Photophysical properties of thin films and solid phase of switchable supermolecular anthracene-based rotaxanes

Polycrystalline powders and thin films of a novel rotaxane, methyl-exopyridine-anthracene rotaxane (EPAR-Me), and of the related thread and stoppers 10-[3,5-di (ter butyl)phenoxy]decyl-2-({2-[(9-anthrylcarbonyl) amino] acetyl}amino) acetate (ANTPEP), have been characterised by photoluminescence, absorption and photoluminescence excitation spectroscopy. A rather unusual, i.e. unstructured and largely red-shifted, photoluminescence spectral behaviour of the rotaxane has been found. Preliminary time resolved measurements indicate a fast energy transfer from the anthracene unit to different species the nature of which is still not assigned.

Optical phonon modes of wurtzite InP

Optical vibration modes of InP nanowires in the wurtzite phase were investigated by Raman scattering spectroscopy. The wires were grown along the [0001] axis by the vapor-liquid-solid method. The A1(TO), E2h, and E1(TO) phonon modes of the wurtzite symmetry were identified by using light linearly polarized along different directions in backscattering configuration. Additionally, forbidden longitudinal optical modes have also been observed. Furthermore, by applying an extended 11-parameter rigid-ion model, the complete dispersion relations of InP in the wurtzite phase have been calculated, showing a good agreement with the Raman experimental data

Optical, magneto-optical properties and fiber-drawing ability of tellurite glasses in the TeO2-ZnO-BaO ternary system

The presented work is focused on the optical and magneto-optical characterization of TeO2-ZnO-BaO (TZB) tellurite glasses. We investigated the refractive index and extinction coefficient dispersion by spectroscopic ellipsometry from ultraviolet, 0.193 um, up to mid infrared, 25 um spectral region. Studied glasses exhibited large values of linear (n632 = 1.91-2.09) and non-linear refractive index (n2 = 1.20-2.67x10-11 esu), Verdet constant (V632 = 22-33 radT-1m-1) and optical band gap energy (Eg = 3.7-4.1 eV). The materials characterization revealed that BaO substitution by ZnO leads (at constant content of TeO2) to an increase in linear and nonlinear refractive index as well as Verdet constant while the optical band gap energy decreases. Fiber drawing ability of TeO2-ZnO-BaO glassy system has been demonstrated on 60TeO2-20ZnO-20BaO glass with presented mid infrared attenuation coefficient. Specific parameters such as dispersion and single oscillator energy, Abbe number, and first-/ third-order optical susceptibility are enclosed together with the values of magneto-optic anomaly derived from the calculation of measured dispersion of the refractive index

Valence-band splitting energies in wurtzite InP nanowires : Photoluminescence spectroscopy and ab initio calculations

We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on"ab initio" calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, respectively, which are in good agreement with the experimental results

Carrier thermalization dynamics in single zincblende and wurtzite InP nanowires

Using transient Rayleigh scattering (TRS) measurements, we obtain photoexcited carrier thermalization dynamics for both zincblende (ZB) and wurtzite (WZ) InP single nanowires (NW) with picosecond resolution. A phenomenological fitting model based on direct band-to-band transition theory is developed to extract the electron-hole–plasma density and temperature as a function of time from TRS measurements of single nanowires, which have complex valence band structures. We find that the thermalization dynamics of hot carriers depends strongly on material (GaAs NW vs InP NW) and less strongly on crystal structure (ZB vs WZ). The thermalization dynamics of ZB and WZ InP NWs are similar. But a comparison of the thermalization dynamics in ZB and WZ InP NWs with ZB GaAs NWs reveals more than an order of magnitude slower relaxation for the InP NWs. We interpret these results as reflecting their distinctive phonon band structures that lead to different hot phonon effects. Knowledge of hot carrier thermalization dynamics is an essential component for effective incorporation of nanowire materials into electronic devices

Convection Induced Self-Organization in Electroless Deposition Experiments

We present the first evidence for spatio–temporal merging dynamics in thin gap electroless deposition experiments. The influence of both the gap thickness and the buoyancy forces on these phenomena is analyzed. The occurrence of this reverse cascading dynamical process is discussed in terms of the interaction of two counter rotating buoyancy driven convection rolls

Optical spectroscopy of unsolvated and solvated crystalline Alq3

Three novel unsolvated crystalline phases of tris-(8-hydroxyquinoline)-aluminum(III) (Alq3), namely \u3b1-, \u3b2- and \u3b3-Alq3, have been synthesized and their crystalline structure determined from X-ray diffraction data on powders and single crystals. Both \u3b1- and \u3b2-Alq3 crystals are triclinic, space group P-1, but differ for the molecular packings. In the \u3b3-Alq3 phase, Alq3 molecules lie about a 3-position of the trigonal P-3 space group. A solvated Alq3(C6H5Cl)1/2 phase (monoclinic, space group P21/n) was also isolated. The optical and vibrational properties of these newly isolated crystal phases of Alq3 have been investigated by absorption, photoluminescence excitation, photoluminescence and Raman spectroscopy. The effect of the different molecular packing on the emission properties has been elucidated, the nature of the photoexcitations clarified, and the vibrational fingerprints of the \u3b1- and \u3b2-crystalline forms highlighted. The origin of the amorphous nature of the vacuum sublimed thin films is discussed on the basis of the accessibility of many different \u3c0-\u3c0 links between homo- and hetero-chiral Alq3 molecules