Ammonium dihydrogen phosphate (ADP) is an available inorganic non-linear optical material needed for laser radiation. The beneficial optical crystals of pure, Fe (II) and Fe (III) (1 mol %) doped ADP crystals were obtained by slow evaporation solution growth technique (SEST). Well acquired crystals were characterized by different experimental techniques. Powder X-ray diffraction (XRD) and Fourier transform-infra-red (FT-IR) spectral studies substantiate the slight distortion of the crystal structure due to doping. The thermo-gravimetric and differential thermal analysis (TG-DTA) studies expose the pureness of the grown crystals. Scanning electron microscopic (SEM) analysis brings out the changes in the surface morphology because of doping. Optical studies were carried out by diffuse reflectance spectra (DRS). The second harmonic generation (SHG) efficiency, an essential requirement for the single crystals to identify the non-linear optical property was carried out by Kurtz powder technique.