Rare-Earth-Free High-Efficiency Narrow-Band Red-Emitting Mg3Ga2GeO8:Mn4+ Phosphor Excited by Near-UV Light for White-Light-Emitting Diodes

A series of novel red emission Mg3Ga2GeO8 (MGG):Mn(4+) phosphors under near-UV (NUV) excitation are synthesized successfully by traditional high-temperature solid-state reaction. The structure of Mg3Ga2GeO8 is investigated by high-resolution transmission electron microscopy, scanning electron microscopy, and powder X-ray diffraction (XRD) Rietveld refinement. It has one octahedral site and one tetrahedral site in the crystal structure. According to XRD and photoluminescence (PL) property analysis, Mn(4+) can occupy an octahedral (Mg(2+)/Ga(3+)) site. The PL properties are investigated by diffuse-reflectance, emission, excitation, and temperature-dependent spectroscopy and decay curves. It can emit red light peaking at 659 nm under NUV excitation. The critical quenching concentration of Mn(4+) was about 0.5 mol %. The concentration quenching mechanism could be a d-d interaction for the Mn(4+) center. The CIE chromaticity coordinates and full-width at half-maximum are (0.295, 0.677) and 24 nm, respectively. It demonstrated that MGG:Mn(4+) has high color purity. The PL intensity of MGG:0.5% Mn(4+) drops to 72% when the temperature is raised up to 150 °C. Furthermore, MGG:0.5% Mn(4+) exhibits outstanding quantum efficiency (64.7%). By tuning of the weight ratio of blue, green, and red phosphors, the fabricated white-light-emitting diodes using a 405 nm GaN NUV chip combined with a blend of blue phosphor BAM:Eu(2+), green phosphor Sr2SiO4:Eu(2+), and red-emitting phosphor MGG:Mn(4+) driven by 40 mA current can get white light with chromaticity coordinates (0.316, 0.375) and CCT = 3340 K. This demonstrates that MGG:Mn(4+) is a potential red phosphor matching NUV LED chips to get white light.