Absorption and Magnetic Circular Dichroism Analyses of Giant Zeeman Splittings in Diffusion-Doped Colloidal Cd_1–<i>x</i>Mn_<i>x</i>Se Quantum Dots

Abstract

Impurity ions can transform the electronic, magnetic, or optical properties of colloidal quantum dots. Magnetic impurities introduce strong dopant-carrier exchange coupling that generates giant Zeeman splittings (Δ<i>E</i>_Z) of excitonic excited states. To date, Δ<i>E</i>_Z in colloidal doped quantum dots has primarily been quantified by analysis of magnetic circular dichroism (MCD) intensities and absorption line widths (σ). Here, we report Δ<i>E</i>_Z values detected directly by absorption spectroscopy for the first time in such materials, using colloidal Cd_1–<i>x</i>Mn_<i>x</i>Se quantum dots prepared by diffusion doping. A convenient method for decomposing MCD and absorption data into circularly polarized absorption spectra is presented. These data confirm the widely applied MCD analysis in the low-field, high-temperature regime, but also reveal a breakdown at low temperatures and high fields when Δ<i>E</i>_Z/σ approaches unity, a situation not previously encountered in doped quantum dots. This breakdown is apparent for the first time here because of the extraordinarily large Δ<i>E</i>_Z and small σ achieved by nanocrystal diffusion doping