Recent research results :

The phosphor CaTiO₃:Pr³⁺ was synthesized via a solid-state reaction in combination with a subsequent annealing under flowing NH₃. Comparatively large off-center displacements of Ti in the TiO₆ octahedra were confirmed for as-synthesized CaTiO₃:Pr³ by XANES. Raman spectroscopy showed that the local crystal structure becomes highly symmetric when the powders are ammonolyzed at 400 °C. Rietveld refinement of powder X-ray diffraction data revealed that the samples ammonolyzed at 400 °C have the smallest lattice strain and at the same time the largest average Ti-O-Ti angles were obtained. The samples ammonolyzed at 400 °C also showed the smallest mass loss during the thermal re-oxidation in thermogravimetric analysis (TGA). Enhanced photolumincescence brightness and an improved decay curve as well as the highest reflectance were obtained for the samples ammonolyzed at 400 °C. The improved photoluminescence and afterglow by NH₃ treatment are explained as a result of the reduced concentration of oxygen excesses with simultaneous relaxation of the lattice strain.