Effective lattice stabilization of gadolinium aluminate garnet (GdAG) via Lu 3+ doping and development of highly efficient (Gd,Lu)AG:Eu 3+ red phosphors

Abstract

The metastable garnet lattice of Gd 3Al 5O 12 is stabilized by doping with smaller Lu 3+, which then allows an effective incorporation of larger Eu 3+ activators. The [(Gd 1xLu x) 1yEu y] 3Al 5O 12(x=0.1-0.5, y = 0.01-0.09) garnet solid solutions, calcined from their precursors synthesized via carbonate coprecipitation, exhibit strong luminescence at 591nm (the 5D 0→ 7F 1 magnetic dipole transition of Eu 3+) upon UV excitation into the charge transfer band (CTB) at 239nm, with CIE chromaticity coordinates of x=0.620 and y=0.380 (orange-red). The quenching concentration of Eu 3+ was estimated at 5at.%(y=0.05), and the quenching was attributed to exchange interactions. Partial replacement of Gd 3+ with Lu 3+ up to 50at.%(x=0.5) while keeping Eu 3+ at the optimal content of 5at.% does not significantly alter the peak positions of the CTB and 5D 0→ 7F 1 emission bands but slightly weakens both bands owing to the higher electronegativity of Lu 3+. The effects of processing temperature (1000-1500°C) and Lu/Eu contents on the intensity, quantum efficiency, lifetime and asymmetry factor of luminescence were thoroughly investigated. The [(Gd 0.7Lu 0.3) 0.95Eu 0.05] 3Al 5O 12 phosphor processed at 1500°C exhibits a high internal quantum efficiency of 83.2% under 239nm excitation, which, in combination with the high theoretical density, favors its use as a new type of photoluminescent and scintillation material. © 2012 National Institute for Materials Science.