Effectively enhancing blue excitation of red phosphor Mg2TiO4:Mn4+ by Bi3+ sensitization

The red phosphors Mg2TiO4:Mn4+, Bi3+, Li+ with strong absorption at blue region were synthesized. Through the excitation and emission spectra, diffuse reflection spectra and Raman spectra, it is proved that Bi3+ ion plays a role of sensitizer to the enhancement of optical property, especially the increased excitation intensity of blue light. It is the first time to report about asynchronous increases of different excitation bands with Bi3+ as a sensitizer, primarily resulting from the perturbation of symmetry and lattice vibration along with crystal defect in the host lattice with larger Bi3+ occupied at a small octahedral site of Mg2+. The sensitization of Bi3+ works not only in the case of powder phosphors but also even better in ceramic phosphors. For powder phosphor, the intensity of the blue excitation band of Mg2−2xTi0.999O4:0.1%Mn4+, xBi3+, xLi+ grows to at least 1.5 times than that of Mg2Ti0.999O4:0.1%Mn4+ when x = 0.5%, following with a uplift at about 410 nm. Meanwhile, Mg2TiO4:Mn4+, Bi3+, Li+-based luminescent ceramic manifests with a more than 2.5 times increase as x = 0.8%. The red phosphors with a broad emission band in the pure red light region show a promising application in blue LEDs as a red component.