Polarized luminescence of MoS$_2$ nanodots

The effect of temperature on the polarization of the luminescence of the colloidal system of MoS$_2$ nanodots in $n$-methylpyrrolidone is studied under the condition of linearly polarized excitation. Nanodots are obtained by chemical exfoliation and dispersion of MoS$_2$ microcrystals in a liquid medium under the action of ultrasound. The photoluminescence spectrum of the ensemble of MoS$_2$ nanodots is significantly shifted towards shorter wavelengths with respect to the luminescence spectrum of bulk crystals, which is explained by the quantum-size effect in the electronic spectrum of MoS$_2$ nanocrystals. It is shown that the temperature dependence of the anisotropy of the radiation of nanodots is described by the Levshin–Perrin equation, which takes into account the rotational diffusion of luminescent particles in the liquid matrix. The size of photoexcited nanodots in the framework of the Levshin–Perrin model turns out to be $\ge$ 1.5 nm and increases with increasing the emission wavelength. It is shown that the sizes of MoS$_2$ nanodots obtained by analyzing the temperature dependence of the emission anisotropy are in satisfactory agreement with the data obtained by analyzing the quantum-size effect in the electronic spectrum of nanodots.