Thermal‐responsive multicolor emission of single NaGdF <sub>4</sub> :Yb/Ce/Ho upconversion nanocrystals for anticounterfeiting application
Yanqing Hu, Qiyue Shao, Xinyi Deng, Jianqing Jiang
Abstract
Abstract This study presents a novel and high‐level anticounterfeiting strategy based on Ce/Yb/Ho triply‐doped NaGdF 4 nanocrystals with temperature‐responsive multicolor emission. A critical factor leading to the multicolor emission is confirmed by comparing the luminescence thermal behaviors of nanocrystals in various atmospheres. Through analyzing the temperature‐dependent lifetimes of Yb 3+ ions in air, we demonstrate that thermally‐induced multicolor emission mainly originates from the gradually‐attenuated H 2 O quenching effect. Because the cross‐relaxations between Ce 3+ and Ho 3+ ions and the nonradiative transitions of Yb 3+ ions create plenty of phonon heat, the multicolor emission of nanocrystals can be achieved under 975 nm excitation at a relatively low power density. This recognition method is efficient and convenient for security authentication. The as‐synthesized core nanocrystals can be directly used to fabricate anticounterfeiting ink without further processing (e.g. core/shell or hybrid). Therefore, the small‐sized β‐NaGdF 4 :Yb/Ce/Ho nanocrystals are promising candidate for security application.