Surface chemistry modification of core-shell structured SiO2@LaOF:Eu3+/Li+ nanophosphors for advanced forensic applications

Abstract

The fabrication of core–shell structured SiO 2 @LaOF:Eu 3+ , Li + nanophosphors and its surface functionalization with oleic acid (OA) by an ultrasonication route are reported. The X-ray diffraction profiles were well indexed to the tetragonal phase of LaOF. The energy band gap of the prepared samples was found in the range ∼4.32–4.21 eV. The morphological studies evidenced the spherical core–shell structure of the prepared nanophosphors. The photoluminescence emission spectra were found to consist of characteristic emission peaks at ∼591 nm ( 5 D 0 → 7 F 1 ), 610 nm ( 5 D 0 → 7 F 2 ), 651 nm ( 5 D 0 → 7 F 3 ) and 707 nm ( 5 D 0 → 7 F 4 ). The enhancement of about 3 times (3-fold) of the photoluminescence emission in the surface functionalized samples is ascribed as due to the efficient ligand energy transfer. The powder dusting technique was adopted to visualize the latent fingerprints using nanophosphor on several porous and non-porous surfaces under sunlight and ultraviolet (254 nm) light excitation. The developed fingerprints display the high sensitivity, selectivity and contrast by enabling up to two levels of friction ridge details. The above-mentioned results revealed that the surface functionalized core–shell structured nanophosphor can be successfully engaged in the area of solid state display and forensic science applications. • Intense red emitting surface functionalized core–shell SiO 2 @LaOF:Eu 3+ ,Li + nanophosphors via grafting oleic acid. • The 3-fold enhancement in the PL emission upon surface functionalized samples due to efficient ligand energy transfer. • Well defined fluorescence fingerprint images on variety of surfaces by revealing type I-II ridge characteristics. • Developed latent fingerprints shows superior contrast, sensitivity, selectivity and negligible background hindrance. • Fabricated invisible security ink and make it highly suitable for dip-pen mode.