Generating yellow and red emissions by co-doping Mn2+ to substitute for Ca2+ and Sc3+ sites in Ca3Sc2Si3O12:Ce3+ green emitting phosphor for white LED applications
We report luminescence properties of Ce3+ and Mn2+ co-activated Ca3Sc2Si3O12 (CSS) silicate garnets. It is observed that Mn2+ may not only occupy Ca2+ sites to generate a yellow emission (Mn2+(I)) at 574 nm but also Sc3+ sites to generate a red emission (Mn2+(II)) at 680 nm. Considerable Mn2+ substitution for Sc3+ can be performed through balancing their charge difference by introducing a trivalent rare earth ion, such as La3+ and Ce3+, to replace Ca2+. Meanwhile, remarkable energy transfer from the green emitting Ce3+ to both Mn2+(I) and Mn2+(II) can occur, making tunable color and white light emission available in CSS:Ce3+,Mn2+ upon blue excitation into Ce3+. White LEDs combined by CSS:Ce3+,Mn2+ phosphors and blue LED chips are fabricated. A CSS:0.03Ce3+,0.2Mn2+ phosphor with deficient red emission is enriched in red by increasing Ce3+ concentration to 0.1, which leads to increase of Mn2+(II) number in case of charge compensation by more Ce3+ ions. Consequently, the color rendering index of the white LEDs is improved from 64 to 76. The results of this work indicate that CSS:Ce3+,Mn2+ garnet could be a promising single phase phosphor for white LEDs.