Excitonic nonlinear absorption in CdS nanocrystals studied using Z-scan technique

TL;DR

This study investigates how excitonic nonlinear absorption in CdS nanocrystals varies with irradiance, wavelength, and particle size using Z-scan measurements, revealing size-dependent enhancement and saturable absorption effects.

Contribution

It provides new insights into size-dependent excitonic nonlinear absorption in CdS nanocrystals using Z-scan technique and a two-level model explanation.

Findings

Nonlinear absorption increases as particle size decreases.

Saturable absorption observed at excitonic transition.

Both third- and fifth-order nonlinear processes are involved.

Abstract

Irradiance dependence of excitonic nonlinear absorption in Cadmium Sulfide (CdS) nanocrystals has been studied by using Z-scan method with nanosecond laser pulses. The wavelength dependence of nonlinear absorption has also been measured near the excitonic transition of 1S(e)-1S3/2(h). We observe the saturable absorption, which can be described by a third-order and a fifth-order nonlinear process for both 3.0-nm-sized and 2.3-nm-sized CdS nanocrystals. The experimental results show that the excitonic nonlinear absorption of CdS nanocrystals is greatly enhanced with decreasing particle size. A two-level model is utilized to explain both irradiance and wavelength dependence of the excitonic nonlinearity.