The fluorescence-excitation and fluorescence spectra as well as the fluorescence decay times were recorded for Hg atoms excited to the 61P1 state by synchrotron radiation in Ar, Kr, Xe, N2, and CH4 matrixes and in Ar matrixes with a low NH3 content. Sequential decays from the 61P1 to different 63PJ levels involve the intersystem crossing and intramultiplet relaxation, the dependence of the relaxation rate on the properties of the matrix being different for the 2 mechanisms. [on SciFinder (R)]