Lanthanide Double Perovskite Nanocrystals with Emissions Covering the UV‐C to NIR Spectral Range

Abstract

Lead halide perovskite nanocrystals (NCs) have recently drawn considerable attention in the fields of materials science and nanotechnology. However, a major drawback of these NCs is the reliance on toxic lead, which hinders widespread application. Herein, a new class of lead‐free perovskite NCs, that is, lanthanide double perovskite (Ln‐DP) NCs, with f‐orbital‐induced optical properties, is introduced. The Pr‐, Ce‐, Tb‐, Eu‐, Sm‐, and Yb‐based Ln‐DP NCs display narrow d→f and f→f emissions ranging from the UV‐C to the near‐infrared spectral region. Experimental data and calculations reveal that the emissive Ln‐DP NCs exhibit small molecule‐like electronic absorptions: f→d atomic transitions or ligand‐to‐metal charge transfer transitions. Last, it is demonstrated that by alloying Ln compositions in the DP NCs, new materials with unique and improved optical properties can be obtained. These Ln‐DP NCs are promising for optical sensing and lighting, and as components in optoelectronic and/or magneto‐fluorescent devices.

Post-Synthetic Doping and Ligand Engineering of Cs2AgInCl6 Double Perovskite Nanocrystals

“…25 For the postsynthetic Mn 2+ doping and aging processes, this STE emission feature was overshadowed by a characteristic Mn 2+ emission peak (through 4 T 1g to 6 A 1g electronic transition) at 630 nm (Figure 1A), suggesting a successful doping of Mn 2+ ions into the DP crystal structure. 25,29,32 The PL excitation (PLE) spectrum measured at the Mn 2+ emission peak (i.e., 630 nm) overlapped well with the corresponding absorption profile of the DP NCs (Figure 1A), indicating an energy transfer process from the photogeneration exciton of the DP-NC to the excited electronic state (i.e., 4 T 1g ) of the Mn 2+ centers in the Mn 2+ -doped Cs 2 AgInCl 6 DP NCs. The 2D emission contour map further highlighted the excitation-independent Mn PL, confirming the invariant radiative relaxation pathway through incorporated Mn 2+ ion centers (Figure 1B).…”

“…18−21 As such, reports indicate that the incorporation of transition metals (e.g., Cu 2+ , Mn 2+ ) or lanthanide ions (e.g., Ce 3+ , Tb 3+ , Yb 3+ ) can modulate the band gap of the Cs 2 AgInCl 6 DPs to exhibit additional strong and narrow absorption peaks in the visible light range or provide a more efficient radiative recombination pathway. 22−25 As one of the most studied systems, doping Mn 2+ cations into Cs 2 AgInCl 6 DP NCs can result in photoexcited energy transfer from the DP NC hosts to Mn 2+ dopants, leading to a signature orange emission (∼620 nm) through d−d transitions (i.e., 4 T 1g → 6 A 1g ) of the incorporated Mn 2+ ion centers. 26−29 photoluminescence (PL) lifetimes, relatively high PL quantum yields (QYs), and large Stokes shifts with a minimized selfabsorption behavior, which are all beneficial to applications including solid-state lighting, displays, or luminescence solar concentrators.…”

“…; M­(III) = Bi 3+ , In 3+ , Sb 3+ , lanthanides, etc . ; and X = Cl – , Br – , I – ) have attracted an extensive amount of research attention in recent years due to their reduced toxicity while maintaining a charge-neutral three-dimensional (3D) crystal structure with unique optoelectronic properties and enhanced stability. − The transition from a single, divalent, B-site metal (i.e., Pb 2+ ) in the conventional lead-halide perovskite to heterovalent dual B-sites (i.e., M­(I) and M­(III)) containing DP structure greatly expands compositional space and expedites the development of new perovskite materials. − In particular, Cs 2 AgInCl 6 DP NCs possess a direct band gap and long photocarrier lifetimes with excellent light, thermal, and moisture stability, making them one of the most promising lead-free perovskite-type alternatives. − However, the low absorption extinction coefficient and weak, broad emission exhibited by the self-trapped excitons (STEs) of Cs 2 AgInCl 6 DP NCs installed by the intrinsic parity-forbidden band gap transition significantly hinder their potential implementation into a wide variety of commercial applications. ,, …”

Revealing the role of a unique local structure in lanthanide-doped Cs2LiInCl6 in boosting visible and NIR-II luminescence

“…Lead-free halide double perovskites (DPs) as promising luminescent materials have received increased interest from researchers for potential applications in various materials science and biomedical fields owing to their low toxicity and high chemical-, thermal-, and photo-stability. 1–8 However, the photoluminescence (PL) performance is very poor for most DPs in view of the indirect bandgaps or parity-forbidden transitions, limiting their further practical photonic and biological applications. Fortunately, DPs have the general formula A 2 M + M 3+ X 6 (where A = Rb + and Cs + ; M + = Ag + and Na + ; M 3+ = In 3+ and Bi 3+ ; and X = Cl − and Br − ) that provides abundant opportunities for the material composition adjustment.…”

Lanthanide/Bismuth-Codoped Lead-Free Halide Double Perovskite Nanocrystals with Upconversion and Short-Wave Infrared Luminescence

“…Thus, Cs 2 NaInCl 6 NCs are selected as hosts in our work. In addition, lanthanide (Ln 3+ )-contained DP NCs have been extensively studied. − ,− Researches are mainly focused on how to further introduce lanthanide ions into Cs 2 NaInCl 6 DP NCs to broaden the photoluminescence (PL) spectra for broadband white-light emission in the visible region. ,− However, other luminescent properties, such as upconversion (UC) and downshifting short-wave infrared (SWIR) emission in In-based halide DP nanomaterials, have rarely been explored. Therefore, it is of great significance to develop environmentally friendly and highly efficient DP NCs with UC and SWIR PL and to elucidate the luminescence mechanism as well.…”