Growth of New Nonlinear Optical Crystals of Hydrochlorides of l-Histidine from Solution

Single crystals of l-histidine monohydrochloride (LHMHCl) and l-histidine dihydrochloride (LHDHCl) have been grown from aqueous solution by a slow evaporation technique. Single-crystal X-ray diffraction analyses reveal that LHMHCl crystallizes in orthorhombic form with space group P212121 while LHDHCl crystallizes in monoclinic form with space group P21. Laser Raman studies confirmed the structure of the crystal, and the vibration modes have been assigned. UV−vis−NIR spectra show excellent transmission through the visible region up to 1100 nm. Differential thermal analysis (DTA) studies indicate that the LHMHCl crystal is more stable and has higher melting point than the LHDHCl crystal. Laser damage threshold study shows that LHDHCl is more resistant to laser damage than LHMHCl. Crystals of the monoclinic form LHDHCl give strong second-harmonic generation (SHG) signals, while orthorhombic forms do not.