Highly Efficient Blue Emission from Self-Trapped Excitons in Stable Sb³⁺-Doped Cs₂NaInCl₆ Double Perovskites

Abstract

Highly efficient blue-emitting three-dimensional (3D) lead−free halide perovskites with excellent stability have attracted worldwide attention. Herein, a doping route was adopted to incorporate Sb 3+ ions into the Cs 2 NaInCl 6 for decorating the electronic band structure. Due to the moderate electron−phonon coupling, the Sb 3+ -doped Cs 2 NaInCl 6 double perovskites showed a narrow and relatively unusual blue emission of self-trapped excitons (STEs). Density functional theory (DFT) calculation indicated that the doped Sb 3+ ions could break the parityforbidden transition rule and modulate the density of state (DOS) population effectively to boost the PLQY of STEs drastically. The optimized Sb 3+ :Cs 2 NaInCl 6 exhibited a PLQY of up to 75.89% and excellent stability under the consecutive illumination of 365 nm UV light for 1000 h. This kind of highly efficient lead-free Sb 3+ -doped Cs 2 NaInCl 6 double perovskites may overcome the bottlenecks of severe toxicity and insufficient stability and therefore have an extensive application in the scarce blue photonic and optoelectronic fields.

Lead‐Free Halide Double Perovskites: Structure, Luminescence, and Applications

“…Recently, Zou and coworkers found doping Sb 3+ into Cs 2 NaInCl 6 could generate a new band above the VBM to boost deep blue STEs with high PL QY and narrowed FWHM. ( Figure a) [ 61 ] Indeed, a small S value of 11.96 has been extracted from temperature‐dependent PL spectra, confirming the illustration in Scheme 3. DFT analysis indicates the doped Sb 3+ ions can break the parity‐forbidden transition rule and boost the PL QY of STEs drastically.…”

“…[ 59 ] The doping ratio of Sb 3+ is less than 10% for efficient self‐trapped excitons (STEs). [ 60,61 ] In conclusion, the additive amounts of Bi 3+ and Sb 3+ are much smaller than that of CsPbX 3 . So, at least for luminescent applications, the environmental risk of Bi and Sb should not be a severe problem.…”

“…Surprisingly, strong blue emission occurred in Sb 3+ ‐doped Cs 2 NaInCl 6 HDPs with narrowed FWHM. [ 61 ] The bandgap changes to indirect after doping and a new band is introduced at the original VBM after Sb 3+ doping, which is composed of the Sb lone pair s states and Cl p states. Therefore, the drastic boosting of the PL QY of STEs mainly resulted from the break of the parity‐forbidden transition rule and modulation of the density‐of‐state population after doping of Sb 3+ ions.…”

“…(a) Reproduced with permission. [ 61 ] Copyright 2020, American Chemical Society. (b) Reproduced with permission.…”

Efficient Lone-Pair-Driven Luminescence: Structure–Property Relationships in Emissive 5s2 Metal Halides

“…In the case of In 3+ , the reported emission characteristics are extraordinarily similar to those of Sb 3+ -doped indium halide materials. 39 , 137 − 139 A new report found that undoped and Sb 3+ -doped Cs 2 InCl 5 ·H 2 O had essentially identical features and temperature-dependent intensities, 39 while recent work in our group showed that pure Cs 2 NaInCl 6 and Cs 2 InCl 5 ·H 2 O do not emit. 140 In our view, trace Sb 3+ dopants in the precursors may be responsible for these emissions, similar to the miniscule levels of Sn impurities that were found by Mitzi et al to generate STE emission in PEA 2 PbBr 4 .…”