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The Gd 3 Al 5 O 12 :Tb/Ce (GdAG:Tb/Ce) garnet solutions effectively stabilized by Lu 3+ have been achieved by calcining their precursor at 1300 °C. Detailed characterizations are given to the materials in terms of XRD, FE-SEM, BET, PL/PLE, and fluorescence decay analysis. The occurrence of Gd 3+ and Tb 3+ transitions from the photoluminescence excitation spectrum monitoring the Ce 3+ yellow emission strongly confirmed the efficient Gd 3+ → Ce 3+ and Tb 3+ → Ce 3+ energy transfer. The [(Gd 0.8 Lu 0.2 ) 0.99− x Ce 0.01 Tb x ]AG ( x = 0–0.1) phosphors with good dispersion and uniform particle size exhibit various luminescent properties under different excitation wavelength of 275, 338, and 457 nm, respectively. The photoluminescence comparison indicated that owing to the Gd 3+ → Ce 3+ and Tb 3+ → Ce 3+ energy transfer, the best luminescent phosphor [(Gd 0.8 Lu 0.2 ) 0.89 Ce 0.01 Tb 0.1 ]AG is almost identical to the well-known YAG:Ce, higher than LuAG:Ce in emission intensity, and has a substantially red-shifted emission band that is desired for warm-white lighting. The Tb 3+ → Ce 3+ energy transfer was suggested to be electric multipolar interactions, and the processes of energy migration among the optically active Gd 3+ , Tb 3+ , and Ce 3+ ions were discussed in detail. Fluorescence decay analysis found the lifetime for the Ce 3+ emission hardly changes with the Tb 3+ incorporation. The [(Gd 0.8 Lu 0.2 ) 0.99− x Ce 0.01 Tb x ]AG garnets developed in this work may serve as a new type of phosphor that hopefully meets the requirements of various lighting, optical display, and scintillation applications. [ABSTRACT FROM AUTHOR]

Abstract: Eu3+ doped Gd4Al2O9 (GdAM), GdAlO3 (GdAP), and Gd3Al5O12 (GdAG, containing 10at% of Lu3+ for lattice stabilization) have been developed in this work as efficient red-emitting phosphors. With coprecipitated carbonate precursors, phase evolution studies found minimum processing temperatures of ~1000, 1100, and 1300°C for the three phosphors to crystallize as pure phases, respectively. Compared with their yttrium aluminate counterparts, the gadolinium-based phosphors exhibit red-shifted O2−–Eu3+ charge transfer excitation band (CTB) centers due to the lower electronegativity of Gd3+ and appreciably higher quantum yields of photoluminescence owing to the occurrence of efficient Gd3+→Eu3+energy transfer. The optimal Eu3+ contents were determined to be ~7.5at% for GdAM and 5.0at% for both GdAP and GdAG, and concentration quenching of luminescence was suggested to be due to exchange interactions. Fluorescence decay analysis found a shorter lifetime for the phosphor powder processed at a higher temperature or with a higher Eu3+ content, and the underlying mechanism was discussed. Fluorescence lifetimes were also compared between the yttrium and gadolinium phosphor systems for the dominant emissions. [Copyright &y& Elsevier]

• Air-calcined TbAG:Eu phosphor exhibits red luminescence of Eu3+ (∼575–725 nm) mostly via Tb3+ → Eu3+ energy transfer. • The optimal Eu3+ content of air-calcined TbAG:Eu is about 3 at.%. • ∼63% of the Eu in (Tb 0.97 Eu 0.03)AG was reduced to Eu2+ by calcination in hydrogen at 1500 °C. • Hydrogen-reduced TbAG:Eu exhibits cyan luminescence, with chromaticity coordinates of around (0.286, 0.381), by Tb3+, Eu3+ and Eu2+. • Forward and backward energy transfer among Tb3+, Eu2+ and Eu3+ was suggested to occur via electron exchange interaction. Calcination of coprecipitated precursors at 1500 °C in air produced (Tb 1- x Eu x) 3 Al 5 O 12 garnet phosphors (x = 0.0025-0.05) that exhibit dominant excitations via 4f8 → 4f75d1 (E 1-4) and 7F 6 → 5D 3,4 transitions of Tb3+ and negligible excitation of Eu3+. Exciting the phosphors with 275 nm light (E 2 transition of Tb3+) produced the typical 5D 0 → 7FJ red emissions of Eu3+. Annealing the x = 0.03 sample in hydrogen at 1500 °C reduced ∼62.8% of Eu3+ to Eu2+ and yielded a cyan phosphor that simultaneously exhibits the luminescence of Eu3+ (red), Tb3+ (green) and Eu2+ (broad-band, 400–725 nm) under 327 nm excitation (E 1 transition of Tb3+). The (Tb 0.97 Eu 0.03)AG optimal phosphors calcined in air and hydrogen were assayed to have external/internal quantum efficiencies (in percentage) of ∼23.2/24.2 and 18.6/23.7, respectively. Luminescence features of the two types of phosphors were investigated in detail, and the energy transfer among Tb3+, Eu2+ and Eu3+ ions was discussed. [ABSTRACT FROM AUTHOR]