Monday, 22 January 2018

Role of other phases in shifting the absorption peak

It is quite interesting where to take a shift of the absorption peaks corresponding to single phase of materials in view of their coexistence with other valid phases. The question is, whether the peaks corresponding to each phase co exist or get modified and shifted to a new value wherein it compromises with two phases? In our recent research on synthesis of Silver nanoparticles from Bread Mold extract, we could get a co existence of zero valent silver nanoparticles and traces of silver oxides. In xrd pattern intense peaks corresponding to both phases were observed. In FTIR pattern as well the metallic oxide phases could identify. Usually, we know that peaks around 410 to 430  nm are observed for zero valent silver nanoparticles which varies slightly as a function of size whereas for silver oxides, at 250 nm. But, in our case we couldn't get the respective peaks even after repetitive attempts, but shifted to a new position which is sought to be compromised with two phases at 373 and 273 nm. What should one say about this interesting peak shift? In my understanding, the possible explanation is sought to the modifications of  energy levels of one phase with other phase. In fact, for a particular phase, say zero valent silver, the other phase, silver oxide, remains continued as impurity phase and vice versa. This would cause accommodative modifications in individual energy level positions of both the species. The compromised position of this accomodation imparts further absorption to occur among some of these modified new levels in accordance with selection rules. Even though chemically of the same composition, depending on the intrisic variations in one to one impurity phases, this modified accommodative positions would further spread, owing to additional absorption peaks as noted by 273 nm apart from one at 373 nm. Still one observed at 228 nm is aslo sought under the purview of this explanation. In presence of the formation of these modified accommodative levels, the absorptions corresponding to individual phase levels of each species get quenched off and as a result of this we shall be observing the peculiar pattern of absorption in uv-visible range.

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