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We discuss collision-induced spontaneous decay in a system of cold atoms and caloric effect manifesting in the heating of the atomic system during spontaneous decay. It is shown that the caloric effect is caused by inelastic atom–atom collisions accompanied by the spontaneous emission of photons. Because of the imbalance between the rate of emission of the photons with the frequency higher and lower than the atomic transition frequency, the atomic system, under some conditions, is heated up. The value of the critical temperature is found, which separates the regions where the collision-induced spontaneous decay is exothermic and endothermic.

We discuss the spontaneous decay in a system of cold identical two-level atoms when, due to the strong dipole-dipole interaction, the collision-induced spontaneous decay plays the leading role in the process. We show that the time profile of the spontaneous transition is essentially non-exponential. Also, we argue that at a low initial temperature of the atomic system the spontaneous decay is accompanied by a strong heating caused by the inelastic atom-atom collisions. We show that the spontaneous emission spectrum is asymmetric. In addition, the width of the emission spectrum is a function of time. While atoms decay the emission spectrum becomes broader. The spectrum’s asymmetry and the atomic system’s heating have the same physical origin coming from the peculiarities of the atoms distribution function.

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Inelastic atom-atom collisions accompanied by absorption or emission of photons of the applied electromagnetic field are discussed. It is shown that depending on the sign (positive or negative) of the detuning between the atomic frequency and the frequency of the electromagnetic field, the system can be cooled down or heated up. The equations describing the cooling rate of atoms are derived and analyzed. It is shown that the atoms' statistics plays a crucial role in the discussed processes. Particularly, the cooling (heating) rate of the system of Bose atoms decreases with the decrease of the temperature, whereas under some conditions, the cooling (heating) rate of the system of Fermi atoms increases with the decrease of the temperature. Various scenarios due to different possible numerical ratios between the atoms' system and electromagnetic field parameters are discussed.