Orange–Red Emitting Sr9Al6O18:Pr3+ Nanophosphors for Advanced Latent Fingerprints and Security Ink.

This study presents the synthesis of orange–red emitting Sr₉Al₆O₁₈:Pr³⁺ nanophosphors (SAO:Pr³⁺ NPs) through the solution combustion process. Photoluminescence (PL) spectra revealed concentration quenching at 5 mol % with a critical distance of R_C = 21.5 Å, indicating that electric multipolar interactions are responsible for the nonradiative energy transfer in the SAO lattice. Dexter's theory confirmed the quadruple–quadruple interaction as the mechanism behind the quenching. The optimized SAO:5Pr³⁺ NPs exhibited exceptional properties, including high color purity (CP = 94.2%), cost-effectiveness, eco-friendliness, scalability, and photostability. A fluorescence-based technique was developed using powder dusting to apply latent fingerprint (LFP) visualization and preservation. This method demonstrated high sensitivity, contrast, and no background interference, enabling the detection of LFPs over extended periods. Furthermore, lip prints (LPs), known for their sex differences and stability, have been effectively utilized for reliable and efficient forensic investigations. An unclonable invisible security ink was developed to combat counterfeiting, exhibiting high stability against UV light, aging, and physical abrasion. Mathematical models were employed for various fingerprint image processing tasks, including segmentation, normalization, ridge orientation estimation, ridge frequency estimation, Gabor filtering, binarization, thinning, and minutiae extraction. These algorithms were implemented by using a Python-based environment, resulting in enhanced fingerprints that displayed level I–II features. These findings underscore the potential applications of SAO:Pr³⁺ NPs in advanced forensic science and data security. This study offers insights into the synthesis, characterization, and application of SAO:Pr³⁺ NPs, highlighting their suitability for advanced forensic investigations, data security, and anticounterfeiting measures. [ABSTRACT FROM AUTHOR]