Intense visible and near-infrared frequency upconversion and a frequency downconversion photoluminescence have been reported for the first time in Tm3+ and Er3+ co-doped transparent -Sialon ceramics under 980 nm excitation. The -Sialon ceramics were prepared by hot-press sintering technique. Intense upconversion bands at 554, 678, 803 nm, and a downconversion band at 1530 nm were observed as a result of the efficient energy transfer between Er3+ and Tm3+ ions. The quadratic dependence of upconversion intensities on the excitation power indicates that the upconversion process is governed by two-photon absorption process. The sintered samples of thickness 0.20 mm have transparency above 80% in the range of 2000 to 4200 nm and it reaches as high as 82% at 3350 nm. Moderately low phonon energy was found with the highest frequency band at 828 cm(-1). These novel properties manifest the potential applications of transparent -Sialon ceramics as a multifunctional material.