Investigating the influence of mono-, di-, and trivalent co-dopants (Li+, Na+, K+, Ca2+, Bi3+) on the photoluminescent properties and their prospective role in data security applications for SrAl2O4:Tb3+ nanophosphors synthesized via an eco-friendly combustion method

Nanostructured SrAl2O4:Tb3+/M (M = Li+, Na+, K+, Ca2+, Bi3+) green nanophosphors (NPs) were synthesized through an environmentally friendly combustion process, employing Areca nut (A.N) as a sustainable fuel source. Alkali metal co-dopants were introduced to optimize luminescent intensity and assess their suitability for data security applications. Photoluminescence (PL) intensity increased with rising Tb3+ concentrations (1–5 mol %) until reaching a maximum at 3 mol %, after which quenching occurred. The phenomenon of Tb3+ concentration quenching at 3 mol % was explained using the Van Uitert equation, which accounts for dipole–dipole interactions. To enhance luminescence efficiency, various metal ions, including Li+, Na+, K+, Ca2+, and Bi3+, were explored. Notably, SrAl2O4:Tb3+ (SAO:Tb3+) co-doped with Li+ ions exhibited the highest PL intensity, surpassing that of Tb3+ by a factor of 41. The estimated CIE value for green emission are x = 0.3541 and y = 0.5562. It is observed that the CIE coordinates of Tb3+ activated SAO NPs are situated in the green region. The CCT value of SAO:Tb3+/Li+ was found to be 5117 K, which is useful for cool LEDs. The Li+ doped samples proved exceptionally effective in latent fingerprints (LFPs) detection, revealing level I-III ridge features crucial for personal identification. Under NUV light, the PDMS wrapping of the SAO:Tb3+/Li+ NPs accomplished a green glow. Based on the results, SAO:Tb3+/Li+ green-emitting phosphors is a promising material for white LEDs, optical temperature sensors, and flexible display applications. This comprehensive study underscores the outstanding multifunctional potential of Li+ co-dopants among the various ions considered.