Irene ng Li

Temperature sensor based on iodine-doped hollow core photonic crystal fiber

Optical transmission property of iodine-doped hollow core photonic crystal fiber has been investigated in the temperature range of 300 K ~ 500 K. The transmitted light intensity is decreased dramatically with increasing temperature. The slope of the temperature-dependent intensity-curve is 3.3x10-3 dB/K.

Refraction Indices Measurement of Hexagonal Zeolite Crystal Using Brewster Angle Method

A simple method for measuring the refraction indices of small hexagonal crystals is studied. The method is based on Brewster angle law. The refractive indices are confirmed by measuring the Brewster angle on two different surfaces. As an example, the measured refractive indices for hexagonal zeolite crystals are ne=1.488 and no=1.327, respectively, which are necessary for further investigations on the nonlinear properties of these zeolite crystal, such as second harmonic generation (SHG) effect. This method avoids the damage of the sample, and is simple and quick, which is suitable for the measurements of small birefringent crystals.

Host-guest interaction between Acridine orange molecules and AFI or CHA zeolite crystals

Acridine orange (AO) molecules were incorporated in AlPO4-5, SAPO-5 and SAPO-47 single crystals by vapor-phase diffusion method. Polarized absorption spectra show that AO molecules are well aligned by the one-dimensional channel systems of AlPO4-5 and SAPO-5 matrices. While the orientation of AO molecules in SAPO-47 crystals is diverse owing to the three-dimensional cage structure of chabazite (structure code CHA). The absorption peak and emission peak of AO/SAPO-5 blue shift compared with that of AO/AlPO4-5 because the channel environment changes from non-polar medium to polar medium when Si substituted in the framework of AlPO4-5. The greater blue shift in absorption band and emission band of AO/SAPO-47 are expected to originate from the polar channel medium and smaller channel size of SAPO-47.

Morphology Control of SAPO-11 and SAPO-47 Crystals in the Presence of Diethylamine

SAPO-11 and SAPO-47 crystals have been synthesized using diethylamine (DEA) as the structure-directing agent (SDA) and their morphology have been controlled successfully by varying aging duration. The single crystals were obtained in a short aging duration while film and island-like crystals were obtained in a long aging duration. The effect of SiO2/Al2O3 ration and content of HF on SAPO-47 crystals have been investigated. High molar ration of SiO2/Al2O3 and high content of HF is tend to synthesize larger crystals of SAPO-47. All the samples were characterized by XRD and SEM.

Optimized conditions for THz photonic crystal fabrication with excimer laser

We theoretically and experimentally investigated the fabrication conditions for THz photonic crystals. A THz photonic crystal with complete band gap from 0.33 THz to 0.36 THz has been designed. The substrate is polytetrafluorethylene (PTFE) which is transparent in THz range. The lattice constant is 320 µm, the hole radius is 85µm. An excimer laser with wavelength 248nm is used to realize the structure. According to a series of testing results, the optimized conditions for this THz photonic crystal fabrication have been confirmed. The excimer laser energy is 13 mJ and the pulses number per burst is 120.

Orientation controlment of disperse red 1 molecules in matrix of zeolite crystals

Polarized absorption spectra for disperse red 1 (DR1) molecules solved in ethanol (DR1@ethanol) and DR1 incorporated in channels of AlPO4-5 crystals (DR1@ AlPO4-5) have been investigated. The results show that the predominant structure of DR1 molecules in AlPO4-5 matrix is trans configuration. Its absorption band is centred at 520 nm, which shows strongly anisotropic polarizability. The absorption band for cis-configuration is centred at 470nm, which does not depend on polarization angle. The experimental energy difference between cis and trans configurations is 0.25 eV. Temperature dependent absorption spectra have also been investgated for DR1@ AlPO4-5. The absorption band shifts to long wavelength with increasing temperature, which may be due to the bond expansion in DR1 molecules.

Polarized Raman Characterization of (2,2) Carbon Nanotubes Formed inside the Channels of AEL Crystals

A pure AlPO4-11 (AEL) zeolite crystal is optically transparent in visible region and a good insulator with thermal stability up to 1173 K. These excellent physical properties, plus their unique elliptical pore structures, make them an excellent template to fabricate ultra-thin single-walled carbon nanotubes (SWNTs).We studied the polarization dependence Raman spectra for (2,2) SWNTs formed inside the channels of AEL crystals. These (2,2) SWNTs acts as a dipolar antenna, polarized along the crystal channels axis. The polarization angle dependence of the Raman intensity indicates that the enclosed (2,2) SWNTs are highly oriented in the channels with their dipole transition moment mostly along the channels.

Template technique-A promising approach for well-aligned quantum wires fabrication

Quantum wire is one of the central subjects of nano-electronics. Quantum wire shows unusual electronic and optical properties attributed to the following effects: quantum confinement effect, surface effects, and quantum tunneling effect. Many different kinds of techniques have been developed for researchers to produce quantum wires, such as laser ablation technique, electrochemical processing, chemical vapor deposition technique, etc. However, controlling the sample size and orientation distribution is a big challenge in these fabrication methods. One promising technique to prepare monosized well-aligned quantum wires is using template technique, i.e., deposition of guests into porous matrices. In this paper, several template synthesis processes for preparations of carbon nanotubes were investigated. The carbon nanotubes produced by template technique have narrow size distributions and involve fragments of highly ordered shapes which are due to the limitation of matrix size and channel direction. Because of the restricted dimension of the matrix, the system shows peculiar properties such as polarization in spectra, strong quantum effects, and faster optical response. These may be used in electric transport, optic switches, nonlinear optics and lasers.

Micro-cavity laser of dye molecules loaded in AlPO4-5 crystals

Micro-cavity laser has attracted extensive attentions due to its potential applications in high-speed integrated opto-electronic device and system. In micro-cavity, spontaneous emission process is enhanced or prohibited, and lasing can occur without a visible threshold. In the past, micro-cavity was realized with semiconductors such as microdisks or vertical cavity surface emitting lasers, with organic dyes embedded in planar resonators as Langmuir-Blodgett films or in spheres, and with gain medium in photonic crystals. In this article, we report a new type of micro-cavity laser based on organic dye molecules incorporated in the channels of AlPO4-5 single crystals by physical diffusion method. The optical measurements reveal that the dipole transition moment of the enclosed organic dye molecules is highly oriented in the channels. Due to size confinement of the AlPO4-5 channels, there is a structure deformation of the dye molecules, which leads to a large blue shift in the absorption spectra for the dye/AlPO4-5 crystal. The micro-sized hexagonal AlPO4-5 single crystal serves as a good natural micro-cavity for the lasing action of the adsorbed dye molecules. The micro-cavity mode of the lasing action is demonstrated.

Resonant Raman technique-a powerful tool for exploring electron-phonon coupling in Se nanoclusters

Raman scattering is an inelastic process, in which we can obtain information about material lattice vibration frequencies. If the wavelength of the excitation laser is within the electronic spectrum of the material, the intensity of some Raman-active vibrations will increase enormously. This resonant Raman effect can be quite useful to explore the electron-phonon coupling in the substance. In this article, we report the investigations on the electron-phonon coupling effect in Se nanoclusters using resonant Raman technique. Up to 10 different laser lines are used in the experiment. The Raman intensity strongly depends on the energy of the laser lines used for excitation. The one-phonon symmetric A1 modes for Se single helix and Se8 rings are enhanced in the vicinity of their absorption bands. Detailed analysis shows that the Raman intensity in the high frequency range 450 - 550 cm-1 is a sum of individual second-order Raman scattering intensities for the confined Se species. These two-phonon Raman shifts occur at twice the frequency shift of the first-order Raman lines, and their intensities are also enhanced when the excitation laser energy matches an electronic transition in Se nanoclusters.