Enhancing thermal quenching characteristic of phosphor for use in high power white-light-emitting diodes (wLEDs) is a significant materials challenge. To achieve this goal, a series of red-emitting carbidonitride phosphors Ca0.992AlSiN3 - 4/3xCx:0.008Eu(2+) have been synthesized by high-temperature solid-state reaction method. Crystal structure, luminescence properties, and thermal quenching process are investigated. The location of carbon in the lattice is proved by the Raman spectra. The preferential crystallographic site of carbon is validated by the first-principles density functional theory calculations combining the Rietveld refinement. With carbon doping from x = 0 to x = 0.24, the emission spectra are blue-shifted from 656.8 to 650.2 nm, and the fitted lifetime of Eu2+ decreases from 775.3 to 721.7 ns. Replacing nitrogen by carbon enhances thermal quenching characteristic by 8.9% at 300 degrees C. Carbon doping enlarges the thermal ionization energy barriers (E-dC) which is calculated at great length, and suppresses thermal ionization process. A wLED fabricated by the combination of a blue chip with the as-synthesized red phosphor and LuAG: Ce3+ green phosphor shows a high color rendering indexes (Ra = 95.9 and R9 = 92). The promising application of Ca0.992AlSiN3 - 4/3xCx:0.008Eu(2+) phosphor for wLEDs is proved by all results above.