I'm working on CuInS2 ternary compound. Material synthesized using solid state melt growth method is confirmed by XRD and it has only CIS phase but still DRS results taken for CIS powder having very low absorbance near 300 nm.
if the defect structure is different - which is already known for the selenides (Cu(In,Ga)Se2 - the band gap changes, e.g. copper vacancies or displacements of sulfur could influence the electronic structure, just check positions and occupation of the elements
The line of my answer is in the same direction of the last answer from Dr. Anke Köhler.
The optical properties of a material (the way photons interact with electrons) are governed by the electrical band structure. It depends if we are dealing with a metal or a semiconductor/insulator. Let's focus on the semiconductors. Considering a perfect crystal structure, a specific semiconductor will possess a band gap between the valence and the conduction band. This semiconductor will only interact with photons with energy bellow the band gap. The magnitude of the band gap depend on the elements composing the material and the crystal structure. How can you tune the band gap? One possibility is by tuning the crystal structure introducing stress/strain in the lattice. Another option is to introducing localized states within the band gap. Here we have different alternatives to proceed. We can intentionally (or not) introduced dopants in the semiconductor structure (that explain why some diamonds are colored). Other way is by the introduction of punctual defects (that is more difficult to accomplish!).
Anyway ... dealing with the same material in different scales (thin films and nanoparticles) prepared by different routes ... it is quite reasonable that you will have the material's structure with different stress/strain and, may be, you can have different contaminants, and, what is more probably, different density of specific defects between one sample to another. That explain the different optical properties!
That is all!
Can I ask what is the size range of these powders?
A classic example of this is Gold, a thin film of gold and gold nano-particle behave differently when it come to interaction with EM.
Absorption of light in semiconductors depend on band gap of semiconductor. For absorption to take place, energy of photons must be more than band gap. The band gap of powder and film may be different. You can check it experimentally.May be you get the answer of your question. If your band gap comes out to be same then you can think in terms of different defects in two cases. These defects may introduce different localized states in the energy gap which may result in different absorption spectrum.
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction