This book is written with two distinct objectives, First to provide various methods to grow bulk single crystals and to discuss their characteristics like photoluminescence, non linear optical property, second harmonic generation efficiency required for LASERS and device applications, second how these properties can be enhanced by adding Rare Earth elements. The fascinating field of nonlinear optics (NLO) has prominent role to play in the era of immense technological excellence attributing to the usefulness of many crystals in important areas of service to the humanity namely science, medicine, engineering, technology and also strategic areas of defense and space science. Materials with large nonlinear optical susceptibilities are of current interest in the area of harmonic generation and optical modulation. In recent years, some inorganic crystals, which form a noncentrosymmetric structure which exhibit second-order nonlinear optical properties that far surpassed those of the conventional materials, have led to the synthesis and evaluation of a wide range of potentially useful solids.