Paper AS-ThP7
Structure, Surface Analysis, Photoluminescent Properties and Decay Characteristics of Tb³⁺-Eu³⁺ Co-Activated Sr₂MgSi₂O₇ Phosphor

Thursday, October 22, 2015, 6:00 pm, Room Hall 3

Strontium magnesium silicate (Sr₂MgSi₂O₇) is an alkaline earth silicate that belongs to a group of natural minerals of the melilites group called sorosilicates. Sorosilicates have the same basic crystal structure and they can be represented by a general formula A₂MT₂O₇ (A = Ca, Sr, Na; M = Mg; and T = Si, Al, B)¹. They usually crystalize in a tetragonal structure with a space group P42₁m. Due to their tetragonal crystal structure without an inversion center, lanthanides or transition metals can be incorporated easily as activators or dopants in melilite hosts². Due to this ease of incorporation, melilites are today widely used as host lattices for rare-earth dopant and transitional metal ions to prepare light emitting materials or phosphors that can be used in many practical applications such as flat panel displays, light emitting diodes, solar cells and many other types of light emitting devices. In this study, we investigated the structure, chemical and electronic states, ionic and atomic distribution and photoluminescent properties of Sr₂MgSi₂O₇ single doped with Eu³⁺ or Tb³⁺ or co-doped with Eu³⁺ and Tb³⁺ by a solid-state reaction method. It turned out that the emission color could be tuned from blue to green or white depending on the dopant concentrations and the excitation wavelength.

The structure, stretching vibrations, chemical and electronic states, and photoluminescent properties were studied using X-ray powder diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Time-of-flight secondary ion mass spectrometer (TOF-SIMS) and Photoluminescence (PL) spectroscopy respectively. The XRD pattern of the Sr₂MgSi₂O₇:Eu³⁺, Tb³⁺ phosphor resemble the standard tetragonal phase of Sr₂MgSi₂O₇. The fitted XPS data demonstrated that there were two different Sr²⁺ sites in the host lattice and a site occupied by Mg⁺ cations which connects the Sr⁺ sites with the Si⁺ ions. The TOF-SIMS results demonstrated localization and distribution of various ions within the host lattice (Sr₂MgSiO₇) including the Tb³⁺ and Eu³⁺ dopants. The photoluminescence data indicated that the emission colour could be tuned from blue-green depending on the concentration of Tb³⁺. The white photoluminescence was observed from the Tb³⁺-Eu³⁺ co-activated system. This tunable emission has potential application in solid state lighting like white and multicolor light emitting diodes (LEDs).

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