In recent years, optically active glasses offer a broad range of applications; the functionality can be modified by appropriate doping. The design and development of optical devices such as solid state lasers, optical fiber amplifiers, optical storage materials, light converters, sensors, phosphors, acousto-optic modifiers and 3D waveguides, etc. require a detailed spectroscopic study of the optical properties such as emission peak wavelength, bandwidth, emission cross-section, lanthanide ion environment, phonon energies, etc. In view of the key role of lanthanide spectroscopy in science and technology especially in lasers, fiber amplifiers, white light phosphors, etc., the present book, therefore, focuses on to study the optical and fluorescence properties of lanthanide-doped oxide glasses.