The recently reported fluorescence, emitted near 10 mu m by laser excited ozone molecules trapped in xenon matrices, is actually a stimulated emission. It is observed, at the 2 nu(3)-->nu(3) frequency, only if the laser pulse, which excites the nu(1) + nu(3) level, contains a sufficient amount of energy. A similar emission is found in the other rare gas matrices and in nitrogen, above a laser energy threshold which is matrix dependent. Above the threshold, the emitted signal grows linearly with the laser pulse energy. An evaluation of the quantum yield is obtained by comparison with the literature data on CO fluorescence. The characteristics of the observed emission (low directionality, laser energy dependence, shortening, and amplification when compared to spontaneous emission) are discussed.