Crystal Growth of DAST

We explore the growth of the highly nonlinear optical trans-4'-(dimethylamino)-N-methyl-4-stilbazolium tosylate) (DAST) crystals from methanol solutions. We determined the key thermodynamic quantities of the DAST/methanol system, which allowed us to optimize the conditions of the crystal growth and to manipulate the size and morphology of the obtained crystals. We developed confined spontaneous nucleation (CSN), a new technique to control the nucleation and produce good quality seeds and platelets for nonlinear optical applications such as the generation of THz waves. We propose the total excess of Gibbs free energy per volume of the solution as a new parameter (Delta G/V-sol) that fundamentally affects the growth rate from solution instead of the commonly used supersaturation. This parameter involves also concentration and temperature dependence and is therefore applicable to a large range of growth conditions. A model for the growth dynamics of DAST crystals based on the mass balance equations and the measurements of the growth rate at different experimental conditions allowed us to determine the optimal temperature cooling profile for the growth of large crystals at a constant rate. We also present a numerical analysis of the growth dynamics under various commonly used cooling rates and their effect on the crystalline quality of crystals. It is demonstrated that high quality, record size crystals with dimensions 28 x 28 x 8 mm(3) can be grown with our new optimized cooling profile based on the constant excess of Gibbs free energy density in the solution during the growth.