Fluorescence Resonance Energy Transfer Of CdTe Quantum Dots/Organic Dye System

In recent years, the light-induced energy transfer process between quantum dots-the organic dye has aroused an increasing interest of many researchers, because quantum dots- organic dye composite system is one of the very promising third-generation photosensitizer and fluorescence biological probe, which has an important significance in the treatment of biomedical tumor. Quantum Dots(QDs) is a kind of newly nano-material. Because of its special size and many special optical properties, which leads a widespread range of applications in chemical manufacturing,biomedical imaging, micro-nano optics. The traditional organic fluorescent dyes, such as Copper phthalocyanine(CuPc) and Rhodamine B(RhB), also have wide applications in the high-technology field due to their special properties of optics,electronics and magnetism.This paper is mainly to study the CdTe quantum dots and organic fluorescent dyes composited system by ultrafast time-resolved spectroscopy technique with two-photon excitation, focusing on the fluorescence resonance energy transfer(FRET)of CdTe QDs-CuPc and CdTe QDs-RhB composite system from theory and experiment. In this article, the main contents, conclusions and innovation spots are as follows:(1) Introduce the fluorescence resonance energy transfer theory. Illustrating the fluorescence excitation spectra and fluorescence absorption spectrum and introducing the principle of fluorescence resonance energy transfer. Meanwhile, pointing out the principles of fluorescence resonance energy transfer and the hypothetical model,providing theoretical basis for following content.(2) The fluorescence resonance energy transfer in CdTe QDs-CuPc is investigated by ultrafast time-resolved spectroscopy technique equipped with femtosecond laser(780nm, 76 MHz, 130fs). The results show that the fluorescence lifetime of CdTe quantum dots decreases with the increase of CuPc concentration, and the energy transfer efficiency is found to increase with the increase of CuPc concentration. Moreover, the influence of the laser excitation power on the energy transfer efficiency is also studied. It is found that transfer efficiency decreases asexcitation laser power increasing. The physical mechanism is the thermal activation with the high power as well as the excited state transitions induced by two-photon excitation. The energy transfer efficiency can reach to be 43.8% when the laser power is 200 mW via two-photon excitation. It indicates that the CdTe QDs-CuPc composite system has high potential as the third generation of photosensitizers.(3) The fluorescence resonance energy transfer between CdTe quantum dots with different sizes and Rhodamine B(RhB) in aqueous solution is investigated by using the ultrafast time-resolved fluorescence system under two-photon excitation. With the excitation of 800 nm femtosecond laser, result shows that the FRET efficiency of the QDs-RhB system increases with the spectral overlap increase of the CdTe emission spectrum and the Rhodamine B absorption spectrum. Specifically, the fluorescence intensity of QDs decreases and the lifetime of QDs decreases while RhB shows the opposite tendency. Moreover, the relationship of the ratio of acceptor/donor concentration and the FRET efficiency is investigated experimentally. When the ratio of acceptor/donor concentration increases, the lifetime of QDs gets shorter, and the FRET efficiency of the QDs-RhB system becomes higher. However, the number of effective donor molecules limits the growing efficiency of FRET. The two-photon excited FRET efficiency can reach to 41.4% when the concentration of RhB is7.5×10-5mol/L. It shows that there is a bright future for these materials in bio-probing,bio-imaging, bio-labelling and other biological and optoelectronic applications.