Eu 3+ and Sm 3+ co-doped molybdate phosphors have been synthesized via hydrothermal method. The phosphors have the advantages of narrower particle size distribution and regular homogeneous shape. The luminescent properties of the molybdate phosphors were systematically studied. The introduction of Sm 3+ into the red-emitting phosphors can generate a strong excitation line at 405 nm, originating from the 6 H 5/2 → 4 K 11/2 transition of Sm 3+ , significantly extending the excitation region for matching the near-ultraviolet light-emitting diodes (−400 nm). Energy transfer from Sm 3+ to Eu 3+ was observed.
Eu3+ and Yb3+ codoped Y2O3 phosphors were synthesized by the sol-gel method. The phosphors possess absorption in the region of 300-550 nm, exhibiting an intense NIR emission of Yb3+ around 1000 nm, which is suitable for matching the maximum spectral response of c-Si solar cells. The optimum composition of Eu3+ and Yb3+ codoped Y2O3 was (Y1.94Yb0.04Eu0.02)2O3. It is observed that two-step energy transfer occurs from the 5D2 level of Eu3+ situated around (466 nm) exciting two neighboring Yb3+ ions to the 2F5/2 level (1000 nm). The down-conversion material based on Eu(3+)- Yb3+ couple may have great potential applications in c-Si solar cells to enhance their photovoltaic conversion efficiency via spectral modification.
The red phosphor Gd2(MoO4)3:Eu3+,Sm3+ was prepared by sol-gel method. The morphology and luminescence characteristics of the phosphor particles were characterized by scanning electron microscopy (SEM) and fluorophotometer. The results showed that the phosphor had the advantages of small particle size and the uniform particle size distribution. The luminescence properties of Eu3+ ions in Gd1.37Eu0.6Sm0.03(MoO4)3 could be evidently improved by co-doping of Sm3+ ions, which was due to the efficient energy transfer process from Sm3+ to Eu3+ ions. The chromaticity coordinates for Eu3+ doped Gd1.4Eu0.6(MoO4)3 and Eu3+ and Sm3+ codoped Gd1.37Eu0.6Sm0.03(MoO4)3, are(0.662, 0.329) and (0.668, 0.331), respectively. Because of the introduction of Sm3+ into the red-emitting phosphors, the chromaticity coordinates of Gd1.37Eu0.6Sm0.03(MoO4)3 phosphor is closer to the standard values of International chromaticity coordinates(0.67, 0.33). So Gd1.37Eu0.6Sm0.03(MoO4)3 shows good prospect for red phosphors of white LED.
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