I have prepared nanoparticle in de-ionized water using laser ablation at 180 mJ laser energy...i calculated band gap as 4.26 eV using tauc plot and kept my sample in liquid for and after 15 days again i go for UV absorption spectroscopy and my Tauc plot showed that two band gaps appears one at 3.41 eV and other at 4.25. What might be the reason? I´m attaching my result.