Structural and luminescent properties of red-emitting SrGe4O9:Mn4+ phosphors for white light-emitting diodes with high color rendering index

A red-emitting SrGe3.99Mn0.01O9 (SGO:Mn4+) phosphor have been prepared by a solid-state reaction. The structural and optical properties of SGO:Mn4+ phosphors, together with their thermal quenching property have been investigated. The 3d electrons of Mn4+ at octahedral sites of the SGO host showed a crystal field splitting Dq of 2380 cm−1 and Racah parameters, B and C of 1970 and 860 cm−1, respectively. Due to the 4A2g→4T1g and 4A2g→2T2g transitions, broad photoluminescence excitation bands were observed at the spectral region spanning from ultraviolet to blue light. The transition from 2Eg to 4A2g results in a sharp emission peak at 655 nm. When the yellow-emitting Y3Al5O12:Ce3+ and red-emitting SGO:Mn4+ phosphors were incorporated into a blue light-emitting diode (LED), the fabricated white LED showed an emission in the natural white light region with an excellent color rendering index of 92 and a color stability against an increase in the forward current. Thus, SGO:Mn4+ can be a potential red-emitting phosphor in the fabrication of white LEDs.