Exploring Mn 2+ -location-dependent red emission from (Mn/Zn)–Ga–Sn–S supertetrahedral nanoclusters with relatively precise dopant positions

Mn 2+ -Doped semiconductor nanocrystals or quantum dots have been extensively studied as potential yellow/orange/red phosphors due to the stable Mn 2+ -related emission tuned by its tetrahedral coordination environment in host lattices. However, it is still very difficult to objectively explore the location–performance relationship in conventional Mn 2+ -doped nanomaterials since the precise location information on Mn 2+ dopants is generally unavailable due to their random distribution in host lattices. Herein, we purposely selected a specific supertetrahedral-nanocluster-based molecular crystal (OCF-40-ZnGaSnS, composed of isolated supertetrahedral T4-ZnGaSnS nanoclusters (NCs) with the formula [Zn 4 Ga 14 Sn 2 S 35 ] 12− ) as a host lattice, and effectively controlled the relatively precise position of Mn 2+ dopants in host lattices of T4-ZnGaSnS NCs by in situ substitution of Zn 2+ sites by Mn 2+ ions, and investigated the Mn 2+ -location-dependent red emission properties. The current study clearly indicates that a long-lifetime (∼170 μs) red emission centred at 625 nm at room temperature for lightly-doped [Zn 3 MnGa 14 Sn 2 S 35 ] 12− NCs with one Mn 2+ dopant in its surface centre is very sensitive to temperature and dramatically red-shifts to 645 nm at 33 K upon the excitation of 474 nm. However, heavily-doped OCF-40-MnGaSnS (composed of T4-MnGaSnS NCs with the formula [Mn 4 Ga 14 Sn 2 S 35 ] 12− , in which four Mn 2+ dopants are accurately located at its core in the form of Mn 4 S) gives the temperature-insensitive red emission with a longer wavelength (641 nm) and a shorter lifetime (42 μs) at room temperature. This phenomenon is pretty uncommon compared to other heavily Mn 2+ -doped semiconductors. Such differences in their PL properties are ascribed to Mn 2+ -location-induced lattice strain to different degrees in two Mn 2+ -doped supertetrahedral NCs. In addition, the Mn 2+ -related red emission of both samples can be predominantly induced by the direct excitation of Mn 2+ ions and secondarily by indirect excitation through exciton energy transfer from host lattices to Mn 2+ dopants. Consistently, the DFT calculations suggest that the emission of NCs originated from the transition from the low spin excited state of Mn 2+ ( 4 T 1 ) to its high spin ground state ( 6 A 1 ). The calculation results also revealed that the emission wavelength of lightly-doped [Zn 3 MnGa 14 Sn 2 S 35 ] 12− NCs is not obviously affected by the temperature-induced therma