The sintering behavior and doping concentration profile of the planar waveguide YAG/Nd:YAG/YAG ceramics by the tape casting and solid-state reaction method were investigated on the basis of densification trajectory, microstructure evolution, and Nd3+ ions diffusion. The porosity of the green body by tape casting and cold isostatic pressing is about 38.6%. And the green bodies were consolidated from 1100 degrees C to 1800 degrees C for 0.5-20 h to study the densification and the doping diffusion behaviors. At the temperature higher than 1500 degrees C, pure YAG phase is formed, followed by the densification and grain growth process. With the increase of temperature, two sintering stages occur, corresponding to remarkable densification and significant grain growth, respectively. The mechanism controlling densification at 1550 degrees C is grain boundary diffusion. The diffusion of Nd3+ ions is more sensitive to temperature than the sintering time, and the minimum temperature required for the obvious diffusion of Nd3+ ions is higher than 1700 degrees C. Finally, planar waveguide YAG/1.5 at.%Nd:YAG/YAG transparent ceramics with in-line transmittance of 84.8% at 1064 nm were obtained by vacuum-sintering at 1780 degrees C for 30 h. The fluorescence lifetime of F-4(3/2) state of Nd3+ in the specimen is about 259 mu s. The prepared ceramic waveguide was tested in a laser amplifier and the laser pulse was amplificated from 87 mJ to 238 mJ, with the pump energy of 680 mJ. (C) 2016 Elsevier B.V. All rights reserved.