A comprehensive investigation of the structural and optical properties of l-Dopa doped ADP crystals

Abstract

L-Dopa (levodopa or L-3,4-dihydroxyphenylalanine, C₉H₁₁NO₄) doped ammonium dihydrogen phosphate (ADP) crystals were synthesized to investigate how doping influences their structural and optical behavior. Powder X-ray diffraction confirms that both pure and doped crystals retain the tetragonal crystal structure without secondary phase formation, indicating successful dopant incorporation with only minor lattice distortions. The grown crystals were subjected to Fourier transform infrared (FTIR) spectroscopy which reveals systematic peak shifts and band broadening associated with –NH, –OH, and PO₄ related vibrational modes, suggesting modification of the local bonding environment upon doping. UV-visible (UV-vis) spectroscopy shows high optical transparency in the visible region, with a progressive decrease in UV cut-off wavelength and an increase in optical band gap from 5.08 eV (pure ADP) to 5.14 eV for 1 mol% and 5.33 eV for 2 mol% L-Dopa doped crystals. The increase in the band gap values indicates dopant-induced modulation of electronic transitions and reduction in defect-related absorption. The optical analyses demonstrate that doping of L-Dopa provides an effective way for tuning the optoelectronic response of ADP crystals, highlighting their potential for nonlinear optical and photonic device applications. The presence of L-Dopa enables strong hydrogen bonding within the ADP lattice, improving structural stability and maintaining high transparency across a wide optical wavelength range, which is an essential requirement for effective nonlinear optical (NLO) applications.