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We constructed a comprehensive model atom for C\ione\ -- C\ii\ using the mostup-to-date atomic data available and evaluated the non-local thermodynamicequilibrium (NLTE) line formation for C\ione\ and C\ii\ in classical 1D modelsrepresenting the atmospheres of A and late B-type stars. Our NLTE calculationspredict the emission that appears at effective temperature of 9250 to 10\,500~Kdepending on log~$g$ in the C\ione\ 8335, 9405\,\AA\ singlet lines and at\Teff~$>$~15\,000~K (log~$g$ = 4) in the C\ione\ 9061 -- 9111\,\AA\,, 9603 --9658\,\AA\, triplet lines. A prerequisite of the emission phenomenon is theoverionization-recombination mechanism resulting in a depopulation of the lowerlevels of C\ione\ to a greater extent than the upper levels. Extra depopulationof the lower levels of the transitions corresponding to the near-infraredlines, is caused by photon loss in the UV lines C\ione\ 2479, 1930, and1657\,\AA. We analysed the lines of C\ione\ and C\ii\ in Vega, HD~73666,Sirius, 21~Peg, $\pi$~Cet, HD~22136, and $\iota$ Her taking advantage of theirobserved high-resolution spectra. The C\ione\ emission lines were detected inthe four hottest stars, and they were well reproduced in our NLTE calculations.For each star, the mean NLTE abundances from lines of the two ionizationstages, C\ione\ and C\ii, including the C\ione\ emission lines, were found tobe consistent. We show that the predicted C\ione\ emission phenomenon dependsstrongly on whether accurate or approximate electron-impact excitation ratesare applied.

NLTE carbon abundance determination in selected A- and B-type stars and the interpretation of C\ione\ emission lines