Fig. 4. (A) The absorbance spectra of UCNP-T in the absence or presence of TCO at different concentrations (inset: photograph of UCNP-T before and after incubation of TCO). (B) The plot of intensity of absorbance at 540 nm with a linear equation. (C) Upconversion luminescence spectra of 20 μM UCNP-T (PBS) with the gradual addition of TCO. (D) Plots of UCL540/UCL650 of UCNP-T versus different concentrations of TCO.
