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Strong quantum confinement in Mn-doped semiconductor nanocrystals enhances dopant–carrier exchange interactions. Here, we report the synthesis and optical properties of strongly quantum confined, quasi two-dimensional, Mn-doped CsPbCl3 nanoplatelets. A room-temperature synthesis was employed to prepare the platelets with thickness 2.2 nm (4 monolayers), which is significantly smaller than the Bohr excitonic diameter of CsPbCl3 (5 nm). Efficient transfer of excitonic energy from the host to the Mn2+ dopant ions leads to a spin-forbidden 4T1–6A1 Mn d-electron emission with the highest quantum yield of ∼20% and exhibits a long lifetime of 1.6 ms. Subsequent anion exchange reactions at room temperature lead to the formation of Mn-doped CsPbBr3 nanoplatelets, with weak Mn emission. These newly developed Mn-doped cesium lead halide nanoplatelets are suitable candidates for exploring the effects of quantum confinement on dopant–carrier exchange interaction and exhibiting interesting magneto-optic properties.

Lead bromide (PbBr 2 ,99.999%), lead iodide (PbI 2 , 99.999%), lead chloride (PbCl 2 , 98%), manganese (II) bromide (MnBr 2 , 98%), ytterbium (III) nitrate pentahydrate {Yb(NO 3) 3 .5H 2 O, 99.99%}, caesium carbonate (Cs 2 CO 3 , 99.9%), oleic acid (OA, 90%), 1-octadecene (ODE, 90%), oleylamine (OLA, 98%), trioctylphosphine (TOP, 90%), methyl acetate (MeOAc, 99.5%), N,N-dimethylformamide (DMF, 99.8%), hydrogen bromide (HBr, 43 wt%, 99.99%) were purchased from Aldrich and were used without further purification. Acetone (99.0%, SDFCL), Hexane (99.99%, Rankem), Toluene (99.5%, Rankem) solvents are used as obtained.

Lanthanides have been widely explored as optically active dopants in inorganic crystal lattices, which are often insulating in nature. Doping trivalent lanthanide (Ln 3+) into traditional semiconductor nanocrystals, such as CdSe, is challenging because of their tetrahedral coordination. Interestingly, CsPbX 3 (X = Cl, Br, I) perovskite nanocrystals provide the octahedral coordination suitable for Ln 3+ doping. Over the last two years, tremendous success has been achieved in doping Ln 3+ into CsPbX 3 nanocrystals, combining the excellent optoelectronic properties of the host with the f-f electronic transitions of the dopants. For example, the efficient quantum cutting phenomenon in Yb 3+-doped CsPb(Cl,Br) 3 nanocrystals yields a photoluminescence quantum yield close to 200%. Other approaches of Ln 3+ doping and codoping have enabled promising proof-of-principle demonstration of solid-state lighting and solar photovoltaics. In this perspective article, we highlight the salient features of the material design (including doping in Pb-free perovskites), optical properties and potential optoelectronic applications of lanthanide-doped metal halide perovskite nanocrystals. While review articles on doping different metal ions into perovskite nanocrystals are present, the present review-type article is solely dedicated to lanthanide-doped metal halide perovskite nanocrystals.

Cs2AgInCl6 double perovskite (DP) is a direct band gap, stable, and environmentally benign material with a three-dimensional perovskite structure. However, the band gap (∼3.3 eV) is too wide for optoelectronic applications in the near-infrared (NIR) region. To achieve optical functionality in the NIR window, we have doped Yb3+ in both microcrystals and colloidal nanocrystals of Cs2AgInCl6 DPs. Our Yb-doped Cs2AgInCl6 DP microcrystals and nanocrystals show NIR emission at ∼994 nm (1.24 eV), whereas the band gap of the hosts is in the UV region. Therefore, the Yb-emission does not suffer from self-absorption. The microcrystals exhibit a single-exponential decay with 2.7 ms long lifetime corresponding to 2F5/2 → 2F7/2 transition of Yb3+ f electrons. The nanocrystals show biexponential decay (3 ms and 749 μs), probably because of the proximity of Yb to the surface of nanocrystals. Interestingly, NIR emission and perovskite structure of samples are stable for >3 months in ambient conditions for future optoelectronic applications.