Two-mode upconversion color-tuning of Er:NaYbF4 nanocrystals and their high-efficiency photothermal conversion

Abstract

Color-tunable upconverting luminescence of lanthanide nanomaterials is attractive in many application fields. To date, the available strategies towards real-time color-tuning are still limited. Herein, we reveal a relatively universal technique to release orthogonal emission with different colors at a single nanocrystal level. Using Er:NaYbF₄@NaLuF₄ core-shell nanocrystals as an example, besides their traditional excitation power-induced color tuning, green/red-dominant emission is activated accordingly by short/long pulse excitation. The key for this time-domain color-tuning is the evidently varied population rate and number of lanthanide activators. In addition, the efficient photothermal conversion of the formed core-shell nanocrystals is proven, and their possible laser ablation application is demonstrated. The Er:NaYbF₄@NaLuF₄ core-shell nanocrystals, with color-tunable luminescence, small particle size, high photothermal conversion efficiency, and effective laser ablation ability, are highly promising for non-invasive cancer diagnosis and treatment.