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 Yb3+ have emerged as a promising approach to achieve broader spectral coverage with improved performance. Herein, a series of Li3Cs2Sr2B3P6O24: Cr3+, Yb3+ 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 F-2(5/2) -> F-2(7/2) transitions of Yb3+. Co-doping results in a remarkable 61-fold increase in Yb3+ emission compared to mono-doped Yb3+ 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 degrees C (39.5%), the distinct thermal responses of Cr3+ and Yb3+ emissions enable ratiometric temperature sensing with a high relative sensitivity (S-r) of 1.93% K-1 at 30 degrees 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.