Herein, we introduce a strategy for the fabrication of sunlight-activated green luminescent Eu2+/Dy3+ doped strontium aluminate (Sr1-x-yAl2O4: Eux2+/Dyy3+) assisted long persistent, transparent, flexible and water resistant phosphorescent layer via customized solid state reaction-solution cast method. The XRD result of as-synthesized phosphor shows the pure monoclinic crystal structure with space group P21. This as-synthesized phosphor exhibits green afterglow emission with 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, brighter afterglow intensity with longer time more than 5 hours is observed for the optimal concentration of Eu2+/Dy3+ in Sr1-x-yAl2 O4:Eux2+/ Dyy3+, (x=0.1 and y=0.2) long persistent phosphor. The incorporation of sunlight-activated as-synthesized Sr0.7Al2O4:Eu0.12+/Dy0.23+ phosphor in commercial available PVC gold medium offers a highly dispersive transparent luminescent paint, which can be used for spray coating of monuments as well as for the fabrication of transparent, flexible and water resistant phosphorescent layer. Hence, these striking features of luminescent paint as well as flexible transparent phosphorescent layer could be potentially utilized in optical display and defence applications.