Boosting Near‐Infrared Luminescence of Lanthanide in Cs₂AgBiCl₆ Double Perovskites via Breakdown of the Local Site Symmetry

Abstract

Currently, lanthanide (Ln3+)‐doped near‐infrared (NIR)‐emitting double perovskites (DPs) suffer from low photoluminescence quantum yield (PLQY). Herein, we develop a new class of NIR‐emitting DPs based on Ln3+‐doped Cs2(Na/Ag)BiCl6. Benefiting from the Na+‐induced breakdown of local site symmetry in the Cs2AgBiCl6 DPs, effective NIR emissions of Ln3+ are realized through Bi3+ sensitization. Specifically, 7.3‐fold and 362.9‐fold enhanced NIR emissions of Yb3+ and Er3+ are achieved in Cs2Ag0.2Na0.8BiCl6 DPs relative to those in Na‐free Cs2AgBiCl6 counterparts, respectively. The optimal absolute NIR PLQYs for Yb3+ and Er3+ in Cs2Ag0.2Na0.8BiCl6 DPs are determined to be 19.0 % and 4.3 %, respectively. Raman spectroscopy and first‐principles density functional theory calculations verify the sublattice distortion in Cs2(Na/Ag)BiCl6 DPs via Na+ doping. These findings provide fundamental insights into the design of efficient NIR‐emitting Ln3+‐doped DPs for versatile optoelectronic applications.

K-Alloyed Lead-free Double-Perovskite Cs2AgBiBr6 Nanocrystals for Use in Light-Emitting Diodes

“…This phenomenon is attributed to the transitions from 1 S 0 → 3 P 1 and 1 S 0 → 1 P 1 of Bi 3+ , respectively. 35 As the doping amount increased, the absorption peak intensity at 382 nm increased, which means that the transitions of 1 S 0 → 1 P 1 increased. Furthermore, all these NCs had long absorption tails at longer wavelengths, indicating that these NCs had indirect band gaps.…”

“…With an increase in the amount of K alloying, a new absorption peak at 382 nm appeared, resulting in a bimodal phenomenon. This phenomenon is attributed to the transitions from 1 S 0 → 3 P 1 and 1 S 0 → 1 P 1 of Bi 3+ , respectively . As the doping amount increased, the absorption peak intensity at 382 nm increased, which means that the transitions of 1 S 0 → 1 P 1 increased.…”

Near‐infrared emitting metal halide materials: Luminescence design and applications

“…Reproduced with permission. 235 Copyright 2022, Wiley-VCH. (F) Schematic of an imaging system using the NIR LED as light source.…”

“…The as-fabricated Cs 2 NaInCl 6 :Cr 3+ NC film showed potential application in high-resolution images and NIR fluorescent signs. Chen's group 235 developed a new class of NIR-emitting double perovskites based on Ln 3+ -doped Cs 2 (Na/Ag) BiCl 6 . The emission spectra of Cs 2 Ag 1Àx Na x BiCl 6 :Yb 3+ presented a broad band from 400 to 1000 nm and a set of sharp peaks at $995 nm, ascribing to the STE states of Cs 2 Ag 1Àx Na x BiCl 6 and 2 F 5/2 !…”

“…NIR LMHs have been extensively developed for night vision. Pei et al 235 fabricated the NIR pc-LED devices by combining bright Cs 2 Ag 0.8 Na 0.2 BiCl 6 :Ln 3+ phosphors with a commercial 365 nm UV-LED chip, which serves as NIR light sources in the imaging system (Figure 11D). By contrast, NIR pc-LEDs based on the Cs 2 AgBiCl 6 :Ln 3+ and Cs 2 Ag 0.8 Na 0.2 InCl 6 :Ln 3+ with less brightness were also fabricated.…”