Colloidal synthesis of nanocrystals and nanocrystal superlattices

Murray, C. B.; Sun, Shouheng; Gaschler, Wolfgang; Doyle, Hugh; Betley, Theodore A.; Kagan, Cherie R.

doi:10.1147/rd.451.0047

Cited by 1,008 publications

(873 citation statements)

References 20 publications

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“…Formally allowed interband transitions are "symmetric", between valence and conduction states of identical envelope angular momenta (e.g., 1S h -1S e , or 1P h -1P e ). However, an unexpectedly strong asymmetric interband transition involving the 1S and 1P states (1S h -1P e and 1P h -1S e transitions) occurs in PbSe QDs, 19,22,33,34 a result also shown clearly in our PbSe absorption spectra (see, e.g., Figure 1a) as well as for PbS. 19,35,36 This suggests that asymmetric transitions above the 1S-1P transition may also have significant oscillator strength.…”

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confidence: 72%

Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots

et al. 2005

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We report ultra-efficient multiple exciton generation (MEG) for single photon absorption in colloidal PbSe and PbS quantum dots (QDs). We employ transient absorption spectroscopy and present measurement data acquired for both intraband as well as interband probe energies. Quantum yields of 300% indicate the creation, on average, of three excitons per absorbed photon for PbSe QDs at photon energies that are four times the QD energy gap. Results indicate that the threshold photon energy for MEG in QDs is twice the lowest exciton absorption energy. We find that the biexciton effect, which shifts the transition energy for absorption of a second photon, influences the early time transient absorption data and may contribute to a modulation observed when probing near the lowest interband transition. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs, and we also introduce a new model for MEG based on the coherent superposition of multiple excitonic states.

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confidence: 72%

Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots

et al. 2005

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“…PbSe Qdots are synthesized based on the procedure developed by Murray et al 41 The synthesis is described in detail elsewhere. 16 Determination of the PbS Qdot Size.…”

Section: Methodsmentioning

confidence: 99%

Size-Dependent Optical Properties of Colloidal PbS Quantum Dots

et al. 2009

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We quantitatively investigate the size-dependent optical properties of colloidal PbS nanocrystals or quantum dots (Qdots) by combining-the Qdot absorbance spectra with detailed elemental analysis of the Qdot suspensions. At high energies, the molar extinction coefficient epsilon increases With the Not volume d(3) and agrees with theoretical calculations using the Maxwell-Garnett effective medium theory and bulk values for the Qdot dielectric function. This demonstrates that quantum confinement has no influence on E in this spectral range, and it provides an accurate method to calculate the Qdot concentration. Around the band gap, epsilon only increases with d(1.3), and values are comparable to the epsilon of PbSe Qdots. The data are related to the oscillator strength f(if) of the band gap transition and results agree well with theoretical tight-binding calculations, predicting a linear dependence of f(if) on d. For both PbS and PbSe Qdots, the exciton lifetime tau is calculated from f(if). We find values ranging between 1 and 3 mu s, in agreement with experimental literature data from time-resolved luminescence spectroscopy. Our results provide a thorough general framework to calculate and understand the optical properties of suspended colloidal quantum dots. Most importantly, it highlights the significance of the local field factor in these systems

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“…[2,3] Since the room-temperature bandgap of the bulk material is only 0.278 eV, it is possible to tune the NC bandgap from 0.278 eV (ca. 4400 nm) to over 1.1 eV (ca.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, lead chalcogenide quantum dots are promising building blocks for a wide number of optoelectronic applications in the near infrared. [3][4][5][6] For example, PbSe QDs hold great promise in the field of photovoltaics because of the recently observed multiple exciton generation (MEG) in these nanocrystals. [7][8][9][10] Here we report on detailed investigations of the optical absorption spectra of PbSe QDs.…”

Section: Introductionmentioning

confidence: 99%

Optical Investigation of Quantum Confinement in PbSe Nanocrystals at Different Points in the Brillouin Zone

Koole

Allan

Delerue

et al. 2008

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We present detailed investigations on the optical properties of PbSe nanocrystals. The absorption spectra of monodisperse, quasispherical nanocrystals exhibit sharp features as a result of distinct optical transitions. To study the size dependence, absorption spectra of nanocrystals ranging from 3.4 to 10.9 nm in diameter are analysed and a total of 11 distinct optical transitions are identified. The assignment of the various optical transitions is discussed and compared to theoretically calculated transition energies. By plotting all transitions as a function of nanocrystal size (D) we find that the energy (E) changes with the following relationship E / D À1.5 for the lowest energy transitions. The transition energy extrapolates to approximately 0.3 eV for infinite crystal size, in agreement with the bandgap of bulk PbSe at the L-point in the Brillouin zone. In addition, high-energy transitions are observed, which extrapolate to 1.6 eV for infinite crystal size, which is in good agreement with the bulk bandgap of PbSe at the S-point in the Brillouin zone. Tight-binding calculations confirm that the high-energy transitions originate from the S-point in the Brillouin zone. The S-character of the high-energy transitions may be of importance to explain the mechanism behind multiple exciton generation in PbSe nanocrystals.

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Colloidal synthesis of nanocrystals and nanocrystal superlattices

Cited by 1,008 publications

References 20 publications

Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots

Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots

Size-Dependent Optical Properties of Colloidal PbS Quantum Dots

Optical Investigation of Quantum Confinement in PbSe Nanocrystals at Different Points in the Brillouin Zone

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