Upconversion luminescence reversible modulation of photochromic NaYF₄: Yb, Er @N-TiO₂ core-shell structures toward dual-field anti-counterfeiting

Upconversion luminescent materials exhibit significant potential for optical storage and anti-counterfeiting applications. However, conventional upconversion-encoded materials lack dynamic control over optical states and color modulation, particularly in both visible and NIR modes. Herein, we propose that combining an excellent upconversion luminescent material with photochromic materials provides an efficient strategy for developing a wider variety of photochromic luminescent systems. Novel NaYF₄: Yb, Er @N-TiO₂ core-shell structures were designed to integrate upconversion luminescence and photochromic properties. The core-shell structures exhibit distinct photochromic behavior, demonstrating reversible color changes from white to dark blue under 365 nm irradiation. Using reversible photochromism, the upconversion luminescence intensity can be modulated reversibly with a maximum luminescence modulation rate of 83.4 %. We demonstrated the utility of dual-field stimulus-responsive anti-counterfeiting labels and light-printing applications, where both color and luminescence intensity are recovered via laser thermal treatment. This work establishes a new strategy for designing advanced functional materials for high-security anti-counterfeiting and dynamic information display technologies.