Development of next generation red phosphors for commercial lighting requires understanding of how increased luminescence is achieved by various treatment strategies. In this work, we compare co-doping with Nb to NH3 treatment of CaTiO3:Pr phosphors to reveal a general mechanism responsible for the increased luminescence. The phosphors were synthesized using standard solid-state synthesis techniques and the fluorescence was characterized for potential use in fluorescent lighting, with 254 nm excitation. The lifetime of the fluorescence was determined and used to identify a change in a trap state by the co-doping of Nb 5+ in the phosphor. The oxidation state of the Pr was probed by NEXAFS and revealed that both Nb 5+ co-doping and NH3 treatment reduced the number of nonfluorescing Pr 4+ centers. Calculations were performed to determine the energetically favorable defects. Vacuum annealing was also used to further probe the nature of the trap state. It was determined that NH3 treatments reduce the number of Pr 4+ non-fluorescing centers, while Nb 5+ co-doping additionally reduces the number of excess oxygen trap states that quench the fluorescence.