New Mg/Ge-Stabilized GdMgGeAlO:Ce Garnet Phosphor with Orange-Yellow Emission for Warm-White LEDs ( = 2.0-2.5).

By stabilization of the GdAlO garnet by replacing 80% or more of Al with Mg/Ge pairs, a series of new orange-yellow-emitting GdMgGeAlO:Ce ( = 2.0-2.5) phosphors were successfully developed for potential application in warm-white-light-emitting diodes (WLEDs). Rietveld structure refinement proved that Mg first substitutes the octahedral Al ion, followed by the replacement of the tetrahedral Al together with Ge. The band structure of the = 2.0 typical garnet was analyzed via density functional theory (DFT) calculations. The incorporation of an increasing content of Mg/Ge was experimentally shown to narrow the band gap and expand the unit cell of the garnet host and blue shift the emission/excitation wavelength and shorten the fluorescence lifetime of Ce. The photoluminescence behaviors were rationalized by considering the influence of Mg/Ge on the crystal structure, band structure, and local coordination. An LED lamp fabricated by combining the (GdCe)MgGeAlO optimal phosphor with a 450 nm-emitting InGaN blue LED chip exhibited a color-rendering index of 71.6, luminous efficacy of 16.1 lm/W, and a low correlated color temperature of 2201 K under a driving current of 20 mA, indicating that phosphor may have potential application in warm WLEDs.