Tb 3+ and Bi 3+ Co-Doping of Lead-Free Cs 2 NaInCl 6 Double Perovskite Nanocrystals for Tailoring Optical Properties.

Lead halide perovskites have achieved remarkable success in various photovoltaic and optoelectronic applications, especially solar cells and light-emitting diodes (LEDs). Despite the significant advances of lead halide perovskites, lead toxicity and insufficient stability limit their commercialization. Lead-free double perovskites (DPs) are potential materials to address these issues because of their non-toxicity and high stability. By doping DP nanocrystals (NCs) with lanthanide ions (Ln 3+ ), it is possible to make them more stable and impart their optical properties. In this work, a variable temperature hot injection method is used to synthesize lead-free Tb 3+ -doped Cs 2 NaInCl 6 DP NCs, which exhibit a major narrow green photoluminescence (PL) peak at 544 nm derived from the transition of Tb 3+ 5 D 4 → 7 F 5 . With further Bi 3+ co-doping, the Tb 3+ -Bi 3+ -co-doped Cs 2 NaInCl 6 DP NCs are not only directly excited at 280 nm but are also excited at 310 nm and 342 nm. The latter have a higher PL intensity because partial Tb 3+ ions are excited through more efficient energy transfer channels from the Bi 3+ to the Tb 3+ ions. The investigation of the underlying mechanism between the intrinsic emission of Cs 2 NaInCl 6 NCs and the narrow green PL caused by lanthanide ion doping in this paper will facilitate the development of lead-free halide perovskite NCs.