Characterization. High-resolution transmission electron microscopy (HR-TEM) images were collected using an FEI Tecnai G2 F20 ST FE-TEM operated at an accelerating voltage of 200 kV. Absorbance and PL spectra were collected on an Ocean Optics Flame-S-UV-Vis spectrometer with an Ocean Optics DH-2000-BAL deuterium and halogen lamp as the light source. Powder X-ray diffraction (XRD) measurements were performed using a Bruker-AXS D8 Advanced Bragg-Brentano diffractometer with a Cu Kα radiation source (λ = 1.5418 Å).