microscopy (TEM)
and high-resolution transmission electron microscopy (HR-TEM) images
were collected using a JEM-2100 transmission electron microscope (JEOL,
Ltd., Tokyo, Japan). Proton nuclear magnetic resonance (1H NMR) spectra were measured in dimethyl sulfoxide (DMSO) using an
AVANCE III HD 500 MHz spectrometer (BrukerCorp, Karlsruhe, Germany).
X-ray photoelectron spectroscopy (XPS) was carried out using an Escalab
250Xi X-ray photoelectron spectrometer (Thermo Fisher Scientific Co.,
Ltd., Shanghai, China). The FTIR spectra were collected using a frontier
Fourier transform infrared spectrometer (PerkinElmer Co., Ltd., Waltham,
MA). The UV–vis absorption spectra were recorded using a TU-1950
ultraviolet–visible spectrofluorometer (Persee General Instrument
Co., Ltd., Beijing, China). Photoluminescence (PL) measurements were
carried out using an LS55 fluorescence spectrometer (PerkinElmer Co.,
Ltd.). Fluorescence decay curves were measured using a DeltaFlex modular
fluorescence lifetime instrument (Horiba Jobin Yvon IBH Ltd., Glasgow,
U.K.). PL quantum yields were measured using an FLS1000 fluorescence
spectrometer (Edinburgh Instruments, Ltd., Edinburgh, U.K.). Fluorescence
images were captured using a DMI4000 B inverted fluorescence microscope
(Leica Microsystems Inc., Wetzlar, Germany).