Development of Eu3+ activated monoclinic, perovskite, and garnet compounds in the Gd2O3-Al2O3 phase diagram as efficient red-emitting phosphors

Eu3+ doped Gd4Al2O9 (GdAM), GdAlO3 (GdAP), and Gd3Al5O12 (GdAG, containing 10 aft. 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 similar to 1000, 1100, and 1300 degrees 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 similar to 7.5 at%, for GdAM and 5.0 at% 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. (C) 2013 Elsevier Inc. All rights reserved.