The fluorescence-excitation and fluorescence spectra as well as the fluorescence decay times were recorded for Hg atoms excited to the 6P-1(1) state by synchrotron radiation in Ar, Kr, Xe, N2, and CH4 matrices and in Ar matrices with a low ammonia content. It was shown that sequential decays from the 6P-1(1) to different 6(3)P(J) levels involve the intersystem crossing and intramultiplet relaxation, the dependence of the relaxation rate on the properties of the matrix being different for the two mechanisms.