Redefining near-unity luminescence in quantum dots with photothermal threshold quantum yield

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Science  15 Mar 2019:
Vol. 363, Issue 6432, pp. 1199-1202
DOI: 10.1126/science.aat3803
  • Fig. 1 Characterization of highly emissive CdSe/CdS quantum dots.

    (A) PLQY for many samples with different shell thicknesses grown with our synthesis procedure. (B) Absorption factor (Abs) (dotted lines), PLE (shaded regions), and PL spectra (solid lines) for 5-, 8-, 10-, and 11-ML CdS shells, respectively. A.u., arbitrary units. (Inset) Representative transmission electron micrographs. Scale bars, 25 nm. (C) Wavelength-resolved PLQY of the 8- and 10-ML samples shown in Fig. 1B. Full characterization (SM4) dataset in figs. S1 to S9.

  • Fig. 2 Measurement scheme for the PTQY technique.

    (A) Excitation light is absorbed by an electron, which moves from a low energy state to a higher energy state. The excited electron and hole emit heat Q to relax to their lowest energy excited states and then can recombine through PL or nonradiative processes (the latter of which emits heat QNR). (B) A plot of the heat emitted per excitation versus the excitation energy shows how the PLQY can be determined from the threshold energy E0 above which heat is emitted and the photoluminescence energy EPL. A near-perfect emitter at the thermal limit (Q + QNR = 0) where the deviation of EPLE0 represents the deviation in PTQY (i.e., PLQY ≤ 1). (C) The instrumental realization of the PTQY technique uses a photothermal deflection spectrometer to measure heat, synchronized to a PL spectrometer, which determines both EPL and the number of excitation events (SM5, SM6, and figs. S17 to S25).

  • Fig. 3 Detailed optical characterization of CdSe/CdS quantum dots and PTQY measurement uncertainty.

    (A) PTQY of the best CdSe/CdS (core-shell) particles (8.5 ML). The inset displays probability distributions and uncertainties associated with PTQY uncertainty (blue and black shading), and integrating sphere PLQY (Gaussian, red shading). (B) High-resolution PTQY of high-quality CdSe core (96.2 ± 0.1%) but with poorly passivated CdS shell (93.6 ± 0.2%) with inset of respective integrating sphere PLQY and PTQY uncertainty (for detailed uncertainty, see SM6 and figs. S10 to S16). (C) Top plot shows PL lifetimes of CdSe/CdS core and shell excited lifetimes, and bottom plot shows PLQY and PTQY of the same near-unity particles with measurement uncertainty plotted against particle Feret diameter. The circle markers represent a constant CdSe core size and varied CdS shell thickness, and the inset diamond markers represent the highest PTQY particles measured thus far, with a slightly larger 3.6 ± 0.2 nm CdSe core and 3.7 ± 0.3 nm (8.5 ML) CdS shell. (D) Table representing the main sources of uncertainty and the general uncertainty budget for the calibrated PTQY spectrometer dependent on photon energy (figs. S17 to S26). CCD, charge-coupled device. (E) TRPL data (log-log scale) taken at 407.1-nm excitation. Despite near-unity PLQY of 4- to 11-ML samples, significant differences in long lifetime components arise across the shelled series. (F) PL lifetime excitation wavelength dependence with varied shell thickness normalized to each particle’s respective core lifetime.

Supplementary Materials

  • Redefining near-unity luminescence in quantum dots with photothermal threshold quantum yield

    David A. Hanifi, Noah D. Bronstein, Brent A. Koscher, Zach Nett, Joseph K. Swabeck, Kaori Takano, Adam M. Schwartzberg, Lorenzo Maserati, Koen Vandewal, Yoeri van de Burgt, Alberto Salleo, A. Paul Alivisatos

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods 
    • Supplementary Text
    • Figs. S1 to S37
    • Tables S1 and S2
    • References 

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