Phase and photoluminescence analysis of dual-color emissive Eu3+-doped ZrO2 nanoparticles for advanced security features in anti-counterfeiting

In the present work, lower concentration-based dual-color emissive Eu3+-doped ZrO2 loose nanosized particles have been developed via precipitation method with sodium borohydride for the potential use of advanced security in anti-counterfeiting application. Stabilization of tetragonal zirconia up to moderate temperature has been explored considering lower Eu3+-concentration, particle size, and strain. Different phases of Eu3+-doped zirconia phosphors induce variation in photoluminescence characteristics such as photoluminescence emission, asymmetric ratio i.e. intensity of red to orange emission ratio, Commission International de I'Eclairage i.e. CIE chromaticity coordinates, and color emission. Also, phases of Eu3+-doped zirconia may produce multi-color emission, including white light depending on Eu3+-concentration, calcination temperature, and excitation wavelength. Photoluminescence emission spectra have been investigated at the excitation wavelengths of 254 nm, 365 nm, 393 nm, and 463 nm. Change in the peak position of the transition 5D0 -> 7F2 and 5D0 -> 7F1 in emission spectra indicates the presence of either mixed-phase or tetragonal zirconia polycrystals in Eu3+-doped zirconia samples. It was mainly due to the unlike site symmetry position of Eu3+-ions in different phases of Eu3+doped zirconia. The intensity variation of the transitions in different phases of Eu3+-doped zirconia affects the asymmetric ratio, and thus produces shades of dual color emission, including near-white. In addition, the dualcolor emissive sample, i.e., 0.5 mol% Eu3+-doped ZrO2 nanopowders, has been explored for anti-counterfeiting applications using a standard screen-printing technique.