Zero-dimensional (0D) perovskite derivative Cs₄PbX₆ (X = Cl, Br, and I) nanocrystals (NCs) have shown great promise but their applications are limited by the insulator nature. Manganese ion doping is an effective approach for tailoring the optical properties of perovskite NCs and expanding their applications.

Although extensive studies have focused on Mn²⁺-doped 3D CsPbX₃ perovskites, the photoluminescence (PL) properties of Mn²⁺ in pure-phase Cs₄PbX₆ perovskites including the exciton-to-Mn²⁺ energy transfer and excited-state dynamics of Mn²⁺ remain elusive and unexplored.

In a recent study published in Adv. Sci., the research group led by Prof. CHEN Xueyuan from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences (CAS) reported a unique strategy for the controlled synthesis of pure-phase Mn²⁺-doped Cs₄PbCl₆ perovskite NCs that are free of CsPbCl₃ impurity, which enable an accurate elaboration of the PL properties of Mn²⁺ in Cs₄PbCl₆ NCs.

The researchers found that the substitution of Pb²⁺ by Mn²⁺ in isolated [PbCl₆]^4- octahedra resulted in intense Mn²⁺ emission at ~617 nm through efficient Pb²⁺-to-Mn²⁺ energy transfer. By means of temperature-dependent steady-state/transient PL and electron paramagnetic resonance (EPR) spectroscopies, they unveiled the excited-state dynamics of Mn²⁺ in Cs₄PbCl₆ perovskite NCs.

Owing to the spatially confined 0D structure of Cs₄PbCl₆ perovskite, Mn²⁺ ions in these NCs exhibited a large binding energy (145 meV) and strong electron-phonon coupling strength (75 meV), which led to a remarkably long PL lifetime (26.2 ms) of Mn²⁺ and a superior PLQY (25.8%) for NC powder to their 3D CsPbCl₃ analogues.

Specifically, the researchers observed an anomalous temperature evolution of Mn²⁺-PL decay from a dominant slow decay with a time constant of ≈30.4 ms at 300 K to a fast decay with a time constant of ≈1.47 ms at 10 K, as a result of strong Mn-Mn dipole-dipole coupling interactions induced by lattice contraction at low temperatures.

These findings provide fundamental insights into the excited-state dynamics of Mn²⁺ in 0D Cs₄PbCl₆ NCs, and lay a foundation for future design of 0D perovskite NCs through metal ion doping towards versatile applications such as solid-state lighting.

Schematic illustration of Mn²⁺-doped 0D Cs₄PbCl₆ perovskite NCs: TEM image (background), crystal structure, PL photograph, PL emission spectrum, and PL decay. (Image by Prof. CHEN’s group)