Linear Absorption in CdSe Nanoplates: Thickness and Lateral Size Dependency of the Intrinsic Absorption

We investigate the optical absorption properties of colloidal CdSe nanoplatelets and compare them to CdSe quantum dots. Starting from inductively coupled plasma atomic emission spectroscopy (ICP-AES) measurements on their intrinsic absorption coefficients mu(i), we compare these results with a theoretical approach by a continuum absorption Lorentz local field model. We show that the platelets' intrinsic absorption coefficients mu(i) are strongly thickness and aspect ratio dependent, which results in the possibility to tune the absorption properties of this material class by the lateral size and thickness. The continuum intrinsic absorbance of the platelets is considerably larger if compared with quantum dots making them more efficient absorbers with higher light matter interaction that is essential for their use in, for example, solar cells. The obtained mu(i) values can be used for concentration determination of CdSe nanoplatelets in solution and solid films which is essential for all optical experiments with controlled generated population density upon optical excitation.