Chen Yonghu

Quantum cutting downconversion by cooperative energy transfer from Bi 3+ to Yb 3+ in Y 2 O 3 phosphor

Bi3+ and Yb3+ codoped cubic Y2O3 phosphors are prepared by pechini sol–gel method. Strong near-infrared (NIR) emission around 980 nm from Yb3+ (2F5/2 →2 F7/2) is observed under ultraviolet light excitation. A broad excitation band ranging from 320 to 360 nm, owing to the 6s2 → 6s6p transition of Bi3+ ions, is recorded when the Yb3+ emission is monitored, which suggests a very efficient energy transfer from Bi3+ ions to Yb3+ ions. The Yb3+ concentration dependences of both the Bi3+ and the Yb3+ emissions are investigated. The decay curve of Bi3+ emission under the excitation of 355 nm pulse laser is used to explore the Bi3+ → Yb3+ energy transfer process. Cooperative energy transfer (CET) is discussed as a possible mechanism for the near-infrared emission.

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.