Sol-gel synthesized far-red chromium-doped garnet phosphors for phosphor-conversion light-emitting diodes that meet the photomorphogenetic needs of plants

We report the sol-gel synthesis and characterization of far-red garnet phosphors Gd3Ga5O12 (GGG:Cr), Y3Ga5O12 (YGG:Cr), Lu3Ga5O12 (LGG:Cr), and Gd3Sc2Ga3O12 (GSGG:Cr) doped with different chromium (III) concentration (3, 5, and 8 mol. %). The morphological and luminescence properties of the phosphors annealed at different temperatures (1000°C, 1300°C, 1400°C, and 1500°C) were examined using x-ray diffraction, scanning electron microscopy, photoluminescence (PL), and PL excitation (PLE) spectroscopy, and by the measurements of diffuse reflection, PL internal quantum efficiency (QE), and PL decay time. The PLE spectra of the samples were found to peak at around 450 nm depending on the host, and luminescence was observed in the region of 700–760 nm. The QE was found to strongly depend on doping concentration and calcination temperature, and the PL decay exhibited biexponential behavior. The investigated far-red garnet phosphors, in particular GGG:Cr and YGG:Cr, show a potential for use in phosphor-converted light-emitting diodes that meet the photomorphogenetic needs of plants.