<p>Ion implantation is a unique technique that tailors the optical properties and enhances the second harmonic generation (SHG) efficiency of semi-organic materials. In this work, L-histidine amino acid-doped potassium hydrogen phthalate thin films were synthesized in different concentrations and implanted with 10&#xa0;keV N₂⁺ ions at various fluences of 1 × 10¹⁵, 5 × 10¹⁵, 1 × 10¹⁶, and 5 × 10¹⁶ ions/cm² to enhance their nonlinear optical property. The samples were characterized using Grazing Incidence X-Ray Diffraction (GIXRD), UV–visible spectroscopy, photoluminescence spectroscopy, FT-IR spectroscopy, SEM images, and non-linear optical (NLO) behaviour. The study reveals that the N₂⁺ ion irradiation led to physical and chemical changes that altered the mechanical and optical properties of the samples. The N₂⁺ ion irradiated L-histidine amino acid-doped potassium hydrogen phthalate thin films showed an enhanced second-harmonic generation (SHG) efficiency compared to the non-irradiated L-histidine-doped potassium hydrogen phthalate thin films. Z-scan analysis indicated an increase in the nonlinear absorption coefficient with increasing ion irradiation. This is the direct indicator of enhancement for third-order nonlinear optical behaviour. The energy deposition by the ion beam in the sample was studied using the SRIM-2013 program. Our results show that N₂⁺ ion irradiation tunes the optical properties of the materials that could have potential for various electronic and industrial applications.</p>