Fig. 7. UC luminescence spectra of NaGdF₄:18% Yb³⁺,2%Er³⁺@NaYF₄ core/shell particles in the with different concentrations of Dox. (a) 20 μg mL⁻¹; (b) 50 μg mL⁻¹; (c) 70 μg mL⁻¹; (d) 100 μg mL⁻¹ at 980 nm-excitation under different laser powers.