Luminescent properties of BaAl12O19:Tb, Dy phosphors prepared by sol-gel method.

BaAl12O19:Tb, Dy phosphor was prepared by the sol-gel technique using citric acid as a complextant. XRD was used to characterize the relevant crystallization behavior of the phosphor. The luminescence properties and energy transfer between Tb3+ and Dy3+ were investigated. The results revealed that energy transfer exists between Dy3+ and Tb3+ at appropriate Tb3+ concentrations. The emission intensity of Tb3+ increases and energy transfer happens from Dy3+ to Tb3+ ions at the higher content of Tb3+ when Tb3+ and Dy3+ ions were co-doped. BaAl12O19 phosphors doped with Tb3+ or Dy3+ ions only were studied to compared with BaAl12O19:Tb, Dy phosphors. The results showed that the maximum excitation peak of BaAl12O19:Tb is 240 nm and the emission spectrum consists of four peaks at 490, 545, 590, and 625 nm, originating from 5D4 --> 7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ion, respectively. The excitation peaks of BaAl12O19:Dy are at 291, 324 nm and the emissions of Dy3+ are at 370, 447 and 578 nm, originating from 4F9/2 --> 6P5/2, 4F9/2 --> 6H15/2 and 4F9/2 --> 6H13/2 transitions of Dy3+ ion, respectively.

Near-infrared luminescence from Y2O3:Eu3+, Yb3+ prepared by sol-gel method.

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.