The interaction between photons and electrons in a substance is governed by the principles of quantum mechanics. According to quantum mechanics, electrons in an atom can only occupy certain discrete energy levels. When a photon interacts with an electron, the energy of the photon must match the energy difference between the electron's initial and final energy levels for the interaction to occur.
The energy of a photon is directly proportional to its frequency, and since the speed of light is constant, it is inversely proportional to its wavelength. Different energy levels in an atom correspond to specific discrete energies, and thus, only photons with energies matching those energy differences can be absorbed or emitted by the electrons.
This phenomenon is known as quantization of energy levels. Electrons can transition between energy levels by absorbing a photon with the right energy to move to a higher level or by emitting a photon with the energy corresponding to the energy difference between levels while moving to a lower energy level.
Therefore, only photons with specific wavelengths (and hence specific energies) can interact with electrons in a substance, causing transitions between energy levels. Photons with wavelengths that do not match the energy differences between the electron's energy levels will not be absorbed or interact with the electrons in a significant way.
This behavior explains why certain wavelengths of light can affect electrons in a substance, while others do not. The specific wavelengths that can interact with the electrons depend on the energy level structure of the atom or material. This concept is fundamental to various phenomena, such as absorption, emission, and scattering of light, which form the basis for many applications in spectroscopy, laser technology, and other fields.