Raman gain efficiency and structure of tellurite glasses in the TeO2-TaO5/2-ZnO system have been investigated by Raman and IR spectroscopies. It has been found that replacement of TaO5/2 by ZnO does not significantly modify the respective proportion of TeO4, TeO3 and TeO3+1 entities but induces an important decrease of the TeO4 structural units Raman cross section. Change of the glass structure at the middle range length scale is proposed to be at the origin of the large decrease of the Raman cross section of the TeO4 units. (C) 2012 Elsevier B.V. All rights reserved.