Luminescence characteristics and site-occupancy of Eu2+- and Eu3+-doped MgZn2(PO4)2 phosphors

Abstract

Eu²⁺- and Eu³⁺-doped MgZn₂(PO₄)₂ were prepared using the high temperature solid-state reaction method. The excitation spectra in the UV and VUV region, the emission spectra, and the luminescence decay curves of the Eu²⁺ and Eu³⁺ ions were investigated. The crystallographic distributions of the Eu²⁺ and Eu³⁺ sites in MgZn₂(PO₄)₂ lattices are different. MgZn₂(PO₄)₂:Eu²⁺ presents a bluish green luminescence with two distinct emission centers at 450 and 525 nm. MgZn₂(PO₄)₂:Eu³⁺ presents an reddish orange color with luminescence transitions from the ⁵D₀ level of the Eu³⁺ ions. There exist two Eu²⁺-crystallographic sites in MgZn₂(PO₄)₂:Eu²⁺, which occupy both Mg²⁺ and Zn²⁺ sites. However, there is only one Eu³⁺-site in the MgZn₂(PO₄)₂:Eu³⁺ lattices, which was confirmed by site-selective excitation and emission spectroscopy, and the luminescence decay in the ⁵D₀ → ⁷F₀ region of the Eu³⁺ ions under a pulsed, tunable, narrowband dye laser. The Eu³⁺ ion was suggested to occupy the octahedral Mg²⁺-site in the MgZn₂(PO₄)₂ lattices. The spectral characteristics, the temperature-dependent luminescence intensity and activation energies of thermal stabilities and the microstructures were discussed on the basis of the crystal structure and the luminescence results.