1/infinity [ZrPSe6-]: a soluble photoluminescent inorganic polymer and strong second harmonic generation response of its alkali salts

Zirconium selenophosphate compounds with a unique polar structure show strong second harmonic generation and they dissolve in polar solvent to produce photoluminescent solutions.     

High-quality Cu2O crystals with various morphologies grown by thermal oxidation

We present an improved preparation method for, and experimental results on, high-quality crystals of cuprous oxide (${\mathrm{Cu}}_2\mathrm{O}$) grown by thermal oxidation. X-ray diffraction and low-temperature optical measurements at 2 K confirm excellent characteristics that are on par with natural-growth cuprite crystals. Synthetic ${\mathrm{Cu}}_2\mathrm{O}$ crystals were prepared in different geometries including platelets, cylindrical wires, and spheroids. Interestingly, we observed that the oxidation of Cu wires at high temperatures leads to the formation of hollow tubules of ${\mathrm{Cu}}_2\mathrm{O}$. Such unconventional structures of ${\mathrm{Cu}}_2\mathrm{O}$ could be utilized to confine excitonic matter, or serve as high-density exciton–polariton cavities.     

Negative refraction

Light bends the wrong way in materials where both ε and μ are negative as was pointed out in 1968, but the absence of natural materials with this property led to neglect of the subject until 1999 when it was shown how to make artificial materials, metamaterials, with negative μ. The rapid advance of the subject since that date, both in theory and experiment, is reflected in the exponential growth of publications now at the 200 per year level and still growing. This interest is explained by the sudden availability of a qualitatively different class of electromagnetic materials combined with the quite startling properties which these materials appear to have; all of which provokes debate as each new facet of their behaviour is revealed. Experiment has been vital to resolution of controversy and has chiefly been in the microwave region of the spectrum though there is potential in the optical region currently being explored by several groups.     

Experimental investigations of the nuclear level density by using heavy ion reactions

The transition of the level density parameter a _off from the low excitation energy value a _off=A/8 MeV⁻¹ to the Fermi gas value a _FG ∼ A/15 MeV⁻¹ was discovered a few years ago studying particle spectra evaporated from hot compound systems of A∼ 160. A number of experiments have been recently performed to confirm the earlier findings and extend the investigation to other mass regions and to higher excitation energies. Furthermore, precision coincidence experiments have been done in the lead region in which evaporation residues are tagged by low energy gammarays. Those experiments open the possibility of a detailed study of the level densities in nuclei where the shell effects are important.     

Study of the 1s orthoexciton luminescence in Cu2O under two-photon excitation

We have studied the luminescence of 1s orthoexcitons in Cu₂O under both resonant and non-resonant two-photon excitation. The intensity of the luminescence was enhanced while resonantly exciting at the 1s or 2s orthoexciton levels. The direct and phonon-assisted emissions were observed over a wide range of temperatures (1.8-294 K) under two-photon resonant excitation. The phonon-assisted spectra can be well fit with a Maxwellian distribution with a fitting temperature close to the lattice temperature. The integrated intensity shows a minimum at 20 K and a maximum around 180 K. The existence of the direct emission feature enables us to deduce the temperature dependent bandgap and the orthoexciton line width directly up to relatively high temperatures. The red-shift of the orthoexciton energy and the increase of its line width as the temperature increases are interpreted as a temperature dependence of the real and imaginary parts of the exciton self energy.     

Direct measurements of the mechanical properties of polymerized and unpolymerized langmuir-blodgett films

Mechanical measurements can be made on Langmuir-Blodgett (LB) films that have been peeled from their substrates, and are floating on the surface of water, by compressing them between the moving barrier and the Langmuir balance float in a standard monolayer trough. We have used this technique, which utilizes apparatus commonly available where LB films are made, to study multilayers of lead 10,12-tricosadiynoate (a diacetylene carboxylic acid) that were first polymerized and then peeled from the substrate. For comparison we have performed the same measurements on pieces of mylar, on unpolymerized films, and on films of calcium octadecanoate (a saturated chain fatty acid). We found Young's modulus for films of the saturated chain material, the unpolymerized diynoate, and the polymerized films, to be 6 GPa (900 kpsi), 0.5 GPa, and 6 GPa, respectively.