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Polarized Raman spectroscopy has been performed to investigate the effects of the electric field on 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 (PMN–33%PT) single crystal. The electric-field-evolution of Raman spectra differed from one microarea to another. In the crossed polarization geometry, the abrupt changes in the intensities of the Raman bands at around 570 and 780 cm-1 indicated the occurrence of the field induced phase transition from the MC-type to the MA-type monoclinic structure. On the other hand, the Raman spectra for the microarea that was initially in the MA phase exhibited no obvious changes. All these results revealed the microheterogeneity in PMN–33%PT single crystal, which is useful for understanding the field-induced superior electromechanical properties. [ABSTRACT FROM AUTHOR]

Using the bandmixing model of direct and indirect gaps, we calculate the energy levels of electrons and holes confined in the Si/FeSi2 nanocomposite consisting of nanocrystalline Si core, interfacial FeSi2 layer, and outer Fe2O3 crust. The obtained results explain very well the intensity enhancement and pinning behavior of the observed photoluminescence peaks after the nanocomposite is stored in air. We also theoretically obtain the photoluminescence excitation characteristics. Good agreement is achieved between the theory and experiments. [ABSTRACT FROM AUTHOR]

A uniform array of one-dimensional molecular iodine wires is fabricated by introducing iodine molecules into the channels of AFI zeolite crystals through the vapor phase. The only possible wire structures are formed by linking individual iodine molecules along intramolecular bond axis into a single line. Polarization dependence of Raman intensity at modes of iodine species indicates that the wires are aligned perfectly along the c axis of AFI crystal. Polarized optical absorption as well as resonant Raman scattering reveal two wire species inside the channels of AFI zeolite: In- and (I2)n wires. [ABSTRACT FROM AUTHOR]

This work investigates the evolution of micro-Raman spectra of a [001]-oriented 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystal in the temperature range from -120 to 200 °C. For a poled sample, the T1u mode splits into an E mode (remaining at 51 cm-1) and a new A1 mode (shifting to 95 cm-1 at -120 °C) at the tetragonal to rhombohedral phase transition (Tc∼ 70 °C), while other modes remain the same. This A1 mode belongs to the rhombohedral phase. If the sample is depoled, this A1 mode persists for temperatures much above Tc on heating, implying that local regions with rhombohedral symmetry still exist in the tetragonal phase. The underdevelopment of long-range order in the depoled crystal causes the sample to have typical characteristics of a relaxor while poling will enhance the long-range order to make it into a regular ferroelectric. [ABSTRACT FROM AUTHOR]

Unique structured SiOxNy-capped Si nanowire arrays were fabricated via electroless metal deposition on α-SiOxNy-covered Si wafer in ionic silver HF solution through selective chemical etching. A self-assembled localized microscopic electrochemical cell model and a diffusion-limited aggregation process are associated with the formation of the SiOxNy-capped Si nanowire arrays. An enhanced blue photoluminescence band has been recorded. Emission and excitation spectral analyses suggest that generation of photoexcited carriers takes place mainly in the quantum confined Si nanowires, whereas their radiative recombination occurs in the Si–N binding states of SiOxNy nanocaps. [ABSTRACT FROM AUTHOR]

SiO[SUB2]/LiNbO[SUB3](LN)/SiO[SUB2] sandwich structures were fabricated for exploring efficient light emission. After annealing at 1000 °C in O[SUB2] for 30 min, this kind of sandwich structure shows a strong ultraviolet photoluminescence (PL) with an asymmetric spectral shape. This PL spectrum may be Gaussian divided into two bands peaked at 310 (α-band) and 346 nm (β-band). If the layer of LN film is replaced by an Fe-doped LN (LN:Fe) one, the β-band vanishes and the α-band redshifts. The α-band is greatly enhanced and simultaneously becomes asymmetrical after this kind of SiO[SUB2]/LN:Fe/SiO[SUB2] structure is annealed for 60 min. Spectral analysis suggests that the α-band arises from an optical transition in positively charged E8 centers at the interfaces between the LN(:Fe) film and the two SiO[SUB2] layers, while the β-band arises from intrinsic defects in the LN(:Fe) films. The mechanism for the PL enhancement is discussed in terms of a photorefractive effect in the LN(:Fe) films. [ABSTRACT FROM AUTHOR]

We have demonstrated that gas pressure (p[sub G]) is a key parameter for fabricating stoichiometric LiNbO[sub 3] thin films during laser ablation. To theoretically describe the influence of p[sub G], a cylindroid rigid-wall model was presented. It was shown that there exist two critical pressures related to Li and Nb: p[sub Li] and p[sub Nb](P[sub Li]

Studies photoluminescence properties of the crystalline SiO[sub 2] coated with LiNbO[sub 3]/liTaO[sub 3] multilayers. Division of the band observed at room temperature into Gaussian subbands; Linear dependence of intensity on excitation power; Optical transitions of the self-trapped excitons.

SiO[sub 2]/Ge:SiO[sub 2]/SiO[sub 2] sandwiched structure was fabricated for exploring efficient light emission. After annealed in N[sub 2] (O[sub 2]<1%), this structure shows three photoluminescence (PL) bands at 293, 395, and 780 nm. The intensity of the 395 nm band is largely enhanced in comparison with that from the monolayered Ge:SiO[sub 2] film. Spectral analyses suggest that the three PL bands originate from S[sub 1]→S[sub 0], T[sub ∑](T[sub ∏])→S[sub 0], and T[sub ∏][sup ′]→S[sub 0] optical transitions in GeO color centers, respectively. The improvement of the GeO density resulting from the confinement on Ge diffusion is responsible for the enhanced ultraviolet PL. This structure is expected to have important applications in optoelectronics. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

C[sub 60] molecules were chemically coupled in the pores of porous Si through a coupling agent and then coated with a layer of Si, and followed by N[sub 2] annealing. X-ray diffraction results indicate that the fabricated samples contain β-SiC particles which may exist in the pores, in addition to Si, SiO[sub 2], and graphite. The photoluminescence (PL) spectra show an asymmetrical broadband, which can be Gaussian divided into two bands at 380 (3.26 eV) and 454 (2.73 eV) nm. Spectral analyses and the experimental results from infrared spectroscopy and PL excitation measurements suggest that the 380 nm PL band is related to oxygen-vacancy defects in the SiO[sub 2] matrix, whereas the blue PL band is closely connected with the β-SiC particles. Our experiments provide a way for fabricating stable blue-emitting β-SiC materials. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]