Calcium Tungstate Doped with Rare Earth Ions Synthesized at Low Temperatures for Photoactive Composite and Anti-Counterfeiting Applications

Soung-Soo Yi,Jae-Yong Jung

doi:10.3390/cryst11101214

Abstract

A precursor was prepared using a co-precipitation method to synthesize crystalline calcium tungstate. The prepared precursor was dried in an oven at 80 °C for 18 h. The dried powders, prepared without a heat treatment process, were observed in XRD analysis to be a crystalline CaWO4 phase, confirming that the synthesis of crystalline CaWO4 is possible even at low temperature. To use this crystalline CaWO4 as a light emitting material, rare earth ions were added when preparing the precursor. The CaWO4 powders doped with terbium (Tb3+) and europium (Eu3+) ions, respectively, were also observed to be crystalline in XRD analysis. The luminescence of the undoped CaWO4 sample exhibited a wide range of 300~600 nm and blue emission with a central peak of 420 nm. The Tb3+-doped sample showed green light emission at 488, 545, 585, and 620 nm, and the Eu3+-doped sample showed red light emission at 592, 614, 651, and 699 nm. Blue, green, and red CaWO4 powders with various luminescence properties were mixed with glass powder and heat-treated at 600 °C to fabricate a blue luminescent PiG disk. In addition, a flexible green and red light-emitting composite was prepared by mixing it with a silicone-based polymer. An anti-counterfeiting application was prepared by using the phosphor in an ink, which could not be identified with the naked eye but can be identified under UV light.

Highlights

IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
The crystallinity and structure of CaWO4 :Tb3+ and CaWO4 :Eu3+ powder doped with rare earth ions were confirmed in the same manner as pure CaWO4
The lattice spacing of the rare earth doped CaWO4 :Tb3+ (0.298 nm) and CaWO4 :Eu3+ (0.279 nm) were increased. This is thought to be the result of doping with rare earth ions with relatively when the doped rare earth ions were calculated using a single unit cell of CaWO4, it was large ionic radii (r(Tb3+ ) = 0.92 Å, r(Eu3+ ) = 0.95 Å) in19 the CaWO4 lattice calculated that the doped amount was about 1.59 × 10 RE atoms/cm3 (RE = Tb3+, Eu3+)

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. CaWO4, Phurangr et al prepared 0.005 mole of calcium nitrate (Ca(NO3)2) and sodium tungstate (Na2WO4·2H2O) and dissolved them in 15 mL of ethylene glycol This solution was put in an autoclave and heated for 20 min using a microwave (600 W), and studies on and dissolved them chemical in 15 mLbond of ethylene glycol. A precursor was prepared by co-precipitation with calcium nitrate and sodium tungstate and drying at 80 ◦°C to synthesize crystalline CaWO4 white powder. It sodium tungstate and drying at 80 C to synthesize crystalline CaWO white powder It can be potentially used as a light emitting material by doping with rare4earth ions such as can be potentially used as a light 3+. Cannot be observed with the naked eye and can only be confirmed using UV light

Crystalline CaWO44 Synthesized

Characterization

Fabrication of Photoactive Composite and Anti-Counterfeiting Application

Structural and Morphology

Chemical States and Phtoluminescence Proeprties

Conclusions