Ultrawide UV to NIR Emission in Double Perovskite Nanocrystals via the Self-Trapping State Engineering Strategy

By codoping Ag+ and Nd3+ ions in Cs2NaBiCl6 nanocrystals, we extend the photoluminescence range of inorganic double perovskite nanocrystals to the near-infrared (NIR) region for the first time. Specifically, the Ag+ and Nd3+ codoped Cs2NaBiCl6 nanocrystals exhibit photoluminescence of f-electrons of Nd at 887, 1069, and 1350 nm. Meanwhile, transient fluorescence and femtosecond transient absorption spectroscopy studies show that Ag+ doping induces self-trapped exciton (STE) states. Furthermore, the formation of STE helps construct suitable stepped energy levels, which improves the energy transfer efficiency and thus produces significant NIR photoluminescence. Based on the above results, AgNd-codoped double perovskite nanocrystals were assembled into a prototype photodetector. The photodetector exhibits a responsivity of 11.13 mA/W with detection rate D* of 2 x 10(10) Jones, which is a relatively high value among the lead-free double perovskite photodetectors. In addition, the photodetector has a response time of less than 40 ms due to the limitation of the instrument resolution. This work sheds light on the realization of efficient NIR photoluminescence and high-efficiency UV double perovskite nanocrystal photodetectors.