Structure and photoluminescence properties of novel Ca2NaSiO4F:Re (Re = Eu2+, Ce3+, Tb3+) phosphors with energy transfer for white emitting LEDs

Abstract

A series of Eu²⁺ and Ce³⁺/Tb³⁺ doped Ca₂NaSiO₄F (CNSOF) phosphors have been synthesized and their structure and photoluminescence properties have been investigated in detail. Rietveld structure refinement indicates that the phosphors crystalized in an orthorhombic system with a space group of Pnma (no. 62) and there are two kinds of cation sites for the doped ions to occupy in forming emission centers. The CNSOF:Eu²⁺ and CNSOF:Ce³⁺ phosphors both have broad excitation bands, which match well with the commercial UV LED chips. The CNSOF:Eu²⁺ phosphor can have intense green emission with a maximum at 530 nm under irradiation at 380 nm, while the CNSOF:Ce³⁺ sample can emit intense blue light, peaking at 470 nm with excitation at 365 nm. By codoping the Tb³⁺ and Ce³⁺ ions into an CNSOF host and varying their relative ratio, tunable blue-green colors are obtained due to efficient energy transfer from the Ce³⁺ to Tb³⁺ ions. Moreover, energy transfer mechanisms for the Eu²⁺ ions in CNSOF:Eu²⁺ and Ce³⁺ → Tb³⁺ in CNSOF:Ce³⁺,Tb³⁺ have been studied systematically. Our investigation indicates that CNSOF:Eu²⁺ and CNSOF:Ce³⁺,Tb³⁺ may be potential green and blue-green phosphors for UV WLEDs, respectively.