I am working with optically active nanomaterials (quantum dots, perovskites), that have pretty large exciton binding energies and can form multiexcitonic complexes, e.g. biexcitons, relatively easily. It has been well established that they also exhibit biexcitonic lasing/ASE under above threshold excitation, so here I have a question.
To have lasing behavior/ASE, stimulated emission process should occur which requires population inversion between upper (biexciton) and lower (exciton) states.
However, in the current literature when this effect is reported for any new material, population inversion requirement is barely ever mentioned and I wonder why. Is it for some reason biexcitonic recombination is a "special" transition, and therefore this requirement is lifted, or population inversion indeed takes place?
If any of these options is correct, could you, please, elaborate why that happens? What is the mechanism lasing or inversion build-up?
Thank you!
