Dear

Ramesh

If your transmittance measurement procedure is correct negative value of Reflection should not be meaningless. What is your material? Is it free standing or what is your substrate? Have you done baseline correction properly? Did you consider optical losses in R=1-(A+T) ?

Better measure R with your spectrometer.

If this ( A+T>1 ) was correct, your sample would "produce" energy - more light is transmitted and absorbed than incident. I would consider this to be highly unlikely and rather double-check the setup. It would be interesting to know how you do the measurement, especially for A.

Dear Dr. Ram Prasanth Ramesh,

you can recording the transmittance spectra and then the absorbance spectra, after this you can use the relation R=1-(A+T) to find the reflectance.

I mean not calculate the absorbance or transmittance, but measure these spectra

Respected Sir,Khalid Haneen

I used this formula sir I got negative reflection sir.

positive or negative refractive index appears only in nonlinear regime and it is a sign not a magnitude