Duan Changkui

Thermally Controllable Break Junctions with High Bandwidths and High Integrabilities

Break junctions are important in generating nanosensors and single molecular devices. The mechanically controllable break junction is the most widely used method for a break junction due to its simplicity and stability. However, the bandwidths of traditional devices are limited to about a few hertz. Moreover, when using traditional methods it is hard to allow independent control of more than one junction. Here we propose on-chip thermally controllable break junctions to overcome these challenges. This is verified by using finite element analysis. Adopting microelectromechanical systems produces features of high bandwidth and independent controllability to this new break junction system. The proposed method will have a wide range of applications on on-chip high speed independent controllable and highly integrated single molecule devices.

First-principles study of the local structure and crystal field of Yb2+ in sodium and potassium halides

The local coordination structures around the doping Yb2+ ions in sodium and potassium halides were calculated by using the first-principles supercell model. Both the cases with and without the charge compensation vacancy in the local environment of the doping Yb2+ were calculated to study the effect of the doping on the local coordination structures of Yb2+. Using the calculated local structures, we obtained the crystal-field parameters for the Yb2+ ions doped in sodium and potassium halides by a method based on the combination of the quantum-chemical calculations and the effective Hamiltonian method. The calculated crystal-field parameters were analyzed and compared with the fitted results.

Rare-earth doped optical spectral conversion materials with their applications

Based on the research work carried out in our laboratory in recent years, we focus on three categories of rare-earth doped spectral conversion materials, i.e., red phosphor for white-LED lighting, near-infrared downconversion materials and upconversion nanosized biological fluorescent labeling materials. Our work on the red phosphor for white-LED has been mainly focused on Eu3+ doped materials, and the energy transfer from sensitizers to Eu3+ ions is investigated in order to enhance the efficiency under the excitation of near-ultraviolet light. For the purpose of enhancing the efficiency of silicon-based solar cells, we have carried out the studies on near-infrared downconversion materials based on stepwise and cooperative energy transfer mechanisms and have clarified the downconversion mechanisms in NaYF4:Ho3+, Yb3+ and YVO4:Yb3+ materials. Biological fluorescent labeling is another important application of luminescent materials, which has some stringent requirements on the materials, such as the nanoparticle size, water-solubility, non-toxicity and luminescent efficiency. In our recent work, core/shell NaYF4:Yb3+, Er3+(Tm3+)/NaYF4 UCNPs have been successfully synthesized and transferred to aqueous phase by coating a cross-linked PMAO polymer. The cross-linked core/shell nanoparticles are very stable for several days, and are successfully internalized into human prostate cancer cells, which substantiates the utility of these nanoparticles in biolabeling applications. To sum up, due to significant existing and potential applications in biological and chemical sensing, new energy resources, energy saving and environmental protection, rare-earth doped spectral conversion materials have been attracting extensive attention. The future of rare-earth doped optical spectral conversion materials would be bright.