Cai Zhi-gang

EXCITON RECOMBINATION DYNAMICS IN CdTe/CdZnTe QUANTUM WELLS

Quantum wells of CdTe/CdZnTe were grown by molecular beam epitaxy. The highest order of satellite peak of the sample is 5 from XRD spectra and excition emission linewidth is about 4.8 nm at 77 K. It was shown that our samples are very good. The recombination dynamics of exciton in high-quality CdZnTe/CdTe multiquantum wells were investigated by means of time-resolved photoluminescence(PL) spectra with different excitation power at 77 K and photoluminescence spectra with different temperature. When weaker excitation was used, radiative recombination decay time of the exciton was reduced as the excitation intensity was decreased; the results indicate that the dominant mechanism may be the quenching of exciton emission by impurities and defects. The linewidth of the exciton emission becomes broader with increasing temperature, the linewidth at low temperature is only due to the well thickness, and the broadening linewidth at high temperature is contributed by the interactions among the exciton and LO and TO phonons and ionized donor impurities. The PL intensities are reduced with increasing temperature, which is mainly due to the thermal dissociation of excitons, i.e., the electrons or holes jump into the barriers from the wells by thermal excitations. The exciton emission from n=2 heavy hole exciton at 77 K has been observed, and the n=2 heavy hole exciton luminescence decay time is shorter than that from n=1. The investigation indicates that there is the exciton energy relaxation from the n=2 to n=1 heavy hole exciton state by phonons.

LB Films exhibiting SHG coupled with electric properties

Abstract The preparation of stable monomolecular layers and semiconducting Langmuir–Blodgett films exhibiting coupled SHG effect based on hemicyanine dye and nickel maleonitrilodithiolate is described.

Pattern Formation and Quasicrystal Structure in Azobenzene Polymer Film

Pattern formation in azobenzene polymer film by degenerate four-wave mixing is reported. Island arrays with specific patterns are analyzed with scanning electron microscopy and polarizing optical microscopy. It is demonstrated that the control of photo-induced nanostructure sized micropattern in the nonlinear organic film is possible by using properly polarized writing beams with the total incident power exceeding a certain threshold.

Photoluminescence of fullerene[60] in ultrathin ordered multilayers: The dissociation of molecular aggregation

The aggregation behavior of a substituted fullerene compound, 1-benzyl-2-hydro[60]fullerene (C60-Be), in Z-type ultrathin ordered (e.g. LB) multilayers has been studied by UV-vis absorption, steady state and time-resolved fluorescence spectroscopies. The LB multilayers of pure C60-Be showed J-aggregate formation, characterized by a large red-shift of two absorption peaks (ΔE∼2 098 cm1 from 260→275 nm and ΔE∼1 076 cm-1 from 328→340 nm, respectively). The main fluorescence emission bands were found at 710, 646, 603, 600 and 595 nm for pure (C60-Be, mixed C60-Be (molar percentage 50%, 25% and 20%. respectively) multilayers and monomeric C60-Be in solution, respectively. The aggregates were dissociated by mixing with some inert materials. The fluorescence decay profiles of C60-Be, mixed C60-Be (molar percentage 50%, 25% and 20%, respectively) in LB films could be best-fitted by using a bi-exponential decay model.