Hi,
My experiment is about the fabrication of ZnO NWs on glass substrate via thermal evaporation method. This experiment involved no dopant and free-catalyst.The excitation energy was 3.39 eV (365 nm). Three samples involved in this work: on-top, 16 cm and 18 cm samples.
I study the optical characterization using PL and UV-Vis analysis. For UV-Vis analysis, the energy band gap obtained (using Tauc plot) is 3.05 eV.
My questions are:
1) For PL analysis, am I suppose to focus on the peak at UV region or the peaks at visible region?Most of papers i referred to, they have been talking about the UV peak (ZnO 3.37 eV). But some said I need to observe and focus on the peak in the visible range.
2) Is it true that the peak at UV region is the result of the excitation energy which i gave to the sample at the beginning of the experiment?
3) Is it correct for me to say the structure of my sample has no defect, if there has no peaks in the visible range but only the highest peak appears at the UV range.
4) If I want to make a comparison on the value of energy band gap from UV-vis with PL analysis, which peak should I observe to obatain the energy band gap?
Thank you in advance....
Hi,
Answers:
1) For PL analysis, am I suppose to focus on the peak at UV region or the peaks at visible region?Most of papers i referred to, they have been talking about the UV peak (ZnO 3.37 eV). But some said I need to observe and focus on the peak in the visible range.
Ans. You have to focus on the UV peak. Visible peaks denotes defects.
2) Is it true that the peak at UV region is the result of the excitation energy which i gave to the sample at the beginning of the experiment?
Ans. No, it results from the "Near band edge (NBE) emission" from ZnO nanowires. It is in 382 nm wavelength, which means Eg = hc/wavelength =1.241x1000/ 382 nm)= 3.24eV which follows 3.37eV for ZnO closely.
3) Is it correct for me to say the structure of my sample has no defect, if there has no peaks in the visible range but only the highest peak appears at the UV range.
Ans. You samples seems to have defects. Defect order is-- On-top
I largely agree with Avishek, but want to add the following:
For #2, it may be near-band emission as he says, but this energy is incredibly close to your excitation energy. You want to double-check that you are not measuring stray excitation light. You can do this using a non-luminescent scatterer instead of a sample (UV-vis reflection standards work for this).
#3: If you observe no visible PL, you have no luminescent defects. There are also defects that give no PL at all, but if you see visible PL, it is defects.
haa...i see,,thank you so much for the answers :)
@avishek @manuel