Amino Acids Doping in KHP Crystals: A Critical Review

Potassium Hydrogen Phthalate (KHP) is an important Semi-Organic Crystal for Non-Linear Optical (NLO), photonic, and optoelectronic applications. KHP shows good crystal growth behavior, high optical transparency, and structural stability. This review summarizes the effects of amino acid dopants such as Glycine, L-Tryptophan, L-Phenylalanine, and L-Lysine. Slow evaporation method has been used to grow KHP crystals so that their structural, optical, dielectric, mechanical, thermal, and nonlinear optical properties are retained. Use of amino acid induces lattice distortion and modifies the hydrogen bonding without changing the orthorhombic crystal structure. The resulting property variations depend strongly on dopant concentration and growth conditions. Crystal growth challenges, defect formation, and future research directions are also discussed.