Crystal structure, tunable luminescence and energy transfer properties of Na3La(PO4)2:Tb3+,Eu3+ phosphors†
Abstract
A series of Tb3+ and/or Eu3+ doped Na3La(PO4)2 phosphors were successfully synthesized and their crystal structure and photoluminescence (PL) properties were investigated in detail. Double phosphates with the compositions Na3Tb(PO4)2 and Na3Eu(PO4)2 were obtained by the substitution of Tb or Eu for La in the Na3La(PO4)2 host. XRD pattern analysis indicates that these obtained compounds crystallize in the orthorhombic system with the space group Pbc21. The crystal structure of the Na3RE(PO4)2 (RE = Tb, Eu) is made up of isolated PO4 tetrahedra and of sodium and RE atoms arranged in an ordered way. The REOy polyhedra are isolated from one another, resulting in a high critical concentration of Tb3+ or Eu3+ activators. Under excitation of near-ultraviolet (NUV) irradiation, Tb3+ doped Na3La(PO4)2 shows a blue-greenish emission with a predominant peak at 546 nm, while the emission spectra of Eu3+-doped Na3La(PO4)2 exhibits a reddish orange emission due to the 5D0 → 7FJ transitions of Eu3+ ions. The energy transfer from Tb3+ to Eu3+ in the Na3La(PO4)2 host is demonstrated by the luminescence spectra and fluorescence decay dynamics. Meanwhile, the emission color of Na3La(PO4)2:Tb3+,Eu3+ can be tuned from green to red through tuning the Tb3+/Eu3+ ratio. These results indicate that the Na3La(PO4)2:Tb3+,Eu3+ phosphor exhibits broadband NUV absorption and green-reddish orange tunable emission, which might serve as a down-converting phosphor for NUV light-emitting diodes.