We will solve this problem using the direct concept related to band gap energy, that is, a band gap is the distance between the valence band of electrons and the conduction band, i. e, the energy range in a solid where no electron states (Electronic state) can exist Mathematically can be described as,
![E_n = (h^2n^2)/(8mcR^2)](https://img.qammunity.org/2021/formulas/physics/college/65kkbuq93jmr2d62i4i3py20vtnbxo39ao.png)
Where,
h = Planck's constant
n = Energy level
mc = Effective mass of the point charge
R = Size of the particle
As you can see the energy is inversely proportional to the size of the particle:
![E_n \propto (1)/(R^2)](https://img.qammunity.org/2021/formulas/physics/college/u69yf6cpzyaw29i1za5u2xebhtuxjzu5cu.png)
Therefore if the size is decreased, the amount of energy is increased.