What is the major difference between optical band gap and photonic band gap?
Optical band gap has the same units as that of energy band gap while photonic band gap is the range of forbidden frequencies in a material. How is the optical band gap related to energy band gap and in what way does it differ from photonic band gap?
Optical band gap is the same as material band gap. In materials the electrons are distributed inside bands of energy separated by energy gaps. If the last occupied band is only half occupied (metal) then the electrons of this band can absorb any photon with energy between 0 and a few eVs. If the last band is fully occupied (insulators and semiconductors) then the electrons can only be promoted on the next band at higher energy and that can only be done by photons having an energy at least equal to that of the band gap that separates the last occupied electron band from the next.
The Photonic band gap corresponds to the reflection of light by a periodic object which period is equal to half the wavelength of the light that falls onto it. It is the result of an interference of the various wavelets that are reflected by the periodic individual elements of the object. No light is absorbed in the process. The wavelengths not matching the periodicity of the object just do pass through the object.
Typically optical band gap refers to material properties (optical band gap is related to the threshold for photons to be absorbed in a particular homogenous material), while photonic band gap refers to engineered structures with periodic spatial distributions of different materials (such as disallowed bands of wavelengths in photonics crystals).
http://en.wikipedia.org/wiki/Band_gap
http://en.wikipedia.org/wiki/Photonic_crystal
Energy levels of atoms splits to form a band of energies when comes close to each other to make a solid. Energy difference between successive energy levels in a band is so small that electric field is able to move electrons from one level to other nearby level provided it is empty. However, there may be a situation where the highest energy band is completely filled and next empty band starts at much higher energy as compared to filled band. Electric field itself can not move electrons from this filled band called valence band to next empty band called conduction band at zero K. This energy difference between maxima of valence band and the minima of conduction band is called electronic gap or band gap. When light is incident on such a system, light can not take a electron from valence band to conduction band unless photon energy is equal to or more than band gap. This energy at which electron and hole pair is generated is called optical gap above which light will be absorbed and hence a sharp absorption edge will be observed. In case of photonic crystals we have alternate nano structures of two different dielectric materials which has forbidden energy for photons as semiconducting lattices has energy gap for electrons.
It are the identical terms. But do not confuse it with semiconductor bang gap.
Optical band gap is the same as material band gap. In materials the electrons are distributed inside bands of energy separated by energy gaps. If the last occupied band is only half occupied (metal) then the electrons of this band can absorb any photon with energy between 0 and a few eVs. If the last band is fully occupied (insulators and semiconductors) then the electrons can only be promoted on the next band at higher energy and that can only be done by photons having an energy at least equal to that of the band gap that separates the last occupied electron band from the next.
The Photonic band gap corresponds to the reflection of light by a periodic object which period is equal to half the wavelength of the light that falls onto it. It is the result of an interference of the various wavelets that are reflected by the periodic individual elements of the object. No light is absorbed in the process. The wavelengths not matching the periodicity of the object just do pass through the object.
I agree with Lin Zhang:-). Alexander S. Solntsev gives the main points and Charles Hirlimann presents the good reasons. No more words are needed!
It is very important to observe in the Photonic band gap that :
"No light is absorbed in the process" is just a reflection of light by a periodic object.
It is very interesting to observe it in a laboratory ... !!
This question touches upon two concepts: the electron energy band gaps and photonic band gaps. The optical band gap is related to the spectrum of the light absorbed by electrons in natural materials, so it reflects the electron band gaps. There is not any electron state located in band gaps. . The photonic band or band gaps exist in photonic crystals (metamaterials). The photonic band gaps do not allow the electromagnetic waves to travel in the photonic crystal with the frequencies located in the gaps. As the light energy is related to its frequency, no matter the photonic band gaps or optical band gaps, the units can be energy dimension or frequency dimension, and can be transformed mutually by Plank-Einstein relationship
In order to determine optical band gap using UV-Vis, one must use transmission mode and photonic using reflectance?
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