Efficient blue-luminescence in boracite Zn3B7O13Cl and its further enhancement via anion substitution and post-annealing treatment

Abstract

A series of blue phosphors based on Eu2+-activated boracite Zn3B7O13Cl were synthesized by high-temperature solid-state reaction. The phase composition and crystal structure were confirmed by XRD Rietveld refinements, while the optical transitions and band natures were analyzed using absorption spectra. The blue luminescence of Zn3B7O13Cl:Eu2+ shows a narrow band spectrum peaked at 405 nm due to the 4f65 d→4f7(8S7/2) transitions. Additionally, the sharp line transition of 4f7 (6P7/2)→4f7 (8S7/2) was also detected even at 300 K. The experiments confirm that the blue luminescence efficiency of Zn3B7O13(Cl1-xFx):0.03Eu2+ (x = 0, 0.05, 0.1, 0.2, 0.3) is improved with the increase of the substitution of F− for Cl−. To further improve the luminescence efficiency, the samples were post-annealed at 850 °C in a reducing atmosphere. The results demonstrate that the post-annealing can improve the luminescence efficiency and thermal stability in as-prepared Zn3B7O13(Cl1-xFx):0.03Eu2+ (x = 0, 0.05, 0.1, 0.2, 0.3) by eliminating the residual Eu3+. The maximum efficiency and thermal activation energy were confirmed in post-annealed Zn3B7O13(Cl1-xFx):0.03Eu2+ (x = 0.3), which are 65% and 0.31 eV, respectively. The luminescence mechanisms and thermal stability of Eu2+ activators were discussed.