Figure 4.

Size‐dependent properties of quantum dots (QDs) and SPIONs. A) Size‐dependent optical properties of QDs. As the mean diameter of QDs decreases from 10 to 2 nm, emission maxima shift to smaller peak wavelengths (from 655 to 443 nm), resulting in a color change of the emitted light from red to blue. Reproduced with permission.^[43] Copyright 2015, American Chemical Society. B) Splitting of energy levels in quantum dots due to the quantum confinement effect. Bandgap increases with decrease in size of the nanocrystal. Depending on the size of NPs, the bandgap, which is between the highest valence band and the lowest conduction band, fluctuates leading to color shifts from blue to red in the emitted light. Smaller QDs emit blue light, whereas bigger ones red. C) Size‐dependent magnetic properties of SPIONs. The electrons of SPIONs with a mean diameter lower than 20 nm spin in the same direction, while SPIONs with a higher diameter have multiple domains of electrons which spin in opposite directions. Reproduced with permission.^11] Copyright 2010, Massachusetts Medical Society.