Phosphors are a class of materials which emit visible light when impacted by either electrons or photons. Phosphors are the critical material in all self-emissive displays. The major display technologies which depend on phosphors are cathode ray tubes, flat cathode ray tubes (especially, field emission displays), thin film electroluminescent displays, and gas discharge plasma displays. Each of these technologies started with phosphors prepared in powder form, sprayed or screen printed onto a faceplate suitable for viewing. Electroluminescent displays have largely converted to thin film phosphors. It can be expected that, for many applications, the other competing technologies will also come to rely on more robust, high definition, thin film phosphors. Presently, full color displays must utilize several deposition and etching procedures to prepare the red, green, and blue pixels. Ion implantation of color centers is now paving the way for producing full color displays in a single host phosphor. We shall discuss the present limitations that compromise full color self-emissive displays, and present state-of-the-art solutions based on thin films and ion implantation.