Sunlight-activated Eu2+/Dy3+ doped SrAl2O4 water resistant phosphorescent layer for optical displays and defence applications

Abstract

Herein, we introduce a strategy for the fabrication of a sunlight-activated green luminescent Eu²⁺/Dy³⁺ doped strontium aluminate (Sr_1−x−yAl₂O₄:Eu_x²⁺/Dy_y³⁺) assisted long persistent, transparent, flexible and water resistant phosphorescent layer via a customized solid state reaction-solution casting method. The XRD result of as-synthesized phosphor shows a pure monoclinic crystal structure with the space group P2₁. This as-synthesized phosphor exhibits green afterglow emission with a broad band peaking ∼528 nm upon a broad range of excitation wavelengths from 368–418 nm, which is ascribed to the characteristic 4f⁶5d¹ → 4f⁷ electronic dipole allowed transition of Eu²⁺ ions. Moreover, the role of Dy³⁺ as an auxiliary activator significantly prolongs the afterglow duration to a large extent by increasing the number of electron traps and their trap depths in the vicinity of Eu²⁺. Accordingly, a brighter afterglow intensity with a time more than 5 hours is observed for the optimal concentration of Eu²⁺/Dy³⁺ in Sr_1−x−yAl₂O₄:Eu_x²⁺/Dy_y³⁺, (x = 0.1 and y = 0.2) in the long persistent phosphor. The incorporation of the sunlight-activated as-synthesized Sr_0.7Al₂O₄:Eu_0.1²⁺/Dy_0.2³⁺ phosphor in a commercially available PVC gold medium offers a highly dispersive transparent luminescent paint, which can be used for the spray coating of monuments, as well as for the fabrication of transparent, flexible and water resistant phosphorescent layers. Hence, these striking features of the luminescent paint, as well as the flexible transparent phosphorescent layer could be potentially utilized in optical displays and defence applications.