Sonochemical Synthesis and Properties of YVO₄:Eu³⁺ Nanocrystals for Luminescent Security Ink Applications

Abstract

Solutions and redispersible powders of nanocrystalline, europium-doped YVO4, are prepared via a wet chemical method using the ultrasonic processor (sonochemical) and microwave and thermal stirring. From X-ray diffraction (XRD) results, YVO4:Eu3+ nanoparticles synthesized using sonochemical method have better crystallinity than those prepared using thermal stirring and microwave methods exhibiting the tetragonal structure known for bulk material. From field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results, it is found that the size of nanoparticles is around 25 nm and increasing after annealing at 900°C. From UV-Vis result, there is a peak at 270 nm corresponding to the absorption of VO43− groups. The photoluminescence (PL) results clearly show the strongest red emission peak at the wavelength around 618 nm. The highest luminescent intensity is obtained for the sample prepared by the sonochemical method at pH = 12 and annealing temperature at 900°C for 4 h. The average lifetimes of the Eu3+ ions in the samples annealed at 300, 600, and 900°C for 1 h at 618 nm emission under 275 nm excitation are 0.36, 0.62, and 0.64 ms, whereas sample annealed at 900°C for 4 h has lifetime of 0.70 ms. The security ink, containing synthesized YVO4:Eu3+ nanoparticles, is dispersed in glycerol and other necessary solvents. The experimental security labels are printed by inkjet using the electrohydrodynamic printing technique. The resulting lines represented to the security labels are analyzed by the 3D microscope equipment and UV 20 W mercury lamp with a wavelength of ∼254 nm. The seamless line of the printed security label has the value of the width at ∼230 μm, thickness at ∼0.68 μm, and distance between two adjacent lines at 800 μm. This result is compatible for producing security labels in small size (millimeter) in order to increase security property.

Eu-Doped Pyrochlore Crystal Nano-Powders as Fluorescent Solid for Fingerprint Visualization and for Anti-Counterfeiting Applications

“…In recent years, much attention has been devoted to performing fluorescent inks using nanomaterials. However, as far as we know, no serious attempts have been reported to synthesize these transparent and stable Y 2 Sn 2 O 7 : Eu 3+ colloids for use as fluorescent ink, but the synthesis of stable and transparent luminescent NP colloids in an aqueous medium is a challenging task [ 34 , 35 , 36 ]. We prepared a luminescent aqueous ink for anti-counterfeiting applications.…”

Brilliant Nonlinear Optical Response of Ho3+ and Yb3+ Activated YVO4 Nanophosphor and Its Conjugation with Fe3O4 for Smart Anticounterfeit and Hyperthermia Applications

“…There are reports on the use of nanoparticles for anticounterfeiting applications . Most of the reported anticounterfeiting applications are based on UV light excitation. , However, reports on NIR light excitation based anticounterfeiting applications are very less due to small-sized spots of the laser (1–2 mm in diameter) that it cannot cover larger areas (a few cm in any dimensions), which can be done easily by UV light. , In this work, we overcome this problem using a proper collimator as well as a suitable filter. For its implication, a demonstration has been carried out by dispersing the YVO 4 :Ho 3+ /Yb 3+ nanophosphor into methanol and dispersed particles are used to write letters or numerals over a sheet of paper (shown in Figure ).…”

Enrichment of Crystal Field Modification via Incorporation of Alkali K+ Ions in YVO4:Ho3+/Yb3+ Nanophosphor and Its Hybrid with Superparamagnetic Iron Oxide Nanoparticles for Optical, Advanced Anticounterfeiting, Uranyl Detection, and Hyperthermia Applications

“…Generally, vanadate and molybdate hosts are also used in the upconversion process due to low phonon vibrations possessed by them. Many materials such as rare-earth-doped luminescent nanomaterials, metal–organic frameworks, quantum dots (semiconductor and carbon based), and plasmonic nanomaterials were used as a security ink in anticounterfeit applications for many years. − Recently, Xu et al have reported dual-mode color-tunable Y 2 O 3 :Er 3+ /Yb 3+ for anticounterfeit applications using a UV source. However, UV light is hazardous for the surrounding environment including the persons who are working.…”