Enhanced red emission of Eu ³⁺ in ZnO-TiO ₂ :Dy ³⁺ , Eu ³⁺ nanocomposites by UV downconversion process

ZnO-TiO ₂ :0.4 mol. %Dy ³⁺ _, x mol. %Eu ³⁺ (x = 0.05, 0.15, 0.25, 0.50, and 0.75) nanophosphors were synthesized using the solgel method. X-ray diffraction data confirmed crystallization of a mixture of wurtzite hexagonal ZnO and tetragonal TiO ₂ (anatase and rutile) nanocomposite phases. The nanocomposites were excited in the ultraviolet region with a wavelength of 248 nm, and the major narrowband emissions were observed in the visible range at 496, 584, 593, and 614 nm. The emissions at 496 and 584 nm were assigned to f → f transitions of Dy ³⁺ ions from the upper ⁴ F _9/2 level to lower ⁶ H _15/2 and ⁶ H _13/2 levels, respectively, while those at 593 and 614 nm were assigned to f → f transitions of Eu ³⁺ ions from the ⁵ D ₀ level to the ⁵ F ₁ and ⁵ F ₂ levels, respectively. The effects of changing the Eu ³⁺ concentrations on the PL intensity and energy transfer mechanisms from the charge transfer states and Dy ³⁺ to Eu ³⁺ are discussed. Energy transfer from Dy ³⁺ to Eu ³⁺ was confirmed by measuring the decay curves of orange-yellow and red emission of Dy ³⁺ and Eu ³⁺ , respectively, in ZnO-TiO ₂ :Dy ³⁺ ,Eu ³⁺ .