Site-selective and cooperative doping of Gd3Al5O12:Ce garnets for structural stabilization and warm WLED lighting of low CCT and high CRI

Abstract

Synergistic doping of the metastable Gd₃Al₅O₁₂:Ce garnet with a Ca²⁺/Hf⁴⁺ pair and Sc³⁺ to form Gd_2.97−xCa_xHf_xSc_yAl₃O₁₂:0.03Ce (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 Ca²⁺/Hf⁴⁺/Sc³⁺ dopants and the effects of doping on the 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 spectroscopy. A decrease in Ca²⁺/Hf⁴⁺ and an increase in the Sc³⁺ 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 Ce³⁺. The spectral changes were rationalized by considering the local coordination and crystal field splitting of the Ce³⁺ 5d energy level. Application of typical Gd_0.97Ca₂Hf₂Al₃O₁₂:0.03Ce (x = 2.0, y = 0) cyan and Gd_2.47Ca_0.5Hf_0.5Sc_1.5Al₃O₁₂:0.03Ce (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.