Dear Samiyah Alghamdi

Peace be upon you,

You are very welcome,

Have a nice day and good times

To calculate the optical band gap of your samples, you should estimate firstly the absorption coefficient by using the transmission and reflection spectra.

Experimentally, the absorption coefficient (α) can be calculated  from this simple relation:

α = 1/t  ln [(1-R)2 / T]

where t  is the sample thickness, T and R are the transmission and  reflection.But if you don't have T and R and you have Absorbance, then:

absorption coefficient  (α) = 2.303 A / t 

where (A) is absorbance  and (t) is thickness of thin film.

The appended papers may help you; they are examples of direct and indirect allowed transitions.

You can also go througth my RG page to get more information may help you.

Regards and Good luck

Your,

Ahmed Saeed Hassanien

https://www.researchgate.net/publication/283338024_Effect_of_Se_addition_on_optical_and_electrical_properties_of_chalcogenide_CdSSe_thin_films

https://www.researchgate.net/publication/281495242_Influence_of_composition_on_optical_and_dispersion_parameters_of_thermally_evaporated_non-crystalline_Cd50_S50-xSex_thin_films

https://www.researchgate.net/publication/304150361_Study_of_optical_properties_of_thermally_evaporated_ZnSe_thin_films_annealed_at_different_pulsed_laser_powers

Absorption coefficient= 2.303A/ thickness of the film

Dear Samiyah,

Absorbance:

x(λ) = exp(-αd)

Absorption coeff.:

α=1/d ln (((1-R)^2+((1-R)^4+4R^2T^2)^(1/2))/(2T))

or in simplified form:

α=1/d ln (((1-R)^2)/T)

If the incident intensity is I then I = A + R + T, while for the absorption part the intensity is impacted by the abruption coefficient as an exponential factor that is multiplied by the thickness.

Dear Samiyah Alghamdi

Peace be upon you,

You are very welcome,

Have a nice day and good times

To calculate the optical band gap of your samples, you should estimate firstly the absorption coefficient by using the transmission and reflection spectra.

Experimentally, the absorption coefficient (α) can be calculated  from this simple relation:

α = 1/t  ln [(1-R)2 / T]

where t  is the sample thickness, T and R are the transmission and  reflection.But if you don't have T and R and you have Absorbance, then:

absorption coefficient  (α) = 2.303 A / t 

where (A) is absorbance  and (t) is thickness of thin film.

The appended papers may help you; they are examples of direct and indirect allowed transitions.

You can also go througth my RG page to get more information may help you.

Regards and Good luck

Your,

Ahmed Saeed Hassanien

https://www.researchgate.net/publication/283338024_Effect_of_Se_addition_on_optical_and_electrical_properties_of_chalcogenide_CdSSe_thin_films

https://www.researchgate.net/publication/281495242_Influence_of_composition_on_optical_and_dispersion_parameters_of_thermally_evaporated_non-crystalline_Cd50_S50-xSex_thin_films

https://www.researchgate.net/publication/304150361_Study_of_optical_properties_of_thermally_evaporated_ZnSe_thin_films_annealed_at_different_pulsed_laser_powers

In thin films interference occurs - you must not use the Beer-Lambert law in this case, since absorbance changes non-linearly with thickness... it even can become smaller with increasing thickness. See for yourself:

Article The electric field standing wave effect in infrared transfle...

Article The Electric Field Standing Wave Effect in Infrared Transmis...

Article Removing interference-based effects from the infrared transf...

"Apparent absorption coefficient" would fit perfectly to "apparent absorbance"! In any way, since the absorption coefficient is not really a material specific parameter, it is no longer clear for me if it is of any particular use to know it ... see e.g.Article Beer's law derived from electromagnetic theory

I think the main problem with the complex indices of refraction (and their imaginary part) is that they are seen equivalent to the complex dielectric function. In isotropic scalar and homogenous media this is the case, as Maxwell's wave equation then tells us that eps = n2. If the film consists of matrix and inclusions or is anisotropic, this concept immediately breaks down, and the dielectric function tensor is the material property whereas for every direction of the wave inside the film two different absorption coefficients exist. The relation between R (reflectance), T (transmittance), A (absorptance, not absorbance), thickness, angle of incidence and polarization of the incident wave then become very complex, also depending on the substrate and if it is itself absorbing and/or anisotropic etc... this is then definitely far outside the bounds where one can use non-Maxwellian concepts like absorbance and the Beer-Lambert law...

📷

t: thin film thickness. α: Absorption coefficient is measured in units(cm-1)

α=2.303 A /t

A:Absorption

Kawther Ali Before you add something to a thread, please read the previous answers. Your answer is correct only under preconditions which are usually not fulfilled.

α=1/d ln (1/T) when transmission data is given

T is transmission,d is thickness of film ,α is absorption coefficient

Chandra Kumar Srivastava ... and the next contestant... here is some literature for you to be better prepared next time: Article The Bouguer-Beer-Lambert Law: Shining Light on the Obscure

Thanku very much dear Thomas Mayerhöfer , I will read this article

Absorption coefficient is inversely related to the thickness of the films.

M N H Liton Of course not! The absorption coefficient has the unit of an inverse length, but at least in the formulation of the Beer-Lambert law it is independent of the pathlength. To what it is inversely related is the index of refraction...

@Thomas Mayerhofer

My answer based on the following relation. α=1/d ln (1/T) when transmission data is given

T is transmission,d is thickness of film ,α is absorption coefficient.

Yes I know it may not be satisfied in all conditions.