As all we know, when the size of a luminescence material is lower than it's bohr exciton radius, it can be excited by radiation of photon and when the carriers recombine, there would be a photoluminescence in a specific wavelength according to that kind of material.
The question is that, in the field of perovskites, if it's three dimensions are larger than it's bohr exciton radius (for instance in the order of 100 to 500nm), can we expect to see photoluminescence?
If the answer is positive, what is the mechanism of this phenomenon?
Dear Nima,
Perovskites are semicondcutor materials having conduction in two bands the valence band by holes and electrons by conduction band. Even if their material size is in the order of 100s of nano meters they will have photo luminescence effect. When they illuminated by photons with proper wavelength to generate electron hole pairs in case of Eph>Eg where Eph is the incident photons energy and Eg is the energygap of the material. The photogenerated electrons and holes will recombine again either radiatively or nonradiatively. In case of radiative recombination emission of photons occur and observed as photo-luminescence.
If the material has direct bandgap the radiative recombination becomes appreciable when one reduces the nonradiative recombination centers in the materials caused by crysatllographic defects in the volume and surface of the materials.
Decreasing the size of the materials to quantum mechanical sizes of nanometers or fractional nanometer the bandgap will increase and the bandgap tends to be direct, if the material is originally indirect bandgap, which enhances the light emission.
Best wishes
Dear Nima,
Perovskites are semicondcutor materials having conduction in two bands the valence band by holes and electrons by conduction band. Even if their material size is in the order of 100s of nano meters they will have photo luminescence effect. When they illuminated by photons with proper wavelength to generate electron hole pairs in case of Eph>Eg where Eph is the incident photons energy and Eg is the energygap of the material. The photogenerated electrons and holes will recombine again either radiatively or nonradiatively. In case of radiative recombination emission of photons occur and observed as photo-luminescence.
If the material has direct bandgap the radiative recombination becomes appreciable when one reduces the nonradiative recombination centers in the materials caused by crysatllographic defects in the volume and surface of the materials.
Decreasing the size of the materials to quantum mechanical sizes of nanometers or fractional nanometer the bandgap will increase and the bandgap tends to be direct, if the material is originally indirect bandgap, which enhances the light emission.
Best wishes
Hello,
At particle sizes below 10 nm, these sizes are counted as critical radius, and the quantization (quantum size effect) (QSE) yields, so, the band gap increases as the particle size decreases, and the band edges shift to obtain a large redox potential, thus improvement in the photocatalytic activity, in spite of the optical absorption peak of this particle shifts toward the blue shift ..........Please, read CH1 in my thesis page 29.
@Abdelhalim Zekry
Thanks Dr. Zekry
But I want to know if there is an upper limit which above that we can't see that phenomenon.
Dear Nima,
In semiconductors the photo luminescence is observed also in large size crystals as the effect which i described in my first comment is still working.
Best wishes
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