Abstract
Barium tungstate (BaWO4) powders with various sintering temperatures, and BaWO4:Dy3+ phosphor samples with concentrations of different rare-earth (RE) activator ions (Dy3+, Sm3+, Tb3+) were prepared through co-precipitation. The structural, morphological, and photoluminescent characteristics of barium tungstate phosphors depend on the concentration of RE ions. The crystallographic characteristics of the synthesized BaWO4 were analyzed using X-ray diffraction (XRD) patterns. The size and shape of the crystalline particles were estimated based on images measured with a field emission scanning electron microscope (FE-SEM). As the sintering temperature of the BaWO4 particles increased from 400 °C to 1000 °C, the size of the particles gradually increased and showed a tendency to clump together. In the sample doped with 7 mol % Dy3+ ions, the intensity of all emission bands reached their maximum. The emission spectra of the RE3+-doped BaWO4 powders by excitation at 325 nm were composed of yellow (Dy3+), red (Sm3+), and green (Tb3+) band at 572, 640, and 544 nm. This indicates that most of the RE3+ ions absorbed the position without reversal symmetry in the BaWO4 lattice. These results propose that strong emission intensity and tunable color for the phosphors can be accomplished by rare-earth doped host with an suitable quantity. In addition, the phosphor thin films, having high transparency from aqueous colloidal solutions, were deposited on banknotes, and it is considered whether it is suitable for anti-counterfeiting applications.
Highlights
Rare-earth (RE) ion activated metal tungstates (MXO4, M = Ca, Ba or Sr, X = W or Mo) have excellent luminescence properties as well as high chemical and thermal stability
We showed three colors of RE3+ -doped BaWO4 phosphors—yellow, green, and red—deposited on bank notes to demonstrate the phosphors’ thin films, which can realistically be applied in anti-counterfeiting due to their concealment ability
BaWO4 particles and BaWO4 :RE3+ (RE = Dy, Tb, Sm) phosphors were described with various sintering temperatures and quantities of rare-earth ions via co-precipitation
Summary
Various studies that can be used in broad fields such as solar cells, solid-state lasers, white-light emitting diodes (w-LEDs), and display are being conducted [1,2,3,4,5]. Among these tungstates, tetragonal scheelite-like structure barium tungstate (BaWO4 ) is an encouraging luminescent host material for phosphors, because the WO2−. Representative anti-counterfeiting materials that have recently been in the spotlight include phosphors, organic dyes, and quantum dots.
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