Photoinduced Absorption Spetcroscopy

[mtrl]

I am studying on the electrical properties of organic compounds and having a problem with photoinduced absorption spectroscopy applied to these materials. Because in all the books, articles, etc , information given is on the results of applying this method. However i need to learn what PIA exactly is, what happens in terms of charge carriers when an organic compound is excited during PIA...

For example, the following picture is from an article that I am reading.

I do not even know what the variable on the vertical axis stands for.

Can someone please advice me a source which supplies information on the theory of PIA and similar studies applied to organics?

 

[BigJDubs]

Photoinduced absorption spectroscopy (PIA) is a technique used to study the optical properties of organic materials. It is based on the principle that when light of a specific energy is shone onto a material, it will absorb some of the energy and cause a change in its optical properties. The amount of energy absorbed depends on the material's electronic structure. By measuring the amount of energy absorbed at different wavelengths, it is possible to gain insight into the material's electronic structure. A good source of information on the theory of PIA and related studies applied to organic materials is the book "Organic Photochemistry" by Jean-Marie Lehn. This book covers the principles of photochemistry, with detailed explanations of the various processes involved in organic photochemistry. It also provides a comprehensive overview of the applications of photoinduced absorption spectroscopy in organic materials, and discusses the effects of light on various classes of organic materials.