Spin-polarized Mn$^{2+}$ emission from Manganese-doped colloidal nanocrystals

TL;DR

This study demonstrates that in strongly quantum-confined Mn-doped colloidal nanocrystals, the Mn$^{2+}$ emission becomes circularly polarized and magnetically responsive, revealing the impact of quantum confinement on magnetic ion photoluminescence.

Contribution

It reveals how strong quantum confinement affects Mn$^{2+}$ emission properties, including polarization and energy splitting, in colloidal nanocrystals, differing from bulk and lower-dimensional DMS materials.

Findings

Mn$^{2+}$ emission is not suppressed by magnetic fields in these nanocrystals.

The emission becomes circularly polarized, tracking Mn$^{2+}$ magnetization.

Energy splitting between circular components scales with exciton-Mn coupling.

Abstract

We report magneto-photoluminescence studies of strongly quantum-confined "0-D" diluted magnetic semiconductors (DMS), realized in Mn$^{2+}$-doped ZnSe/CdSe core/shell colloidal nanocrystals. In marked contrast to their 3-D (bulk), 2-D (quantum well), 1-D (quantum wire), and 0-D (self-assembled quantum dot) DMS counterparts, the ubiquitous yellow emission band from internal \emph{d-d} ($^4T_1 \rightarrow ^6A_1$) transitions of the Mn$^{2+}$ ions in these nanocrystals is \emph{not} suppressed in applied magnetic fields and \emph{does} become circularly polarized. This polarization tracks the Mn$^{2+}$ magnetization, and is accompanied by a sizable energy splitting between right- and left-circular emission components that scales with the exciton-Mn \emph{sp-d} coupling strength (which, in turn, is tunable with nanocrystal size). These data highlight the influence of strong quantum confinement on both the excitation and the emission mechanisms of magnetic ions in DMS nano-materials.