Cr³⁺/Yb³⁺ Codoped Cs₂NaInCl₆ Double Perovskites for Near-Infrared Light-Emitting Diodes

Near-infrared (NIR) light-emitting diodes (LEDs) are potential devices that could become the core components in biological imaging, security monitoring, etc., which are currently constrained by suboptimal luminous efficiency due to the absence of excellent luminescent materials. Here, we report a double perovskite Cs₂NaInCl₆ that is suitable for Cr³⁺ doping and exhibits broad NIR emission. Through direct absorption and energy transfer (ET) from the self-trapped excitons (STEs) induced in the Cs₂NaInCl₆ matrix, Cr³⁺ can be excited to ⁴T₁(P), ⁴T₁(F), and ⁴T₂(F) levels. Then, the broad emission with a full width at half-maximum (<i>FWHM</i>) of ∼150 nm, spanning 800 to 1300 nm, and a high photoluminescence quantum yield (PLQY) of up to 70% can be realized, resulting from the ⁴T₂→⁴A₂ transition of Cr³⁺. Subsequently, the introduction of Yb³⁺ endows Cs₂NaInCl₆:Cr³⁺,Yb³⁺ with a higher PLQY of 76% at the optimal doping ratio than Cs₂NaInCl₆:Cr³⁺. Ultimately, a miniaturized NIR LED device packaged based on Cs₂NaInCl₆:15%Cr³⁺,15%Yb³⁺ has been fabricated, which demonstrates superior performance for night vision, traceless perspective detection, and biological imaging. This work not only screens out a suitable Cs₂NaInCl₆ matrix for Cr³⁺ doping with high PLQY but also promotes its luminescence performance through Yb³⁺ doping for NIR LED applications.