Zebo Zhang

Study of Eu(DBM)3phen-doped optical polymer waveguides

Eu(DBM)3phen-doped polymer optical planar waveguides with low propagation loss of 0.5 dB/cm have been fabricated. The optical properties and concentration quenching of Eu(DBM)3phen-doped poly(methyl methacrylate) (PMMA) have been studied. The Eu3+ ion in Eu(DBM)3phen-doped PMMA can be doped to high concentration (1 wt.%) without clustering. An Eu(DBM)3phen-doped polymer waveguiding film with a very smooth surface was obtained. An atomic force microscope measurement result indicates that rms surface roughness of the waveguiding film is ∼1.185 nm. The near-field fluorescence was observed on Eu(DBM)3phen-doped waveguiding film with 1-wt.% Eu3+ ions.

Exciton interactions in CdS nanocrystal aggregates in reverse micelle

Here we report the formation and spectroscopic properties of cadmium sulfide (CdS) nanocrystal systems: individual nanocrystal and CdS aggregates. The optical absorption and luminescence spectra of the aggregated CdS nanocrystals and individual nanocrystal show exciton aggregate and individual exciton characteristics. Although it is not Bose-Einstein condensation, such aggregated quantum dots (QDs) seem to supply us opportunity to study the interactions and condensation of excitons in multi-QDs system, not in the separated QDs system.

PHOTOLUMINESCENCE EMITTING PROPERTIES OF SINGLE ZnO NANOWIRE STUDIED BY SCANNING NEAR-FIELD OPTICAL MICROSCOPE

Scanning near-field optical microscope (SNOM) was employed to investigate the room temperature photoluminescence (PL) of single ZnO nanowires with different radii excited by 325 nm laser. Two-dimensional distribution of their PL intensity is provided for the analysis of intensity decay from emission source. It is found that the PL intensity at both ends of each ZnO nanowire (end emission) was much stronger than that at the sides of the wire (side emission). Further investigation indicates that the quality of end emission depends on the diameters of the wires. Some of the ZnO nanowires with special diameters emit stronger light, and the shape of the light is close to Gauss beam. In addition, the Gauss shape light can diffuse longer distance than what the side emission does, typically in the range of a few micrometers. It is a sign of the fact that special guided modes of the PL light are formed in the nanowires. The calculation results predicate that the special guiding mode strongly relies on the diameters of the ZnO nanowires. The good directional property and high intensity of the end emission have many potential applications, including optical switch and microanalysis. It has been shown that SNOM can provide direct evidence of light emission properties from single nanowires, and hence provide the clue of increasing light efficiency and the improvement of light-propagating mode.

Study of rhodamine B-doped polymer optical waveguides by using scanning near-field optical microscopy

The rhodamine B-doped polymer optical planar waveguide with low propagation loss of 0.44 dB/cm has been fabricated and measured by using scanning near-field optical microscopy and m-line method. The mode structure, near-field topography and near-field fluorescence are obtained, respectively. This may have potential applications in the study of polymer waveguide laser and amplifier.

Near-field optical research on the azobenzene polymer films

We report the near-field investigation on azobenzene contained polymer films using scanning near-field optical microscopy. Nanometer scale dots and lines were inscribed on these films, and the topographies and transmitting images of these patterns could be obtained at the same time. The transmitting images were in agreements with the topographies, and it proved that trans-cis isomerization of the azobenzene moieties in the illuminated area induced both surface relief and anisotropy. The experimental results helped to discover the mechanism of the photo induced surface relief and anisotropy, and the agreement between the transmitting images and the topographies could be applied in pure optical writing/reading in high-density data storage.