Charge Transfer State: A New Sensitization Route for Blue‐LED‐Excitable Near‐Infrared Phosphors

Abstract

Blue‐LED‐excitable Near‐infrared (NIR) phosphors doped with transition metal or rare‐earth ions hold great promise for next‐generation NIR light sources in phosphor‐converted LEDs (pc‐LEDs). However, current blue‐excitable NIR phosphors mainly rely on Cr3+ ion absorption, which involves forbidden transitions with limited efficiency. Here an allowed charge‐transfer (CT) transition is proposed as a novel sensitization route for blue‐LED‐excitable NIR phosphors. The broad sensitization band arising from the S2−→Yb3+ CT in NaLaS2:Yb3+ fully covers the entire blue wavelength region. Under 450 nm excitation, it exhibits intense NIR emission centered at 994 nm, with an internal quantum efficiency of 64%. This allows CT transition, with high absorption efficiency, leads to a notable external quantum efficiency of 45%. At 420 K, the emission intensity maintains 88.7% of that at room temperature. Coupled with a blue chip, a high‐performance NIR pc‐LED is fabricated with a photoelectric conversion efficiency of 15.5% and demonstrates its potential applications. These findings open new and efficient sensitization avenues for blue‐LED‐excitable phosphors.