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

Herein, we synthesized Cr³⁺/Ln³⁺ (Er³⁺, Tm³⁺)-codoped rare earth-based Cs₂NaScCl₆ double perovskite, and the near-infrared emission of Ln³⁺ can be excited by visible light through the energy transfer (ET) from Cr³⁺ to Ln³⁺. Moreover, there are two independent emission bands, which stems from ⁴T₂ → ⁴A₂ transition of Cr³⁺ (970 nm) and f-f transition of Ln³⁺ (1542 nm for Er³⁺ and 1220 nm for Tm³⁺), respectively. Particularly, both compounds have ultra-high photoluminescence quantum yield (PLQY) of 60% for 10%Cr³⁺/6%Er³⁺-codoped Cs₂NaScCl₆ (Er³⁺ emission: ∼26%) and 68% for 10%Cr³⁺/4.5%Tm³⁺-codoped Cs₂NaScCl₆ (Tm³⁺ emission: ∼56%), which can be attributed to the ultra-high ET efficiency from Cr³⁺ to Ln³⁺ and the similar ionic activity of Sc³⁺ and Ln³⁺ allowing more dopants enter the host lattice. Considering the excellent stability of the samples, we demonstrated Cr³⁺/Tm³⁺-codoped Cs₂NaScCl₆ in the applications of near-infrared imaging and night vision. Finally, we reported 10%Cr³⁺/4.5%Tm³⁺/9%Er³⁺-tridoped Cs₂NaScCl₆ and further applied it for optical thermometry.