The demand for phosphors with advanced performance capabilities is increasing due to recent technical developments in the display, lighting, and fluorescence labeling sectors. Rare-earth doped phosphors have been the focus of the research community, owing to their widespread applications in display devices, temperature sensors, solar cells, etc. This book reviews the broad aspects of organic and inorganic materials-based phosphors, and will be beneficial to undergraduate, graduate, and postgraduate students. It provides an up-to-date account of the advancement of various techniques for the synthesis of phosphors and their applications. Experimental and theoretical approaches related to the rare-earth-doped luminescent materials are explored.