Deep Red Emitting MgAl2O4:Cr3+ Phosphor for Solid State Lighting

In this work, MgAl2O4:Cr3+ phosphor has been synthesized by the co-precipitation approach coupled with heat treatment. The phase structure, morphology, composition and luminescent properties of the phosphor were investigated in detail by x-ray diffraction, field emission-scanning electron microscopy, energy dispersive x-ray spectroscopy and steady-state photoluminescence (PL) measurements. The MgAl2O4:Cr3+ phosphor emits a deep red light that peaked at 687nm, which is attributed to the E-2(g)-(4)A(2g) state transition of Cr3+ ions located at the sites with D-3d local symmetry of host lattice. The phosphor presents a strong absorption with two bands in ultraviolet to visible and yellow regions. The changes of PL and photoluminescence excitation spectra of MgAl2O4:Cr3+ phosphors as a function of sintering temperature and time intervals were observed. The phosphors emit the highest PL intensity when doped with a Cr3+ concentration of about 1.2mol.%. The International Commission on Illumination chromaticity coordinates and internal quantum efficiency of MgAl2O4:1.2%Cr3+ were measured and calculated. A warm white light emitting diode using the deep red phosphor, has shown a high colour rendering index (CRI, Ra=78) and a low correlated colour temperature (CCT=3481K).