Modulation of the near-infrared-I and -II luminescence of thulium-incorporated lead-free double perovskites†

Currently, lanthanide-doped metal halide perovskites with near-infrared (NIR) luminescence are receiving considerable attention. However, they suffer from low NIR efficiency, particularly in the NIR-II emission range, and are primarily excited by high-energy ultraviolet light. In this work, high-performance NIR-I and -II emissions were realized by co-doping a Cs₂NaInCl₆ lattice with Tm³⁺ ions as luminescent emitters and Sb³⁺ and Te⁴⁺ ions as sensitizer ions, where Sb³⁺ ions can enable short-wavelength high-energy excitation and Te⁴⁺ ions can enable long-wavelength blue-light excitation. The NIR photoluminescence quantum yield (PLQY) reaches an unprecedented 58.0% in Cs₂NaInCl₆:Sb³⁺/Tm³⁺ (NIR-II emission: 1224 nm–48.9%), which is attributed to the presence of the ¹G₄ energy level of the Tm³⁺ ion acting as a bridge, efficiently transferring energy from high-energy states of Sb³⁺ to NIR-emissive states. Moreover, Tm³⁺ ions can be sensitized by Te⁴⁺ ions that have broadband absorption in the blue region, which enable a high NIR PLQY of 10.3% in Cs₂NaInCl₆:Te⁴⁺/Tm³⁺ under 420 nm excitation. The excellent NIR luminescence performance combined with excellent environmental stability endows Cs₂NaInCl₆:Sb³⁺/Tm³⁺ and Cs₂NaInCl₆:Te⁴⁺/Tm³⁺ with considerable potential for application in night-vision devices.