Site-selective and cooperative doping of Gd 3 Al 5 O 12 :Ce garnets for structural stabilization and warm WLED lighting of low CCT and high CRI.

Synergistic doping of the metastable Gd 3 Al 5 O 12 :Ce garnet with a Ca 2+ /Hf 4+ pair and Sc 3+ to form Gd 2.97- x Ca x Hf x Sc y Al 3 O 12 :0.03Ce ( x = 0.5-2.0, y = 0.0-1.5, x + y = 2.0) solid solution was conducted for the structural stabilization and photoluminescence manipulation. The site selection of Ca 2+ /Hf 4+ /Sc 3+ dopants and the effects of doping on the crystal structure, local coordination, band structure and Ce 3+ luminescence were revealed in detail with the results of XRD, Rietveld refinement, TEM, and UV-Vis/photoluminescence spectroscopy. A decrease in Ca 2+ /Hf 4+ and an increase in the Sc 3+ content were observed to shrink the lattice, widen the bandgap of the garnet host, red-shift the excitation/emission wavelength, broaden the emission band and shorten the fluorescence lifetime of Ce 3+ . The spectral changes were rationalized by considering the local coordination and crystal field splitting of the Ce 3+ 5d energy level. Application of typical Gd 0.97 Ca 2 Hf 2 Al 3 O 12 :0.03Ce ( x = 2.0, y = 0) cyan and Gd 2.47 Ca 0.5 Hf 0.5 Sc 1.5 Al 3 O 12 :0.03Ce ( x = 0.5, y = 1.5) greenish-yellow phosphors in w-WLED lighting produced low correlated color temperatures of ∼3842 and 3514 K, high color rendering indices of ∼88 and 93 and favorable luminous efficacies of ∼32.9 and 14.7 lm/W under the excitation of 395 nm n-UV and 450 nm blue LED chips, respectively.