Structure, valence change, and optical properties of BaMgSiO4:Eu phosphor

Abstract Optical properties of stuffed tridymite green color phosphor BaMgSiO4:Eu (BMSO:Eu) are systematic investigated in view of the structure, different synthetic atmosphere and ultraviolet (UV) stimulation. Three different Ba2+ sites are existed in equal amounts within the lattice, and considering the different ion radius between Ba2+, Mg2+, Si4+ and Eu2+/3+, dopants would be only replaced Ba2+ sites due to other sites are too small to accommodate the large Eu2+/3+. The assignments of emission bands to different Ba2+ sites are carried out according to the values of bond valence. BMSO:EuR synthesized under reducing atmosphere shows long-lasting phosphorescence (~1.2 h) while BMSO:EuA exhibits short phosphorescence (~5 min) calcined in air condition due to different concentrations of oxygen vacancies located in the vicinity of photogenerated Eu3+ cations. Photoionization of Eu2+ to Eu3+ in BMSO:EuR after UV irradiation is confirmed, and the photogenerated Eu3+ cannot change back spontaneously to Eu2+ at room temperature. The self-reduction of Eu3+ to Eu2+ is also observed for BMSO:EuA via a substitution defect model. Altogether, the green emission of BMSO:EuA and long afterglow of BMSO:EuR indicates that this kind of phosphors have numerous potential applications, such as in white light emitting diodes (wLEDs), bioimaging and other related fields.