Oxyfluoride glasses doped with rare earth ions (Dy3+, Er3+ or Ho3+) were fabricated, and their visible and near infrared emissions were evaluated before and after the formation of β-PbF2 nanocrystals. Upon heat treatment of the parent glass to precipitate β-PbF2 nanocrystals, both the intensity and lifetime of radiative emissions from the Dy3+ ion were improved conspicuously, whereas changes in the emissions from Er3+ and Ho3+ turned out to be relatively insignificant. In addition to the hypersensitive nature of some 4f↔4f transitions of Dy3+, its spatial distribution inside the heat-treated oxyfluoride samples is believed to be responsible for this interesting observation. Our finding thus exemplifies the chemical effects of rare earth ions on the formation of nanocrystals via heat treating oxyfluoride glasses. Various probes including X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy and Judd-Ofelt analysis were applied to elucidate the rare earth dependence of the fluoride nanocrystals within the oxyfluoride glasses.