Abstract The effects of addition of trivalent metal oxides: Gd2O3, Dy2O3, Eu2O3, Er2O3, Y2O3, and B2O3 on the size and distribution of anti-glass phases of BiNbTe2O8 in the system: xR2O3-(10-x)Bi2O3-10Nb2O5-80TeO2 (x = 1 and 2 mol%) are studied. The samples prepared by melt-quenching are predominantly glassy phase but contain co-existing inclusions (droplets) of anti-glass BiNbTe2O8. The incorporation of Gd2O3, Dy2O3, Eu2O3, Er2O3, and Y2O3 in the glass system enhances the glass transition temperature and promotes the growth of the anti-glass droplets. On the other hand the addition of B2O3 decreases the glass transition temperature and inhibits the growth of the inclusions and produces purely amorphous samples. The photoluminescence spectra show intense red emission in Eu3+-doped samples while yellow light is emitted from Dy3+ doped samples. The micro-Raman spectra of the glass and anti-glass inclusions are very similar which indicates same chemical composition and short-range structure of the glass and anti-glass phases.