Nucleation kinetics and growth of high-quality DAST crystals with the aid of activated carbon as the adsorbent to micro-crystals in solutions

Growth of highly nonlinear optical 4-N, N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST) crystals had been carried out with the addition of activated carbon into the methanol solutions. The metastable zone width and induction period were experimentally determined for the modified growth conditions. Nucleation kinetics and fundamental growth parameters such as surface free energy, critical radius and critical free energy change were also evaluated according to the experimental data. The observations indicated that adsorption to tiny nuclei by activated carbon favored to improve the stabilities of growth solutions. Twin-free seeds and platelets with good qualities were effectively obtained under the optimized conditions. The introduction of activated carbon into growth solutions favors the growth of bulk DAST crystals at a relatively high rate, and high quality bulk crystal with dimensions of 8.3×8.4×2.5 mm3 was obtained under the optimized growth conditions. In addition, the obtained DAST crystals with well-developed (0 0 1) and (0 0 −1) faces facilitate the direct utilization for electro-optic and nonlinear optical applications. The grown crystals were also characterized by the micro-hardness test, optical transmission and etching investigation.

► As a simple but effective method, the introduction of active-carbon into growth solutions improves the solution stability and favors to obtain twin-free DAST single crystals.
► Under the improved growth conditions, it is easy to obtain DAST crystals with well-developed (0 0 1) and (0 0−1) faces, which facilitates the direct utilization for EO and NLO applications.
► Large-size DAST crystal with dimensions of 8.3×8.4×2.5 mm3 had been well-grown with a high rate under the optimized growth conditions.