The paper presents evidence of the existence of infrared characteristic radiation accompanying phase transitions of the first order, especially crystallization. Experimental results of the author and other researchers concerning crystallization from the melt of some infrared transparent substances (alkali halides, sapphire) and non-transparent ones (tellurium, ice, copper) are presented, as well as condensation of water vapor. The author has critically analyzed these experimental data in terms of correspondence to the theoretical models. The last ones are based on the assumption that the particle, during transition from higher energetic level (vapor or melt) to the lower energetic level (crystal), emits one or more photons equal to the latent energy of the transition, or part of the energy. Based on the experimental data, the author proposes a model explaining the appearance of a window of transparency for the characteristic radiation in the substances when first-order phase transitions take place. It is possible to imagine several applications of this phenomenon in different fields. For instance, new types of crystallization process regulation, crystallization stimulated by the characteristic radiation, an infrared laser based on the condensation of water vapor, or crystallization of lithium fluoride or sapphire. Formation of hailstorm clouds in the atmosphere should be accompanied by intensive characteristic infrared radiation that could be detected for process characterization and meteorological warnings. (C) 2007 Published by Elsevier B.V.