title: Two-photon absorption in CdSe colloidal quantum dots compared to organic molecules.
abstract: We discuss fundamental differences in electronic structure as reflected in one- and two-photon absorption spectra of semiconductor quantum dots and organic molecules by performing systematic experimental and theoretical studies of the size-dependent spectra of colloidal quantum dots. Quantum-chemical and effective-mass calculations are used to model the one- and two-photon absorption spectra and compare them with the experimental results. Currently, quantum-chemical calculations are limited to only small-sized quantum dots (nanoclusters) but allow one to study various environmental effects on the optical spectra such as solvation and various surface functionalizations. The effective-mass calculations, on the other hand, are applicable to the larger-sized quantum dots and can, in general, explain the observed trends but are insensitive to solvent and ligand effects. Careful comparison of the experimental and theoretical results allows for quantifying the range of applicability of theoretical methods used in this work. Our study shows that the small clusters can be in principle described in a manner similar to that used for organic molecules. In addition, there are several important factors (quality of passivation, nature of the ligands, and intraband/interband transitions) affecting optical properties of the nanoclusters. The larger-size quantum dots, on the other hand, behave similarly to bulk semiconductors, and can be well described in terms of the effective-mass models.
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics Georgia Institute of Technology , Atlanta, Georgia 30332, United States.
authors.forename: Nikolay S
authors.initials: NS
authors.lastname: Makarov
authors.forename: Pick Chung
authors.initials: PC
authors.lastname: Lau
authors.forename: Christopher
authors.initials: C
authors.lastname: Olson
authors.forename: Kirill A
authors.initials: KA
authors.lastname: Velizhanin
authors.forename: Kyril M
authors.initials: KM
authors.lastname: Solntsev
authors.forename: Khanh
authors.initials: K
authors.lastname: Kieu
authors.forename: Svetlana
authors.initials: S
authors.lastname: Kilina
authors.forename: Sergei
authors.initials: S
authors.lastname: Tretiak
authors.forename: Robert A
authors.initials: RA
authors.lastname: Norwood
authors.forename: Nasser
authors.initials: N
authors.lastname: Peyghambarian
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Perry
keywords: CdSe; effective-mass model; quantum dot; quantum-chemical calculations; two-photon absorption