The Empirical Correlation Between Size and Two-Photon Absorption Cross Section of CdSe and CdTe Quantum Dots

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2006-11, Vol.2 (11), p.1308-1313
• Main Authors: Pu, Shih-Chieh, Yang, Meng-Ju, Hsu, Cheng-Chih, Lai, Chih-Wei, Hsieh, Cheng-Chih, Lin, Sheng Hsien, Cheng, Yi-Ming, Chou, Pi-Tai
• Format: Article
• Language: English
• Subjects: Absorption; cadmium; Cadmium Compounds - chemistry; chalcogenides; fluorescence; Light; Metal Nanoparticles - chemistry; Microscopy, Fluorescence; Models, Statistical; Nanotechnology - methods; Photochemistry; Photons; Quantum Dots; Selenium Compounds - chemistry; Tellurium - chemistry; two-photon absorption
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.200600157

The tuning of CdSe quantum dot (QDs) sizes, and consequently their corresponding two‐photon absorption (TPA) cross section, has been systematically investigated. As the size (diameter) of the quantum dots increases, the TPA cross section is found to be empirically related via a power‐law proportionality of 3.5±0.5 and 5.6±0.7 to the diameters of CdSe and CdTe QDs, respectively. The results are tentatively rationalized via a theoretical model of two‐photon excitation properties in a system incorporating excitons and defects. Double crossed! The size‐dependent, two‐photon absorption (TPA) cross section of CdSe and CdTe quantum dots (QDs) is investigated using both experimental and theoretical approaches. For CdSe (4.8 nm) and CdTe (5.4 nm) QDs, the TPA cross sections were measured to be as high as ≈10 000 and 8000 GM, respectively (see image). This correlation is important as these QD materials are being increasingly used for two‐photon fluorescence biomicroscopy. (GM: Göppert‐Mayer unit, 1 GM=10−50 cm4 s photon−1.