Abstract: By spark plasma sintering (SPS) and post-sintering heat treatments at 1700℃ for 7h and 17h
respectively, the optical transmission of R_0.33Si_9.3Al_2.7O_1.7N_14.3 (R=Gd, Y and Er) in 4000～1500cm^-1 (2.5～6.6μm) was studied.
The results indicate that fully densified specimens obtained by SPS are with homogenous distributed α’ grains. Among three SPS-ed specimens, Y
α-sialon ceramic has the highest transmittance and it reaches 56% for the specimen with 0.5mm in thickness. The heat treatment for 7h causes
the decrease in optical transmittance due to the formation of the second crystallized phase in the specimens. The optical
transmittance of specimens can be improved by suitable heat treatment, and the maximum optical transmittance value of Gd117 can be increased from 47% as
SPS-ed to 56% after heat-treated at 1700℃ for 17h.

Key words: α-sialon, polycrystalline ceramics, optical transmission