Structure and photoluminescence studies on europium- and manganese-substituted eulytite-type orthophosphate phosphors

Abstract

A family of eulytite-type orthophosphate phosphors with formula Ba₃La(PO₄)₃:Eu²⁺,Mn²⁺ (BLaP:Eu²⁺,Mn²⁺) were studied by using a combination of Rietveld powder structure refinement and photoluminescence. The crystal structure of the obtained phosphors was refined using a split-atom model, where the oxygen atoms are distributed over several partially occupied sites. The Rietveld refinement analysis confirm that the BLaP:0.005Eu²⁺,0.06Mn²⁺ phosphor crystallizes in a cubic system (space group I3d, no. 220) with unit cell parameters: a = b = c = 10.4817 Å and Z = 4. The La³⁺/Ba²⁺/Eu²⁺/Mn²⁺ cations are disordered on a single site with the special Wyckoff position (16c), while the oxygen anions occupy the general Wyckoff position (48e) and two oxygen atom sites were identified in the crystal structure. According to the luminescence spectra and fluorescence decay curves, we confirm that the energy transfer process from the Eu²⁺ to Mn²⁺ ions takes place in the BLaP:Eu²⁺,Mn²⁺ phosphors system. The possible energy transfer mechanism was proposed in terms of the experimental results and analysis. In addition, the relationship between the red shift of Mn²⁺ emission and its doping concentration was studied as well. Utilizing the red shift of Mn²⁺ emission and the energy transfer from Eu²⁺ to Mn²⁺, the emission colors can be tuned from yellowish-green through yellow, orange, and ultimately to reddish-orange by appropriately adjusting the Mn²⁺ concentration.