Comments on the paper: “Analysis on linear and nonlinear optical properties of an efficient semi-organic crystal: Thiourea borate”

•The title paper is critiqued.•‘Thiourea borate’ is a dubious crystal.•Many points of criticisms are highlighted.•Experimental data reported in the title paper are discussed. The authors of the title paper (Optics and Laser Technology 107 (2018) 428–434) report to have grown a so-called ‘thiourea borate’ crystal by slow evaporation of an aqueous solution containing thiourea and boric acid, and have also described the electrical properties of ‘thiourea borate’ (Journal of Electronic Materials, 48 (2019) 5632–5639). In this Letter to the Editor, we prove that the ‘thiourea borate’ is a dubious crystal. Hence all claims of nonlinear optical (NLO) properties of this material are untenable.