What is a radiationless transition (in spectroscopy)?

Answer

Hi Tim,

To answer this question, we must first give a small introduction to the structure of the atom. As you know, an atom consists of a nucleus, made up of protons (which are positively charged) and neutrons (which have no charge). A cloud of electrons (which therefore have a negative charge) floats around the positively charged nucleus. Although I speak of a “cloud” of electrons, each electron has a certain energy, which we call quantization (this is the so-called shell model of the atom or Bohr’s model). That means that each electron cannot have any energy, but only a number of certain energy levels. Compare it to a staircase: you cannot have any height relative to the ground, but only a certain number of heights, corresponding to the height of the steps.

Now, when an electron, for example by radiating light, receives a certain amount of energy, it can be brought to a higher energy level. In analogy with the stairs, it then receives the right amount of energy to go up one step. However, this state is not stable, and the electron will go back down one step, again emitting light (or some other form of electromagnetic radiation, of course). We call this process a radiative (radiative = with radiation) transition.

However, certain transitions from a higher to a lower energy level can happen without the release of electromagnetic radiation. We call them radiationless transitions. It is, among others, these transitions that are at the basis of fluorescence or phosphorescence.

We call a very visual and comprehensible representation of such processes Jablonski diagrams, of which there are many examples on the internet. These will no doubt make the difference between radiative and non-radiative transitions even clearer and will also help you understand the concepts of fluorescence and phosphorescence; so be sure to check them out.

Conclusion:
A radiationless transition is a transition of an electron from a higher to a lower energy level without releasing electromagnetic radiation.

Regards,
Benjamin