Abstract
The incorporation of rare earth lanthanide ions (Ln(3+)) into lead-free halide perovskite nanocrystals (NCs) is an effective and promising strategy to expand their optical, magnetic, and electrochemical properties. Herein, we designed and synthesized various Ln(3+) (including Yb(3+), Er(3+), and Nd(3+)), doped Sb(3+)- or Bi(3+)-based and Sb(3+)/Bi(3+) alloyed lead-free perovskite NCs, including vacancy-induced perovskite (A(3)B(III)(2)X(9)), double perovskite (A(2)B(I)B (III)X(6)), and layered-double perovskite (A(4)B(II)B(III)(2)X(12)) NCs with different energy transfer pathways to study the Ln(3+) dopant photoluminescence (PL). While a small size mismatch between dopant ions and host substitutional sites are critical for efficient doping of many first-row transitional metal ion doped metal chalcogenides, surprisingly, the Ln(3+) ions, including the large Nd(3+) ions (112 pm), prefer smaller isovalent Sb(III) octahedral (O(h)) sites (90 pm) instead of Bi(III) O(h) sites (117 pm) in these lead-free perovskite NCs. Significantly, similar substitutional site-dependent Ln(3+) doping efficiencies were obtained across all three different perovskite host lattices, despite differences in host-to-dopant energy transfer mechanisms, which can provide strong evidence of the preferred Sb(3+) substitutional sites for lanthanide dopants in these lead-free perovskite lattices. The efficient Ln(3+) doping in Sb(3+)-rich perovskite NCs leads to enhanced Ln(3+) ion PL of the doped NCs. The preference of smaller Sb (III) over Bi(III) substitutional sites for Ln(3+) dopants is attributed to the relatively high polarizabilities of lanthanide ions and the smaller cationic sites inside [SbX(6)](3-) compared with [BiX(6)](3-) octahedra. This study provides a fundamental understanding of Ln(3+) doping behavior in lead-free perovskite NCs and opportunities for designing efficient Ln(3+)-doped functional materials by tuning the microenvironment of the host lattice for enhanced properties.