Yambo Community Forum

Dear developers:
Now I have some results with yambo about dark exciton.I give a picture to demonstrate it as following,
picture1:
______ bright2
.........dark2

_______bright1
..........dark1

picture2:
.........dark2
______bright2

........dark1
______bright1

In picture1, the dark excitons below the bright ones, we could say the dark ones may give the nonradiative channel which make the luminescence efficiency low.
But in picture2, the dark one are above the bright ones, can we make the same conclusion as the picture1? I thinch maybe the bright2 in picture2 would relax to the dark1 level, so it also quench the luminescence efficiency .
Are my conclusions right above? (the dark ones and the bright ones are seperated by tens meV)
And, if the dark and bright ones are degenerate, what the seperated energy they should have ?
Thanks in advance!!!
Shudong Wang
Department of Physics
Southeast University,Nanjing,China
Email:sd.wang000@gmail.comsdwang

sdwang wrote: In picture1, the dark excitons below the bright ones, we could say the dark ones may give the nonradiative channel which make the luminescence efficiency low.
But in picture2, the dark one are above the bright ones, can we make the same conclusion as the picture1? I thinch maybe the bright2 in picture2 would relax to the dark1 level, so it also quench the luminescence efficiency .
Are my conclusions right above? (the dark ones and the bright ones are seperated by tens meV)
And, if the dark and bright ones are degenerate, what the seperated energy they should have ?

Dear Sdwang, your question regards a physical interpretation that is really hard to base on so few informations. What you suggest COULD be reasonable but how can you estimate the transition probability of one excitonic state in another ? Yambo does not give access to this information and, therefore, your conclusions appear to me too speculative.

If you have found a photoluminescence model that maps the light emission to the excitonic lines (that stricktly speaking can be used only to interpret the absorption) than you can try to better motivate your interpretation.

I am sorry I cannot help more.

Andrea

Hi SD Wang

Why the dark exciton gives the nonradiative channel? Are there any experimental evidence? The relaxation of bright 2 to dark 1 is a dynamical picture, how can we infer it from the static regime?

To YAMBO developer -
The dark exciton means that it does not absorb the photon, right? Can it give additional information?

thanks

sdwang wrote:Dear developers:
Now I have some results with yambo about dark exciton.I give a picture to demonstrate it as following,
picture1:
______ bright2
.........dark2

_______bright1
..........dark1

picture2:
.........dark2
______bright2

........dark1
______bright1

In picture1, the dark excitons below the bright ones, we could say the dark ones may give the nonradiative channel which make the luminescence efficiency low.
But in picture2, the dark one are above the bright ones, can we make the same conclusion as the picture1? I thinch maybe the bright2 in picture2 would relax to the dark1 level, so it also quench the luminescence efficiency .

damao4361556 wrote:To YAMBO developer -
The dark exciton means that it does not absorb the photon, right? Can it give additional information?

Dear Eric
yes, it means that one photon transition is not allowed. Looking at the composition of the exciton in terms of KS transitions, and analysing the KS states involved in such transitions then it is possible to interpret why it is dark with symmetry arguments.
I cannot see any other information that one can extract from the calculations.

Regards,
Myrta