Long-wave photoluminescence (PL) spectra of n-ZnSe single crystals doped with Au in different concentrations are studied in the temperature range from 81 to 300 K. A narrow band of infrared (IR) radiation centred at 878 nm manifests itself in the low-temperature PL spectrum. The intensity of this band first increases and then decreases with increasing concentration of doping impurity. The nature of the luminescence centre, its structure and the mechanism of radiative recombination are discussed on the ground of complex investigation of luminescence properties of ZnSe:Zn:Au crystals. It is shown that the observed IR radiation is caused by recombination of free electrons with holes localised on associative acceptors, which contain native defects V_Zn and impurity defects Au_i. It is established that gold is a chemically amphoteric impurity in ZnSe crystals and forms both donor (Au_i) and acceptor (Au_Zn) centres.