In the present work, luminescent Sr 2 CeO 4 :Eu 3+ (5 mol %), Zn 2+ (0.25–3 mol %) nanophosphors were fabricated by the ultrasound irradiated sonochemical method. The samples prepared with 3 h ultrasound treatment exhibit well crystalline and single phase Sr 2 CeO 4 . The dumbbell shaped morphology of the prepared samples was elucidated from both SEM and TEM results. The energy band gap of the prepared samples was estimated and found to be in the range ∼3.18–3.63 eV. The incorporation of Zn 2+ greatly influences the defect and emission intensities, as revealed from photoluminescence and positron lifetime spectroscopy measurements. The enhancement in the photoluminescence emission intensity after Zn 2+ incorporation was observed, which may be due to the creation of defects and efficient energy transfer between Zn 2+ and Eu 3+ or defects that can act as emission centers. The positron lifetime spectroscopy qualitatively explains the concentration of defects (vacancy and voids) which are induced by Zn 2+ co-doping. The encryption strategies are provided using the photoluminescent chalk for high level information protection. We believe that the versatile, convenient and user-friendly strategy demonstrated herein will open a new insight for on-site information protection.