Enhancing photoluminescence in ZrO2:Eu3+ phosphor Co-doped with mono/di/trivalent ions for flexible displays, advanced data security, and biomedical applications through charge compensation

Red emitting cubic ZrO2:Eu3+ (1–6 mol %) nanophosphors (NPs), emitting red light (1–6 mol %), are co-doped with alkali metal ions (A+ = K+, Na+, Li+), (B2+=Ca2+), (C3+ = Bi3+) using a low-temperature, self-propagating solution combustion method with Alanine as a novel fuel. The optimal concentration is 4 mol % (ZrO2:4 % Eu3+), exhibiting enhanced photoluminescence (PL) intensity in the order Li+ (40 folds) > Na+ (5 folds) > Bi3+ (4 folds)> K+ (3 folds) > Ca2+ (2 folds). ZrO2:4 % Eu3+/Li+ co-doped phosphors display robust red emission, closely matching commercial red phosphors CIE coordinates (0.620, 0.374). This optimized phosphor is applied for latent fingerprints (LFPs) development on various surfaces using a powder dusting approach. In the co-doped samples with Li+, K+, Na+, Ca2+, Bi3+, levels I-II were observed, while Li+ co-doped samples displayed level III ridge features, enhancing personal identification. The developed fingerprinting materials exhibit high sensitivity, resolution, and minimal background interference. Additionally, ZrO2:4 % Eu3+/Li+ NPs and soluble poly (vinyl alcohol) (PVA) are employed to craft transparent anti-counterfeiting (AC) films, showcasing AC properties through intense red emission under UV 365 nm light. Their notable flexibility, durability, and foldability expand the potential applications in AC techniques. These findings highlight ZrO2:4 % Eu3+/Li+ NPs as versatile luminous platforms for displays, high-quality lighting, fingerprinting, anti-counterfeiting, and biomedical applications.