This paper presents a high-performance fiber-optic carbon dioxide (CO 2) sensor based on hybrid xerogels composed of alkyl and perfluoroalkyl ORMOSILs (organically modified silicates) doped with pH-sensitive fluorescent dye. The sensor film consists of 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt (HPTS, PTS-), tetraoctylammonium cation (TOA+), and a tetraoctylammonium hydroxide (TOAOH) phase transfer agent (i.e. the base) immobilized within the hybrid xerogels. The sensor has a sensitivity of approximately 18 and exhibits a linear response for CO2 concentrations in the range 0 ∼ 30 %. The response time of the sensor is 1.7 s when switching from a pure nitrogen atmosphere to a pure CO2 atmosphere and 38.5 s when switching from CO2 to nitrogen.