What kind of "spectrum" do you have?  Absorption spectrum?  Transmission spectrum?  Reflection spectrum?

From the absorption spectrum, you will need to use the Kramers-Kroenig relation.  From transmission and reflection you will need to follow standard procedures from ellipsometry.

It is difficult to obtain exact relation between UV-Visible absorption and refractive index of material. In order to find the absorption coefficient Beer-Lambert Law is used.

http://pubs.acs.org/doi/pdf/10.1021/ma00036a008 will help you to connect the refractive index and absorbance of material.

In order to estimate corresponding refractive index with wavelength  Cauchy’s equation will be useful. https://www.quora.com/Whats-the-Relation-between-refractive-index-of-the-medium-and-wave-length-of-the-incident-light-ray

Dear Siva 

you can use the article

Dear Siva ,

you can use the article.

Best regards

Refractive index =speed of light/Velocity of light in medium. U know the light velocity in the. Chosen medium u can easily calculate

You can also use envelope method to find the refractive index from reflection or transmission spectra.

Article Determination of dynamic variations in optical properties of...

Swanepoel method can also be used to find Refractive index using transmittance spectra

Hello,Refractive index of any medium is the calculation of tilting of a any EM waves when it passes from one medium to another.

So formula for RI is n =c/v where c is the speed of light and v is the velocity of EM wave so from the same formula we can calculate the Approximate RI of medium.

Regards,

Sneha

Dear Siva Vadivel,

You can calculate refractive index from UV data by using the equations provided by following articles.

https://doi.org/10.1002/pssb.2220930257.

https://doi.org/10.1016/1350-4495(95)00008-M.

https://doi.org/10.1002/pssb.2221000240

Hello sir,

If you have transmittance data, first you need to calculate the absorption

coefficient (alpha-a)

alpha = 2.303 log (1/T)/t where t-thickness of the sample

then, reflectance(R) in terms of absorption

coefficient (alpha-a)

R = (exp(−at)+(or)-((exp(−at)T -exp(-3at)T+exp(-2at)T2)1/2)/exp(−at)+exp(-2at)T

then

n = (-(R + 1)+(or)- 2R1/2)/R-1

where n is refractive index

I hope this information may help you.

Regards,

Aravind Rudrarapu