I am having trouble any signal from my 60-90nm thick ZnO films. I am not using chopper/lock-in amplifier. We are getting a signal if we put a piece of paper in place of sample, a broad spectrum is observed. We also see a sharp peak of HeCd laser line but nothing from the sample at even low temp of around 20K. Any suggestion will be appreciated.
The laser wavelength is 325nm and the excitation power is 50mW. I appreciate your help Dr. Gnatenko.
The laser wavelength and the excitation power are sufficient to excite the photoluminescence of ZnO films. And so the problem can be caused with the measurement metodology or with the quality of the investigated films. You see a sharp peak of HeCd laser line if you put a piece of paper in place of the sample. Do you see the laser line from the sample?
Yes we do observe laser line from the sample as well. Our samples seems high quality from X-ray diffraction. We observe a sharp peak of ZnO(002) from XRD.
I see only one explanation: usually ZnO shows significant quantum confinement effect when its size reaches the Bohr radius (1.8 nm). In a paper, which is attached, it was found the photoluminescence at 3.98 eV for a particle size of 1.7 nm. If you have realized this situation, the energy of a laser (3.81), which you use, is not sufficient to excite the photoluminescence of such ZnO nanoparticles.
Thank you very much Dr. Gnatenko. This does make sense. Let me analyze the particle size of my films.
I agree with Prof Yuriy, but Baseer sir have you also tried LT PL for slightly higher thicknesses (like 200-300nm), that may give you the rough idea about whether the measurement or the sample is having any issues ?
papers (tissue papers) emits blue light when it is excited by UV light with very high intensity. it is dangerous for PL spectra of ZnO. If the sample signal is low and there are very few lint of the tissue papers with your sample, then you will get emission in blue region.
Thank you Saptarshi, We were not using papers with the ZnO samples. To see if we get any signal, we were using paper separately to see any kind of spectra.
That I understand sir that you have used the papers separately. But, as a precaution I have mentioned that point because we face the problem for a long time before identifying this problem
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