Wet-chemistry-assisted synthesis of BaS:Eu near-infrared phosphors: Core-shell precursor engineering for enhanced Eu²⁺ luminescence and suppressed defect emission

Core-shell precursor boosts Eu 2+ dispersion and NIR emission in BaS host. • Wet-chemistry-assisted synthesis suppresses S-related defects, enabling NIR emission. • S-related defects act as both luminescent and quenching centers in BaS:Eu. This study develops an innovative wet-chemistry-assisted method for synthesizing BaS:Eu near-infrared (NIR) phosphors. By sequentially precipitating Eu 3+ and Ba 2+ in alkaline solution, a core-shell BaSO 4 @Eu(OH) 3 precursor is obtained, in which the subsequently formed BaSO 4 is inferred to encapsulate the preformed Eu(OH) 3 nuclei. SEM/EDS and XPS analysis show no detectable Eu on the particle surface, supporting this core–shell-like configuration. After sintering in CO reducing atmosphere at 1300 °C, BaS:Eu 2+ is obtained. Under 450 nm excitation, the material exhibits strong NIR broadband emission centered at 715 nm, attributed to the 4 f 6 5d 1 →4 f 7 transition of Eu 2+ in the octahedral crystal field of BaS. Compared with conventional solid-state routes using Eu 2 O 3 or Eu 2 (SO 4 ) 3 , this wet-chemistry-assisted approach appears to improve doping homogeneity in the product system and reduce Eu 2+ aggregation on the particle surface, as reflected in enhanced absorption characteristics and NIR emission intensity. The core-shell precursor configuration is suggested to suppress sulfur-related defect emission by limiting Eu exposure at the particle surface and by controlling the Ba-to-S ratio. Analysis of the luminescence behaviors indicates that sulfur-related defects act as both emission and quenching centers. Overall, this work offers a precursor-engineering strategy that may be extended to develop high-performance NIR-emitting materials. Download: Download high-res image (175KB) Download: Download full-size image