Steady increase toward UV wavelengths starting from Absorption Discrete bands, FWHM 35 nm to absorption onset; enables spectra 80–100 nm free selection of excitation wavelength 105–106 M-1 cm-1 at first exitonic absorption peak, 2.5 104–2.5 105 M-1 cm-1 (at Molar absorption increasing toward UV long-wavelength absorption coefficient wavelengths; larger (longer maximum) wavelength) QDs generally have higher absorption Asymmetric, often tailing to Symmetric, Gaussian profile; Emission spectra side; FWHM, 35 nm to FWHM, 30–90 nm 70–100 nm Typically <50 nm for visible Stokes shift Normally <50 nm, up to >150 nm wavelength–emitting QDs 0.1–0.8 (visible), 0.2–0.7 Quantum yield 0.5–1.0 (visible), 0.05–0.25 (NIR) (NIR) Fluorescence 10–100 ns, typically 1–10 ns, mono-exponential decay lifetimes decay 1 10-52–5 10-48 cm4 s photon-1 Two-photon action 2 10-47–4.7 10-46 cm4 s (typically about 1 10-49 cm4 s cross-section photon-1 photon-1) Solubility or Control via surface chemistry Control by substitution pattern dispersibility (ligands)
Absorption spectra Discrete bands, FWHM 35 nm to 80–100 nm Steady increase toward UV wavelengths starting from absorption onset; enables free selection of excitation wavelength Molar absorption coefficient 2.5 104–2.5 105 M-1 cm-1 (at long-wavelength absorption maximum) 105–106 M-1 cm-1 at first exitonic absorption peak, increasing toward UV wavelengths; larger (longer wavelength) QDs generally have higher absorption Emission spectra Asymmetric, often tailing to side; FWHM, 35 nm to 70–100 nm Symmetric, Gaussian profile; FWHM, 30–90 nm Stokes shift Normally <50 nm, up to >150 nm Typically <50 nm for visible wavelength–emitting QDs Quantum yield 0.5–1.0 (visible), 0.05–0.25 (NIR) 0.1–0.8 (visible), 0.2–0.7 (NIR) Fluorescence lifetimes 1–10 ns, mono-exponential decay 10–100 ns, typically decay Two-photon action cross-section 1 10-52–5 10-48 cm4 s photon-1 (typically about 1 10-49 cm4 s photon-1) 2 10-47–4.7 10-46 cm4 s photon-1 Solubility or dispersibility Control by substitution pattern Control via surface chemistry (ligands)
56043505-Quantum-Dots.docx