A novel quaternary crystal system of the class Ag-Ga-Ge-Se was studied in detail. A process was developed to react 120 g and larger batches of material from the pure Ag, Ga, Ge and Se elements. Crystals 19-25 mm in diameter and several cm long with AgGaGe5Se12 and AgGaGe3Se8 stoichiometric compositions were grown by the vertical Bridgman method. Optical measurements of parallel polished crystals showed transparency from 0.60 to 16 mu m. Both crystals belong to the orthorhombic class and showed very good fabricability. The heat capacity of the AgGaGe3Se8 material was 0.28 J/g degrees C and the thermal conductivity was 0.30 W/m K. Experimental second harmonic generation (SHG) gave a "d(31)" coefficient of 29 pm/V for both compositions. The optical parametric oscillation (OPO) analysis indicates that type-I phase matching is possible with the AgGaGe5Se12 crystal for conversion to the IR using 1.06 mu m pump wavelength. The combination of transparency, low loss and phase matching results indicate that this material will enable 1.06 mu m conversion to mid-wave IR (MWIR) and long-wave IR (LWIR) regions. (C) 2009 Elsevier B.V. All rights reserved.