Enhancement of Eu2+ photoluminescence behavior in NaBaB9O15 based on the K+ doping

Cation substitution is one of the prevalent strategies to improve the luminescence performance of phosphors. NaBa1-xKxB9O15: 0.03Eu2+ (0 < x < 0.4) phosphors were synthesized via a high-temperature solid-state reaction. The PL emission of NaBaB9O15: 0.03Eu2+ has enhanced 4.13-fold after K+ doping with content x = 0.2. Under excitation at around 254 nm, NaBa0·77K0·2B9O15: 0.03Eu2+ phosphor exhibits the excellent luminescent performance, including higher color purity 97.7% and outstanding quantum yield (99.6%), remaining 101% emission intensity at 423 K. The effect and mechanism of K+ substitution of Ba2+ on the emission intensity and thermal stability were systematically investigated and clarified in detail by virtue of the Rietveld refinement, XPS, IR, and TL spectra, etc. Introducing K+ ions will trigger O vacancy and induce abnormal lattice shrinkage, thus, increase the effective luminescence center Eu2+ ions, finally resulting in the improving luminescence performance. Moreover, higher local symmetry and the thermal compensation radiation effect depending on defect traps improve thermal stability. We believe that the present work will provide help for other non-equivalent substituted luminescent materials to optimize optical performance.