Mercurous chloride, Mercurous bromide and mercurous iodide belong to the mercurous halide family and have very attractive properties suitable for acousto-optic devices. We have developed the techniques to purify the source materials, grow large crystals into <110> orientation, a direction needed for the devices and fabricate the crystals into acousto-optic tunable filter (AOTF). Low defect densities, low optical and acoustic loss were achieved by control of crystal purity, growth rate and orientation. To understand the role of thermal convection we measured the growth velocity as a function of gvector. Experiments clearly showed that convection level affects the fluid flow and growth velocity and deteriorates the quality of crystals.