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Raman spectra of single-wall carbon nanotubes produced in the channels of zeolite AFl single crystals have been analyzed in the light of the full symmetry group, the line group. The phonon dispersion curves of the tubes (5,0), (3,3), and (4,2) are calculated based on the lattice dynamical model and the phonon branches are assigned to their quantum numbers (irreducible representations). The structures of Raman spectra of different samples are reproduced well by the density of states of relevant Raman-active phonons. The result is useful to evaluate the contents of these tubes in real crystals where the contents are not well defined before. [ABSTRACT FROM AUTHOR]

Reports on the measurement of third-order optical nonlinearity of ZnO microcrystallite thin films near the excitonic resonance at various temperatures. Use of the femtosecond degenerate four-wave-mixing technique in the study; Response times measured.

Examines the temperature dependence of the optical absorption spectra of isolated selenium chains stabilized in channels of AlPO[sub 4]-5 crystals. Linear shift of the excitonic energy with increasing chain temperature; Attribution of the temperature dependence to interchain interaction and electron-optical-phonon coupling weakening.

Investigates the absorption spectra of selenium (Se) and mercuric iodide in channels of AlPO[sub 4]-5 (AFI) single crystal. Shift of the lowest electronic excitation states of the isolated chains; Congruence of the results with the theoretical expectation; Differences in the behavior of Se and AFI and mercuric iodide and AFI.

The mechanism of ultraviolet stimulated emission was investigated in ZnO/ZnMgO multiquantum wells. Stimulated emission induced by exciton-exciton scattering occurred throughout a range of temperatures from 5 K to room temperature. At temperatures higher than 160 K, stimulated emission due to electron-hole plasma recombination was also observed with a higher excitation threshold than that of exciton-exciton scattering. The exciton binding energies of multiquantum wells were larger than that of bulk ZnO and increased with a decrease in the well widths. This enhancement of exciton binding energy is due to the quantum-confinement effect and is favorable for the stability of exciton states. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the observation of stimulated emission in ZnO/Mg[sub x]Zn[sub 1-x]O superlattices well above room temperature. Two kinds of superlattices grown by laser molecular-beam epitaxy showed clear systematics on the quantum subband levels in absorption and spontaneous emission spectra. Stimulated emission with excitonic origin could be observed at very low optical pumping levels. The threshold excitation intensity changed from 11 to 40 kW/cm[sup 2], and the emission energy could be tuned between 3.2 and 3.4 eV, depending on the well thickness and/or the Mg content in the barrier layers. The excitonic stimulated emission could be observed up to 373 K and the characteristic temperature was as high as 87 K. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]