Phosphors can be used in conjunction with UV or near-UV LEDs in a solid-state lighting device to generate white light. These devices offer the advantages of being efficient, long-lasting, durable, and non-toxic. Three known phosphor compounds have been studied: Y4Si2O7N2, MgYSi2O5N, and CaMgSi2O6. When these phosphors are doped with Ce3+ or Eu2+ the compounds emit blue light. Co-doping with Mn2+ (substituted for Mg) gives red emission, with the Ce3+ or Eu2+ acting as a sensitizer for the weakly absorbing Mn2+. In this study the synthesis of these compounds has been attempted or accomplished using conventional solid-state methods. Optical properties, characterized by fluorimetry, have been tuned by cation substitutions.  The crystal structures have been examined by Rietveld refinement of X-ray diffraction, and related to the optical properties of the phosphors. The result of this study will provide information about the characteristics of these compounds and what can be done to control their optical properties.