How to get defect-energy level diagram from PL data

I am reading this article [Phys. Chem. Chem. Phys. , 2011, 13, 14902-14905](http://pubs.rsc.org/en/content/articlehtml/2011/cp/c1cp21527b) and seen that the authors have drawn a image of defect level using PL data
![enter image description here](https://i.stack.imgur.com/PmYgG.gif)


Can you explain me how this diagram can be drawn from PL data. And if possible can you explain this using some other simplest PL data.


