Single Magnetic Impurities in Colloidal Quantum Dots and Magic-Size Clusters

Abstract

Impurity doping can be used to dramatically alter the physical properties of semiconductor nanostructures and endow them with promising new technological potential. This review summarizes recent progress toward the development of colloidal semiconductor quantum dots (QDs) doped with individual magnetic impurity ions. Such singly doped quantum dots (SDQDs), as well as related magic-sized nanoclusters, represent an exciting class of materials for cultivating unique physical effects arising from magnetic exchange coupling between delocalized charge carriers and the single impurity ions. Key exchange effects can be enhanced by carrier confinement in such small structures. The physical properties displayed by these materials may prove valuable for new technologies based on the manipulation of individual spins in semiconductor nanostructures, such as spintronics, spin-photonics, or quantum computing. Interesting chemical and analytical challenges also emerge when exploring this research frontier. Here, we describe cluster and QD results from recent literature related to these challenges. We summarize (magneto-)­optical investigations of SDQDs on both the ensemble and single-particle levels. Comparisons to analogous bulk materials and self-assembled QDs are drawn and used to highlight some of the rich and unique characteristics found within this class of materials.

Magnetic Circular Dichroism in Nanomaterials: New Opportunity in Understanding and Modulation of Excitonic and Plasmonic Resonances

“…[67,[87][88][89] Incorporation of open-shell magnetic impurities with nonmagnetic semiconductors leads to coupling of the localized unpaired spins with the relaxed photogenerated electron-hole pair (exciton), which is termed as sp-d exchange interactions (s-d and p-d interaction indicates coupling of dopants with electrons and holes, respectively). [90] The excitonic Zeeman splitting of DMSs considering the sp-d exchange induced contribution is quantitatively expressed by Equation (6) [91] Zeeman…”

“…An exceptionally high excitonic g-factor of − 907 was achieved with x = 0.19 at 1.8 K. On the other hand, fabricating semiconductor nanocrystals with single dopant will benefit coherent optical spin manipulations for solotronic information processing technologies. [91,97,98] Fainblat et al reported successful doping of colloidal CdSe QDs with a very small number of dopants down to single Mn 2+ ion. [99] The singly doped QDs showed enhanced excitonic Zeeman splitting that was dominated by sp-d exchange interactions.…”

“…The excitonic Zeeman splitting of DMSs considering the sp‐d exchange induced contribution is quantitatively expressed by Equation …”

“…MCD inspected the doping process, which showed inversed and enhanced band edge Zeeman splitting with increasing concentration of Mn 2+ . An exceptionally high excitonic g‐factor of − 907 was achieved with x = 0.19 at 1.8 K. On the other hand, fabricating semiconductor nanocrystals with single dopant will benefit coherent optical spin manipulations for solotronic information processing technologies . Fainblat et al reported successful doping of colloidal CdSe QDs with a very small number of dopants down to single Mn 2+ ion .…”

Diffusion doping of cobalt in rod-shape anatase TiO2 nanocrystals leads to antiferromagnetism

“…14 Recently developed 'solotronic' nanocrystals, in which a single impurity or defect is present in a semiconductor nanocrystal, exhibit remarkable properties. [15][16][17] Optical or electrical stimulus of quantum dots with single atom manganese impurity led to specic changes in the manganese spin state, 18,19 and gave rise to well-resolved splitting of the photoluminescence due to the spin projections of the S ¼ 5/2 Mn 2+ ion. 20 Despite signicant advances in the synthesis of doped nanocrystals, the ability to selectively locate impurities at specic sites (substitutional vs. interstitial), control the concentration and spatial density of the impurity in the host, and control the charge compensation mechanism remain as open challenges in the preparation of doped nanocrystals.…”