What is difference between optical absorption and photoluminescence in terms of application? Both of the spectroscopy of are used in determination of bandgap. So why do we use these two different set ups?
Both ABS and LUM has much more importance than to determine the bandgap! Word contains not only simple semiconductors or simple dielectrics! Even if we test ABS and LUM of the same material we get additional information on structure of bands and relaxation in the conduction band. LUM must be studied obligatorily if we look for new luminescent materials/ And so on and on and on....
Optical aborption is not necessary with presence of photo-luminescence but photo-luminescence needs of absorption: (i) when the energy from the ligth is absorbed, the material can relax the energy through non-radiative paths (i.e. without light emission -> non photo-luminescence). (ii) photo-luminescence can come from electonic energetic level well lower than the absorption gap.
When a sample is too thick, the band gap value obtained from an absorption spectrum may be incorrect. Using photoluminescence (PL) you also cannot get the band-gap value straightforward (see the comment above by Guillaume). In such cases, PL excitation (PLE) spectra could be useful. A PLE spectrum is some kind of combination of both - absorption and PL - spectra.
the PL can provide information on optically active defects, material quality ....
the ABS allow to observe some PL forbidden transition energies
In general these two techniques are rather complementary
Absorption and luminescence are different ways to analyze a sample. The particles /samples having absorption at UV,Vis ,NIR range need not to have fluorescence/Luminescence. Certain molecules only have luminescence not all the absorbing samples.
In practical for absorption we need higher quantity of sample ad for luminescence we need very small quantity
Can any information be taken from the non-radiative processes in PL? Could PL be specifically used to obtain information about these non-radiative processes or are they just side effects?
Why measured band gap energy is different when experimentally determined by PL and absorption?
While both optical absorption and photoluminescence involve the interaction of light with materials, they have distinct differences in terms of their applications.
Optical absorption is primarily used to analyze the absorption properties of materials, identify substances, and determine their concentrations. It is also crucial in fields such as solar cells, coloration, and phototherapy.
Photoluminescence, on the other hand, is used in applications where the emission of light is desired, such as LEDs, display technologies, sensors, and optical imaging. Photoluminescent materials absorb light and re-emit it at longer wavelengths, allowing for the generation of light in various devices and techniques.
Regards
Lemma Tirfie, Ethiopia
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