Improved pH performance of cresol red radiochromic dye for spectroscopic investigations

Optical properties of a synthetic dye cresol red (CR) were investigated at its absorption band maxima (${\lambda }_{\max }$) using double beam scanning UV/VIS spectrophotometer for the sample solutions having initial optimized dye-concentration. Urbach Edge method was utilized for the investigations of absorption edge ($A_E=$ 2.35 eV) while Mott and Davis model was utilized for the investigations of band gap energy for direct ($E_{g,\mathrm{direct}}=$ 2.45 eV) and indirect ($E_{g,\mathrm{indirect}}=$ 2.23 eV) allowed transitions. The spectrophotometric-evaluations assisted most-sensitive working pH of sample solutions was optimized for a long spectrum of pH values from 1 to 12 for further investigations. Some spectrophotometric and comercial parameters e.g., molar extinction coefficient $\left(\epsilon \right)$, stability, reproducibility and fading were figured out. The response efficacy was also observed to enhanc the sensitivity and stability of the CR solutions by incorporating a selected amount (by %vol) of a polar additive ethanol. The invariant aborbance related isosbestic wavelength for both acidic and alkaline samples remained unaffected from pH and firmly stood at 475 nm. The improved and reasonable pH values were found to be pH 4 and pH 9 and hence were opted for CR solutions and may further be applicable to the radiation-induced degradation phenomenon based on radiolytic bleaching.