Improving Lead‐Free Double Perovskite Cs2NaBiCl6 Nanocrystal Optical Properties via Ion Doping

• Published in: Advanced optical materials Vol. 8; no. 8
• Main Authors: Yao, Ming‐Ming, Wang, Li, Yao, Ji‐Song, Wang, Kun‐Hua, Chen, Chen, Zhu, Bai‐Sheng, Yang, Jun‐Nan, Wang, Jing‐Jing, Xu, Wei‐Ping, Zhang, Qun, Yao, Hong‐Bin
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.04.2020
• Subjects: Doping; double perovskites; Emission spectra; Europium; ion doping; Lattices; Lead compounds; lead‐free metals; Manganese ions; Materials science; Metal halides; Nanocrystals; Optical properties; Optics; Perovskites; Photoluminescence; self‐trapped excitons; Toxicity
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.201901919

The exploration of lead‐free halide perovskite nanocrystals (NCs) with intriguing optical properties is highly desirable owing to the toxicity and instability of lead halide perovskite NCs. Here, a new kind of uniform lead‐free double perovskite Cs2NaBiCl6 NCs are reported as versatile hosts to accommodate ionic dopants for improving optical properties especially the photoluminescence (PL). In contrast to the low deep‐blue PL with a quantum yield of only 1.7% of the as‐synthesized pristine Cs2NaBiCl6 NCs, the PL of the Cs2NaBiCl6 NCs can be impressively regulated and enhanced via doping Ag+, Mn2+, or Eu3+ ions in the double perovskite lattices. The femtosecond time‐resolved transient absorption spectroscopy is adopted to unravel the PL enhancement mechanism of the ion doping in the Cs2NaBiCl6 NCs. For the Ag+‐doping, the excitonic absorption energy of the Cs2NaBiCl6 NCs can be tuned from 3.82 to 3.48 eV with the significant improvement of the PL quantum yield (PLQY) from 1.7% to 20%. The Mn2+‐doped Cs2NaBiCl6 NCs show broad orange–red emission peak centered at 585 nm with a PLQY of 3%, owing to the 4T1→6A1 transition of octahedrally coordinated Mn2+. Eu3+‐doped Cs2NaBiCl6 NCs are endowed with strong Eu3+5D0→7FJ (J = 1, 2) orange–red emission at 591 and 615 nm. A series of ions (Ag+, Mn2+, and Eu3+) doped lead‐free double perovskite Cs2NaBiCl6 nanocrystals (NCs) with uniform morphologies and good air stability are synthesized, exhibiting impressively enhanced photoluminescence in comparison to pristine Cs2NaBiCl6 NCs. The ion doping mechanisms for improving the PL are unraveled by the femtosecond time‐resolved transient absorption spectroscopy characterizations as well.