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Two-photon absorption in CdSe colloidal quantum dots compared to organic molecules.

Nikolay S Makarov1, Pick Chung Lau, Christopher Olson

  • 1School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics Georgia Institute of Technology , Atlanta, Georgia 30332, United States.

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|November 27, 2014
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Summary

This study compares optical spectra of semiconductor quantum dots and organic molecules. It reveals size-dependent electronic structures and the applicability of different theoretical models for nanoclusters and larger quantum dots.

Keywords:
CdSeeffective-mass modelquantum dotquantum-chemical calculationstwo-photon absorption

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Area of Science:

  • Materials Science
  • Quantum Chemistry
  • Spectroscopy

Background:

  • Semiconductor quantum dots (QDs) and organic molecules exhibit distinct electronic structures influencing their optical properties.
  • Understanding size-dependent spectral behavior is crucial for QD applications.

Purpose of the Study:

  • To investigate fundamental differences in electronic structure between QDs and organic molecules.
  • To compare experimental and theoretical one- and two-photon absorption spectra of colloidal QDs.
  • To determine the range of applicability for quantum-chemical and effective-mass models.

Main Methods:

  • Systematic experimental studies of size-dependent spectra.
  • Theoretical modeling using quantum-chemical calculations for small QDs (nanoclusters).
  • Theoretical modeling using effective-mass calculations for larger QDs.

Main Results:

  • Quantum-chemical calculations accurately model small QDs, including environmental effects like solvation and surface functionalization.
  • Effective-mass calculations describe larger QDs, similar to bulk semiconductors, but are insensitive to surface effects.
  • Small QDs show similarities to organic molecules, while larger QDs behave like bulk semiconductors.

Conclusions:

  • The choice of theoretical model depends on QD size and the specific optical properties being investigated.
  • Factors such as passivation quality, ligand nature, and transition types significantly impact QD optical properties.
  • This work quantifies the applicability of different theoretical approaches for studying QD electronic structure and spectra.