There is some confusion in the literature with the various definitions used by scientists.

Referring more specifically to lanthanide luminescent compounds the emission of which is sensitized by the metal-ion surroundings, extrinsic or overall, or external quantum yield is the quantum yield that you get when exciting into the surroundings (i.e. the ligand of coordination compounds). Intrinsic or internal quantum yield is the quantum yield measured upon direct excitation of the metal ion.

I have been using "overall" and "intrinsic" quantum yields for a long time but now I think that "external" and "internal" quantum yields are more explicit.

The external quantum yield is at most equal to the internal quantum yield (when the energy transfer process is 100% efficient); it is usually smaller. The ratio between the external quantum yield and the internal quantum yield is the so-called sensitization efficiency.

Dear Peter Kapusta,

I also believe that the above question is too basic to be answered by a great scholar like you. But I am sorry for your answer. The link provided by you doesn't give the answer of my question. Please go through with the question once again.

Thanks for your suggestion. Certainly I will try to improve. However, I am more curious to know how you will answer this question to your student. I am not merely asking the definition/formulae given on wikipedia. Certainly the depth of answer depends on the knowledge one can have.

There is some confusion in the literature with the various definitions used by scientists.

Referring more specifically to lanthanide luminescent compounds the emission of which is sensitized by the metal-ion surroundings, extrinsic or overall, or external quantum yield is the quantum yield that you get when exciting into the surroundings (i.e. the ligand of coordination compounds). Intrinsic or internal quantum yield is the quantum yield measured upon direct excitation of the metal ion.

I have been using "overall" and "intrinsic" quantum yields for a long time but now I think that "external" and "internal" quantum yields are more explicit.

The external quantum yield is at most equal to the internal quantum yield (when the energy transfer process is 100% efficient); it is usually smaller. The ratio between the external quantum yield and the internal quantum yield is the so-called sensitization efficiency.

Dear@Peter Kapusta,

https://en.wikipedia.org/wiki/Quant...iciency#Types_of_quantum_efficiency

Such type of link anybody can search on following link very easily

https://www.google.co.in/?gfe_rd=cr&ei=u7klWM7GBa_v8wf4l4KYAQ&gws_rd=ssl

If anyone is asking something on some forum like RG means he/she wants key concept, clarification and good literature from expert in that field. If anyone is interested can give answer on that forum, it depends on his/her choice completely.

We should not waste time by giving sarcastic comment and diverting the true answer of anybody's doubt and query.

Dear  Peter Kapusta

I think there are some misunderstood on this question. Before I go to the field of Solid state lighting based on LED, I am also in the same case with Chandresh. The concept of QE or other related concept is different a little bit. So I hope you can understand for Chandresh. I think it really is not like what you thinked. 

Thank you for your understanding with my comment.

My best regards

Quang-Khoi Nguyen

Dear Chandresh

I have check your profile and i saw your field is relate to lighting field . So I want to share some more information. I hope my information can help you

LEDs are semiconductor devices that emit light via the recombination of electrons and holes within the active region (a sequence

of specially designed layers) of the device. Most of these recombination events are termed “radiative” because they result in the

production of a photon of light.

The wavelength of the emitted light is determined by the bandgap of the active region ­ a wider bandgap results in higher energy

emission, which equates to a shorter wavelength.

In turn, the bandgap is determined by the chemical composition and sequence of the semiconductor layers within the active region.

External Quantum Efficiency (EQE)

The ratio of the number of photons emitted from the LED to the number of electrons passing through the device ­ in other words,

how efficiently the device coverts electrons to photons and allows them to escape.

EQE = [Injection efficiency] x [Internal quantum efficiency] x [Extraction efficiency]

Injection Efficiency

In order that they can undergo electron­hole recombination to produce photons, the electrons passing through the device

have to be injected into the active region. Injection efficiency is the proportion of electrons passing through the device that are

injected into the active region

Internal Quantum Efficiency (IQE ­ also termed Radiative Efficiency)

Not all electron­hole recombinations are radiative. IQE is the proportion of all electron­hole recombinations in the active region

that are radiative, producing photons.

Extraction Efficiency (also termed Optical Efficiency)

Once the photons are produced within the semiconductor device, they have to escape from the crystal in order to produce a

light­emitting effect. Extraction efficiency is the proportion of photons generated in the active region that escape from the

device.

**********

Wall­Plug Efficiency (also termed Radiant Efficiency)

Wall­plug efficiency is the ratio of the radiant flux (i.e the total radiometric optical output power of the device, measured in watts)

and the electrical input power i.e the efficiency of converting electrical to optical power.

Wall­Plug Efficiency = [EQE] x [Feeding efficiency]

Feeding Efficiency

Each electron­hole pair acquires a certain amount of energy from the power source when the LED is operating. Feeding

efficiency is the ratio of the mean energy of the photons emitted and the total energy that an electron­hole pair acquires from

the power source.

@Khoi Quang Nguyen: Nice copy and paste from:

http://www.ledsmagazine.com/articles/2004/01/terminology-led-efficiency.html

It doesn't seem that you've indicated your source.  Did you write the article for LEDS magazine?  If not this is pure plagiarism and thus unethical.

together with the spelling mistake: converts -> coverts in the original

The term quantum yield = quantum efficiency may refer to different processes because it is employed in chemical kinetics, photochemistry and in spectroscopy, for example, and for different devices such as electroluminescent and photoluminescent materials. The definition given in the Gold Book is therefore quite general: http://goldbook.iupac.org/Q04991.html. Certainly, as mentioned by Prof. Bunzli, there may be some confusion or vagueness in some areas. For example, he refers to "direct excitation of the metal ion" but this does not specify an excitation wavelength or target energy level and these are also variables. Hence when using this term in a publication it is necessary to be rigorous in its definition.

Dear Chandresh Kumar Rastogi,

Please check the lectures of Pr. Buonassisi (MIT) in the link below to find the answer to your question :

https://ocw.mit.edu/courses/mechanical-engineering/2-627-fundamentals-of-photovoltaics-fall-2013/lecture-videos-slides/MIT2_627F13_lec07.pdf

Best wishes.