Luminescent materials with dual-mode excitation and tunable emission color for anti-counterfeiting applications

GdVO4-based dual-mode phosphors were successfully synthesized via a hydrothermal approach. The X-ray diffraction analysis determined the tetragonal structure as well as I4(1)/amd space group of products by comparing with a reference pattern no. ICDD #01-072-0277. The morphology of yielded phosphors was confirmed by transmission electron microscopy and scanning electron microscopy. Detailed spectroscopy analysis revealed tunable luminescence properties with an increasing Yb3+ content in series of GdVO4: x% Yb3+, y% Tm3+, 5% Eu3+ (x = 5, 10, 15, 20; y = 0.1, 0.5, 1) phosphors. For Yb3+, Tm3+, and Eu3+- codoped phosphors we observed bands related to the (1)G(4) & RARR; H-3(6) and (1)G(4) & RARR; F-3(4) transitions of Tm3+ ions, occurred through the cooperative up-conversion mechanism, where two nearby Yb3+ ions were involved in near-infrared absorption. Moreover, the GdVO4: 20% Yb3+, 0.5% Tm3+, 5% Eu3+ showed the most outstanding color tunability from red color (x = 0.6338, y = 0.3172) under UV to blue color (x = 0.2640, y = 0.1988) under NIR excitation, which can be applied in anti-counterfeiting activity.