Efficient near‐infrared emission in lanthanum ion doped double perovskite Cs₂NaScCl₆ via Cr³⁺ sensitization under visible light excitation

Herein, we synthesized Cr 3+ /Ln 3+ (Er 3+ , Tm 3+ )‐codoped rare earth‐based Cs 2 NaScCl 6 double perovskite, and the near‐infrared emission of Ln 3+ can be excited by visible light through the energy transfer (ET) from Cr 3+ to Ln 3+ . Moreover, there are two independent emission bands, which stems from 4 T 2 → 4 A 2 transition of Cr 3+ (970 nm) and f‐f transition of Ln 3+ (1542 nm for Er 3+ and 1220 nm for Tm 3+ ), respectively. Particularly, both compounds have ultra‐high photoluminescence quantum yield (PLQY) of 60% for 10%Cr 3+ /6%Er 3+ ‐codoped Cs 2 NaScCl 6 (Er 3+ emission: ∼26%) and 68% for 10%Cr 3+ /4.5%Tm 3+ ‐codoped Cs 2 NaScCl 6 (Tm 3+ emission: ∼56%), which can be attributed to the ultra‐high ET efficiency from Cr 3+ to Ln 3+ and the similar ionic activity of Sc 3+ and Ln 3+ allowing more dopants enter the host lattice. Considering the excellent stability of the samples, we demonstrated Cr 3+ /Tm 3+ ‐codoped Cs 2 NaScCl 6 in the applications of near‐infrared imaging and night vision. Finally, we reported 10%Cr 3+ /4.5%Tm 3+ /9%Er 3+ ‐tridoped Cs 2 NaScCl 6 and further applied it for optical thermometry.