Calculating Band Gap Energy When Absorption Spectra Shifts with Concentration?

[![enter image description here](https://i.stack.imgur.com/RKL3e.png)](https://i.stack.imgur.com/RKL3e.png)


I am not a chemist. However, from some experimental work I have been doing, I have found that the intensity of the spectrum changes with dilution, this makes sense. However, when calculating the band gap energy through Tauc's equation for band gap (ie: taking the line of the energy vs $(ahv)^p$ x intercept) will be affected by the dilution. The line of best fit on the energy graph gets less and less sloped resulting in a changing bandgap. A


If the band gap is an intrinsic property of the material, how can this be a trustable method for measuring bandgap if it is affected by concentration?


