Three-dimensional ABX 3 perovskite material has attracted immense interest and applications in optoelectronic devices, because of their enabling properties. Recently, Mn 2+ doping directly into APbCl 3 -type three-dimensional (3D) nanocrystals, manifesting host-to-dopant energy transfer, have been reported for LED display applications. Strongly bound excitons in the doped system can enhance the dopant-carrier exchange interactions, leading to efficient energy transfer. Here, we report the simple and scalable synthesis of Mn 2+doped (C 4 H 9 NH 3 ) 2 PbBr 4 two-dimensional (2D) layered perovskites. The Mn 2+ -doped 2D perovskite shows enhanced energy transfer efficiency from the strongly bound excitons of the host material to the d electrons of Mn 2+ ions, resulting in intense orange-yellow emission, which is due to spin-forbidden internal transition ( 4 T 1 → 6 A 1 ) with the highest quantum yield (Mn 2+ ) of 37%. Because of this high quantum yield, stability in ambient atmosphere, and simplicity and scalability of the synthetic procedure, Mn 2+ -doped 2D perovskites could be beneficial as color-converting phosphor material and as energy downshift coating for perovskite solar cells. The newly developed Mn 2+ -doped 2D perovskites can be a suitable material to tune dopant-exciton exchange interactions to further explore their magneto-optoelectronic properties.

Lead (II) bromide (99%), Lead (II) chloride (99%), Hydrochloric acid (37%) were purchased from Sigma Aldrich. Dimethyl sulfoxide (DMSO), Dichloromethane (DCM, anhydrous), 1-(2-Aminoethyl) piperazine and Hydrobromic acid (47%) were purchased from TCI Chemicals. All chemicals were used as purchased without further purification. Synthesis of powdered PzPbBr 1D Perovskites: For the preparation of powdered (Pz) 2 PbBr 10 perovskite, 1 mmol (365 mg) of PbBr 2 was dissolved in 3 mL of hydrobromic acid. To this, 1 mmol (140 µL) 1-(2-Aminoethyl) piperazine was added drop by drop. The solution turns turbid white immediately after addition and

Reported here are the low-temperature photoluminescence (PL), energy-transfer mechanism, and exciton dynamics of Mn 2+ -doped two-dimensional (2D) perovskites that show interesting differences from their three-dimensionally doped counterpart. Dopant emission in 2D system shows increased PL intensity and shortened lifetime with increase of temperature and strong dopant emission even at low temperatures. Transient absorption (TA) spectroscopy reveals the dominant role of "hot" excitons in dictating the fast energy-transfer timescale. The operative dynamics of the generated hot excitons include filling up of existing trap states (shallow and deep) and energy-transfer channel from hot excitons to dopant states. Global analysis and target modeling of TA data provide an estimate of excitons (hot and band edge) to a dopant energy-transfer timescale of ∼330 ps, which is much faster than the band edge exciton lifetime (∼2 ns). Such fast energy-transfer timescale arises due to enhanced carrier exchange interaction resulting from higher exciton confinement, increased covalency, and involvement of hot excitons in the 2D perovskites. In stark contrast to three-dimensional systems, the high energy-transfer rate in 2D system results in high dopant emission intensity even at low temperatures. Increased intrinsic vibronic coupling at higher temperatures further supports efficient Mn 2+ sensitization that ultimately dictates the observed temperature dependence of the dopant emission (intensity, lifetime).