An airway adapter is disclosed herein. The airway adapter includes a flow channel (26) for carrying a respiratory gas including oxygen and a body (14) having a surface at least partly coated with a luminophore (13) excited by a radiation received, the luminophore being in contact with the respiratory gas and emitting luminescent radiation indicative of oxygen concentration of the respiratory gas. The body (14) includes a transparent radiation path surrounded by the surface, which body guides at least one of the radiation received and the luminescent radiation emitted by the luminophore (13). A gas analyzer for measuring oxygen concentration of a respiratory gas is also provided. (Fig. 2)