Further, the carrier concentration during the application of electrochemical potential was also estimated using equation 2,3. Even though Drude model was initially developed for metals, by including the effective mass of the carrier and accounting for the background polarizability of undoped semiconductor, this can be extended to calculate the plasmon frequency of semiconductors and thereby estimate the changes in N (See Section 11 in SI). During the CV, N varied from 2.57 x 10 21 cm -3 at OCP to a maximum of 2.91 x 10 21 cm -3 (anodic Even though, spectroelectrochemistry experiment demonstrate the plasmon modulation, its solution phase nature limits the structural characterisation during the redox process. To supplement our investigation with structural characterisation, we adopted chemical redox treatment and did powder XRD on the treated samples. Similar treatment has been widely used to tune the plasmons in copper chalcogenide nanocrystals. Rachkov et al have done a systematic estimation on the structural transformation of Cu 3-x P in similar redox condition. In the present case, redox reagents were added to a solution of Cu 3-x P in THF.