AgGaGeS4 and AgGaGe5Se12 are promising new nonlinear optical crystals for frequency-shifting 1-mu m solid state lasers into the mid-infrared (2-12 mu m) spectral range. The quaternary compounds were synthesized by vapor transport in sealed ampoules from high purity elemental starting materials, and crystals were grown by the horizontal gradient freeze technique in transparent furnaces. AgGaGe5Se12 exhibited incongruent melting behavior, and small optical samples extracted from an as-grown polycrystalline boule had high scattering losses. AgGaGeS4 growth was far more favorable, resulting in a crack-free single crystal measuring 19 mm in diameter and > 80 mm in length with as-grown 2.05-mu m absorption losses < 0.05 cm(-1). The measured laser damage threshold of an uncoated AgGaGeS4 crystal at 2.05 mu m was 1.1 J/cm(2), and room-temperature measurements of thermal diffusivity, heat capacity, and thermal conductivity yielded values of 0.224 mm(2)/s, 0.448 J/g/K, and 0.399 W/mK respectively, for the sulfide. (c) 2005 Elsevier B.V. All rights reserved.