Enhancement of Luminescence Efficiency of Y2O3 Nanophosphor via Core/Shell Structure

Abstract

We successfully fabricated Y₂O₃:RE³⁺ (RE = Eu, Tb, and Dy) core and core-shell nanophosphors by the molten salt method and sol-gel processes with Y₂O₃ core size of the order of 100~150 nm. The structural and morphological studies of the RE³⁺-doped Y₂O₃ nanophosphors are analyzed by using XRD, SEM and TEM techniques, respectively. The concentration and annealing temperature dependent structural and luminescence characteristics were studied for Y₂O₃:RE³⁺ core and core-shell nanophosphors. It is observed that the XRD peaks became narrower as annealing temperature increased in the core-shell nanophosphor. This indicates that annealing at higher temperature improves the crystallinity which in turn enhances the average crystallite size. The emission intensity and quantum yield of the Eu³⁺-doped Y₂O₃ core and core-shell nanoparticles increased significantly when annealing temperature is varied from 450 to 550 °C. No considerable variation was noticed in the case of Y₂O₃:Tb³⁺ and Y₂O₃:Dy³⁺ core and core-shell nanophosphors.

Keywords: RE ions; Y2O3 nanophosphor; core–shell structure; luminescence efficiency; quantum yield.

Figure 1

Schematic diagram of the structure of RE-doped (a) active core and (b) active core@passive shell.

Figure 2

XRD patterns of the RE-doped Y₂O₃ for different annealing temperatures at 450, 500, 550 °C. (a) 0.05 mM of Eu³⁺-doped Y₂O₃ core, (b) 0.05 mM of Tb³⁺-doped Y₂O₃ core and (c) 0.05 mM of Dy³⁺-doped Y₂O₃ core, and (d) FWHM of RE (Eu, Tb and Dy)-doped Y₂O₃ at 450, 500, 550 °C.

Figure 3

SEM and TEM images (a) Y₂O₃ NP core sintered at 550℃ for 3 h, (b) Eu-doped Y₂O₃ NP active core with a passive Y₂O₃ shell, (c) Tb-doped Y₂O₃ NP active core with a passive Y₂O₃ shell, (d) Dy-doped Y₂O₃ NP active core with a passive Y₂O₃ shell. The inset TEM images show the coating thickness of each sample.

Figure 4

Luminescence spectra of (a) 0.05 mMol% Eu:Y₂O_3, (b) 0.05 mMol% Tb:Y₂O_3,, and (c) 0.05 mMol% Dy:Y₂O₃ nanophosphors.

Figure 5

(a) Variation of emission intensity with annealing temperature at 450, 500, 550 °C, (b) Variation of emission intensity with concentration at 0.05, 0.10, 0.15, 0.20 mMol%, (c) Variation of quantum yield with annealing temperature at 450, 500, 550 °C, and (d) Variation of quantum yield with concentration at 0.05, 0.10, 0.15, 0.20 mMol% in RE³⁺ (Eu, Tb, Dy)-doped nanophosphors.

Figure 6

XRD patterns of the RE-doped Y₂O₃ core coated with Y₂O₃ passive shell via different annealing temperatures at 450, 500, 550 °C. (a) An amount of 0.05 mM of Eu³⁺-doped Y₂O₃ core with a Y₂O₃ passive shell, (b) 0.05 mM of Tb³⁺-doped Y₂O₃ core with a Y₂O₃ passive shell and (c) 0.05 mM of Dy³⁺-doped Y₂O₃ core with a Y₂O₃ passive shell, and (d) FWHM of RE (Eu, Tb and Dy)-doped Y₂O₃ core with a Y₂O₃ passive shell at 450, 500, 550 °C.

Figure 7

Relative luminescence spectra of the RE-doped Y₂O₃ core and Y₂O₃ passive shell-coated Y₂O₃:RE core. (a) Relative luminescence spectra of 0.10 mM of Eu³⁺-doped Y₂O₃ core and Y₂O₃:Eu@Y₂O₃, (b) relative luminescence spectra of 0.05 mM of Tb³⁺-doped Y₂O₃ core and Y₂O₃:Tb@Y₂O₃, (c) relative luminescence spectra of 0.05 mM of Dy³⁺-doped Y₂O₃ core and Y₂O₃:Dy@ Y₂O₃. All the core samples were annealed at 550 °C for 3 h and passive shells were annealed at 750 °C for 3 h.

Figure 8

Relative quantum yield spectra of the RE-doped Y₂O₃ core and Y₂O₃ passive shell-coated Y₂O₃:RE core. (a) Relative quantum yield of 0.10 mM of Eu³⁺-doped Y₂O₃ core and Y₂O₃:Eu@Y₂O₃, (b) relative quantum yield of 0.05 mM of Tb³⁺-doped Y₂O₃ core and Y₂O₃:Tb@ Y₂O₃, (c) relative quantum yield of 0.05 mM of Dy³⁺-doped Y₂O₃ core and Y₂O₃:Dy@ Y₂O₃. All the core samples were annealed at 550 °C for 3 h and passive shells were annealed at 750 °C for 3 h.