Abstract

Colloidal quantum dot (QD) research is driven by the combination of tunable electronic and optical properties, depending on the size and shape of the QDs, and an easy, solution-based fabrication and processing. For practical applications and fast synthesis optimization, a precise knowledge of the absorption coefficient is key to determine the concentration of QD suspensions. Recently, the research field has shifted focus from plain QDs consisting of a single material, to more complex heterostructures, consisting of at least two materials. We use PbSe/CdSe and PbS/CdS core/shell colloidal quantum dots QDs as model system to study the absorption coefficient of colloidal QD heterostructures, consisting of at least two semiconductor materials. We show that at energies far above the band gap 3.1 and 3.5 eV􏰀the experimental intrinsic absorption coefficient is in excellent agreement with the Maxwell–Garnett effective medium theory for core/shell heterostructures and bulk values for the dielectric function. This allows for a straightforward measurement of the QD concentration from the absorbance spectrum. It also implies that basic optical measurements on core/shell heterostructures, such as measurements of the oscillator strength and photoluminescence lifetime, can be corrected for the local field reduction in QD heterostructures.

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