title: White Light Emission and Luminescence Dynamics in Eu³⁺/Dy³⁺ Codoped ZnO Nanocrystals.
abstract: In order to expand the use of ZnO in advanced display and lighting device applications, such as distinguishable emissive flat panel displays and liquid crystal display backlights, Eu³⁺/Dy³⁺-codoped ZnO nanocrystals were synthesized using a low temperature wet chemical doping technique and chemical surface modification. X-ray diffraction patterns revealed that co-doping Eu³⁺ and Dy³⁺ does not change the wurtzite structure of ZnO. A high-resolution TEM image showing obvious lattice fringes confirmed the high crystallinity of the nanosized sample. The luminescence and dynam- ics of Eu³⁺/Dy³⁺-codoped ZnO nanocrystals of various doping concentrations were studied under ultraviolet excitation. Excitation into the ZnO conduction band was also studied. ZnO doped with Eu³⁺ and Dy³⁺ ions exhibited a strong blue (483 nm) emission from the ⁴F₉/₂ --> ⁶H₁₅/₂ transition of Dy³⁺ ions, a yellowish-green (575 nm) emission from the ⁴F₉/₂ --> ⁶H₁₃/₂ transition of Dy³⁺ ions and a red (612 nm) emission from the ⁵D₀ --> ⁷F₂ transition of Eu³⁺ ions, without a defect background. Undoped ZnO emitted a broadband green light, demonstrating an efficient energy transfer from the ZnO host to the Eu³⁺ and Dy³⁺ ions. Moreover, energy transfer from the Eu³⁺ ions to the Dy³⁺ ions in the ZnO host was also observed by analyzing luminescence decay curves. The luminescence dynamics of the Eu³⁺/Dy³⁺-codped ZnO sample indicate that as the Eu³⁺ concentration increased, both the rise and the decay time constants of the ⁴H₉/₂ level of the Dy³⁺ ions became longer, while the decay time constants of the ⁵D₀ level of the Eu³⁺ ions became shorter, suggesting an energy transfer from the Eu³⁺ ions to the Dy³⁺ ions in the ZnO host. Furthermore, by adjusting the doping concentration ratio of Eu³⁺ and Dy³⁺ ions, the Eu³⁺/Dy³⁺-codoped ZnO phosphors emitted strong white luminescence with a high color purity and high color rendering index. The results indicate that the Eu³⁺/Dy³⁺-codoped ZnO phosphors are promising light-conversion materials, and have the potential to be used in field emission display devices and LCD backlights.
authors.forename: L
authors.initials: L
authors.lastname: Luo
authors.forename: F Y
authors.initials: FY
authors.lastname: Huang
authors.forename: G S
authors.initials: GS
authors.lastname: Dong
authors.forename: Y H
authors.initials: YH
authors.lastname: Wang
authors.forename: Z F
authors.initials: ZF
authors.lastname: Hu
authors.forename: J
authors.initials: J
authors.lastname: Chen
mesh_terms: D005063:Europium / Q000737:chemistry*; D008027:Light; D049449:Luminescence; D053758:Nanoparticles / Q000737:chemistry*; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D005063:Europium; D015034:Zinc Oxide