Excitation enhanced and tuned in Cs2KGaF6: Cr3+, Mn4+ with significantly improved EQE applied for NIR pc-LEDs

https://doi.org/10.1016/j.jallcom.2025.182636

Recently, Cr³⁺-doped fluoride materials for phosphor-converted near-infrared light-emitting diodes (NIR pc-LEDs) have been extensively studied, however, their external quantum efficiency (EQE) must be improved. In addition, designing broadband NIR-emitting fluoride phosphors that are sufficiently excited by blue light to match with commercial 460 nm InGaN LED chips is still challenging. In this work, broadband NIR-emitting Cs₂KGaF₆:Cr³⁺, Mn⁴⁺ (CKGF:Cr, Mn) phosphors are synthesized through ion exchange route. Tunable excitation of CKGF:Cr NIR phosphor shifts from 430 nm to 460 nm by co-doping with Mn⁴⁺, which could serve as an additional strategy to improve the photoluminescence of Cr³⁺-doped broadband NIR-emitting phosphors. The NIR emission of CKGF:Cr, Mn is significantly improved, with internal quantum efficiency (IQE) and EQE of 85.9% and 29.0%, respectively. The Mn-free CKGF:Cr phosphor, in comparison, has an EQE of only 15.8% (�ex �ex = 467 nm) and 20.0% (�ex = 433 nm). Furthermore, with excellent thermal stability, CKGF:Cr, Mn phosphor are well suitable for LED applications and the fabricated NIR pc-LED device has high photoelectric efficiency (19.4%@20 mA) and it well performs in night vision, quick inspection and strengthening for deep colors. The described ion exchange method of Cr³⁺-doped fluoride NIR phosphors by co-doping with Mn⁴⁺ is an attractive strategy for optimizing the luminescent properties of blue-excited NIR phosphors.