2 research outputs found
Absorption and Magnetic Circular Dichroism Analyses of Giant Zeeman Splittings in Diffusion-Doped Colloidal Cd<sub>1–<i>x</i></sub>Mn<sub><i>x</i></sub>Se Quantum Dots
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><sub>Z</sub>) of excitonic excited
states. To date, Δ<i>E</i><sub>Z</sub> 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><sub>Z</sub> values detected
directly by absorption spectroscopy for the first time in such materials,
using colloidal Cd<sub>1–<i>x</i></sub>Mn<sub><i>x</i></sub>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><sub>Z</sub>/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><sub>Z</sub> and small σ achieved by nanocrystal
diffusion doping
Valence-Band Mixing Effects in the Upper-Excited-State Magneto-Optical Responses of Colloidal Mn<sup>2+</sup>-Doped CdSe Quantum Dots
We present an experimental study of the magneto-optical activity of multiple excited excitonic states of manganese-doped CdSe quantum dots chemically prepared by the diffusion doping method. Giant excitonic Zeeman splittings of each of these excited states can be extracted for a series of quantum dot sizes and are found to depend on the radial quantum number of the hole envelope function involved in each transition. As seven out of eight transitions involve the same electron energy state, 1S<sub>e</sub>, the dominant hole character of each excitonic transition can be identified, making use of the fact that the <i>g</i>-factor of the pure heavy-hole component has a different sign compared to pure light hole or split-off components. Because the magnetic exchange interactions are sensitive to hole state mixing, the giant Zeeman splittings reported here provide clear experimental evidence of quantum-size-induced mixing among valence-band states in nanocrystals