Enhancement of NIR Luminescence Properties in Li₃Cs₂Sr₂B₃P₆O₂₄: Cr³⁺ Phosphor via Yb³⁺ Co‐Doping for Spectroscopy Applications

The extension of near‐infrared (NIR) emission beyond the conventional 700‐ to 900‐nm range is crucial for advancing next‐generation NIR phosphor‐converted light‐emitting diodes (NIR pc‐LEDs). In this regard, co‐doping strategies involving Yb 3+ have emerged as a promising approach to achieve broader spectral coverage with improved performance. Herein, a series of Li 3 Cs 2 Sr 2 B 3 P 6 O 24 : Cr 3+ , Yb 3+ co‐doped phosphors are developed for the first time. Upon 450‐nm excitation, the optimal LCSBPO: 0.1Cr 3+ , 0.02Yb 3+ phosphor delivers intense emission covering 900–1150 nm, which originated from the Stark‐split 2 F 5/2 → 2 F 7/2 transitions of Yb 3+ . Co‐doping results in a remarkable 61‐fold increase in Yb 3+ emission compared to mono‐doped Yb 3+ and a three‐fold enhancement in overall luminescence relative to LCSBPO: 0.1Cr 3+ . Specifically, the internal quantum efficiency (IQE) improves from 33.7% to 50.6%. Despite the poor luminous thermal stability at 120°C (39.5%), the distinct thermal responses of Cr 3+ and Yb 3+ emissions enable ratiometric temperature sensing with a high relative sensitivity ( S r ) of 1.93% K −1 at 30°C. Additionally, an NIR pc‐LED fabricated by integrating LCSBPO: 0.1Cr 3+ , 0.02Yb 3+ with a 450‐nm blue LED demonstrates promising practical applications in night vision imaging and non‐destructive analysis.