Absorption, emission and fluorescence-excitation spectra are reported for Hg atoms and Hg2 mols. in Ar, Kr, Xe and N2 matrixes upon excitation by synchrotron radiation in the 260-90 nm range. The fluorescence emitted from all levels issued from the 6s6p configuration (including strongly forbidden 3P0 -> 1S0 and 3P2 -> 1S0 transitions) upon the excitation of autoionized (5d)9(6s)2(np) levels is explained by ionization-recombination processes. Upon excitation of the 1P1 level, the efficiency of the 1P1 -> 3PJ relaxation depends strongly on the host properties. Preliminary conclusions concerning environmental effects on oscillator strengths, relaxation and ionization-recombination processes are discussed. [on SciFinder (R)]