In order to search efficient red-emitting phosphors for white LEDs application, CaAl12O19:Mn4+ phosphors have been prepared by a combustion method assisted with GeO2 flux. The influence of GeO2 concentration and annealing temperature on the structure and luminescence intensity for the phosphors has been investigated. The mechanism for luminescence enhancement has been discussed. At GeO2 doping concentration of 1.5mol%, the red emission intensity increases by 81% under 330nm UVA excitation. More isolated luminescence center Mn4+ ions rather than pairs of Mn4+–Mn2+ ions are formed in the lattice with the introduction of GeO2 at high temperature oxidation, leading to the enhancement of the red emission. A feasible new way to enhance the red emission in CaAl12O19:Mn4+ phosphor is obtained.

Fe3+, B3+ co-doping LiAl5O8 phosphor has been successfully synthesized by a solid-state reaction method assisted with wet chemical mixing route. Photoluminescence emission peak is observed at around 672nm excited at both 290nm ultraviolet and 565nm green light. With introduction of a small amount of boric acid, the red emission intensity can be enhanced by 2.62 times under 290nm excitation and 2.31 times under 565nm excitation, respectively. It is believed that the substitution of B3+ ions for Al3+ sites decreases the symmetry of the luminescence center, intensifying the red emission. (C) 2011 Published by Elsevier B. V.