During the past few decades, lanthanide-doped
luminescent nanomaterials
have been widely applied in many fields, such as display devices,
white light-emitting diodes (WLEDs), lasers, data storage, development
of latent fingerprints, and anticounterfeiting. Herein, we report
the synthesis of Bi0.95–x
Gd
x
Eu0.05PO4 solid solutions
through a co-precipitation method and their potential for anticounterfeit
tags. The prepared samples show excellent photoluminescence properties
and emit orange-red, yellowish-green, and fuchsia colors under 254,
365, and 394 nm UV illumination, respectively. Furthermore, the replacement
of Bi3+ ions with Gd3+ in Bi0.95Eu0.05PO4 enhances the luminescent intensity due to
energy transfer from Gd3+ to Eu3+ ions. Optimum
luminescence properties are observed in the Bi0.50Gd0.45Eu0.05PO4 sample, and it is used
for anticounterfeiting applications on various surfaces. The security
patterns are printed on black paper and aluminum foil using luminescent
ink containing Bi0.50Gd0.45Eu0.05PO4 nanomaterials. In addition, anticounterfeiting letters
are directly written on different colored surfaces such as wood, black
plastic, white plastic, and a colored plastic card. These security
patterns/letters exhibit different colors under different UV irradiation
wavelengths and are clearly visible with high contrast and sensitivity.
These patterns are stable under various humidity and temperature conditions.
The intensity of these patterns/letters remains unchanged under these
conditions. From systematic investigations of the optical properties
and stabilities, it has been proposed that the Bi0.50Gd0.45Eu0.05PO4 nanomaterials have the
potential for unclonable anticounterfeiting tags to protect valuable
documents/goods from counterfeiters.
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