Some articles say they are same but some of them say they are different, I am pretty confused.
This is indeed a confusing subject, especially that depending on the field (photoluminescence, photochemistry, photovoltaics), the definitions may vary.
From the photophysical point of view, one definition is clearly established:
the quantum yield is the ratio of the number of emitted photons to the number of absorbed photons.
This concept can be broadened to accomodate other phenomena (e.g. in photochemistry): number of events/number of absorbed photons
In photoluminescence, the quantum yield reflects the ratio of radiative transitions to the sum of radiative and nonradiative transitions, expressed with the rate constants: k(r)/[k(r)+k(nr)]
A subtle distinction can be made: the above defined quantum yield is sometimes referred to as "internal quantum yield, iQY", whereas the "external quantum yield, eQY" then refers to the number of photons impinging on the sample. This quantity is always smaller (or at most equal) to the internal quantum yield. A compound with high iQY but with low absorbance will have a small eQY
Efficiencies (Greek letter eta) in principle refer to energy, but they are also defined differently (see below):
quantum efficiency = energy output/energy input
It is only equal to the quantum yield if the photoluminescent system is a 2-level system and if there is no nonradiative process.
As for QY, QE can be defined as internal or external. For instance in solar cells:
iQE = number of electrons produced/number of absorbed photons
eQE = number of electrons produced/number of incident photons
The important point when reporting QY or QE data is to always define exactly what is meant.
Hope it helps....
JC
Dear Orhan Kıbrıslı I think in this link you have a quite clear description of both:
https://www.sciencedirect.com/topics/chemistry/quantum-yield
Hope it helps!
The article recommended by Dr. Manuel Gómez thoroughly explains these to concepts. Very good explanation.
Dear manuel gomez,
Thank you for your response. There some explanations on those kind of articles but in my opinion they are not quite clear. I have been reading those before asking the question. I think I might need an explanation from an expert that actually calculates an evaluates both of them.
Some of them says quantum yield is the ratio of absorbed and emitted photons while the quantum efficiency is related with excited electrons by the absorption of photons. In some articles they simply mention from the quantum yield is an equal concept as the quantum efficiency.
This is indeed a confusing subject, especially that depending on the field (photoluminescence, photochemistry, photovoltaics), the definitions may vary.
From the photophysical point of view, one definition is clearly established:
the quantum yield is the ratio of the number of emitted photons to the number of absorbed photons.
This concept can be broadened to accomodate other phenomena (e.g. in photochemistry): number of events/number of absorbed photons
In photoluminescence, the quantum yield reflects the ratio of radiative transitions to the sum of radiative and nonradiative transitions, expressed with the rate constants: k(r)/[k(r)+k(nr)]
A subtle distinction can be made: the above defined quantum yield is sometimes referred to as "internal quantum yield, iQY", whereas the "external quantum yield, eQY" then refers to the number of photons impinging on the sample. This quantity is always smaller (or at most equal) to the internal quantum yield. A compound with high iQY but with low absorbance will have a small eQY
Efficiencies (Greek letter eta) in principle refer to energy, but they are also defined differently (see below):
quantum efficiency = energy output/energy input
It is only equal to the quantum yield if the photoluminescent system is a 2-level system and if there is no nonradiative process.
As for QY, QE can be defined as internal or external. For instance in solar cells:
iQE = number of electrons produced/number of absorbed photons
eQE = number of electrons produced/number of incident photons
The important point when reporting QY or QE data is to always define exactly what is meant.
Hope it helps....
JC
Dear Jean-Claude G Bünzli ,
Thank you for your detailed, clear and helpful answer.
Have a nice one.
I think that the quantum efficiency (η) is the ratio of the measured to the calculated radiative lifetime of the luminesence (fluoresence).
Quantum yield (Φ) of a radiation can be defined by a process of the number of times for a specific event occurs per photon absorbed by the system. is the emission efficiency of a given fluorophore.
(Photons emitted by Photons absorbed)
We have now published a commentary about quantum yield and brightness in the Journal of Luminescence.
There are some errors in the above manuscript which will soon be corrected in the revised paper which replaces the above in J Lumin
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