This book deals, the rare earth ions (RE3+) are used to probe the local structural variations in the host glass matrices, because of their unique spectroscopic properties resulting from the 4f-4f intra-configurational radiative transitions. Glasses containing rare earths as luminescent centers are of great interest due to their unique optical, electrical and magnetic properties. In the development of RE3+ ions doped optical devices; the host glass plays a very important role. Photoluminescence properties of RE3+ ions change drastically from host to host as well as by the variation of their...