Comments on the paper 'Growth and investigation of novel nonlinear optical single crystal of urea potassium dichromate by solution growth technique for photonic application'

The authors of the title paper (Journal of Optics 49:181–186, 2020) claim to have grown a so-called urea potassium dichromate (UPDC) by slow evaporation of an aqueous solution containing equimolar amounts of urea and potassium dichromate and characterized it based on a unit cell study. A critical analysis reveals that the claims in the title paper are erroneous. Hence, we reinvestigated the crystal growth reaction and determined the structure of the product crystal. Based on these studies, we prove that due to no chemical reaction between the reagents fractional crystallization of potassium dichromate (K2Cr2O7) occurs and not formation of any so-called UPDC crystal. Taking the title crystal as an example we show the importance of reporting single-crystal structure for new compound characterization.