Persistent luminescence features in hexagonal Sr_1-x/2Al_2-xSi_xO₄:Eu²⁺,Dy³⁺ compounds

Rare earth doped aluminates, such as SrAl₂O₄ :Eu²⁺,Dy³⁺ and CaAl₂O₄ :Eu²⁺,Nd³⁺, are among the best known materials for persistent luminescence or afterglow emission [1]. Numerous studies have been carried out on this strontium aluminate to find different elaboration ways and to elucidate its persistent luminescence mechanism (see for instance [2]). It recently appeared that its hexagonal phase polymorph, which is not stable at room temperature, could have promising properties. A recently efficient way to elaborate the hexagonal Sr_1-x/2Al_1-xSi_xO₄: Eu²⁺,Dy³⁺ phases has been developed by glass crystallization. We report here the optical features of Eu²⁺, Dy³⁺ co-doped Sr_1-x/2Al_1-xSi_xO₄ (0 ≤ × ≤ 0.6) powders elaborated by this method. The experimental results show that the photoluminescence as well as the afterglow emissions shift from green to white/blue range as x increases (see Fig. 1-left). This color change toward the white color is due to two effects: the blue shift of Eu²⁺ broad emission and the appearance of Dy³⁺ emission.