Papers by Author: Kui Ying Li

Abstract: Nonradiative transitions (NRTs) are relaxation processes competing with radiative process. In light emitting diodes and room temperature laser devices, NRTs lower the emission efficiency. In order to prohibit these processes, better understanding is practically needed. But nowadays knowledge of NRTs comes from the analyses of the steady-state and time-resolved photoluminescence spectra, which are indirect evidences because of their radiative nature. Here we report a direct detection of nonradiative processes of ZnO nanocrystallines by combination of photoacoustic spectroscopy (PAS) with field-induced photovoltaic spectroscopy (FISPS) methods. In photoacoustic spectrum of ZnO nanocrystals, a main feature centered at 374 nm and a shoulder feature at 441 nm have been recorded. The surface photovoltage spectrum (SPS) displays a main peak at about 364 nm, which is assigned to band-gap transition. And the FISPS spectrum shows a main feature at 380 nm and a pronounced shoulder at 450 nm. The relative energy of the PAS main feature locates at about 0.1 eV lower than that of band-gap, and the relative energy of the PAS main and shoulder features locates at 60 meV higher than that of FISPS main and shoulder features. These energy spaces are in good consistent with the exciton binding energy reported for ZnO nanostructures. Thus we tentatively ascribe the NRTs to the trapping of the photogenerated excitons to the surface states of ZnO nanocrystallines.

Abstract: A water-soluble CdTe QDs capped by 3-Mercaptopropionic acid (MPA) were synthesized. The results confirmed that the grain size of the QDs was controlled by changing the reflux time of precursor solution and that the QDs possessed obviously quantum size effect. The results showed that a depletion layer CdTe_1-xS_x (0£x≤1) formed in between CdTe nanoparticle and ligand MPA. It is believed that two heterojunction-like structures possess quite distinct surface photovoltaic characteristic excited between the core-CdTe and the shell-CdS, and between CdTe/CdS and the ligand MPA, respectively, according to the EFISPS results of the MPA-capped CdTe QDs.

Abstract: The Macroporous Nanocrystalline TiO₂ Thin Film Was Prepared by Dipping-Coating Method. Polystyrene (PS) Microspheres Template Was Used as Pore-Forming Assistant and TiO₂ Sol Was Used as Precursor. the Photoelectric Characteristics of the Samples Were Studied Using Surface Photovoltage (SPV) and Photoacoustic (PA) Techniques. the Presence of a Small Amount of Residual Template Damages the Integrity of the Porous TiO₂ Film with Inverse Opal Structure, and TiO₂ May Be Restricted in Certain Application Fields as Photonic Crystals. a Small Amount of Residual Template Changes the Surface Photovoltaic Properties of the Porous TiO₂ Film, Resulting Mainly in the Broadened Scope and the Increased Intensity of SPV Response.