Tb3+ and Bi3+ Co-Doping of Lead-Free Cs2NaInCl6 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 (Ln3+), 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 Tb3+-doped Cs2NaInCl6 DP NCs, which exhibit a major narrow green photoluminescence (PL) peak at 544 nm derived from the transition of Tb3+ 5D4→7F5. With further Bi3+ co-doping, the Tb3+-Bi3+-co-doped Cs2NaInCl6 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 Tb3+ ions are excited through more efficient energy transfer channels from the Bi3+ to the Tb3+ ions. The investigation of the underlying mechanism between the intrinsic emission of Cs2NaInCl6 NCs and the narrow green PL caused by lanthanide ion doping in this paper will facilitate the development of lead-free halide perovskite NCs.