The laser beam can heat the sample if your experiment takes longer time!
Since the PL intensity highly depends on the sample temperature, there should be further nonradiative decays, and losses on intensity, in some occasions, but not all.
is there any investigation, report or note showing this phenomenon? I guess this is an important point to be noted, but .... I am actually looking for details and any proof showing that "scanning time" can change the results. Isn't it?
I advice you to make 2 experiment for the same sample.
Make exactly the same PL experiments:
i) with short scan time
ii) with long scan time
then try to interprete the difference. This will give you the best answer.
Dear Reza,
I think this depends on the intensity of the laser beam you are using to excite your sample. In general and for semiconductor materials, I feel you do not need such strong intensity laser beams to have a detectable signal.
Moreover, your sample holder should be kept in thermal contact with an heat sink (I usually have a copper sample holder mounted on a cryostat), so that you can keep the temperature stable.
Apart from Emre's suggestion, I could advise you to mount a thermocouple as close as possible to the sample and record the temperature changes vs. the laser intensity and the scanning speed. Keep in mind that by changing the scanning speed you can have other effects (changes in detector response, variation of laser intensity, other spurious effects in the system), so if you find some variation in your data with the scanning speed, the change of sample temperature may not be the only reason.
all the best
Luca
Luca described in great detail how to conduct an experiment to avoid the effect of thermal heating of the sample. Observe these experimental conditions and all will be well.
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