Synthesis and luminescence properties of novel host-sensitized germanate phosphors NaYGeO4:Ln (Ln= Eu3+, Sm3+, Dy3+)

The rare earth ions doped germanate phosphors NaYGeO4:Ln (Ln= Eu3+, Sm3+ and Dy3+) as well as pure NaYGeO4 host were synthesized by conventional high-temperature solid-state reaction method. The results of X-ray diffraction along with Rietveld refinement revealed the formation of the single orthorhombic phase of the as-prepared phosphors. The pure host NaYGeO4 showed broad excitation/emission band in UV-vis region, which could result from the transition of self-activated optical centers in the GeO4 anion. The host sensitization for Eu3+/Sm3+/Dy3+ emission in NaYGeO4 was confirmed and the energy transfer efficiency from the host to Eu3+/Sm3+/Dy3+ was calculated. Upon excitation with ultraviolet light (300 nm), the as-synthesized NaYGeO4:Ln (Ln= Eu3+, Sm3+ and Dy3+) phosphors showed both the blue broadband emission of the NaYGeO4 host and the characteristic emission of Eu3+/Sm3+/Dy3+ ions, which led to apparent change of the CIE chromaticity coordinates compared to the pure NaYGeO4 host. These results implied the potential application of the as-prepared phosphors in UV light-emitting diodes.