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Optical Properties of CdSe/ZnS Nanocrystals



Paul C. DeRose, Yu-Zhong Zhang, Adolfas Gaigalas


Measurements are presented of the absorbance, fluorescence emission, fluorescence quantum yield, and fluorescence lifetime of CdSe/ZnS nanocrystals, also known as quantum dots (QDs). The study included three groups of nanocrystals whose surfaces were either passivated with organic molecules, modified further with carboxyl groups, or conjugated with CD14 mouse anti-human antibodies. The surface modifications had observable effects on the optical properties of the nanocrystals. The oscillator strength (OS) of the band edge transition was about 1 for the nanocrystals emitting at 565, nm, 605 nm, and 655 nm. The OS could not be determined for QDs with emission at 700 nm and 800 nm. The fluorescence lifetimes varied from 26 ns for nanocrystals emitting near 600 nm to 150 ns for nanocrystals emitting near 800 nm. The quantum yield ranged between 0.3 and 0.9 for the nanocrystals in this study. A brightness index (BI) is proposed to evaluate the suitability of the nanocrystal labels for flow cytometer measurements. The BI is a factor of the number of absorption-emission cycles, and the likelihood of emission during each cycle. Most QD labels are at least as bright as fluorescein for applications in flow cytometer assays with 488 nm excitation, however for optimal brightness the QDs should be excited with 405 nm light. When using 405 nm excitation, QDs are significantly brighter than fluorescein. We observed a strong dependence of the QD absorbance at 250 nm on the surface modification of the QD.
Journal of Research (NIST JRES) - 119.026
Report Number


CdSe/ZnS, absorption, fluorescence quantum yield, fluorescence life time


DeRose, P. , Zhang, Y. and Gaigalas, A. (2014), Optical Properties of CdSe/ZnS Nanocrystals, Journal of Research (NIST JRES), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed April 15, 2024)
Created December 31, 2014, Updated January 27, 2020