Lanthanide-Induced Photoluminescence in Lead-Free Cs₂AgBiBr₆ Bulk Perovskite: Insights from Optical and Theoretical Investigations

Abstract

Emphasis was recently placed on the Cs2AgBiBr6 double perovskite as a possible candidate to substitute toxic lead in metal halide perovskites. However, its poor light-emissive features currently make it unsuitable for solid-state lighting. Lanthanides doping is an established strategy to implement luminescence in poorly emissive materials, with the additional advantage of fine-tuning the emission wavelength. We discuss here the impact of Eu-and Yb-doping on the optical properties of Cs2AgBiBr6 thin films, obtained from solution-processing of hydrothermally synthesized bulk crystalline powders, by combining experiments and density functional theory calculations. Eu(III) incorporation does not lead to the characteristic 5 D0→ 7 F2 emission feature at 2 eV, while only a weak trap-assisted sub band-gap radiative emission is reported. Oppositely, we demonstrate that incorporated Yb(III) leads to an intense and exclusive photoluminescence emission in the nearinfrared as a result of the efficient sensitization of the lanthanide 2 F5/2→ 2 F7/2 transition.

Lead‐Free Double Perovskite Cs2AgInCl6

“…7 F 2 emission, but underwent at rap-like recombination. [33] So one can expect the further work on these phenomena and the related emission mechanism deserves to be explored in rare earth ion doped Cs 2 AgInCl 6 .…”

“…The orange and violet regions indicate decomposition pathways involving only binary compounds and ternary compounds,respectively.M odified with permission from the American Chemical Society and Wiley-VCH. [8,33] Figure 9. a) Calculated charge density difference upon X-site vacancy formation in Cs 2 AgInCl 6 .b )Calculated transitione nergy levels for intrinsic donor (blue lines) and acceptor (red lines) defects.…”

“…b) Calculated decomposition enthalpies (DH dec )of Cs 2 AgInX 6 (X = Cl, Br,and I). The orange and violet regions indicate decomposition pathways involving only binary compounds and ternary compounds,respectively.M odified with permission from the American Chemical Society and Wiley-VCH [8,33].…”

Lattice Doping of Lanthanide Ions in Cs 2 AgInCl 6 Nanocrystals Enabling Tunable Photoluminescence

“…Therefore, to explore doped Cs 2 AgInCl 6 NCs with improved PLQY and tunable emission is a main challenge. Generally, lanthanide (Ln 3+ ) ions would be the most suitable dopants for their rich and unique PL emissions in the visible to near-infrared range [28,29], which could be utilized to achieve tunable luminescence and increased PLQY [30]. Moreover, the successful incorporation of rare earth ions for the lead-based halide perovskites [31,32] and the structural similarity between lead-based and lead-free perovskites (both with the six octahedral coordination number) have provided the reference and opportunities to conduct the further lanthanide doping study on Cs 2 AgInCl 6 NCs [33][34][35].…”

Lead‐Free Double Perovskite Cs2AgInCl6

“…A recent experimental–computational work by Schmitz et al on Eu‐ and Yb‐doped Cs 2 AgBiBr 6 bulk perovskite, whose structure is very similar to that of Cs 2 AgInCl 6 , showed that Yb III in Cs 2 AgBiBr 6 exhibited the characteristic intense emission in the NIR region. In contrast, Eu III in Cs 2 AgBiBr 6 did not exhibit characteristic 5 D 0 → 7 F 2 emission, but underwent a trap‐like recombination [33] . So one can expect the further work on these phenomena and the related emission mechanism deserves to be explored in rare earth ion doped Cs 2 AgInCl 6 .…”