Site-selective and cooperative doping of Gd3Al5O12:Ce garnet for structure stabilization and warm w-LED lighting of low CCT and high CRI

Synergistically doping the metastable Gd3Al5O12:Ce garnet with Ca2+/Hf4+ pair and Sc3+ to form Gd2.97−xCaxHfxScyAl3O12:0.03Ce (x = 0.5−2.0, y = 0.0−1.5, x + y = 2.0) solid solution was conducted for structure stabilization and photoluminescence manipulation. The site selection of Ca2+/Hf4+/Sc3+ dopants and the effects of doping on crystal structure, local coordination, band structure and Ce3+ luminescence were revealed in detail with the results of XRD, Rietveld refinement, TEM, and UV-Vis/photoluminescence spectroscopies. Decreasing Ca2+/Hf4+ and meanwhile increasing Sc3+ content was 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 Ce3+. The spectral changes were rationalized by considering local coordination and crystal field splitting of the Ce3+ 5d energy level. Appling the typical Gd0.97Ca2Hf2Al3O12:0.03Ce (x = 2.0, y = 0) cyan and Gd2.47Ca0.5Hf0.5Sc1.5Al3O12:0.03Ce (x = 0.5, y = 1.5) greenish-yellow phosphors in w-WLED lighting produced the 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.