The glasses of the composition 19Na 2SO 4-20MO-60P 2O 5: 1.0Ho 2O 3/1.0Er 2O 3 (M = Mg, Ca, and Ba) have been synthesized. Optical absorption and fluorescence spectra (in the spectral range 350-2100 nm were studied at ambient temperature. The spectra were characterized using Judd-Ofelt theory. From the luminescence spectra, various radiative properties like transition probability A, branching ratio β and the radiative life time τ for blue (B), green (G) and red (R) emission levels of these glasses have been evaluated. The energy transfer between the two rare earth ions (Ho 3+ and Er 3+) in co-doped Na 2SO 4-MO-P 2O 5 glass systems in the visible and NIR regions has also been investigated. Highest intensity, the highest quantum efficiency and maximum energy transfer with low phonon losses of B, G, and R lines has been observed in BaO mixed glasses. The reasons for such higher values of these parameters have been discussed in the light of varying field strengths at the rare earths ion site due to replacement of one modifier oxide with the other. The enhanced intensity of NIR emission (at 2.0 μm) has also been discussed in terms of cross relaxation of Er 3+ ions from 4I 13/2 level to 5I 7 of Ho 3+ ions. © 2011 Elsevier B.V. All rights reserved.