Emission color tuning based on core-shell microcrystals through modulation of laser power for anti-counterfeiting

Manipulating color with lanthanide doped upconversion luminescence materials is an excellent approach for anti-counterfeiting, thanks to their abundant energy levels and convenient NIR-to-VIS luminescence property. However, most of the materials are limited by the single-color emission and low photoluminescence efficiency. Herein, pumping-dependent multicolor upconversion luminescence core-shell microcrystals have been obtained through a facile hydrothermal method . In comparison to nanomaterials , core-shell microcrystals possess a smaller surface area-to-volume ratio and fewer surface defects , leading to enhancing the luminescence. A naked-eye recognizable color can be switched from green to blue with increasing the laser power. Furthermore, the mechanism of tunable color with laser power varying has been systematically studied. Due to emission colors of the core-shell materials with excitation power sensitivity and being distinguished by naked-eye easily, core-shell microcrystals reveal promising applications for anti-counterfeiting.