Publication date: 8th June 2021
CuInS2 (CIS) colloidal nanocrystals are environmentally friendly, cheap and non-toxic materials whose optical properties can be efficiently tuned by changing the size, shape, and chemical composition during the synthesis. These properties makes them interesting candidates for many applications, e.g. in optoelectronics, photovoltaics and bio imaging. From an application point of view in novel information technologies, understanding the spin processes in these materials is essential.
In this report, we study the spin properties of photoexcited carriers in colloidal CIS quantum dots (QDs) at 2 K and in magnetic fields (B) up to 10 T. Colloidal QDs were synthesized according to a procedure from Ref. [1]. CIS QDs exhibit photoluminescence (PL) peak that originate from the radiative recombination of a delocalized electron in the conduction band with the copper-localized hole. The PL signal in σ− polarization is stronger than in σ+ polarization. The continuous wave degree of circular polarization (Pcw) increases with increasing B and it reaches a saturation level of 12% at 10 T. As the temperature is increased, at a given B, Pcw decreases. From the analysis of polarization- and time-resolved PL signals in magnetic fields, we find that spin polarization is very slow, on the order of 1 µs at 2 K and B=1 T. With increasing B the spin relaxation accelerates and at B=10 T is 2 orders of magnitude faster. The observed slow spin relaxation is due to electron and/or hole spins interaction with the uncompensated spins at the QD surface. We interpret the extremely slow spin relaxation to the limited surface penetration of the exciton wave function due to the hole trapping at the Cu site. Therefore, we find that the spin relaxation mechanism is analogous to the one observed for Cu-doped CdSe QDs [2].
[1] L. Li et al. J. Am. Chem. Soc. 133, 1176 (2011).
[2] Kłopotowski et al. J. Phys. Chem. C 124, 1042−1052 (2020).
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