Program

I.13 -- Invited, IWTCP-3

Date: Wednesday, 29 July 2015

Time: 14h35 - 15h10

Emission in Maganese -Doped Semiconductor Nanocrystals

Que Huong Nguyen

Marshall University, One John Marshall Drive, Huntington WV 25701 USA

With recent development of nanotechnology such as colloidal synthesis and molecular -beam epitaxy, magnetic ion-doped quantum dots (QDs) become a great interest and have been studied intensively. Well known as an activator for photoluminescence (PL) and electroluminescence, the ion Mn2+ has been among the first magnetic ion to be doped into a semiconductor nanocrystals (NCs)Up to date, considerable interest has been attracted in the Mn-doped semiconductor NCs. The Mn-Doped QD can not only maintain nearly all the intrinsic advantages of QDs, but also bring the additional merits such as larger Stokes shifts, enhanced thermal and chemical stabilities, as well as longer excited state lifetimes. We theoretically investigate the magneto- PL of Mn2+doped semiconductor core-shell colloidal QD to explain the experiment results from a recent magneto-PL study (1,2) of strongly confined diluted magnetic semiconductor (DMS) in Mn2+-doped ZnSe/CdSe core-shell colloidal NCs. Unlike the cases in bulks or in other conventional DMS materials, the yellow emission characterized for in Mn2+ which is associated with the d-d internal transition 4T1- 6A1, was reported not suppressed in an applied B//z magnetic field and circularly polarized as usual and instead, developed a circular polarization. More interestingly, Mn2+ PL has been found to have a large splitting between $\sigma$+ and $\sigma$-components which depends on the applied field. This behaviour has not been found in characteristics of the Mn2+ PL in bulks and other conventional DMS materials and is the result of the strong confinement of the NCs.

Our theory shows that, the reason the yellow Mn2+ PL band in QDs, indifferent to their counterparts in bulks and other low-dimensional systems, is not suppressed under applied magnetic field originates from the dot geometry and properties. The theory of Coulomb exchange interaction of the impurity ions with the confined electrons inside the dot as well the existence of the internal electric field inside the dot show that these two effects might be the reasons of the observed behaviors. The competition and combination between these two effects give different results depending on parameters and conditions.

References
1. Beaulac, R., Schneider, L., Archer, P. I., Bacher, G. \& Gamelin, D. R. Light-induced spontaneous magnetization in doped colloidal quantum dots. Science 325, 973–976 (2009).
2. Liu, Q., Deng, R., Ji, X. \& Pan, D. Alloyed Mn-Cu-In-S nanocrystals: a new type of diluted magnetic semiconductor quantum dots. Nanotechnology 23, 255706 (2012).

Presenter: Que-Huong Nguyen