I have got the enhancement of UV/VIS value (RTPL emission at 380 nm/550 nm) (from 2.2 to 9.5) for sol-gel derived doped zinc oxide thin films. What might be the possible explanations?
There are too few indications to provide a sensitive answer. What is the dopant (I suppose you are observing PL from the dopant)? If the dopant is a metal ion, one explanation might be that chloride is replacing hydroxyl or water molecules, henceforth lowering quenching by these molecules.
Have you recorded excitation spectra of the samples without and with chloride? Are there different?
@Jean-Claude G Bünzli: Dear Sir: I have clearly mentioned that the dopant is anion (Cl-) which may or may not replace lattice O- as it has larger radii than O- . It might also sit @interstitial position I guess.
You are still missing some important details or indicators that I would be looking for. First, was there a temperature cycle as there usually in a doping process. If so was there grain growth or crystallization. CdCl is typically used to promote grain growth in CdS/CdTe solar cells. Both grain growth and crystallization would give higher PL. If there is no temperature cycle then whatever chlorine compound you are using my be getting defects in the ZnO effectively increasing the quality of the material. Finally, you might have a local field effect such as a Poole-Frenkel, if that were present then look at the rate of decay to see if it is different between the two preparation methods. Longer or multiple decay rates would tend to indicate multiple energy transfer mechanisms. Do you know if there is any segregation?
Emission (or absorption) intensity enhancement may not be a good indicator to look for reasons of the role of cl(-) dopant anion.
The intensity may vary with the thickness of the film as well. So i would suggest to see this in terms of quantum yield measurement (if possible) and lifetime measurements would definitely help.
You may follow this paper to look for reasons.
http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.5b01327
Increase in intensity of UV-VIS absorption generally corresponds to the increase in thickness. But increase in absorption width is related to the decrease in band width and vice versa.
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