The optical properties of manganese-activated zinc silicate Zn2(1-x)Mn2xSiO4 are investigated using pulse selective photon excitation. The light response due to the 4T1g - 6A1g transition is directly linked to the relative concentration of isolated Mn2+ and Mn2+ pairs in this structure. The decay curves can be fitted by a diffusion-limited relaxation mechanism by considering two types of centers with radiative lifetimes tau0 equal to 15 and 1.75 ms, respectively.