Figure 2

(a) Transmission electron microscope (TEM) image of β−NaGdF₄:Yb,Tm@NaGdF₄ nanoparticles. (b) High-resolution TEM image of β−NaGdF₄:Yb,Tm@NaGdF₄ nanoparticle. (c) TEM images of UCNP–PEG–FA/PC₇₀ (upconversion–nanoparticles–trismethylpyridylporphyrin–fullerene nanocomposite). Inset is enlarged image and the scale bar is 5 nm. (d) X-ray diffraction pattern of as-prepared β-NaGdF₄:Yb,Tm@NaGdF₄ nanoparticles, consistent with the standard pattern of β-NaGdF₄ (JCPDS 06-0342). (e) Optical photographs of UCNP–PEG–FA/PC₇₀ in water, phosphate-buffered saline, fetal bovine serum and Dulbecco’s modified Eagle’s medium respectively: before centrifugation (top) and after centrifugation (bottom). (f) Absorption spectra of UCNP–PEG–FA/PC₇₀, UCNPs, FA and PC₇₀. (g) Upconversion emission spectrum of UCNPs and absorption spectrum of PC₇₀. Inset is the digital luminescence photograph of UCNPs. (h) Upconversion emission spectra of UCNP–PEG–FA solutions treated with PC₇₀ at different concentrations upon 980 nm irradiation (excitation power was 4 W cm⁻²). The concentrations of UCNPs in samples are identical. Inset is a local amplification profile of spectra. (i) Photodegradation of Na₂-ADPA treated with UCNP–PEG–FA/PC₇₀ at different time points due to generation of singlet oxygen upon 980 nm irradiation.