Effect of pH on nanoparticle synthesis. Nanoparticle formation ratio (NFR) (solid line, left) and apoferritin concentration in supernatant (broken line, right) at various pHs for (a) Y, (b) Eu, and (c) Tb. NFR was calculated by dividing the number of holoferritin molecules by the total number of protein molecules in TEM images. Initial protein concentration was 0.1 mg/ml in each case.
TEM images of Y nanoparticles synthesized at pH 7.0. The samples were either (a) negatively stained by Nano-W or (b) left unstained. The insets in (b) are HRTEM images of amorphous (left) and crystal (right) nanoparticles. Selected area electron diffraction pattern of Y nanoparticles is shown in (c). The lattice spacing obtained from (c) was 0.307 nm for (1) and 0.189 nm for (2). These d-spacings correspond well to the Y2O3 lattice spacings of 0.306 and 0.187 nm for Miller indices (222) and (440), respectively.
EDX spectra of (a) Y and (b) Y:Eu nanoparticles. The spectra were obtained from (a) a single nanoparticle and (b) an area of 4 × 4 μm. Specific peaks were detected for Y Lα, Kα, and Eu Mα, Lα, and Lβ. Cu peaks originate from the specimen grid, while Si and C peaks originate from the supporting carbon film.
Size distribution of Y nanoparticles in apoferritin (N = 810). The average nanoparticle diameter was 5.7 ± 0.9 nm.
Excitation spectra of (a) Y:Eu nanoparticles and (b) bulk Y(OH)3:Eu at an emission wavelength of 614 nm. Eu molar content was 57% in both cases. Inset shows the expanded region from 280 to 400 nm.
Emission spectra of (a) Eu and Y:Eu nanoparticles, and (b) bulk Eu(OH)3 and Y(OH)3:Eu at an excitation wavelength of 396 nm.
Emission peak intensities at 614 nm for various Eu3+ contents of Y:Eu nanoparticles (green triangles) and bulk Y(OH)3:Eu (open red circles) at 396 nm excitation. The peak intensities at 610 nm emission (excitation 248 nm) of sintered Y:Eu nanoparticles were also plotted (closed orange circles). The peak intensities are normalized with the highest peak of each sample.
Emission spectra of sintered Eu, Y:Eu nanoparticles, (a) and bulk sample (b) at an excitation wavelength of 248 and 251 nm, respectively.
Excitation spectra of (a) Y:Tb nanoparticles and (b) bulk Y(OH)3:Tb at an emission wavelength of 544 nm. Tb molar content was 41% in both cases. Inset shows the expanded region from 270 to 420 nm.
Emission spectra of Tb and Y:Tb nanoparticles at 237 nm excitation.
The peak intensities for varying Tb3+ content. Circles show emission peaks at 544 nm from Y:Tb nanoparticles (excitation: 237 nm) and squares show emission peaks at 542 nm from sintered samples (excitation: 275 nm). The peak intensities are normalized with the highest peak of each sample.
Emission spectra of sintered Tb and Y:Tb nanoparticles at 275 nm excitation.
Initial dopant concentration at synthesis and resultant Eu and Tb molar contents of the nanoparticle.
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