Solvent effects and polymorphic transformation of organic nonlinear optical crystal L-pyroglutamic acid in solution growth processes: I. Solvent effects and growth morphology

Abstract Single crystals of a new promising nonlinear optical material for the tunable UV harmonic generation, l -pyroglutamic acid 60×20×20 mm 3 in size were obtained from aqueous solution by using the temperature-lowering method. Solubility of l -pyroglutamic acid in different solvents was measured. The single crystals showed different morphological characteristics and growth rate in different solvents with different crystallographic orientations. Methanol or ethanol solutions yielded needle-like crystals. In mixed solution such as methanol/H 2 O or ethanol/ H 2 O plate-like crystals with a thickness in the direction [0 1 0] were observed. The water as a good solvent, however, produced long prism-like crystals. The two polymorphs of L -pyroglutamic acid (α and β phases) were found for the first time. The growth shapes of α-phase is mainly a prism and β phases is a rhombic plate.The growth rate of α and β phases is mainly a function of the supersaturation of the L -pyroglutamic acid in solution.