LAUSR

Abstract A series of Ca9NaZn(PO4)7: Eu2+/Eu3+, Tb3+ (CNZP: Eu2+/Eu3+, Tb3+) phosphors were synthesized by the solid-state reaction method. The results of structure refinement indicate that the chemical formula of CNZP can be written as Ca9.12(5)Zn0.88(5)Na1.0(2)(PO4)7. Ca2+ ions fully occupy M1 site and partly occupy M2, M3 and M5 sites. The M4 sites are 100% occupied by Na+ ions and Na+ ions didn't participate in other sites. Zn2+ ions partly occupy M2, M3 and M5 sites and the biggest occupation 81(2)% of Zn2+ was observed for M5 sites. There are both 6-coordinated and 8-corrdinated Ca2+ and Zn2+ in CNZP matrix. According to Davolos's theory, we speculated that Eu3+ ions could substitute both Ca2+ and Zn2+ ions in CNZP matrix, while Eu2+ ions could only replace Ca2+ ions but not Zn2+ ions in CNZP host. Eu3+ ions doped in CNZP matrix only partly were reduced to Eu2+ state under the preparation conditions. The reaction mechanism was proposed. The emission color of the as-prepared phosphor were tuned from blush-violet to warm-white and yellowish-green by energy transfer of Eu2+→Tb3+ and Tb3+→Eu3+ in CNZP: Eu2+/Eu3+, Tb3+ phosphor. The samples showed good thermal stability. All the results imply that CNZP: Eu2+/Eu3+, Tb3+ phosphor is a potential color-tunable phosphor candidate for n-UV LEDs.