Cr3+-induced broadband near-infrared I combined with near-infrared II emission via rare earth co-doping in Cs2NaInCl6 for multifunctional detection†

Abstract

The increasing need for simultaneous detection of multiple components and precise analysis has driven the search for high-performance, broadband-emitting near-infrared (NIR) materials. Herein, the Cr³⁺-doped Cs₂NaInCl₆ (CNIC) lead-free double perovskites (DPs) are fabricated by a hydrothermal approach. The as-synthesized DPs exhibit a remarkable photoluminescence quantum yield (PLQY) of 92.41%, with a broad emission spectrum centered at 960 nm and a full width at half maximum (FWHM) of 160 nm. This exceptional performance is attributed to the Cr³⁺ ions with the spin-allowed ⁴T₂ → ⁴A₂ transition in a weak crystal field. The CNIC:Cr³⁺ DPs demonstrate not only excellent air and thermal stability but also impressive photostability. Furthermore, Cr³⁺/Ln³⁺ (Ln³⁺ = Ho³⁺, Tm³⁺, and Er³⁺) co-doped CNIC DPs are employed to achieve multi-peak emissions from NIR I to NIR II by facilitating energy transfer from Cr³⁺ to Ln³⁺. The optimal PLQYs of the co-doped DPs are found to be 69.34% (Ho³⁺ emission: 14.67%), 79.94% (Tm³⁺ emission: 31.95%), and 71.07% (Er³⁺ emission: 25.88%), respectively. These co-doped DPs have been successfully incorporated into high-performance NIR phosphor-converted light-emitting diodes (NIR pc-LEDs), with promising applications in synchronous multi-substance analysis, biological detection, and food safety monitoring, highlighting their potential for multifunctional applications.