Design of Bi-functional composite core–shell SiO2@ ZnAl2O4: Eu3+ array as a fluorescent sensors for selective and sensitive latent fingerprints visualization protocol

Abstract

Core–shell SiO2@ZnAl2O4:Eu3+ (5 mol%) nanophosphor (NP) with coatings up to the level IV has been pre- 37 pared by a facile solvothermal route, followed by heat treatment. Scanning electron microscopy studies of 38 fabricated core–shell particles displays good spherical shape and non-agglomeration with a narrow size 39 distribution. The thickness of the shell increased with increase in coating cycles. Photoluminescence (PL) 40 studies exhibited strong red emission peaks at 612 nm corresponding to the 5Do? 41 7F2 transition of the Eu3+ ions. PL intensity increased with calcination temperature and coating cycles. The color coordinates 42 of the coated NP were turned towards intense pure red emission with color purity 95%. Powder dusting 43 method was used to visualize latent fingerprints (LFPs) by staining uncoated and coated NP on various 44 porous and non-porous surfaces under UV light. It was clear that core–shell NP display high sensitivity, 45 reproducibility, selectivity, reliability, and can obtain the complete three levels of friction ridge details. 46 Judd–Ofelt (J-O) intensity parameters and radiative properties, namely transition probabilities, radiative 47 lifetimes, branching ratios, and quantum efficiency were evaluated. The aforementioned results estab- 48 lished that the SiO2@ZnAl2O4:Eu3+ (5 mol%) NP can be used as an ideal candidate for multifunctional 49 applications such as WLEDs, LFPs, anticounterfeiting etc.