This Tutorial provides a fundamental discussion on the lattice dynamics of physical systems introduced with disorder and, hence, the importance of Raman spectroscopy (RS) technique to probe these impacts. The article first discusses, analytically, the impact of disorder on the symmetry allowed phonon modes of the system by considering the finite probability of discrete-continuum interference in terms of electron–phonon interactions in the system, thereby briefly discussing the relevant experimental reports, followed by providing an ephemeral description on the loss of translational symmetry in the lattice environment under the strain field generated due to disorder and its consequence as relaxation of the $\overrightarrow{q}=0$ selection rule in terms of RS; thus, correlating these discussions with the observation of the symmetry-forbidden disorder induced phonon modes. The same is also elaborated with the experimental reports on various systems of ABO₃ and AO₂ kinds, where A and B are cations that exhibit the occurrence of disorder induced phonon modes in the respective Raman spectra because of the disorder introduced into the host lattice, and which is emphasized to be not originating due to any structural phase transitions.

We demonstrate a methodology for quantitative estimation of electron-phonon coupling (EPC) for each phonon mode taking base from second-order correction in polaron-energy resulting bandgap renormalization of the semiconductor by treating EPC as perturbation. This gives coupling constant (${\alpha }_p$) for the $p\mathrm{th}$ phonon mode in terms of phonon energy and renormalized bandgap due to EPC. These theoretical inferences are experimentally explored using combination of optical absorption and Raman spectroscopies for $\mathrm{\Gamma }$ phonons of temperature-varied GaN and ${\mathrm{TiO}}_2$; results reveal a systematic enhancement in ${\alpha }_p$ with temperature that exhibits unique percent variation of ${\alpha }_p$ for each mode. A higher percent change is observed for the mode known to exhibit greater coupling strength, thereby supporting the theoretical discussions. In this paper, we provide a simpler method to directly probe quantum level phonon-specific interactions with electrons, otherwise probed with much advanced techniques.