Electron confinement or quantum confinement is another process that occurs in nanoparticles. We know that when atoms are isolated, then their energy levels are discrete but when they are in packed form and in large numbers (in solid form), the energy levels split and form bands (band means group of levels). Nanoparticles represents intermediate stage.
As we have discussed the problem of particle in a box that when the dimensions of such box is of the order of the de Broglie wavelength of electrons or mean free path of the electrons, then the energy levels of the electrons change. This process is called electron confinement or quantum confinement. This process results from the electrons and holes being squeezed into a dimension that approaches a critical quantum measurement known as excit or Bohr radius. It can affect the electrical, magnetic and optical properties of nanoparticles.