Growth of high-quality 4-N,N-dimethylamino-4-N'-methyl stilbazolium tosylate (DAST) crystal by slope nucleation method with controlled nucleation has been achieved when the DAST solution was subjected to a few successive thermal cycles. The ionic conductivities measured for the stirred and unstirred pre-crystalline solutions showed that the persisting cluster formation in the unstirred solution might have facilitated controlled nucleation. These efficient and high-quality organic-ionic nonlinear optical crystals can be directly utilized for electro-optic and terahertz applications. (c) 2006 Elsevier B.V. All rights reserved.