Recently we reported that phosphorescent light emission was observed upon irradiation of WF6/H2/noble gas (Ar, Kr, Ne, Xe) mixtures by ArF excimer laser [P. Heszler, P. Mogyorósi, and J.-O. Carlsson, J. Appl. Phys. 78, 5277 1995], originating from tungsten nanoparticles. In this work results of additional measurements on the same system are presented, and we conclude that the reported phosphorescence is a blackbody-like radiation. Taking into account the emissivity of the particles calculated on the base of the Mie theory, it was possible to determine the dependence of the temperature of the tungsten nanoparticles on time after the laser pulse by means of time-resolved spectroscopy. It is shown that surface reactions on the hot nanoparticles contribute significantly to the growth. The size distribution was found lognormal by transmission electron microscopy measurements. © 2001 American Institute of Physics.