Highly Luminescent Manganese‐Doped 2D Hybrid Perovskite Nanoplatelets with Dual Emissions Controlled Through Layer Thickness Modulation

Abstract Doping semiconductor nanomaterials with manganese ion (Mn 2+ ) introduce a well‐defined photoactive d‐d level within the band structure, paving the way for diverse applications. Although Mn doping in single‐layer 2D hybrid perovskites ( n = 1) has been extensively studied, limited research has been conducted on doping with modulation of the layer thickness. Herein, Mn 2+ doping in hybrid 2D perovskite nanoplatelets (NPLs), L 2 A n‐1 [Pb 1‐x Mn x ] n Br 3n+1 (where L = butylammonium, A = methylammonium), with variations in Mn concentration ( x = 0–0.60) and layer thickness ( n = 1–3) is reported. Substitutional doping of Mn significantly increases the photoluminescence quantum yield as well as the rate of energy transfer efficiency, which strongly depends on the layer thickness of NPLs. The Mn concentration in 2D NPLs determines the rate of forward and backward energy transfer. Low‐temperature emission spectra allow to determine thickness‐dependent exciton binding energy for Mn‐doped 2D NPLs ( x = 0.5) with values of 410 ± 11 meV ( n = 1), 188 ± 9 meV ( n = 2), and 151 ± 17 meV ( n = 3). The faster dissociation of band‐edge excitons into free carriers at Mn 2+ sites results in high brightness with an excellent CRI of 89.2 for the white light‐emitting diode.