Spinodal Decomposition During Anion Exchange in Colloidal Mn²⁺-Doped CsPbX₃ (X = Cl, Br) Perovskite Nanocrystals

Abstract

Manganese­(II)-doped cesium–lead–chloride (Mn2+:CsPbCl3) perovskite nanocrystals have recently been developed as promising luminescent materials and attractive candidates for white-light generation. One approach to tuning the luminescence of these materials has involved anion exchange to incorporate Br–, but the effects of anion exchange on Mn2+ speciation in doped metal-halide perovskites is not well understood at a microscopic level. Here, we use a combination of X-band electron paramagnetic resonance (EPR) and photoluminescence spectroscopies to monitor the Mn2+ dopants in Mn2+:CsPbCl3 nanocrystals during Cl– → Br– anion exchange. Analytical measurements show that the nanocrystals retain their Mn2+ over the course of Cl– → Br– anion exchange and they continue to show strong Mn2+ d–d luminescence but, surprisingly, the Mn2+ EPR intensities all but vanish. Further results suggest that Mn2+ ions migrate during anion exchange to form clusters that are still luminescent but show no EPR signal due to antiferromagnetic superexchange coupling. Monte Carlo simulation and analysis of the Mn2+:CsPb­(Cl1–x Br x )3 lattice at various halide compositions (x) bolsters this interpretation by indicating a propensity for Mn2+–Cl– units to cluster as the Br– content increases, increasing the probability of the nearest-neighbor Mn2+–Mn2+ interactions. The driving force for this clustering is retention of the stronger Mn–Cl bonds compared to Mn–Br bonds. In addition, modeling predicts spinodal decomposition to form Mn2+-enriched domains even at the end point compositions of x = 0 and 1, with Mn2+ ordering in next-nearest-neighbor positions driven by Coulomb interactions and lattice-strain minimization. These results have important implications for both fundamental studies and applications of doped and alloyed metal-halide perovskites.

Recent Advances in Bismuth Ion‐Doped Phosphor Materials: Structure Design, Tunable Photoluminescence Properties, and Application in White LEDs

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Ion exchange for halide perovskite: From nanocrystal to bulk materials

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Hydrothermal synthesis of water-soluble Mn- and Cu-doped CdSe quantum dots with multi-shell structures and their photoluminescence properties

“…50 Subsequently, Mn ions were doped into II–VI semiconductors including ZnSe, 51–53 CdSe, 42,45,46,54 CdS, 55,56 and ZnTe 57,58 QDs and perovskite QDs such as CsPbCl 3 . 59–61 Their optical and magneto-optical properties have also been studied. 23–28…”