I have prepared nanoparticles using laser ablation method. I have used 2nd harmonic beam, and prepared four different samples in de-ionized water by changing laser energy (60, 120, 180 and 240 mJ) . I kept the time constant i.e 40 min.
I have observed that the PL and Raman peaks increases when the laser energy was 120mJ then peaks intensity decreases at 180mJ laser energy and then again increases at 240 mJ. What is the reason behind it?
I have read that the intensity increases due to the increase in particle size
However in my case the particle size increases with the increase of laser energy.
The peaks intensities are increasing randomly
Laser ablation produces nanoparticles of different shapes and with a wide distribution in size. You get random nanoparticles. Therefore, you have random spectra. In order to obtain the intensity dependence on the size, you should investigate, for example, nanopyramids of different sizes.
Increase and decrease in Raman Intensity is related to a particular mode of vibration which appears in a specific bond which shows that that specific Raman active mode related to specific raman intensity is active. Sometimes Raman active modes Diminish and IR active modes become active (Visible in FTIR) This peak intensity fall and rise shows supresing and dominating bond which is being formed at that specific energy. What do I feel 240= 120*2 which shows that material needs n*120 mJ of energy to form that specific bond which appears in Raman peak. Now talking about PL rise in PL intensity is related to radiative recombination of excitons in semiconductors which shows that n* 120 mJ favours the formation of such nanoparticles which are luminiscent in the energy range of PL excitation source. i.e such material can be a good emmitter ( Usually LED's, Bio markers in imaging, Gain Medium) in that incident energy range (i.e. laser energy of PL excitation source)
Hello
I agree with Mr. Yuri Mirgorod. So I think you must consider the marked side of your substrate to repeat your experiment again and again with the same substrate and different powers. In this experiment temperature has a key role. You must control the temperature of laser in Raman spectroscopy because the more the temperature, the more the intensity. Then, control key is in your hand and you can obtain very good spectra.
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