Relationship between structure and luminescence properties in Ce3+ or Ce3+, Mn2+-doped garnet phosphors for use in white LEDs

A series of Ce3+ or Ce3+ and Mn2+ doped garnets of the general formula A3B2X3O12 (A=Sr,Ca; B=Sc,Y; X=Si,Ge) was obtained using a high temperature solid state reaction. These compounds were characterized by X-ray diffraction and photoluminescence spectroscopy. The relation between luminescence properties of phosphors and their host lattice composition was studied. It was found that Ce3+ ions occupied the A site and emitted in the green spectral region. Mn2+ ions can exchange cations in both A and B sites showing green and red emissions, respectively and getting excited due to an energy transfer from Ce3+. This study showed the relationship between Ce3+ and Mn2+ emission/excitation wavelengths and the symmetry around the activator ions expressed by means of the distortion factor of the dodecahedral A site (d88/d81). Decay times of the Ce3+ and Mn2+ luminescence were measured and correlated with the compositional dependent structural changes.