Dissertation > Mathematical sciences and chemical > Physics > Solid State Physics > Solid nature of the > Optical Properties

Synthesis and Optical Property of White Luminescence of Dy3+ Ions Doped 12CaO·7Al2O3 Nanopowders Under UV Light Excitation

Author ZhuHanCheng
Tutor LiuYuXue
School Northeast Normal University
Course Condensed Matter Physics
Keywords 12CaO·7Al2O3 Dy3+ LED white luminescence fluorescence enhancement
CLC O482.3
Type Master's thesis
Year 2011
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The objective of this work was to develop a kind of phosphors, which is trivalent dysprosium (Dy3+)-doped 12CaO·7Al2O3 phosphors for white luminescence under ultraviolet light excitation. In this thesis, analysis had been made about the relationships of composition, structure and optical properties of Dy3+-doped 12CaO·7Al2O3 (12CaO·7Al2O3:Dy3+) phosphors, which were synthesized by the chemical co-precipitation method. The microstructure of 12CaO·7Al2O3:Dy3+ phosphors was investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectra (FTIR), while the optical properties of 12CaO·7Al2O3:Dy3+ were characterized by photoluminescence, photoluminescence excitation, the temperature dependent luminescence, and so on.The XRD study revealed that the cage structural polycrystalline 12CaO·7Al2O3 powders of single cubic phase were obtained. It demonstrated that Dy3+ had been incorporated into 12CaO·7Al2O3 lattice site without destroying the lattice structure. The FE-SEM micrographs show that the surface topography of 12CaO·7Al2O3:Dy3+ annealed in vacuum ambient was spherical shape and covered a narrow distribution of particle sizes.The emission spectra show two dominant emission bands in the blue region and yellow region, one was attributed to the magnetic dipole transition of 4F9/2→6H15/2 centered at 484 nm, the other was forced electric dipole transition of 4F9/2→6H13/2 centered at 575 nm, respectively, were observed. There is also a weak red emission band at 659 nm from 4F9/2→6H11/2 transition. The 4F9/2→6H13/2 is a hypersensitive transition, which is strongly influenced by the surrounding environment around the Dy3+ ion. In general, 4F9/2→6H13/2 transition is prominent when Dy3+ ions are located at low-symmetry sites with no inversion center, whereas the 4F9/2→6H15/2 transition is stronger when Dy3+ is located at high symmetry sites with an inversion center. The blue emission (4F9/2→6H15/2) is stronger than the yellow emission, which indicates that the Dy3+ ions occupy a high-symmetry site with inversion symmetry in this matrix.The spectrum consists of many excitation bands of f-f transitions, which are originated from different transitions from the ground state 6H15/2 to the various excited states of 4f9 electronic configurations of the Dy3+ ions. The abundant excitation peaks in the 300–420 nm range implies that the Dy3+ ions can be efficiently excited by the near-UV (350–400 nm) LEDs. This is of promise for the white-light emissions in practical application.According to the field emission scanning electron microscopy micrographs and the FT-IR spectra, the enhanced emission intensities of 12CaO·7Al2O3:Dy3+ annealed in vacuum ambient could be ascribed to the decrease of OH- groups and the change in the surface topography.All the results indicate that Dy3+-doped 12CaO·7Al2O3 phosphor may be a good candidate for emissive display technology, the solid state lighting phosphor, white LEDs, and so on.

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