Intense red-emitting core-active shell SiO2@CaAl2O4:Eu3+ surface sensitive fluorescent probe for dactylography applications

Rational design and synthesis of hierarchical core-shell structures have been regarded as an operative approach to enhancing the luminescence performance of the phosphors. In this work, intense red-emitting CaAl2O4:Eu3+(1–9 mol %) nanophosphors and SiO2@CaAl2O4:Eu3+(7 mol %) structures were fabricated by the ultrasound-assisted sonochemical route. The powdered x-ray diffraction studies of prepared core-shell structure confirm the monoclinic phase of the CaAl2O4 layer and amorphous SiO2 cores. The morphological and elemental analysis clearly evidences the formation of spherical and uniform core-shell structures. Upon 463 nm excitation, the photoluminescence emission spectra of CaAl2O4:Eu3+(1–9 mol %) nanophosphors consist intensive and sharp peaks at ∼ 507, 532, 551, 615, 654, 702 and 759 nm, owing to 5D1→7F2, 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3, 5D0→7F4 and 5D0→7F5 transitions of Eu3+ ions, respectively. Almost 1.6-fold enhancement in the emission intensity without any change in the spectral shape was noticed in core-shell SiO2@CaAl2O4:Eu3+(7 mol %) structures as compared to CaAl2O4:Eu3+ (7 mol %) nanophosphor, which attributed to the improved surface area, diminished surface defects and surface hanging bonds. The photometric properties signify the pure red emission of the structures and are useful for multi-functional applications. The prepared spherical and uniform-sized core-shell structures are used as fluorescent labeling material for the visualization of latent fingerprints on various surfaces. The fingerprints developed using prepared structures show excellent contrast, high sensitivity, and negligible background disruption. This work demonstrated that the synthesized core-shell structures are a versatile material and can find their practical applications in solid-state lighting and dactylography.