Preparation, structural and photoluminescence characteristics of novel red emitting Mg7Ga2GeO12:Mn4+ phosphor

Abstract In order to obtain a deep red emitting Mn 4+ doped phosphor for applications in white LEDs, we choose Mg 7 Ga 2 GeO 12 with AO 6 polyhedra favoring the emission of Mn 4+ ions as host and design a novel Mg 7 Ga 2 GeO 12 :Mn 4+ phosphor by solid state method at 1400 °C in air. The photoluminescence properties were investigated in conjunction with a structural analysis. The crystallographic occupancy of Mn 4+ ion in the Mg 7 Ga 2 GeO 12 host was studied based on the Rietveld refinement results and the crystal chemistry rules as well as luminescence properties. It reveals that the Mn 4+ ion occupies the trivalent Ga site in GaO 6 polyhedra, resulting in efficient emission of Mn 4+ ion. The excitation spectrum exhibits a broad peak at 420 nm due to the characteristic 4 A 2g → 4 T 2g transitions of Mn 4+ ions, and it indicates that this Mg 7 Ga 2 GeO 12 :Mn 4+ material can be availably excited in 400–450 nm region. Upon excitation at 420 nm, the composition-optimized Mg 7 Ga 2 GeO 12 :0.5 mol%Mn 4+ sample shows broad deep red emission band ( 2 E g → 4 A 2g transition) in 600–750 nm with the CIE chromaticity ( x  = 0.7133, y  = 0.2866). An analysis of the thermal quenching shows that the emission intensity of the optimal Mg 7 Ga 2 GeO 12 :Mn 4+ sample at 250 °C is 78% of their initial intensity at room temperature. Therefore, the Mg 7 Ga 2 GeO 12 :Mn 4+ material could serve as a potential red phosphor for white LEDs.