Anti-counterfeiting applications by photochromism induced modulation of reversible upconversion luminescence in TiO₂: Yb3+,Er3+ ceramic

Photochromism-induced reversible upconversion luminescence modulation has received extension attention due to its promising applications in anti-counterfeiting, optical storage, and switches. In this work, photochromic TiO₂:Yb³⁺,Er³⁺ ceramics were prepared by a high temperature solid state method. The white TiO₂:Yb³⁺,Er³⁺ ceramics turn to pink-gray color under 405 nm LED illumination for 27 min, and the color of the photochromic sample was restored to the primitive state after 808 nm laser irradiation for 170 s. The photochromic mechanism of TiO₂:Yb³⁺,Er³⁺ ceramics is related to the formation of Ti³⁺ defects and oxygen vacancy caused by Yb³⁺ and Er³⁺ codoping. The cycle measurements between alternate irradiation of 405 nm and 808 nm light stimulation show the good reversibility between photochromic and bleaching processes. Under 980 nm excitation, the upconversion luminescence properties of photochromic TiO₂:Yb³⁺,Er³⁺ ceramics were investigated, exhibiting excellent reproducibility for the photochromism-induced upconversion luminescence modification. The application of TiO₂:Yb³⁺,Er³⁺ ceramics as an anti-counterfeiting agent was designed, and the results reveal the potential application of TiO₂:Yb³⁺,Er³⁺ ceramics in the anti-counterfeiting field.