with an average diameter of 10 nm were synthesized via a solvothermal method. In situ photoluminescence and Raman spectra measurements on the ZnS nanorods under high pressure were carried out using a diamond anvil cell. The disappearance of the photoluminescence (PL) band and longitudinal-optical (LO) phonon mode indicates that the ZnS nanorods transform to the rock salt phase near 16.7 GPa. A visible change in the pressure dependence of the full width at half magnitude for the PL band and LO phonon was found near 9 GPa, indicating that a phase transition of the ZnS nanorods from the wurtzite phase to the zinc blende phase probably occurs. High pressure can obviously modulate the PL band of the ZnS nanorods-it shifts to a long wavelength band with increasing high pressure.

Photoluminescence properties of high-pressure-polymerized C60 nanorods in the orthorhombic and tetragonal phases

C60 nanorods in two polymeric phases have been synthesized under different high pressure and high temperature conditions. Orthorhombic and tetragonal phases have been identified from Raman spectra. The rod shape can be kept under quasihydrostatic pressure. The photoluminescence intensity of the polymeric C60 nanorods has been greatly enhanced compared with that of pristine C60 nanorods. The main fluorescence band shifted from 730nm in the unpolymeric phase to 748nm and near infrared 780nm in the orthorhombic and tetragonal phases, respectively. The enhanced photoluminescence with tunable frequency for different polymeric C60 nanorods suggests potential applications in luminescent nanomaterials.

Study of the hydrostatic pressure dependence of the raman spectrum of W/WS2 fullerene-like nanosphere with core-shell structure

The structural behavior of a W/WS2 fullerene-like nanosphere with a core–shell structure has been studied in the hydrostatic pressure range from atmospheric pressure to 18 GPa by Raman spectroscopy using a methanol–ethanol–water mixture (16:3:1) as the pressure transmitting medium (PTM). We found that it is interesting that the intensity ratio of the LA+TA mode and the A1g mode changes with increasing pressure. We attribute this change to the shape transformation of an inorganic fullerene-like IF-W/WS2 nanosphere under high hydrostatic pressure. By comparing the Raman spectra of an IF-W/WS2 nanosphere released from high pressure with that of the original one, we found that the change in morphology is reversible. This indicates that the spherical shape of the IF-W/WS2 has excellent behavior in resisting compression.

Analysis of the upconversion photoluminescence spectra as a probe of local microstructure in Y2O3/Eu3+ nanotubes under high pressure

In situ upconversion photoluminescence measurements of Y2O3/Eu3+ nanotubes under high pressure were carried out with 632.8 nm laser light excitation. The intensity of 5D0–7FJ (J = 0,1,2) transitions increased up to 8.2 GPa due to the enhanced crystal filed with pressure, while above 8.2 GPa, the photoluminescence intensity decreased rapidly. Full width of half maximum (FWHM) of 5D0–7F0,1,2 transitions and I0–2/I0–1 of the Eu3+ ion luminescence both exhibited obvious changes near 8.2 GPa, indicating the presence of short-range structural changes in the vicinity of the Eu3+-ion. The observed changes reflected a disordering of local micro-structure in the vicinity of Eu3+-ions resulting from the short-range distortion of YO6 octahedra under pressure. The luminescence of doped Eu3+ ions acted as an effective probe to reveal slight changes in structure and the local crystalline environment of Y2O3/Eu3+ nanotubes under high pressure.

Comparative study of pressure-induced polymerization of C60 nanorods and single crystals

In this paper, we report a comparative study of pressure-induced polymerization in C60 nanorods and bulk single crystals, treated simultaneously under various pressures and temperatures in the same ...