Luminescence improvement of (Ti,Si)O2:Eu3+/Li+ spherical particles for anti-counterfeiting application

Eu3+-doped TiO2 as a security material was synthesized by spray pyrolysis. The effect of the SiO2 introduction and Li + co-doping on the crystallographic and optical properties of TiO2:Eu3+ were investigated as changing the calcination temperature. TiO2:Eu3+ has an intense peak at 618 nm due to the electrical dipole transition 5D0 -> 7F2 of Eu3+ located in a site without inversion symmetry. The SiO2 introduction suppressed the grain growth of TiO2 and improved the thermal stability of anatase phase. Thus, (Ti,Si)O2:Eu3+ could have a larger band gap while maintaining anatase phase at higher calcination temperature and showed an improved emission of about 38% compared to TiO2:Eu3+. In addition, the co-doping of Li+ with Eu3+ into the (Ti,Si)O2 matrix was found to be an effective way to substantially improve PL intensity due to the charge compensation effect. As a result, (T,Si) O2:Eu3+/Li+ showed about 143% enhanced luminescence intensity compared to TiO2:Eu3+, and was confirmed to have high luminescence under near-ultraviolet light when applied to the logo mark.