Triboluminescence (TL) has gained increasing attention in the past two decades due to its potential for many applications such as an in situ damage sensor, X-ray source, spectroscopic probe, and optical switch. So far the mechanisms by which TL is excited are not well understood. We have investigated the TL emitted during the sliding contact between silica wafer and YSZ (yttria-stabilized zirconia) wafers in CO2 gas, ambient air, and vacuum. We discovered that the mean intensity of photons emitted in CO2 gas is nearly a hundred times stronger than that in air. TL induced in the sliding experiment is proposed to be due to a combination of chemical luminescence, impurities and vacancies luminescence. In addition, the intensity of the light emission of YSZ may be controlled by changing the concentration of CO2 gas.