Question

What are the significances of optical absorption plots? Which information we can get from absorption vs energy plots for materials?

What does it mean if the intensity of the absorption peak changes?

What does it mean if the whole absorption spectrum shifts for similar other materials?

What does it mean if there are multiple peaks for absorption?

Please explain in details (starting from its basic ideas) with some relevant diagrams or plots.

Answer 1

Optical absorption spectrum provides essential information on the electronic structures of semiconductors. It is used to calculate Band Gap Of a material.

The peak position change may be because of  the actual frequency shift of a single absorption band or alternatively by the relative intensity changes of overlapped bands.

It means that their atomic spectra is a bit different.. The production of linespectra  by the atoms of elements indicate that an atom can radiate only a certain amount of energy.

Generally speaking, it is probably the result of having muliple allowed transitions from the ground state to the excited state of the molecule in your sample.
This could arise from either an impure sample (multiple types of molecules in a sample, all with different ground and excited states) or the inherent properties of the molecule in question.